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Biology library

Course: biology library   >   unit 12.

  • Overview of glycolysis
  • Steps of glycolysis

Introduction

What is glycolysis, highlights of glycolysis.

  • Energy-requiring phase. In this phase, the starting molecule of glucose gets rearranged, and two phosphate groups are attached to it. The phosphate groups make the modified sugar—now called fructose-1,6-bisphosphate—unstable, allowing it to split in half and form two phosphate-bearing three-carbon sugars. Because the phosphates used in these steps come from ATP ‍   , two ATP ‍   molecules get used up.
  • Energy-releasing phase. In this phase, each three-carbon sugar is converted into another three-carbon molecule, pyruvate, through a series of reactions. In these reactions, two ATP ‍   molecules and one NADH ‍   molecule are made. Because this phase takes place twice, once for each of the two three-carbon sugars, it makes four ATP ‍   and two NADH ‍   overall.

Detailed steps: Energy-requiring phase

Detailed steps: energy-releasing phase.

  • Glyceraldehyde-3-phosphate is converted into 1,3-bisphosphoglycerate. This is a redox reaction in which NAD+ is converted to NADH (with the release of an H+ ion). An inorganic phosphate is also a reactant for this reaction, which is catalyzed by glyceraldehyde-3-phosphate dehydrogenase.
  • 1,3-bisphosphoglycerate is converted to 3-phosphoglycerate by phosphoglycerate kinase. This step converts an ADP to an ATP.
  • 3-phosphoglycerate is converted to 2-phosphoglycerate by phosphoglycerate mutase.
  • 2-phosphoglycerate is converted to phosphoenolpyruvate (PEP) by enolase. This reaction releases a water molecule.
  • Phosphoenolpyruvate (PEP) is converted to pyruvate by pyruvate kinase. An ADP is converted to an ATP in this reaction.

What happens to pyruvate and NADH ‍   ?

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Incredible Answer

  • 4.2 Glycolysis
  • Introduction
  • 1.1 Themes and Concepts of Biology
  • 1.2 The Process of Science
  • Chapter Summary
  • Visual Connection Questions
  • Review Questions
  • Critical Thinking Questions
  • 2.1 The Building Blocks of Molecules
  • 2.3 Biological Molecules
  • 3.1 How Cells Are Studied
  • 3.2 Comparing Prokaryotic and Eukaryotic Cells
  • 3.3 Eukaryotic Cells
  • 3.4 The Cell Membrane
  • 3.5 Passive Transport
  • 3.6 Active Transport
  • 4.1 Energy and Metabolism
  • 4.3 Citric Acid Cycle and Oxidative Phosphorylation
  • 4.4 Fermentation
  • 4.5 Connections to Other Metabolic Pathways
  • 5.1 Overview of Photosynthesis
  • 5.2 The Light-Dependent Reactions of Photosynthesis
  • 5.3 The Calvin Cycle
  • 6.1 The Genome
  • 6.2 The Cell Cycle
  • 6.3 Cancer and the Cell Cycle
  • 6.4 Prokaryotic Cell Division
  • 7.1 Sexual Reproduction
  • 7.2 Meiosis
  • 7.3 Variations in Meiosis
  • 8.1 Mendel’s Experiments
  • 8.2 Laws of Inheritance
  • 8.3 Extensions of the Laws of Inheritance
  • 9.1 The Structure of DNA
  • 9.2 DNA Replication
  • 9.3 Transcription
  • 9.4 Translation
  • 9.5 How Genes Are Regulated
  • 10.1 Cloning and Genetic Engineering
  • 10.2 Biotechnology in Medicine and Agriculture
  • 10.3 Genomics and Proteomics
  • 11.1 Discovering How Populations Change
  • 11.2 Mechanisms of Evolution
  • 11.3 Evidence of Evolution
  • 11.4 Speciation
  • 11.5 Common Misconceptions about Evolution
  • 12.1 Organizing Life on Earth
  • 12.2 Determining Evolutionary Relationships
  • 13.1 Prokaryotic Diversity
  • 13.2 Eukaryotic Origins
  • 13.3 Protists
  • 14.1 The Plant Kingdom
  • 14.2 Seedless Plants
  • 14.3 Seed Plants: Gymnosperms
  • 14.4 Seed Plants: Angiosperms
  • 15.1 Features of the Animal Kingdom
  • 15.2 Sponges and Cnidarians
  • 15.3 Flatworms, Nematodes, and Arthropods
  • 15.4 Mollusks and Annelids
  • 15.5 Echinoderms and Chordates
  • 15.6 Vertebrates
  • 16.1 Homeostasis and Osmoregulation
  • 16.2 Digestive System
  • 16.3 Circulatory and Respiratory Systems
  • 16.4 Endocrine System
  • 16.5 Musculoskeletal System
  • 16.6 Nervous System
  • 17.1 Viruses
  • 17.2 Innate Immunity
  • 17.3 Adaptive Immunity
  • 17.4 Disruptions in the Immune System
  • 18.1 How Animals Reproduce
  • 18.2 Development and Organogenesis
  • 18.3 Human Reproduction
  • 19.1 Population Demographics and Dynamics
  • 19.2 Population Growth and Regulation
  • 19.3 The Human Population
  • 19.4 Community Ecology
  • 20.1 Energy Flow through Ecosystems
  • 20.2 Biogeochemical Cycles
  • 20.3 Terrestrial Biomes
  • 20.4 Aquatic and Marine Biomes
  • 21.1 Importance of Biodiversity
  • 21.2 Threats to Biodiversity
  • 21.3 Preserving Biodiversity
  • A | The Periodic Table of Elements
  • B | Geological Time
  • C | Measurements and the Metric System

Learning Objectives

  • Explain how ATP is used by the cell as an energy source
  • Describe the overall result in terms of molecules produced of the breakdown of glucose by glycolysis

Even exergonic, energy-releasing reactions require a small amount of activation energy to proceed. However, consider endergonic reactions, which require much more energy input because their products have more free energy than their reactants. Within the cell, where does energy to power such reactions come from? The answer lies with an energy-supplying molecule called adenosine triphosphate, or ATP . ATP is a small, relatively simple molecule, but within its bonds contains the potential for a quick burst of energy that can be harnessed to perform cellular work. This molecule can be thought of as the primary energy currency of cells in the same way that money is the currency that people exchange for things they need. ATP is used to power the majority of energy-requiring cellular reactions.

ATP in Living Systems

A living cell cannot store significant amounts of free energy. Excess free energy would result in an increase of heat in the cell, which would denature enzymes and other proteins, and thus destroy the cell. Rather, a cell must be able to store energy safely and release it for use only as needed. Living cells accomplish this using ATP, which can be used to fill any energy need of the cell. How? It functions as a rechargeable battery.

When ATP is broken down, usually by the removal of its terminal phosphate group, energy is released. This energy is used to do work by the cell, usually by the binding of the released phosphate to another molecule, thus activating it. For example, in the mechanical work of muscle contraction, ATP supplies energy to move the contractile muscle proteins.

ATP Structure and Function

At the heart of ATP is a molecule of adenosine monophosphate (AMP), which is composed of an adenine molecule bonded to both a ribose molecule and a single phosphate group ( Figure 4.12 ). Ribose is a five-carbon sugar found in RNA and AMP is one of the nucleotides in RNA. The addition of a second phosphate group to this core molecule results in adenosine underline di end underline phosphate (ADP); the addition of a third phosphate group forms adenosine underline tri end underline phosphate (ATP).

