chapter 9 cellular energetics. energy production this chapter deals with the catabolic pathways that...
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Chapter 9 Cellular EnergeticsChapter 9 Cellular Energetics
Energy ProductionEnergy Production
• This chapter deals with the catabolic pathways that break down organic molecules for the production of ATP.
• Whether you are talking about gasoline or sugar, the general equation is:
• Organic compound + O2 --> CO2 + H2O + Energy
• This chapter deals with the catabolic pathways that break down organic molecules for the production of ATP.
• Whether you are talking about gasoline or sugar, the general equation is:
• Organic compound + O2 --> CO2 + H2O + Energy
Cell RespirationCell Respiration
• Cellular respiration is the process of oxidizing food molecules into CO2 and H2O.
• Glucose, C6H12O6, is a common “food” used in the equation for cellular respiration, but all of the food you eat gets converted into compounds that can be funneled into cellular respiration.
• Cellular respiration is the process of oxidizing food molecules into CO2 and H2O.
• Glucose, C6H12O6, is a common “food” used in the equation for cellular respiration, but all of the food you eat gets converted into compounds that can be funneled into cellular respiration.
Exergonic ReactionsExergonic Reactions
• In each case, the catabolic pathways give off energy (-ΔG) and the end products are less organized (entropy has increased) than the beginning reactants.
• In each case, the catabolic pathways give off energy (-ΔG) and the end products are less organized (entropy has increased) than the beginning reactants.
Energy TransferEnergy Transfer
• The process takes place as the electrons in the reactants are transferred to oxygen.
• It does so in very discrete (small) steps causing the phosphorylation to ADP creating ATP.
• The ATP is immediately available as a source of energy for the cell.
• The process takes place as the electrons in the reactants are transferred to oxygen.
• It does so in very discrete (small) steps causing the phosphorylation to ADP creating ATP.
• The ATP is immediately available as a source of energy for the cell.
Redox ReactionsRedox Reactions
• The redox reactions, as they are called, involve an oxidation step that occurs when something loses an electron, and a reduction step where a substance gains an electron. Remember, LEO-GER and OIL-RIG
• The redox reactions, as they are called, involve an oxidation step that occurs when something loses an electron, and a reduction step where a substance gains an electron. Remember, LEO-GER and OIL-RIG
Redox ReactionsRedox Reactions
• Oxygen is a very powerful oxidizing agent because of its electronegativity.
• Thus, in redox reactions where electrons are moved closer to oxygen, a lot of chemical energy is given off and is available to do work.
• Oxygen is a very powerful oxidizing agent because of its electronegativity.
• Thus, in redox reactions where electrons are moved closer to oxygen, a lot of chemical energy is given off and is available to do work.
Redox ReactionsRedox Reactions
• Similarities:• Burning gas in a car liberates energy in the
hydrocarbons and powers the car.• Burning glucose within our cells enables us
to do work.• Cells are much more efficient than other
machinery. 40% vs. 15%
• Similarities:• Burning gas in a car liberates energy in the
hydrocarbons and powers the car.• Burning glucose within our cells enables us
to do work.• Cells are much more efficient than other
machinery. 40% vs. 15%
Redox Reactions Within the Cell
Redox Reactions Within the Cell
• C6H12O6 + 6O2 --> 6CO2 + 6H2O + Energy (ATP)
The O2 from respiration oxidizes glucose (O2 itself becomes reduced forming CO2 and H2O (reduced O2)
Anything with a lot of hydrogen is a good fuel because they fall downhill liberating energy which drives the synthesis of ATP (energy).
• C6H12O6 + 6O2 --> 6CO2 + 6H2O + Energy (ATP)
The O2 from respiration oxidizes glucose (O2 itself becomes reduced forming CO2 and H2O (reduced O2)
Anything with a lot of hydrogen is a good fuel because they fall downhill liberating energy which drives the synthesis of ATP (energy).
Redox ReactionsRedox Reactions
• Remember that there is an activation barrier that needs to be overcome before a reaction can take place (enzymes lower this barrier).
• Thus, this is why glucose doesn’t burn in air, but if we ignite it, we supply the activation energy necessary for it to burn.
• If we eat it, our enzymes lower the activation energy enabling our cells to “burn” the fuel for energy production.
• Remember that there is an activation barrier that needs to be overcome before a reaction can take place (enzymes lower this barrier).
