Lecture PowerPoint to accompany
Twelfth Edition
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7.1 Metabolism

7.1 Metabolism
• Catabolism : Breaking down of molecules

7.1 Metabolism
• Catabolism: Breaking down of molecules
• Anabolism : Building up of molecules
(ATP is the energy currency used by these reactions)

Metabolism

7.1 Metabolism
• Catabolism
– Food contains three nutrients that are used as energy sources
– These nutrients can be broken down into smaller molecules
• Carbohydrates Glucose
• Fats Glycerol and Fatty Acids
• Proteins Amino Acids

7.1 Metabolism
• Anabolism
– Many of the building blocks of larger molecules come directly from our food.
• Glucose Glycogen
• Amino Acids Proteins

7.1 Metabolism
• Cellular Respiration
– Release of energy from glucose (usually) coupled to
ATP synthesis
– An aerobic process that requires O
2
CO
2 and releases

Cellular Respiration

7.2 Overview of Cellular
Respiration

7.2 Overview of Cellular
Respiration
• Metabolic pathways allow energy within glucose to be released
• Release of energy does happen all at once
• As glucose is broken down, ATP is built up
• Breakdown of glucose results in 36 or 38 ATP molecules
• The energy released is by the removal of a phosphate group

7.2 Overview of Cellular
Respiration
• NAD + and FAD
• Two coenzymes of oxidation and reduction that are active during cellular respiration
• They carry electrons from the cytoplasm or the mitochondrial matrix and carry them to the cristae of the mitochondria
• NAD + and FAD each carry two electrons and two hydrogen atoms

The NAD + Cycle

7.2 Overview of Cellular
Respiration
• Phases of Cellular Respiration
– Glycolysis
– Preparatory Reaction
– Citric Acid Cycle
– Electron Transport Chain

Phases of Glucose Breakdown

7.2 Overview of Cellular
Respiration
• Glycolysis
– Breakdown of glucose to 2 molecules of pyruvate
– Oxidation by removal of hydrogens releases enough energy to make 2 ATP

7.2 Overview of Cellular
Respiration
• Glycolysis
– Breakdown of glucose to 2 molecules of pyruvate
– Oxidation by removal of hydrogens releases enough energy to make 2 ATP

7.2 Overview of Cellular
Respiration
• Glycolysis
– Breakdown of glucose to 2 molecules of pyruvate
– Oxidation by removal of hydrogens releases enough energy to make 2 ATP

7.2 Overview of Cellular
Respiration
• Preparatory Reaction
– Pyruvate oxidized to acetyl CoA and carbon dioxide is removed
– Prep reaction occurs twice because glycolysis produces 2 pyruvates

7.2 Overview of Cellular
Respiration
• Citric Acid Cycle
– Acetyl CoA is converted to citric acid and enters the cycle
– Cyclical series of oxidation reactions that produces 1
ATP and carbon dioxide
– Citric acid cycle turns twice because 2 acetyl CoA’s are produced per glucose

7.2 Overview of Cellular
Respiration
• Electron Transport Chain
– Series of electron carrier molecules
– Electrons passed from one carrier to another
– As the electrons move from a higher energy state to a lower one, energy is released to make ATP
– Under aerobic conditions 32-34 ATP per glucose molecule can be produced

7.2 Overview of Cellular
Respiration
• Electron Transport Chain
– Series of electron carrier molecules
– Electrons passed from one carrier to another
– As the electrons move from a higher energy state to a lower one, energy is released to make ATP
– Under aerobic conditions 32-34 ATP per glucose molecule can be produced

7.2 Overview of Cellular
Respiration
• Pyruvate
– Pivotal metabolite in cellular respiration
– If no oxygen is available, pyruvate is reduced to lactate (in animals) or alcohol and carbon dioxide (in plants) in a process called fermentation
– Fermentation results in a net gain of 2 ATP/glucose

7.3 Outside the Mitochondria:
Gycolysis

7.3 Outside the Mitochondria:
Gycolysis
• Energy-Investment Steps
– Energy from 2 ATP is used to activate glucose
– Glucose is split into two 3-carbon G3P molecules

7.3 Outside the Mitochondria:
Gycolysis
• Energy-Harvesting Steps
– Oxidation of G3P by removal of hydrogens
– Hydrogen’s are picked up by NAD + to form NADH
– Oxidation of G3P and further substrates yields enough energy to produce 4 ATP by direct substrate phosphorylation

Glycolysis: Inputs and Outputs

7.4 Inside the Mitochondria
• Preparatory Reaction
– Produces the molecule that will enter the citric acid cycle
– 3C pyruvate is converted to 2C acetyl CoA
– Carbon dioxide is produced
– Hydrogen atoms are removed from pyruvate and picked up to form NADH
– This reaction occurs twice per glucose

The Preparatory Reaction

7.4 Inside the Mitochondria
• Citric Acid Cycle
– C
2
C
4 acetyl group from prep reaction combines with a molecule to produce C
6 citrate
– Oxidation of citrate by removal of hydrogens
– Produces 3 NADH and 1 FADH
2
– Produces 1 ATP by direct substrate phosphorylation
– Cycle turns twice per glucose

Citric Acid Cycle:
Inputs and Outputs

Citric Acid Cycle

7.4 Inside the Mitochondria
• Electron Transport Chain
– 2 electrons per NADH and FADH
2 transport chain enter the electron
– Electrons are passed to series of electron carriers called cytochromes
– Energy is captured and stored as a hydrogen ion concentration gradient
– For each NADH enough energy is released to form 3
ATP
– For each FADH
2 there are 2 ATP produced

7.4 Inside the Mitochondria
• Electron Transport Chain
– The final electron acceptor is oxygen
– After receiving electrons oxygen combines with hydrogen ions to form water as an end product
• ½ O
2
+ 2 e- + 2H+  H
2
O
– NAD + and FAD recycle back to pick up more electrons from glycolysis, prep reaction, and citric acid cycle

Electron Transport Chain

7.4 Inside the Mitochondria
• Organization of Cristae
– Electron carriers are arranged along the cristae
• As electrons are passed, energy is used to pump
H + into the intermembrane space of mitochondrion
• As H + moves back into matrix energy is released and captured to form ATP by ATP synthase complexes
– Process is called chemiosmosis

Organization of Cristae

Energy Yield per
Glucose Molecule

7.4 Inside the Mitochondria

7.4 Inside the Mitochondria
• Efficiency of Cellular Respiration
– The difference in energy content of reactants (glucose and oxygen) and products (carbon dioxide and water) is 686 kcal
– ATP phosphate bond has 7.3 kcal of energy
– 36 ATP are produced in respiration 36 X 7.3 = 263 kcal
– 263/686 = 39% efficiency of energy capture
– The rest of the energy is lost as heat

7.5 Fermentation

7.5 Fermentation
• Fermentation
– Occurs when O
2 is not available
– Animal cells convert pyruvate to lactate
– Other organisms convert pyruvate to alcohol and CO
2
– Fermentation regenerates NAD + which keeps glycolysis going

7.5 Fermentation
• Advantages and Disadvantages of Fermentation
– Provides a rapid burst of ATP
– Provides a low but continuous supply of ATP when oxygen is limited and only glycolysis can function
– Lactate is potentially toxic to muscles, lowering pH and causing fatigue

Fermentation:
Inputs and Outputs

Fermentation