The addition of a phosphate group to a molecule requires a high amount of energy and results in a high-energy bond. Phosphate groups are negatively charged and thus repel one another when they are arranged in series, as they are in ADP and ATP. This repulsion makes the ADP and ATP molecules inherently unstable. The release of one or two phosphate groups from ATP, a process called hydrolysis, releases energy.

You have read that nearly all of the energy used by living things comes to them in the bonds of the sugar, glucose. Glycolysis is the first step in the breakdown of glucose to extract energy for cell metabolism. Many living organisms carry out glycolysis as part of their metabolism. Glycolysis takes place in the cytoplasm of most prokaryotic and all eukaryotic cells.

Glycolysis begins with the six-carbon, ring-shaped structure of a single glucose molecule and ends with two molecules of a three-carbon sugar called pyruvate. Glycolysis consists of two distinct phases. In the first part of the glycolysis pathway, energy is used to make adjustments so that the six-carbon sugar molecule can be split evenly into two three-carbon pyruvate molecules. In the second part of glycolysis, ATP and nicotinamide-adenine dinucleotide (NADH) are produced ( Figure 4.13 ).

If the cell cannot catabolize the pyruvate molecules further, it will harvest only two ATP molecules from one molecule of glucose. For example, mature mammalian red blood cells are only capable of glycolysis, which is their sole source of ATP. If glycolysis is interrupted, these cells would eventually die.

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24.2 Carbohydrate Metabolism

Learning objectives.

By the end of this section, you will be able to:

  • Describe how the body digests carbohydrates
  • Describe how, when, and why the body metabolizes carbohydrates
  • Explain the processes of glycolysis
  • Describe the pathway of a pyruvate molecule through the Krebs cycle
  • Explain the transport of electrons through the electron transport chain
  • Describe the process of ATP production through oxidative phosphorylation
  • Summarize the process of gluconeogenesis

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen atoms. The family of carbohydrates includes both simple and complex sugars. Glucose and fructose are examples of simple sugars, and starch, glycogen, and cellulose are all examples of complex sugars. The complex sugars are also called polysaccharides and are made of multiple monosaccharide molecules. Polysaccharides serve as energy storage (e.g., starch and glycogen) and as structural components (e.g., chitin in insects and cellulose in plants).

During digestion, carbohydrates are broken down into simple, soluble sugars that can be transported across the intestinal wall into the circulatory system to be transported throughout the body. Carbohydrate digestion begins in the mouth with the action of salivary amylase on starches, continues in the duodenum with the action of pancreatic amylase , and ends with monosaccharides being absorbed across the epithelium of the small intestine. Once the absorbed monosaccharides are transported to the tissues, the process of cellular respiration begins ( Figure 24.2.1 ). The goal of cellular respiration is to produce ATP for use by the body to power physiological processes. To start the process, a glucose molecule will get modified to two pyruvate molecules in the metabolic pathway called glycolysis. When oxygen is available, the pyruvate molecules will then be converted to acetyl CoA which enters the mitochondria and enters the citric acid cycle. Both glycolysis and the citric acid cycle produce a small amount of ATP (2 ATP per pathway), but the majority of the ATP produced by aerobic metabolism is achieved when the products of glyolysis and the citric acid, NADH and FADH 2 , carry their electrons to the electron transport chain. The electron transport chain transfers electrons through electron carriers, ultimately to oxygen in a process called oxidative phosphorylaton. This final process of cellular respiration harnesses the energy delivered by NADH and FADH 2 to drive ATP synthase to produce 34 ATP per glucose. This first section will focus first on glycolysis, a process where the monosaccharide glucose is oxidized, releasing the energy stored in its bonds to produce ATP.

This figure shows the different pathways of cellular respiration. The pathways shown are glycolysis, the pyruvic acid cycle, the Krebs cycle, and oxidative phosphorylation.

Glucose is the body’s most readily available source of energy. After digestive processes break polysaccharides down into monosaccharides, including glucose, the monosaccharides are transported across the wall of the small intestine and into the circulatory system, which transports them to the liver. In the liver, hepatocytes either pass the glucose on through the circulatory system or store excess glucose as glycogen. Cells in the body take up the circulating glucose in response to insulin and, through a series of reactions called glycolysis , transfer some of the energy in glucose to ADP to form ATP ( Figure 24.2.2 ). The last step in glycolysis produces the product pyruvate .

Glycolysis begins with the phosphorylation of glucose by hexokinase to form glucose-6-phosphate. This step uses one ATP, which is the donor of the phosphate group. Under the action of phosphofructokinase, glucose-6-phosphate is converted into fructose-6-phosphate. At this point, a second ATP donates its phosphate group, forming fructose-1,6-bisphosphate. This six-carbon sugar is split to form two phosphorylated three-carbon molecules, glyceraldehyde-3-phosphate and dihydroxyacetone phosphate, which are both converted into glyceraldehyde-3-phosphate. The glyceraldehyde-3-phosphate is further phosphorylated with groups donated by dihydrogen phosphate present in the cell to form the three-carbon molecule 1,3-bisphosphoglycerate. The energy of this reaction comes from the oxidation of (removal of electrons from) glyceraldehyde-3-phosphate. In a series of reactions leading to pyruvate, the two phosphate groups are then transferred to two ADPs to form two ATPs. Thus, glycolysis uses two ATPs but generates four ATPs, yielding a net gain of two ATPs and two molecules of pyruvate. In the presence of oxygen, pyruvate continues on to the Krebs cycle (also called the citric acid cycle or tricarboxylic acid cycle (TCA) , where additional energy is extracted and passed on.

This flowchart shows the different steps in glycolysis in detail. The top panel shows the energy-consuming phase, the middle panel shows the coupling of phosphorylation with oxidation, and the bottom panel shows the energy-releasing phase.

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Watch this video to learn about glycolysis.

Glycolysis can be divided into two phases: energy consuming (also called chemical priming) and energy yielding. The first phase is the energy-consuming phase , so it requires two ATP molecules to start the reaction for each molecule of glucose. However, the end of the reaction produces four ATPs, resulting in a net gain of two ATP energy molecules.

Glycolysis can be expressed as the following equation:

This equation states that glucose, in combination with ATP (the energy source), NAD + (a coenzyme that serves as an electron acceptor), and inorganic phosphate, breaks down into two pyruvate molecules, generating four ATP molecules—for a net yield of two ATP—and two energy-containing NADH coenzymes. The NADH that is produced in this process will be used later to produce ATP in the mitochondria. Importantly, by the end of this process, one glucose molecule generates two pyruvate molecules, two high-energy ATP molecules, and two electron-carrying NADH molecules.

The following discussions of glycolysis include the enzymes responsible for the reactions. When glucose enters a cell, the enzyme hexokinase (or glucokinase, in the liver) rapidly adds a phosphate to convert it into glucose-6-phosphate . A kinase is a type of enzyme that adds a phosphate molecule to a substrate (in this case, glucose, but it can be true of other molecules also). This conversion step requires one ATP and essentially traps the glucose in the cell, preventing it from passing back through the plasma membrane, thus allowing glycolysis to proceed. It also functions to maintain a concentration gradient with higher glucose levels in the blood than in the tissues. By establishing this concentration gradient, the glucose in the blood will be able to flow from an area of high concentration (the blood) into an area of low concentration (the tissues) to be either used or stored. Hexokinase is found in nearly every tissue in the body. Glucokinase , on the other hand, is expressed in tissues that are active when blood glucose levels are high, such as the liver. Hexokinase has a higher affinity for glucose than glucokinase and therefore is able to convert glucose at a faster rate than glucokinase. This is important when levels of glucose are very low in the body, as it allows glucose to travel preferentially to those tissues that require it more.