• Thus, this is why glucose doesn’t burn in air, but if we ignite it, we supply the activation energy necessary for it to burn.
• If we eat it, our enzymes lower the activation energy enabling our cells to “burn” the fuel for energy production.
Glucose MetabolismGlucose Metabolism
• The most efficient way to harness the energy in chemical bonds of a fuel is to do so in small discrete steps.
• Glucose and other organic fuels used by the body are broken down in a series of steps that are each catalyzed by a specific enzyme.
• The most efficient way to harness the energy in chemical bonds of a fuel is to do so in small discrete steps.
• Glucose and other organic fuels used by the body are broken down in a series of steps that are each catalyzed by a specific enzyme.
Glucose MetabolismGlucose Metabolism
• At key points in the process, H atoms are stripped from the intermediates and transferred to the coenzyme, NAD+, creating NADH.
• In a series of steps, NADH transfers electrons to O2 which makes up the electron transport chain.
• At key points in the process, H atoms are stripped from the intermediates and transferred to the coenzyme, NAD+, creating NADH.
• In a series of steps, NADH transfers electrons to O2 which makes up the electron transport chain.
Electron Transport Chain
Electron Transport Chain
• The electron transport chain consists mostly of proteins found in the inner membrane of the mitochondria.
• The numerous steps of the ETC harness the energy released from the glucose metabolism. Each intermediate is more electronegative than the previous one and eventually the electrons reach O2 forming water. During the electron transfers, small amounts of energy are transferred and energy is released and used to produce ATP.
• The electron transport chain consists mostly of proteins found in the inner membrane of the mitochondria.
• The numerous steps of the ETC harness the energy released from the glucose metabolism. Each intermediate is more electronegative than the previous one and eventually the electrons reach O2 forming water. During the electron transfers, small amounts of energy are transferred and energy is released and used to produce ATP.
Electron Transport Chain Summary
Electron Transport Chain Summary
• In general, the reactions of the ETC can be summed up as:
• Food-->NADH-->ETC & ATP generation -->O2
• In general, the reactions of the ETC can be summed up as:
• Food-->NADH-->ETC & ATP generation -->O2
Cellular RespirationCellular Respiration
• The stages of cellular respiration can be summed up as follows:• 1. Glycolysis• 2. The Citric Acid Cycle• 3. Oxidative Phosphorylation
• The stages of cellular respiration can be summed up as follows:• 1. Glycolysis• 2. The Citric Acid Cycle• 3. Oxidative Phosphorylation
Cell Respiration Overview
Cell Respiration Overview
• Cellular Respiration Overview
• Cellular Respiration Overview
GlycolysisGlycolysis
• Glycolysis is a anaerobic process.• It doesn’t actually use O2, thus it isn’t
technically considered part of cellular respiration.
• Much of the starting material of the citric acid cycle and oxidative phosphorylation comes from glycolysis.
• Glycolysis is a anaerobic process.• It doesn’t actually use O2, thus it isn’t
technically considered part of cellular respiration.
• Much of the starting material of the citric acid cycle and oxidative phosphorylation comes from glycolysis.
GlycolysisGlycolysis
• Glycolysis occurs in the cytosol and breaks down glucose producing 2 ATP, 2 NADH, 2 pyruvates, and 2 water molecules.
• Glycolysis is where the majority of substrate level phosphorylation occurs.
• No CO2 is released during glycolysis.
• Glycolysis occurs in the cytosol and breaks down glucose producing 2 ATP, 2 NADH, 2 pyruvates, and 2 water molecules.
• Glycolysis is where the majority of substrate level phosphorylation occurs.
• No CO2 is released during glycolysis.
Glycolysis MovieGlycolysis Movie
• Glycolysis• Glycolysis
The Link Between Glycolysis and the Citric
Acid Cycle
The Link Between Glycolysis and the Citric
Acid Cycle• This is known as the “link reaction.”• It is here that pyruvate is converted into
acetyl CoA and enters the citric acid cycle where the breakdown of glucose is completed.
• In this process, CO2 is given off and a small amount of ATP is made, and NADH and FADH2 are generated.
• This is known as the “link reaction.”• It is here that pyruvate is converted into
acetyl CoA and enters the citric acid cycle where the breakdown of glucose is completed.
