1. Inquiry into Life Eleventh Edition Sylvia S. Mader
Chapter 7
Lecture Outline
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2. 7.1 Overview of cellular respiration
Overall process
Oxidation of glucose to carbon dioxide, water, and energy. This is an Exergonic reaction used to drive ATP synthesis which is endergonic
4 phases of respiration are required for complete oxidation of glucose
Oxidation involves the removal of hydrogen atoms from substrates by redox coenzymes NAD+ and FAD

3. Cellular respiration

4. Overview of cellular respiration cont’d.
NAD+ and FAD
Redox coenzymes active in respiration
NAD+ is reduced to NADH
FAD is reduced to FADH2
FADH2 and NADH carry electrons to the electron transport chain

5. The NAD+ cycle

6. Overview of cellular respiration cont’d.
Phases of cellular respiration
Glycolysis (Takes place in the Cytoplasm)
Use Energy from 2 ATP’s to activate glucose
Breakdown of glucose to 2 molecules of pyruvate
Oxidation by removal of hydrogens releases enough energy to make 2 ATP’s from each pyruvate results in a Net Gain of 2 ATP’s in this Phase per Glucose Molecule.

7. Phases of cellular respiration, cont’d.
Preparatory reaction (Takes place in Matrix of Mitochondria)
Pyruvate oxidized to acetyl CoA and carbon dioxide is removed
Prep reaction occurs twice per Glucose molecule because glycolysis produces 2 pyruvates
No ATP’s produced in this phase

8. Phases of cellular respiration, cont’d.
Citric acid cycle (Takes place in Matrix of Mitochondria)
Each Pyruvate was oxidized to acetyl CoA in Preparatory Reaction.
Now Acetyl CoA is converted to citric acid and enters the cycle
Cyclical series of oxidation reactions that produces 1 ATP and carbon dioxide per cycle turn
Citric acid cycle turns twice per Glucose Molecule because 2 acetyl CoA’s are produced per glucose
2 ATP’s produced per Glucose Molecule in this phase

9. Overview of cellular respiration cont’d.
Phases of cellular respiration, cont’d.
Electron transport chain (Takes place in Cristae of Mitochondria)
Series of electron carrier molecules which pass Electrons from one carrier to another releasing energy to make ATP
As the electrons move from a higher energy state to a lower one, energy is released to make ATP
Under aerobic conditions ATP per glucose molecule can be produced

10. Phases of cellular respiration, cont’d.
In Anaerobic Conditions (No Oxygen Present)
Glycolysis produces Pyruvate
Pivotal metabolite in cellular respiration
If no oxygen is available, pyruvate is reduced to lactate (in animals) or ethanol and carbon dioxide (in plants) in a process called fermentation

11. Cellular respiration

12. 7.2 Outside the mitochondria: Glycolysis
Energy-investment steps
Energy from 2 ATP is used to activate glucose
Glucose is split into 2 3-carbon G3P molecules
Energy-harvesting steps
Oxidation of G3P by removal of hydrogens
Hydrogens 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, so there’s a net gain of 2 ATP’s.

13. Outside the mitochondria: glycolysis cont’d.
Glycolysis yields:
4 ATP by direct substrate phosphorylation
2 ATP were consumed in the investments steps
Net gain of ATP from glycolysis is therefore 2 ATP
2 NADH which will carry electrons to the electron transport chain
No Oxygen is required for Glycolysis to produce pyruvate.
When oxygen is available pyruvate will enter the mitochondria for further oxidation
If no oxygen is available, pyruvate will enter the fermentation pathway

14. Glycolysis

15. 7.3 Inside the mitochondria
Breathing, eating, and cellular respiration
Oxygen is taken in by breathing
Digested food contains glucose
Oxygen and glucose are carried to cells by the bloodstream
Glucose and oxygen enter cells where respiration occurs
Carbon dioxide is taken by the bloodstream to the lungs