In the next step of the first phase of glycolysis, the enzyme glucose-6-phosphate isomerase converts glucose-6-phosphate into fructose-6-phosphate. Like glucose, fructose is also a six carbon-containing sugar. The enzyme phosphofructokinase-1 then adds one more phosphate to convert fructose-6-phosphate into fructose-1-6-bisphosphate, another six-carbon sugar, using another ATP molecule. Aldolase then breaks down this fructose-1-6-bisphosphate into two three-carbon molecules, glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. The triosephosphate isomerase enzyme then converts dihydroxyacetone phosphate into a second glyceraldehyde-3-phosphate molecule. Therefore, by the end of this chemical-priming or energy-consuming phase, one glucose molecule is broken down into two glyceraldehyde-3-phosphate molecules.

The second phase of glycolysis, the energy-yielding phase , creates the energy that is the product of glycolysis. Glyceraldehyde-3-phosphate dehydrogenase converts each three-carbon glyceraldehyde-3-phosphate produced during the energy-consuming phase into 1,3-bisphosphoglycerate. This reaction releases an electron that is then picked up by NAD + to create an NADH molecule. NADH is a high-energy molecule, like ATP, but unlike ATP, it is not used as energy currency by the cell. Because there are two glyceraldehyde-3-phosphate molecules, two NADH molecules are synthesized during this step. Each 1,3-bisphosphoglycerate is subsequently dephosphorylated (i.e., a phosphate is removed) by phosphoglycerate kinase into 3-phosphoglycerate. Each phosphate released in this reaction can convert one molecule of ADP into one high-energy ATP molecule, resulting in a gain of two ATP molecules.

The enzyme phosphoglycerate mutase then converts the 3-phosphoglycerate molecules into 2-phosphoglycerate. The enolase enzyme then acts upon the 2-phosphoglycerate molecules to convert them into phosphoenolpyruvate molecules. The last step of glycolysis involves the dephosphorylation of the two phosphoenolpyruvate molecules by pyruvate kinase to create two pyruvate molecules and two ATP molecules.

In summary, one glucose molecule breaks down into two pyruvate molecules, and creates two net ATP molecules and two NADH molecules by glycolysis. Therefore, glycolysis generates energy for the cell and creates pyruvate molecules that can be processed further through the aerobic Krebs cycle (also called the citric acid cycle or tricarboxylic acid cycle); converted into lactic acid or alcohol (in yeast) by fermentation; or used later for the synthesis of glucose through gluconeogenesis.

Anaerobic Respiration

When oxygen is limited or absent, pyruvate enters an anaerobic pathway. In these reactions, pyruvate can be converted into lactic acid. In addition to generating an additional ATP, this pathway serves to keep the pyruvate concentration low so glycolysis continues, and it oxidizes NADH into the NAD + needed by glycolysis. In this reaction, lactic acid replaces oxygen as the final electron acceptor. Anaerobic respiration occurs in most cells of the body when oxygen is limited or mitochondria are absent or nonfunctional. For example, because erythrocytes (red blood cells) lack mitochondria, they must produce their ATP from anaerobic respiration. This is an effective pathway of ATP production for short periods of time, ranging from seconds to a few minutes. The lactic acid produced diffuses into the plasma and is carried to the liver, where it is converted back into pyruvate or glucose via the Cori cycle. Similarly, when a person exercises, muscles use ATP faster than oxygen can be delivered to them. They depend on glycolysis and lactic acid production for rapid ATP production.

Aerobic Respiration

In the presence of oxygen, pyruvate can enter the Krebs cycle where additional energy is extracted as electrons are transferred from the pyruvate to the receptors NAD + , GDP, and FAD, with carbon dioxide being a “waste product” ( Figure 24.2.3 ). The NADH and FADH 2 pass electrons on to the electron transport chain, which uses the transferred energy to produce ATP. As the terminal step in the electron transport chain, oxygen is the terminal electron acceptor and creates water inside the mitochondria.

This flowchart shows the processes of anaerobic and aerobic respiration. The top image shows the energy consuming phase of glycolysis. This branches into aerobic respiration on the left and anaerobic respiration on the right.

Krebs Cycle/Citric Acid Cycle/Tricarboxylic Acid Cycle

The pyruvate molecules generated during glycolysis are transported across the mitochondrial membrane into the inner mitochondrial matrix, where they are metabolized by enzymes in a pathway called the Krebs cycle ( Figure 24.2.4 ). The Krebs cycle is also commonly called the citric acid cycle or the tricarboxylic acid (TCA) cycle. During the Krebs cycle, high-energy molecules, including ATP, NADH, and FADH 2 , are created. NADH and FADH 2 then pass electrons through the electron transport chain in the mitochondria to generate more ATP molecules.

The top panel of this figure shows the transformation of pyruvate to acetyl-CoA, and the bottom panel shows the steps in Krebs cycle.

Watch this animation to observe the Krebs cycle.

The three-carbon pyruvate molecule generated during glycolysis moves from the cytoplasm into the mitochondrial matrix, where it is converted by the enzyme pyruvate dehydrogenase into a two-carbon acetyl coenzyme A (acetyl CoA) molecule. This reaction is an oxidative decarboxylation reaction. It converts the three-carbon pyruvate into a two-carbon acetyl CoA molecule, releasing carbon dioxide and transferring two electrons that combine with NAD + to form NADH. Acetyl CoA enters the Krebs cycle by combining with a four-carbon molecule, oxaloacetate, to form the six-carbon molecule citrate, or citric acid, at the same time releasing the coenzyme A molecule.

The six-carbon citrate molecule is systematically converted to a five-carbon molecule and then a four-carbon molecule, ending with oxaloacetate, the beginning of the cycle. Along the way, each citrate molecule will produce one ATP, one FADH 2 , and three NADH. The FADH 2 and NADH will enter the oxidative phosphorylation system located in the inner mitochondrial membrane. In addition, the Krebs cycle supplies the starting materials to process and break down proteins and fats.

To start the Krebs cycle, citrate synthase combines acetyl CoA and oxaloacetate to form a six-carbon citrate molecule; CoA is subsequently released and can combine with another pyruvate molecule to begin the cycle again. The aconitase enzyme converts citrate into isocitrate. In two successive steps of oxidative decarboxylation, two molecules of CO 2 and two NADH molecules are produced when isocitrate dehydrogenase converts isocitrate into the five-carbon α-ketoglutarate, which is then catalyzed and converted into the four-carbon succinyl CoA by α-ketoglutarate dehydrogenase. The enzyme succinyl CoA dehydrogenase then converts succinyl CoA into succinate and forms the high-energy molecule GTP, which transfers its energy to ADP to produce ATP. Succinate dehydrogenase then converts succinate into fumarate, forming a molecule of FADH 2 . Fumarase then converts fumarate into malate, which malate dehydrogenase then converts back into oxaloacetate while reducing NAD + to NADH. Oxaloacetate is then ready to combine with the next acetyl CoA to start the Krebs cycle again (see Figure 24.2.4 ). For each turn of the cycle, three NADH, one ATP (through GTP), and one FADH 2 are created. Each carbon of pyruvate is converted into CO 2 , which is released as a byproduct of oxidative (aerobic) respiration.