• In this process, CO2 is given off and a small amount of ATP is made, and NADH and FADH2 are generated.
NADH and FADH2 are Reducing Power
NADH and FADH2 are Reducing Power
• NADH and FADH2 are a source of electrons which are used as reducing power within the mitochondrial matrix.
• NADH and FADH2 are a source of electrons which are used as reducing power within the mitochondrial matrix.
Oxidative Phosphorylation
Oxidative Phosphorylation
• Oxidative phosphorylation uses NADH and FADH2 to transfer electrons from one molecule to another in the matrix of the mitochondrion.
• These small “packets” of energy are used to drive the synthesis of ATP.
• Oxidative phosphorylation uses NADH and FADH2 to transfer electrons from one molecule to another in the matrix of the mitochondrion.
• These small “packets” of energy are used to drive the synthesis of ATP.
ATP SynthesisATP Synthesis
• Within the mitochondrial matrix, chemiosmosis and the ETC use the small “packets” of energy to drive the synthesis of ATP.
• 90% of the ATP generated comes from oxidative phosphorylation.
• Within the mitochondrial matrix, chemiosmosis and the ETC use the small “packets” of energy to drive the synthesis of ATP.
• 90% of the ATP generated comes from oxidative phosphorylation.
ATP SynthesisATP Synthesis
• The remaining 10% of ATP comes from substrate level phosphorylation (glycolysis) where an enzyme transfers a phosphate group (PO3
2-) from a substrate directly to ADP.
• The substrate in this case comes from an organic intermediate generated from the breakdown of glucose.
• The remaining 10% of ATP comes from substrate level phosphorylation (glycolysis) where an enzyme transfers a phosphate group (PO3
2-) from a substrate directly to ADP.
• The substrate in this case comes from an organic intermediate generated from the breakdown of glucose.
The Junction Between the Citric Acid Cycle and
Glycolysis
The Junction Between the Citric Acid Cycle and
Glycolysis• After glycolysis, most of the energy
from glucose is stored in the pyruvate molecules.
• When O2 is present, pyruvate enters the citric acid cycle (through the “link reaction”) within the mitochondrion completing the breakdown of glucose.
• After glycolysis, most of the energy from glucose is stored in the pyruvate molecules.
• When O2 is present, pyruvate enters the citric acid cycle (through the “link reaction”) within the mitochondrion completing the breakdown of glucose.
The Junction Between the Citric Acid Cycle and
Glycolysis
The Junction Between the Citric Acid Cycle and
Glycolysis
• The “link reaction.”• At the junction
between glycolysis and the citric acid cycle, pyruvate is converted to acetyl CoA, NADH is given off along with 1 molecule of CO2.
• The “link reaction.”• At the junction
between glycolysis and the citric acid cycle, pyruvate is converted to acetyl CoA, NADH is given off along with 1 molecule of CO2.
The “Link Reaction”The “Link Reaction”
• During the link reaction, the three carbon sugar, pyruvate, is converted into the two carbon intermediate, Acetyl CoA, and is ready to enter the citric acid cycle.
• This is the first step in which CO2 is released.
• During the link reaction, the three carbon sugar, pyruvate, is converted into the two carbon intermediate, Acetyl CoA, and is ready to enter the citric acid cycle.
• This is the first step in which CO2 is released.
The Citric Acid CycleThe Citric Acid Cycle
• Upon entering the citric acid cycle, acetyl CoA adds its 2 carbon acetyl group to oxaloacetate, which creates citrate.
• Citrate now undergoes a series of steps that creates 1 ATP molecule, 3NADH and 1FADH2. In the process, 2CO2 are given off, and oxaloacetate is regenerated--hence the “cycle.”
• Upon entering the citric acid cycle, acetyl CoA adds its 2 carbon acetyl group to oxaloacetate, which creates citrate.
• Citrate now undergoes a series of steps that creates 1 ATP molecule, 3NADH and 1FADH2. In the process, 2CO2 are given off, and oxaloacetate is regenerated--hence the “cycle.”
Citric Acid CycleCitric Acid Cycle
• Remember, each molecule of glucose produces two molecules of pyruvate, so the cycle actually spins twice for each molecule of glucose that undergoes glycolysis.
• Remember, each molecule of glucose produces two molecules of pyruvate, so the cycle actually spins twice for each molecule of glucose that undergoes glycolysis.