16. Relationship between breathing, eating, and cell respiration

17. Inside the mitochondria cont’d.
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

18. Inside the mitochondria cont’d.
Citric acid cycle
2C acetyl group from prep reaction combines with a 4C molecule to produce 6C citrate
Oxidation of citrate by removal of hydrogens
Produces 3 NADH and 1 FADH2
Produces 1 ATP per cycle by direct substrate phosphorylation
Cycle turns twice per glucose
Total yield: 6 NADH, 2 FADH2, 2 ATP, 4 CO2

19. Citric acid cycle

20. Inside the mitochondria cont’d.
Electron transport chain (ETC)
2 electrons per NADH and FADH2 enter ETC
Electrons are passed to series of electron carriers called cytochromes
Energy is captured and stored as a hydrogen ion concentration gradient. This process is called chemiosmosis
For each NADH enough energy is released to form 3 ATP
For each FADH2 there are 2 ATP produced

21. Overview of the electron transport chain

22. Inside the mitochondria cont’d.
Electron transport chain cont’d.
the final electron acceptor is oxygen
After receiving electrons oxygen combines with hydrogen ions to form water as an end product ½ O2+ 2 e- + 2H+  H2O
NAD+ and FAD recycle back to pick up more electrons from glycolysis, prep reaction, and citric acid cycle

23. Inside the mitochondria cont’d.
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
This builds an electro-chemical gradient that stores energy
As H+ moves back into matrix energy is released and captured to form ATP by ATP synthase complexes
Process is called chemiosmosis

24. Organization of cristae in the mitochondria

25. Inside the mitochondria cont’d.
Energy yield from cellular respiration is 36 – 38 ATP’s per Glucose Molecule
From direct phosphorylation
Net of 2 ATP from glycolysis
2 ATP from citric acid cycle
From chemiosmosis
Electron transport chain produces 32 – 34 ATP per Glucose Molecule

26. Accounting of energy yield per glucose molecule breakdown

27. Inside the mitochondria cont’d.
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

28. 7.4 Fermentation Fermentation Produces only a net of 2 ATP per glucose
Occurs when O2 is not available
Animal cells convert pyruvate to lactate
Plant cells, yeasts convert pyruvate to ethanol and CO2
Fermentation regenerates NAD+ which keeps glycolysis going
Produces only a net of 2 ATP per glucose

29. Fermentation
Fig 7.10

30. Fermentation cont’d. Advantages and Disadvantages of fermentation
Provides a low but continuous supply of ATP when oxygen is limited and only glycolysis can function
Can provide a rapid burst of ATP in muscle cells, even when oxygen is in limited supply.
Lactate is potentially toxic to muscles, lowering pH and causing fatigue
Transported to liver where it is converted to pyruvate
This process requires oxygen
During exercise an oxygen debt is built up
Oxygen debt is the amount of oxygen “owed” to the liver to convert accumulated lactic acid to pyruvate

31. Fermentation , cont’d. Energy yield of fermentation
Produces only a net of 2 ATP per glucose through direct substrate phosphorylation by allowing glycolysis to continue. MUCH LESS efficient than Aerobic Cellular Respiration.
Following fermentation most of the potential energy from glucose is still waiting to be released
Fermentation is a way to continue an ATP supply to cells when oxygen is in short supply

32. 7.5 Metabolism Catabolism-break down reactions
Carbohydrates-digested to glucose for cell respiration
Fats-digested to glycerol and fatty acids
Glycerol can enter glycolytic pathway
Fatty acids metabolized to acetyl CoA which enters citric acid cycle
Proteins- deamination
Amino acids can enter pathway at different points

33. Metabolism

34. Metabolism cont’d. Anabolism- synthesis reactions
Substrates of glycolysis and citric acid cycle can be substrates for synthesis of macromolecules
G3P can be converted to glycerol
Acetyl groups can be converted to fatty acids
Some citric acid intermediates can be converted to amino acids
Anabolic reactions require the input of energy in the form of ATP generated in catabolic reactions