Oxidative Phosphorylation and the Electron Transport Chain

The electron transport chain (ETC) uses the NADH and FADH 2 produced by the Krebs cycle to generate ATP. Electrons from NADH and FADH 2 are transferred through protein complexes embedded in the inner mitochondrial membrane by a series of enzymatic reactions. The electron transport chain consists of a series of four enzyme complexes (Complex I – Complex IV) and two coenzymes (ubiquinone and Cytochrome c), which act as electron carriers and proton pumps used to transfer H + ions into the space between the inner and outer mitochondrial membranes ( Figure 24.2.5 ). The ETC couples the transfer of electrons between a donor (like NADH) and an electron acceptor (like O 2 ) with the transfer of protons (H + ions) across the inner mitochondrial membrane, enabling the process of oxidative phosphorylation . In the presence of oxygen, energy is passed, stepwise, through the electron carriers to collect gradually the energy needed to attach a phosphate to ADP and produce ATP. The role of molecular oxygen, O 2 , is as the terminal electron acceptor for the ETC. This means that once the electrons have passed through the entire ETC, they must be passed to another, separate molecule. These electrons, O 2 , and H + ions from the matrix combine to form new water molecules. This is the basis for your need to breathe in oxygen. Without oxygen, electron flow through the ETC ceases.

This image shows the mitochondrial membrane with proton pumps and ATP synthase embedded in the membrane. Arrows show the direction of flow of proteins and electrons across the membrane.

Watch this video to learn about the electron transport chain.

The electrons released from NADH and FADH 2 are passed along the chain by each of the carriers, which are reduced when they receive the electron and oxidized when passing it on to the next carrier. Each of these reactions releases a small amount of energy, which is used to pump H + ions across the inner membrane. The accumulation of these protons in the space between the membranes creates a proton gradient with respect to the mitochondrial matrix.

Also embedded in the inner mitochondrial membrane is an amazing protein pore complex called ATP synthase . Effectively, it is a turbine that is powered by the flow of H + ions across the inner membrane down a gradient and into the mitochondrial matrix. As the H + ions traverse the complex, the shaft of the complex rotates. This rotation enables other portions of ATP synthase to encourage ADP and P i to create ATP. In accounting for the total number of ATP produced per glucose molecule through aerobic respiration, it is important to remember the following points:

  • A net of two ATP are produced through glycolysis (four produced and two consumed during the energy-consuming stage). However, these two ATP are used for transporting the NADH produced during glycolysis from the cytoplasm into the mitochondria. Therefore, the net production of ATP during glycolysis is zero.
  • In all phases after glycolysis, the number of ATP, NADH, and FADH 2 produced must be multiplied by two to reflect how each glucose molecule produces two pyruvate molecules.
  • In the ETC, about three ATP are produced for every oxidized NADH. However, only about two ATP are produced for every oxidized FADH 2 . The electrons from FADH 2 produce less ATP, because they start at a lower point in the ETC (Complex II) compared to the electrons from NADH (Complex I) (see Figure 24.2.5 ).

Therefore, for every glucose molecule that enters aerobic respiration, a net total of 36 ATPs are produced ( Figure 24.2.6 ).

This figure shows the different steps in which carbohydrates are metabolized and lists the number of ATP molecules produced in each step. The different steps shown are glycolysis, transformation of pyruvate to acetyl-CoA, the Krebs cycle, and the electron transport chain.

Gluconeogenesis

Gluconeogenesis is the synthesis of new glucose molecules from pyruvate, lactate, glycerol, or the amino acids alanine or glutamine. This process takes place primarily in the liver during periods of low glucose, that is, under conditions of fasting, starvation, and low carbohydrate diets. So, the question can be raised as to why the body would create something it has just spent a fair amount of effort to break down? Certain key organs, including the brain, can use only glucose as an energy source; therefore, it is essential that the body maintain a minimum blood glucose concentration. When the blood glucose concentration falls below that certain point, new glucose is synthesized by the liver to raise the blood concentration to normal.

Gluconeogenesis is not simply the reverse of glycolysis. There are some important differences ( Figure 24.2.7 ). Pyruvate is a common starting material for gluconeogenesis. First, the pyruvate is converted into oxaloacetate. Oxaloacetate then serves as a substrate for the enzyme phosphoenolpyruvate carboxykinase (PEPCK), which transforms oxaloacetate into phosphoenolpyruvate (PEP). From this step, gluconeogenesis is nearly the reverse of glycolysis. PEP is converted back into 2-phosphoglycerate, which is converted into 3-phosphoglycerate. Then, 3-phosphoglycerate is converted into 1,3 bisphosphoglycerate and then into glyceraldehyde-3-phosphate. Two molecules of glyceraldehyde-3-phosphate then combine to form fructose-1-6-bisphosphate, which is converted into fructose 6-phosphate and then into glucose-6-phosphate. Finally, a series of reactions generates glucose itself. In gluconeogenesis (as compared to glycolysis), the enzyme hexokinase is replaced by glucose-6-phosphatase, and the enzyme phosphofructokinase-1 is replaced by fructose-1,6-bisphosphatase. This helps the cell to regulate glycolysis and gluconeogenesis independently of each other.

As will be discussed as part of lipolysis, fats can be broken down into glycerol, which can be phosphorylated to form dihydroxyacetone phosphate or DHAP. DHAP can either enter the glycolytic pathway or be used by the liver as a substrate for gluconeogenesis.

This figure shows the different steps in gluconeogenesis, where pyruvate is converted to glucose.

The human body’s metabolic rate decreases nearly 2 percent per decade after age 30. Changes in body composition, including reduced lean muscle mass, are mostly responsible for this decrease. The most dramatic loss of muscle mass, and consequential decline in metabolic rate, occurs between 50 and 70 years of age. Loss of muscle mass is the equivalent of reduced strength, which tends to inhibit seniors from engaging in sufficient physical activity. This results in a positive-feedback system where the reduced physical activity leads to even more muscle loss, further reducing metabolism.

There are several things that can be done to help prevent general declines in metabolism and to fight back against the cyclic nature of these declines. These include eating breakfast, eating small meals frequently, consuming plenty of lean protein, drinking water to remain hydrated, exercising (including strength training), and getting enough sleep. These measures can help keep energy levels from dropping and curb the urge for increased calorie consumption from excessive snacking. While these strategies are not guaranteed to maintain metabolism, they do help prevent muscle loss and may increase energy levels. Some experts also suggest avoiding sugar, which can lead to excess fat storage. Spicy foods and green tea might also be beneficial. Because stress activates cortisol release, and cortisol slows metabolism, avoiding stress, or at least practicing relaxation techniques, can also help.