Citric Acid CycleCitric Acid Cycle
• Citric Acid Cycle• Citric Acid Cycle
Electron Transport Chain
Electron Transport Chain
• The NADH and FADH2 produced by the citric acid cycle carry energy to the cristae of the mitochondria.
• The NADH and FADH2 produced by the citric acid cycle carry energy to the cristae of the mitochondria.
Electron Transport Chain
Electron Transport Chain
• The energy from the carriers is used by the electron transport chain to couple electron transport with the movement of H+ to the intermembrane space. This is oxidative phosphorylation.
• The energy from the carriers is used by the electron transport chain to couple electron transport with the movement of H+ to the intermembrane space. This is oxidative phosphorylation.
Oxidative Phosphorylation and the Electron Transport Chain
Oxidative Phosphorylation and the Electron Transport Chain
• Reduced NAD and FAD carry the electrons to the ETC.
• The ETC moves the electrons “downhill” to oxygen.
• The binding of the free protons to oxygen maintains the hydrogen gradient and generates water.
• Reduced NAD and FAD carry the electrons to the ETC.
• The ETC moves the electrons “downhill” to oxygen.
• The binding of the free protons to oxygen maintains the hydrogen gradient and generates water.
Oxidative Phosphorylation and the Electron Transport Chain
Oxidative Phosphorylation and the Electron Transport Chain
• No ATP is made directly, but the energy transfer is sliced into small amounts.
• The energy is used to drive hydrogen ions across the membrane.
• ATP synthesis occurs via chemiosmosis.
• No ATP is made directly, but the energy transfer is sliced into small amounts.
• The energy is used to drive hydrogen ions across the membrane.
• ATP synthesis occurs via chemiosmosis.
ATP Synthase and Chemiosmosis
ATP Synthase and Chemiosmosis
• The inner part of the mitochondrial membrane contains many copies of a protein complex called ATP synthase.
• ATP Synthase is the enzyme that actually phosphorylates ADP--making ATP during oxidative phosphorylation.
• It makes use of a H+ gradient.
• The inner part of the mitochondrial membrane contains many copies of a protein complex called ATP synthase.
• ATP Synthase is the enzyme that actually phosphorylates ADP--making ATP during oxidative phosphorylation.
• It makes use of a H+ gradient.
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ChemiosmosisChemiosmosis
• Chemiosmosis is a fancy word that describes the movement of H+ (protons) from a high concentration to a low concentration.
• Chemiosmosis is a fancy word that describes the movement of H+ (protons) from a high concentration to a low concentration.
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ChemiosmosisChemiosmosis
• The mitochondrial membrane generates and maintains this H+ gradient by using the energy releasing flow of electrons to pump H+ across the membrane from the matrix to the intermembrane space.
• The mitochondrial membrane generates and maintains this H+ gradient by using the energy releasing flow of electrons to pump H+ across the membrane from the matrix to the intermembrane space.
ATP Synthase and Chemiosmosis
ATP Synthase and Chemiosmosis
• The proton (H+) gradient that exists between the mitochondrial matrix and the intermembrane space drives the synthesis of ATP into the matrix of the mitochondrion.
• The proton (H+) gradient that exists between the mitochondrial matrix and the intermembrane space drives the synthesis of ATP into the matrix of the mitochondrion.
ChemiosmosisChemiosmosis
• The H+ gradient that forms is called the proton-motive force.
• It is this force that drives H+ back across the membrane through ATP synthase and in the process generates ATP.
• The H+ gradient that forms is called the proton-motive force.
• It is this force that drives H+ back across the membrane through ATP synthase and in the process generates ATP.
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Electron Transport Chain
Electron Transport Chain
• Electron Transport Chain
• Electron Transport Chain
ATP ProductionATP Production
• About 36 to 38 ATPs are produced by the complete oxidation of glucose.
• There are three main reasons why we cannot put an exact number on this.
• About 36 to 38 ATPs are produced by the complete oxidation of glucose.
• There are three main reasons why we cannot put an exact number on this.
ATP ProductionATP Production
• 1. Phosphorylation and redox reactions are not directly coupled to one another in a 1:1 ratio.• One NADH generates a proton motive force that
creates about 3 ATPs.
• FADH2 enters lower in the ETC so it only generates about 2 ATPs.