Chapter Review

Metabolic enzymes catalyze catabolic reactions that break down carbohydrates contained in food. The energy released is used to power the cells and systems that make up your body. Excess or unutilized energy is stored as fat or glycogen for later use. Carbohydrate metabolism begins in the mouth, where the enzyme salivary amylase begins to break down complex sugars into monosaccharides. These can then be transported across the intestinal membrane into the bloodstream and then to body tissues. In the cells, glucose, a six-carbon sugar, is processed through a sequence of reactions into smaller sugars, and the energy stored inside the molecule is released. The first step of carbohydrate catabolism is glycolysis, which produces pyruvate, NADH, and ATP. Under anaerobic conditions, the pyruvate can be converted into lactate to keep glycolysis working. Under aerobic conditions, pyruvate enters the Krebs cycle, also called the citric acid cycle or tricarboxylic acid cycle. In addition to ATP, the Krebs cycle produces high-energy FADH 2 and NADH molecules, which provide electrons to the oxidative phosphorylation process that generates more high-energy ATP molecules. For each molecule of glucose that is processed in glycolysis, a net of 36 ATPs can be created by aerobic respiration.

Under anaerobic conditions, ATP production is limited to those generated by glycolysis. While a total of four ATPs are produced by glycolysis, two are needed to begin glycolysis, so there is a net yield of two ATP molecules.

In conditions of low glucose, such as fasting, starvation, or low carbohydrate diets, glucose can be synthesized from lactate, pyruvate, glycerol, alanine, or glutamate. This process, called gluconeogenesis, is almost the reverse of glycolysis and serves to create glucose molecules for glucose-dependent organs, such as the brain, when glucose levels fall below normal.

Review Questions

Critical thinking questions.

1. Explain how glucose is metabolized to yield ATP.

2. Insulin is released when food is ingested and stimulates the uptake of glucose into the cell. Discuss the mechanism cells employ to create a concentration gradient to ensure continual uptake of glucose from the bloodstream.

Answers for Critical Thinking Questions

  • Glucose is oxidized during glycolysis, creating pyruvate, which is processed through the Krebs cycle to produce NADH, FADH 2 , ATP, and CO 2 . The FADH 2 and NADH yield ATP.
  • Upon entry into the cell, hexokinase or glucokinase phosphorylates glucose, converting it into glucose-6-phosphate. In this form, glucose-6-phosphate is trapped in the cell. Because all of the glucose has been phosphorylated, new glucose molecules can be transported into the cell according to its concentration gradient.

This work, Anatomy & Physiology, is adapted from Anatomy & Physiology by OpenStax , licensed under CC BY . This edition, with revised content and artwork, is licensed under CC BY-SA except where otherwise noted.

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Access the original for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction .

Anatomy & Physiology Copyright © 2019 by Lindsay M. Biga, Staci Bronson, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Kristen Oja, Devon Quick, Jon Runyeon, OSU OERU, and OpenStax is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License , except where otherwise noted.

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Activity: Glycolysis

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#R10597 Glycolysis Concept Map

concept map activity 2 glycolysis

This glycolysis concept map is  a smart way of reviewing glycolysis. The students can easily and very visually review the pathway by entering each term in the approppriate space in the map. Easy to use and helpful. This is a great tool to make complicated metabolism pathways something more managable and attractive to students.

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StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

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StatPearls [Internet].

Biochemistry, glycolysis.

Raheel Chaudhry ; Matthew Varacallo .

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Last Update: August 8, 2023 .

  • Introduction

Glycolysis is a metabolic pathway and an anaerobic energy source that has evolved in nearly all types of organisms. Another name for the process is the Embden-Meyerhof pathway, in honor of the major contributors towards its discovery and understanding. [1] Although it doesn't require oxygen, hence its purpose in anaerobic respiration, it is also the first step in cellular respiration. The process entails the oxidation of glucose molecules, the single most crucial organic fuel in plants, microbes, and animals. Most cells prefer glucose (although there are exceptions, such as acetic acid bacteria that prefer ethanol). In glycolysis, 2 ATP molecules are consumed, producing 4 ATP, 2 NADH, and 2 pyruvates per glucose molecule. The pyruvate can be used in the citric acid cycle or serve as a precursor for other reactions. [2] [3] [4]

  • Fundamentals

Glycolysis ultimately splits glucose into two pyruvate molecules. One can think of glycolysis as having two phases that occur in the cytosol of cells. The first phase is the "investment" phase due to its usage of two ATP molecules, and the second is the "payoff" phase. These reactions are all catalyzed by their own enzyme, with phosphofructokinase being the most essential for regulation as it controls the speed of glycolysis. [1]

Glycolysis occurs in both aerobic and anaerobic states. In aerobic conditions, pyruvate enters the citric acid cycle and undergoes oxidative phosphorylation leading to the net production of 32 ATP molecules. In anaerobic conditions, pyruvate converts to lactate through anaerobic glycolysis. Anaerobic respiration results in the production of 2 ATP molecules. [5]  Glucose is a hexose sugar, meaning it is a monosaccharide with six carbon atoms and six oxygen atoms. The first carbon has an attached aldehyde group, and the other five carbons have one hydroxyl group each. During glycolysis, glucose ultimately breaks down into pyruvate and energy; a total of 2 ATP is derived in the process (Glucose + 2 NAD+ + 2 ADP + 2 Pi --> 2 Pyruvate + 2 NADH + 2 H+ + 2 ATP + 2 H2O). The hydroxyl groups allow for phosphorylation. The specific form of glucose used in glycolysis is glucose 6-phosphate.

  • Cellular Level

Glycolysis occurs in the cytosol of cells. Under aerobic conditions, pyruvate derived from glucose will enter the mitochondria to undergo oxidative phosphorylation. Anaerobic conditions result in pyruvate staying in the cytoplasm and being converted to lactate by the enzyme lactate dehydrogenase. [5]

  • Molecular Level

Glucose first converts to glucose-6-phosphate by hexokinase or glucokinase, using ATP and a phosphate group. Glucokinase is a subtype of hexokinase found in humans. Glucokinase has a reduced affinity for glucose and is found only in the pancreas and liver, whereas hexokinase is present in all cells. Glucose 6-phosphate is then converted to fructose-6-phosphate, an isomer, by phosphoglucose isomerase. Phosphofructose-kinase then produces fructose-1,6-bisphosphate, using another ATP molecule. Dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate are then created from fructose-1,6-bisphosphate by fructose bisphosphate aldolase. DHAP will be converted to glyceraldehyde-3-phosphate by triosephosphate isomerase, where now the two glyceraldehyde-3-phosphate molecules will continue down the same pathway. Glyceraldehyde-3-phosphate will become oxidized in an exergonic reaction into 1,3-bisphosphoglycerate, reducing an NAD+ molecule to NADH and H+. 1,3-bisphosphoglycerate will then turn into 3-phosphoglycerate with the help of phosphoglycerate kinase, along with the production of the first ATP molecule from glycolysis. 3-phosphoglycerate will then convert, with the help of phosphoglycerate mutase, into 2-phosphoglycerate. With the release of one molecule of H2O, Enolase will make phosphoenolpyruvate (PEP) from 2-phosphoglycerate. Due to the unstable state of PEP, pyruvate kinase will facilitate its loss of a phosphate group to create the second ATP in glycolysis. Thus, PEP will then undergo conversion to pyruvate. [6] [7] [8]

Glycolysis occurs in the cytosol of the cell. It is a metabolic pathway that creates ATP without the use of oxygen but can occur in the presence of oxygen. In cells that use aerobic respiration as the primary energy source, the pyruvate formed from the pathway can be used in the citric acid cycle and go through oxidative phosphorylation to undergo oxidation into carbon dioxide and water. Even if cells primarily use oxidative phosphorylation, glycolysis can serve as an emergency backup for energy or as the preparation step before oxidative phosphorylation. In highly oxidative tissue, such as the heart, pyruvate production is essential for acetyl-CoA synthesis and L-malate synthesis. It serves as a precursor to many molecules, such as lactate, alanine, and oxaloacetate. [8]

Glycolysis precedes lactic acid fermentation; the pyruvate made in the former process serves as the prerequisite for the lactate made in the latter process. Lactic acid fermentation is the primary source of ATP in animal tissues with low metabolic requirements and little to no mitochondria. In erythrocytes, lactic acid fermentation is the sole source of ATP, as they lack mitochondria and mature red blood cells have little demand for ATP. Another part of the body that relies entirely or almost entirely on anaerobic glycolysis is the eye's lens, which is devoid of mitochondria, as their presence would lead to light scattering. [8]

Though skeletal muscles prefer to catalyze glucose into carbon dioxide and water during heavy exercise where oxygen is inadequate, the muscles simultaneously undergo anaerobic glycolysis and oxidative phosphorylation. [8]

The amount of glucose available for the process regulates glycolysis, which becomes available primarily in two ways: regulation of glucose reuptake or regulation of the breakdown of glycogen. Glucose transporters (GLUT) transport glucose from the outside of the cell to the inside. Cells containing GLUT can increase the number of GLUT in the cell's plasma membrane from the intracellular matrix, therefore increasing the uptake of glucose and the supply of glucose available for glycolysis. There are five types of GLUTs. GLUT1 is present in RBCs, the blood-brain barrier, and the blood-placental barrier. GLUT2 is in the liver, beta-cells of the pancreas, kidney, and gastrointestinal (GI) tract. GLUT3 is present in neurons. GLUT4 is in adipocytes, heart, and skeletal muscle. GLUT5 specifically transports fructose into cells. Another form of regulation is the breakdown of glycogen. Cells can store extra glucose as glycogen when glucose levels are high in the cell plasma. Conversely, when levels are low, glycogen can be converted back into glucose. Two enzymes control the breakdown of glycogen: glycogen phosphorylase and glycogen synthase. The enzymes can be regulated through feedback loops of glucose or glucose 1-phosphate, or via allosteric regulation by metabolites, or from phosphorylation/dephosphorylation control. [8]

Allosteric Regulators and Oxygen

As described before, many enzymes are involved in the glycolytic pathway by converting one intermediate to another. Control of these enzymes, such as hexokinase, phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase, and pyruvate kinase, can regulate glycolysis. The amount of oxygen available can also regulate glycolysis. The “Pasteur effect” describes how the availability of oxygen diminishes the effect of glycolysis, and decreased availability leads to an acceleration of glycolysis, at least initially. The mechanisms responsible for this effect include allosteric regulators of glycolysis (enzymes such as hexokinase). The “Pasteur effect” appears to mostly occur in tissue with high mitochondrial capacities, such as myocytes or hepatocytes. Still, this effect is not universal in oxidative tissue, such as pancreatic cells. [8]

Enzyme Induction

Another mechanism for controlling glycolytic rates is transcriptional control of glycolytic enzymes. Altering the concentration of key enzymes allows the cell to change and adapt to alterations in hormonal status. For example, increasing glucose and insulin levels can increase hexokinase and pyruvate kinase activity, therefore increasing the production of pyruvate. [8]

Fructose 2,6-bisphosphate is an allosteric regulator of PFK-1. High levels of fructose 2,6-bisphosphate increase the activity of PFK-1. Its production occurs through the action of phosphofructokinase-2 (PFK-2). PFK-2 has both kinase and phosphorylase activity and can transform fructose 6 phosphates to fructose 2,6-bisphosphate and vice versa. Insulin dephosphorylates PFK-2, activating its kinase activity, which increases fructose 2,6-bisphosphate and subsequently activates PFK-1. Glucagon can also phosphorylate PFK-2, which activates phosphatase, transforming fructose 2,6-bisphosphate back to fructose 6-phosphate. This reaction decreases fructose 2,6-bisphosphate levels and decreases PFK-1 activity. [8]

Glycolysis Phases

Glycolysis has two phases: the investment phase and the payoff phase. The investment phase is where there is energy, as ATP, is put in, and the payoff phase is where the net creation of ATP and NADH molecules occurs. A total of 2 ATP goes in the investment phase, with the production of 4 ATP resulting in the payoff phase; thus, there is a net total of 2 ATP. The steps by which new ATP is created has the name of substrate-level phosphorylation. [8]

Investment Phase

In this phase, there are two phosphates added to glucose. Glycolysis begins with hexokinase phosphorylating glucose into glucose-6 phosphate (G6P). This step is the first transfer of a phosphate group and where the consumption of the first ATP takes place. Also, this is an irreversible step. This phosphorylation traps the glucose molecule in the cell because it cannot readily pass the cell membrane. From there, phosphoglucose isomerase isomerizes G6P into fructose 6-phosphate (F6P). Then, phosphofructokinase (PFK-1) adds the second phosphate. PFK-1 uses the second ATP and phosphorylates the F6P into fructose 1,6-bisphosphate. This step is also irreversible and is the rate-limiting step. In the following step, fructose 1,6-bisphosphate undergoes lysis into two molecules, which are substrates for fructose-bisphosphate aldolase to convert it into dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (G3P). DHAP is turned into G3P by triosephosphate isomerase. DHAP and G3p are in equilibrium with each other, meaning they transform back and forth. [8]

Payoff Phase

It is critical to remember that there are a total of two 3-carbon sugars for every one glucose at the beginning of this phase. The enzyme glyceraldehyde-3-phosphate dehydrogenase metabolizes the G3P into 1,3-diphosphoglycerate by reducing NAD+ into NADH. Next, the 1,3-diphosphoglycerate loses a phosphate group through phosphoglycerate kinase to make 3-phosphoglycerate and creates an ATP through substrate-level phosphorylation. At this point, there are 2 ATP produced, one from each 3-carbon molecule. The 3-phosphoglycerate turns into 2-phosphoglycerate by phosphoglycerate mutase, and then enolase turns the 2-phosphoglycerate into phosphoenolpyruvate (PEP). In the final step, pyruvate kinase turns PEP into pyruvate and phosphorylates ADP into ATP through substrate-level phosphorylation, thus creating two more ATP. This step is also irreversible. Overall, the input for 1 glucose molecule is 2 ATP, and the output is 4 ATP and 2 NADH and 2 pyruvate molecules. [8]

In cells, NADH must recycle back to NAD+ to permit glycolysis to keep running. Absent NAD+, the payoff phase will come to a halt resulting in a backup in glycolysis. In aerobic cells, NADH recycles back into NAD+ by way of oxidative phosphorylation. In aerobic cells, it occurs through fermentation. There are two types of fermentation: lactic acid and alcohol fermentation. [8]

  • Clinical Significance

Pyruvate kinase deficiency is an autosomal recessive mutation that causes hemolytic anemia. There is an inability to form ATP and causes cell damage. Cells become swollen and are taken up by the spleen, causing splenomegaly. Signs and symptoms include jaundice, icterus, elevated bilirubin, and splenomegaly. [9] [10] [11]

Arsenic poisoning also prevents ATP synthesis because arsenic takes the place of phosphate in the steps of glycolysis. [12]

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Anaerobic glycolysis Image courtesy O.Chaigasame

Disclosure: Raheel Chaudhry declares no relevant financial relationships with ineligible companies.

Disclosure: Matthew Varacallo declares no relevant financial relationships with ineligible companies.