• 1. Phosphorylation and redox reactions are not directly coupled to one another in a 1:1 ratio.• One NADH generates a proton motive force that
creates about 3 ATPs.
• FADH2 enters lower in the ETC so it only generates about 2 ATPs.
ATP ProductionATP Production
• 2. NADH generated from glycolysis can’t diffuse into the mitochondrion. • Thus, its electrons are passed via a shuttle
system to either NAD+ or FAD+ inside the mitochondrion.
• It’s a matter of chance as to whether NAD+ or FAD+ accepts the electrons.
• If NAD+ is the acceptor, 3 ATP are produced, if FAD+ is the acceptor, 2 ATP are produced.
• 2. NADH generated from glycolysis can’t diffuse into the mitochondrion. • Thus, its electrons are passed via a shuttle
system to either NAD+ or FAD+ inside the mitochondrion.
• It’s a matter of chance as to whether NAD+ or FAD+ accepts the electrons.
• If NAD+ is the acceptor, 3 ATP are produced, if FAD+ is the acceptor, 2 ATP are produced.
ATP ProductionATP Production
• 3. Some of the proton-motive force generated is used to power the uptake of pyruvate from the cytosol and is not used to power ATP production.
• 3. Some of the proton-motive force generated is used to power the uptake of pyruvate from the cytosol and is not used to power ATP production.
The Junction Between the Citric Acid Cycle and
Glycolysis
The Junction Between the Citric Acid Cycle and
Glycolysis
• The “link reaction.”• At the junction
between glycolysis and the citric acid cycle, pyruvate is converted to acetyl CoA, NADH is given off along with 1 molecule of CO2.
• The “link reaction.”• At the junction
between glycolysis and the citric acid cycle, pyruvate is converted to acetyl CoA, NADH is given off along with 1 molecule of CO2.
ATP ProductionATP Production
• Thus, if all of the proton-motive force were used, a maximum of 34 ATPs would be produced + the 4 from substrate level phosphorylation giving a total of 38 ATP.
• Thus, if all of the proton-motive force were used, a maximum of 34 ATPs would be produced + the 4 from substrate level phosphorylation giving a total of 38 ATP.
ATP TransportATP Transport
• The ATP that is made in the mitochondria is manufactured into the matrix of the mitochondrion.
• The ATP that is made in the mitochondria is manufactured into the matrix of the mitochondrion.
https://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/krebs.htm
ATP TransportATP Transport
• ATP-ADP translocase is an enzyme embedded in the inner mitochondrial membrane.
• It transports ATP from the matrix to the intermembrane space, and ADP from the intermembrane space into the matrix.
• ATP-ADP translocase is an enzyme embedded in the inner mitochondrial membrane.
• It transports ATP from the matrix to the intermembrane space, and ADP from the intermembrane space into the matrix.
ATP TransportATP Transport
• The outer membrane of the mitochondrion is permeable to a wide variety of molecules.
• Thus, the intermembrane space and the cytoplasm contain a very similar biochemistry.
• The outer membrane of the mitochondrion is permeable to a wide variety of molecules.
• Thus, the intermembrane space and the cytoplasm contain a very similar biochemistry.
ATP TransportATP Transport
• As the ATP is used in the cytoplasm, the ADP diffuses through the outer membrane and into the intermembrane space.
• ADP-ATP translocase transports the ADP into the matrix and the ATP into the intermembrane space.
• As the ATP is used in the cytoplasm, the ADP diffuses through the outer membrane and into the intermembrane space.
• ADP-ATP translocase transports the ADP into the matrix and the ATP into the intermembrane space.
ATP TransportATP Transport
• The newly made ATP in the intermembrane space then diffuses into the cytoplasm where it is used, and the cycle repeats.
• The newly made ATP in the intermembrane space then diffuses into the cytoplasm where it is used, and the cycle repeats.
FermentationFermentation
• Glycolysis occurs in the cytoplasm of a cell with or without oxygen producing 2 ATPs.
• As long as there is a way to regenerate NAD+ when O2 is not available, the cell can keep functioning via glycolysis. (NAD+ is the oxidizing agent).
• Fermentation is the way the cell continues glycolysis.
• Glycolysis occurs in the cytoplasm of a cell with or without oxygen producing 2 ATPs.