This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits others to distribute the work, provided that the article is not altered or used commercially. You are not required to obtain permission to distribute this article, provided that you credit the author and journal.

  • Cite this Page Chaudhry R, Varacallo M. Biochemistry, Glycolysis. [Updated 2023 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

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22.3: Glycolysis

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Learning Objectives

  • Objective 1
  • Objective 2

Glycolysis is the catabolic process in which glucose is converted into pyruvate via ten enzymatic steps. There are three regulatory steps, each of which is highly regulated.

Introduction

There are two phases of Glycolysis:

  • the "priming phase" because it requires an input of energy in the form of 2 ATP s per glucose molecule and
  • the "pay off phase" because energy is released in the form of 4 ATP s, 2 per glyceraldehyde molecule.

The end result of Glycolysis is two new pyruvate molecules which can then be fed into the Citric Acid cycle (also known as the Kreb's Cycle ) if oxygen is present, or can be reduced to lactate or ethanol in the absence of of oxygen using a process known as Fermentation . Glycolysis occurs within almost all living cells and is the primary source of Acetyl-CoA, which is the molecule responsible for the majority of energy output under aerobic conditions. The structures of Glycolysis intermediates can be found in the following diagram:

clipboard_e760f0a2396098c2bffc635767f9b8393.png

Phase 1: The "Priming Step"

The first phase of Glycolysis requires an input of energy in the form of ATP (adenosine triphosphate).

  • alpha-D- Glucose is phosphorolated at the 6 carbon by ATP via the enzyme Hexokinase (Class: Transferase) to yield alpha-D-Glucose-6-phosphate (G-6-P). This is a regulatory step which is negatively regulated by the presence of glucose-6-phosphate.
  • alpha-D-Glucose-6-phosphate is then converted into D- Fructose -6-phosphate (F-6-P) by Phosphoglucoisomerase (Class: Isomerase)
  • D-Fructose-6-phosphate is once again phosphorolated this time at the 1 carbon position by ATP via the enzyme Phosphofructokinase (Class: Transferase) to yield D-Fructose-1,6-bisphosphate (FBP). This is the committed step of glycolysis because of its large \(\Delta G\) value.
  • D-Fructose-1,6-bisphosphate is then cleaved into two, three carbon molecules; Dihydroxyacetone phosphate (DHAP) and D-Glyceraldehyde-3-phosphate (G-3-P) by the enzyme Fructose bisphosphate aldolase (Class: Lyase)
  • Because the next portion of Glycolysis requires the molecule D-Glyceraldehyde-3-phosphate to continue Dihydroxyacetone phosphate is converted into D-Glyceraldehyde-3-phosphate by the enzyme Triose phosphate isomerase (Class: Isomerase)

Phase 2: The "Pay Off Step"

The second phase of Glycolysis where 4 molecules of ATP are produced per molecule of glucose. Enzymes appear in red:

  • D-Glyceraldehyde-3-phosphate is phosphorolated at the 1 carbon by the enzyme Glyceraldehyde-3-phosphate dehodrogenase to yield the high energy molecule 1,3-Bisphosphoglycerate (BPG)
  • ADP is then phosphorolated at the expense of 1,3-Bisphosphoglycerate by the enzyme Phosphoglycerate kinase (Class: Transferase) to yield ATP and 3-Phosphoglycerate (3-PG)
  • 3-Phosphoglycerate is then converted into 2-Phosphoglycerate by Phosphoglycerate mutase in preparation to yield another high energy molecule
  • 2-Phosphoglycerate is then converted to phosphoenolpyruvate (PEP) by Enolase. H 2 O, potassium, and magnesium are all released as a result.
  • ADP is once again phosphorolated, this time at the expense of PEP by the enzyme pyruvate kinase to yield another molecule of ATP and and pyruvate. This step is regulated by the energy in the cell. The higher the energy of the cell the more inhibited pyruvate kinase becomes. Indicators of high energy levels within the cell are high concentrations of ATP, Acetyl-CoA, Alanine, and cAMP.

Because Glucose is split to yield two molecules of D-Glyceraldehyde-3-phosphate, each step in the "Pay Off" phase occurs twice per molecule of glucose.

  • Garrett, H., Reginald and Charles Grisham. Biochemistry. Boston: Twayne Publishers, 2008.
  • Raven, Peter. Biology. Boston: Twayne Publishers, 2005.
  • What is the net yield of Glycolysis as far as ATP?
  • Name the enzymes that are key regulatory sites in Glycolysis.
  • Why are the enzymes in the previous question targets for regulation?
  • Why is the priming phase necessary?
  • Draw the entire pathway for glycolysis including enzymes, reactants and products for each step.

Contributors and Attributions

  • Darik Benson, (University California Davis)

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13.4: Concept Mapping - Connecting Ideas Visually

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Either individually or as a group, create a concept map on a separate piece of paper or whiteboard that relates the processes of photosynthesis and cellular respiration. The words in the word bank below should go into bubbles. Arrange these bubbles in a way that helps communicate relationships between the words, then connect the bubbles with lines that have a verb or action phrase attached to them. It might help to start by organizing the words into related groups. You can use words more than once.

For example, you could group \(\ce{CO2}\) and ATP together, then draw a line connecting them to RuBisCO and Calvin Cycle . The verb for the connecting line could be “used in”. You could then draw a line from those two that said “produces”. What would that line connect to?

Word Bank: Put these terms in bubbles

\(\ce{O2}\)

\(\ce{H2O}\)

\(\ce{CO2}\)

\(\ce{H+}\)

Chloroplast

Thylakoid membrane

Mitochondrion

Inner mitochondrial membrane

High energy electron carriers

\(\ce{FADH2}\)

Krebs cycle

Electron transport chain

Chemiosmosis

Calvin cycle

Contributors and Attributions

  Maria Morrow  ( College of the Redwoods )

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Biology Teaching Resources

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Cellular Respiration Graphic Organizer

worksheet

Students complete a graphic organizer that shows the process of cellular respiration .  A word bank is provided to help them trace the flow of ATP and NADH in the process as well as identifying where each step occurs.   

Cellular respiration is a series of chemical reactions that take place in the cells The process converts glucose into energy. All living things obtain energy from the food they eat.

Cellular respiration takes place in two stages: glycolysis and the Krebs cycle. Glycolysis is the first stage of cellular respiration. It takes place in the cytoplasm of the cell. In glycolysis, glucose is broken down into pyruvate and two molecules of ATP.

The Krebs cycle is the second stage of cellular respiration and it takes place in the mitochondria of the cell. Pyruvate is broken down into carbon dioxide and energy is released. The energy is used to create ATP.

Cellular respiration is a very important process because it provides energy for all living things. It is also a very efficient process, as it can produce a lot of ATP from a small amount of glucose.

The Graphic Organizer

This graphic organizer starts with glycolysis and includes mention of anaerobic processes (fermentation), then shows how NADH and ATP moves into the Kreb’s cycle . In this cycle, the majority of ATP produced in respiration comes from the electron transport chain .

The overall reaction is

C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + ATP

I’ve used this worksheet in my class and students provided feedback that it really helped them get the “big picture.”  Lecture notes often break the process down into the three steps, focusing on the outputs of each step. 

I have google slides that I use with my AP Bio class and students watch  and offer them several videos to view, including  “ Cellular Respiration ” by the Amoeba Sisters.

This graphic is usually given after these learning activities as a way to pull all of the information back together into one big picture.

Related posts:

animal cell

IMAGES

  1. Concept map of glycolysis

    concept map activity 2 glycolysis

  2. What is Glycolysis? Process, Definition, and Equations

    concept map activity 2 glycolysis

  3. Part 2- Detailed Concept Map- Glycolysis/Biochemistry Basics

    concept map activity 2 glycolysis

  4. Glycolysis: steps, diagram and enzymes involved

    concept map activity 2 glycolysis

  5. Catabolism of Carbohydrates

    concept map activity 2 glycolysis

  6. PART 1- Detailed Concept Map- Glycolysis/Biochemistry Basics|

    concept map activity 2 glycolysis

VIDEO

  1. Glycolysis: all concept no tricks (CEE/NEB CLASS 12) NEPALI #cee #mbbs #respiration

  2. Glycolysis

  3. Glycolysis

  4. Glycolysis biochemistry

  5. Is glycolysis same in plants and humans?

  6. 1. Glycolysis Pathway Explained

COMMENTS

  1. Cellular Metabolism Concept Map- Glycolysis Flashcards

    Cellular Metabolism Concept Map- Glycolysis Flashcards | Quizlet Study with Quizlet and memorize flashcards containing terms like Glycolysis is a _____ _____., Glycolysis occurs with or without presence of ____., glycolysis converts glucose to ______. and more.

  2. 10.3: Carbohydrate Metabolism

    Cells in the body take up the circulating glucose in response to insulin and, through a series of reactions called glycolysis, transfer some of the energy in glucose to ADP to form ATP (Figure 2). The last step in glycolysis produces the product pyruvate. Glycolysis begins with the phosphorylation of glucose by hexokinase to form glucose-6 ...

  3. Glycolysis

    Glycolysis is a series of reactions that extract energy from glucose by splitting it into two three-carbon molecules called pyruvates. Glycolysis is an ancient metabolic pathway, meaning that it evolved long ago, and it is found in the great majority of organisms alive today 2, 3 .

  4. Part 2- Detailed Concept Map- Glycolysis/Biochemistry Basics

    0:00 / 9:52 Part 2- Detailed Concept Map- Glycolysis/Biochemistry Basics The Ten Minute Tutor 179 subscribers Subscribe 238 views 3 years ago Biology Glycolysis Concept Map Part 2...

  5. 4.2 Glycolysis

    Learning Objectives By the end of this section, you will be able to: Explain how ATP is used by the cell as an energy source Describe the overall result in terms of molecules produced of the breakdown of glucose by glycolysis Even exergonic, energy-releasing reactions require a small amount of activation energy to proceed.

  6. 11.4: Glycolysis

    Glycolysis takes place in the cytoplasm of most prokaryotic and all eukaryotic cells. Glycolysis begins with the six-carbon, ring-shaped structure of a single glucose molecule and ends with two molecules of a three-carbon sugar called pyruvate. Glycolysis consists of two distinct phases. In the first part of the glycolysis pathway, energy is ...

  7. 7.2: Glycolysis

    The first step in glycolysis (Figure 7.2.1 7.2. 1) is catalyzed by hexokinase, an enzyme with broad specificity that catalyzes the phosphorylation of six-carbon sugars. Hexokinase phosphorylates glucose using ATP as the source of the phosphate, producing glucose-6-phosphate, a more reactive form of glucose.

  8. 24.2 Carbohydrate Metabolism

    The first step of carbohydrate catabolism is glycolysis, which produces pyruvate, NADH, and ATP. Under anaerobic conditions, the pyruvate can be converted into lactate to keep glycolysis working. Under aerobic conditions, pyruvate enters the Krebs cycle, also called the citric acid cycle or tricarboxylic acid cycle.

  9. Activity: Glycolysis

    Your browser doesn't support HTML5 video. Mark the new pause time. Hour:

  10. LifeSciTRC.org

    This glycolysis concept map is a smart way of reviewing glycolysis. The students can easily and very visually review the pathway by entering each term in the approppriate space in the map. Easy to use and helpful. This is a great tool to make complicated metabolism pathways something more managable and attractive to students.

  11. Solved Glycolysis occurs with or without presence of divides

    Glycolysis occurs with or without presence of divides into is both a + Map II: Glycolysis Energy Pay Off Phase invests is oxidized during 2 NADH to produce 2 G3P (glyceraldehyde 3-phosphate) can transfer electrons to used to drive a substrate level phosphorylation Concept Map Activity 1: Cellular Metabolism using the enzyme which is eventually s...

  12. BioChem Glycolysis Concept Map Diagram

    BioChem Glycolysis Concept Map + − Flashcards Learn Test Match Created by amber_lois PLUS Terms in this set (41) Glycolysis series of reactions that extract energy from a glucose molecule Glucose starting molecule in the glycolysis pathway All Tissues Glycolysis occurs where in the body? Cytosol Where in the cell does glycolysis take place? NADH

  13. Biochemistry, Glycolysis

    Glycolysis is a metabolic pathway and an anaerobic energy source that has evolved in nearly all types of organisms. Another name for the process is the Embden-Meyerhof pathway, in honor of the major contributors towards its discovery and understanding.[1] Although it doesn't require oxygen, hence its purpose in anaerobic respiration, it is also the first step in cellular respiration. The ...

  14. Glycolysis

    The process of cellular respiration is actually many separate reactions, which can be divided into three stages: glycolysis, the Krebs Cycle, and the electron transport chain. During glycolysis, glucose is split into two 3-carbon pyruvate molecules, using 2 ATP but generating 4 ATP, for a net gain of 2 ATP.

  15. Solved Cellular Respiration

    Cellular Respiration - Concept Map Activity Name: GLYCOLYSIS BREAKDOWN OF PYRUVATE CITRIC ACID CYCLE ELECTRON TRANSPORT CHAIN OXIDATIVE PHOSPHORYLATION 1. Where does this step take place in the cell? Glucose NAD FAD 2. How many molecules of Glucose enter this step?

  16. 22.3: Glycolysis

    Introduction. There are two phases of Glycolysis: the "priming phase" because it requires an input of energy in the form of 2 ATPs per glucose molecule and; the "pay off phase" because energy is released in the form of 4 ATPs, 2 per glyceraldehyde molecule.; The end result of Glycolysis is two new pyruvate molecules which can then be fed into the Citric Acid cycle (also known as the Kreb's ...

  17. 13.4: Concept Mapping

    13.4: Concept Mapping - Connecting Ideas Visually. Either individually or as a group, create a concept map on a separate piece of paper or whiteboard that relates the processes of photosynthesis and cellular respiration. The words in the word bank below should go into bubbles. Arrange these bubbles in a way that helps communicate relationships ...

  18. Part 1: Metabolism (Concept Map) Flashcards

    cellular work. Cellular work. mechanical work. chemical work. transport of molecules. Concept map of metabolism. College Level. Biology 1406. Learn with flashcards, games, and more — for free.

  19. Cellular Respiration Graphic Organizer

    Cellular respiration is a series of chemical reactions that take place in the cells The process converts glucose into energy. All living things obtain energy from the food they eat. Cellular respiration takes place in two stages: glycolysis and the Krebs cycle. Glycolysis is the first stage of cellular respiration.

  20. Concept map of glycolysis

    Context 1 ... path in the knowledge base that connects two concepts, because presenting the full concept map where the path was found would make it difficult for the students to clearly see the...