• As long as there is a way to regenerate NAD+ when O2 is not available, the cell can keep functioning via glycolysis. (NAD+ is the oxidizing agent).
• Fermentation is the way the cell continues glycolysis.
Alcohol FermentationYeast
Alcohol FermentationYeast
• 1. CO2 is released from pyruvate creating acetaldehyde.
• 2. NADH reduces acetaldehyde to ethanol regenerating NAD+.
• 3. Glycolysis is allowed to 3. Glycolysis is allowed to continue.continue.
• 1. CO2 is released from pyruvate creating acetaldehyde.
• 2. NADH reduces acetaldehyde to ethanol regenerating NAD+.
• 3. Glycolysis is allowed to 3. Glycolysis is allowed to continue.continue.
Lactic Acid Fermentation
Muscle
Lactic Acid Fermentation
Muscle• 1. Pyruvate is reduced by
NADH forming lactate as an end product.
• 2. Lactate is the ionized form of lactic acid.
• 3. Glycolysis is allowed to 3. Glycolysis is allowed to continue.continue.
• 1. Pyruvate is reduced by NADH forming lactate as an end product.
• 2. Lactate is the ionized form of lactic acid.
• 3. Glycolysis is allowed to 3. Glycolysis is allowed to continue.continue.
FermentationFermentation
• Fermentation• Fermentation
Evolutionary Significance of
Glycolysis
Evolutionary Significance of
Glycolysis• 1. Ancient prokaryotes likely used glycolysis
for energy production before O2 was present in the atmosphere.
• 2. Oldest prokaryotic fossil is 3.5 byo, O2 began accumulating in the atmosphere 2.7 bya.
• 1. Ancient prokaryotes likely used glycolysis for energy production before O2 was present in the atmosphere.
• 2. Oldest prokaryotic fossil is 3.5 byo, O2 began accumulating in the atmosphere 2.7 bya.
Evolutionary Significance of
Glycolysis
Evolutionary Significance of
Glycolysis• 3. Glycolysis is the most widespread form of
energy production indicating it evolved early on.
• 4. Location in the cytosol indicates it’s very old, older than membrane bound organelles.
• 3. Glycolysis is the most widespread form of energy production indicating it evolved early on.
• 4. Location in the cytosol indicates it’s very old, older than membrane bound organelles.
CatabolismCatabolism
• Much of what we’ve discussed regarding cellular respiration deals with glucose as the “food,” but this isn’t always the case.
• The foods we eat are often high in carbohydrates, proteins and fats.
• Many of the carbs get broken down into glucose and other monosaccharides that can be used by cellular respiration.
• Much of what we’ve discussed regarding cellular respiration deals with glucose as the “food,” but this isn’t always the case.
• The foods we eat are often high in carbohydrates, proteins and fats.
• Many of the carbs get broken down into glucose and other monosaccharides that can be used by cellular respiration.
Protein CatabolismProtein Catabolism
• Proteins are also used as fuel. • First, deamination removes an amino
group (excreted in urea), and the intermediates are then fed into glycolysis and the TCA cycle.
• Proteins are also used as fuel. • First, deamination removes an amino
group (excreted in urea), and the intermediates are then fed into glycolysis and the TCA cycle.
Fat CatabolismFat Catabolism
• Fats undergo a series of steps producing various intermediates of glycolysis and the TCA cycle which can then be used as fuel.
• Fats get converted to glycerol and fatty acids.
• Glycerol gets converted to G-3-P. • β-oxidation converts the fatty acids into 2
carbon fragments that enter the TCA cycle as acetyl CoA.
• Fats undergo a series of steps producing various intermediates of glycolysis and the TCA cycle which can then be used as fuel.
• Fats get converted to glycerol and fatty acids.
• Glycerol gets converted to G-3-P. • β-oxidation converts the fatty acids into 2
carbon fragments that enter the TCA cycle as acetyl CoA.
=7 FADH2
7 NADH8 Acetyl CoA
Anabolic MetabolismAnabolic Metabolism
• In addition to using food for energy, some of the food we ingest is diverted away from glycolysis and the TCA cycle and is used for growth and maintenance of the cell. Instead of producing ATP, the body uses it to create building products.
• In addition to using food for energy, some of the food we ingest is diverted away from glycolysis and the TCA cycle and is used for growth and maintenance of the cell. Instead of producing ATP, the body uses it to create building products.