1. Cellular Respiration Part V: Oxidative Phosphorylation

2. Oxidative phosphorylation: electron transport and chemiosmosis
Figure 9.16
Electron shuttles span membrane
MITOCHONDRION
2 NADH or
2 FADH2
2 NADH
2 NADH
6 NADH
2 FADH2
Oxidative phosphorylation: electron transport and chemiosmosis
Glycolysis
Pyruvate oxidation
Citric acid cycle
Glucose
2 Pyruvate
2 Acetyl CoA
What was oxygen’s role in cellular respiration?
 2 ATP
 2 ATP
 about 26 or 28 ATP
About 30 or 32 ATP
Maximum per glucose:
CYTOSOL

3. Without Oxygen… Most cellular respiration requires O2 to produce ATP
Without O2, the electron transport chain will cease to operate
In that case, glycolysis couples with fermentation or anaerobic respiration to produce ATP
Emphasize that last bullet! Students think only in terms of “oxygen-based” respiration. They may not even be aware that respiration is possible anaerobically!

4. Anaerobic respiration uses an electron transport chain with a final electron acceptor other than O2, for example sulfate
Fermentation uses substrate-level phosphorylation instead of an electron transport chain to generate ATP
Also emphasize that anaerobic respiration simply occurs when a different “chemical” accepts the electrons instead of oxygen. Many substances can function as final electron acceptors. These include sulfate (SO42-), nitrate (NO3-), sulfur (S), or fumarate. Often organisms that utilize the molecules are obligate anaerobes.

5. Types of Fermentation
Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis
Two common types are alcohol fermentation and lactic acid fermentation
Emphasize to student that there are many, many types of alcohols and not all are safe for human consumption!

6. Alcoholic Fermentation
In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2
Alcohol fermentation by yeast is used in brewing, winemaking, and baking
We are indeed referring to ethanol when we say “alcohol fermentation”.

7. i i   Figure 9.17 2 ATP  2 ATP Glucose Glycolysis Glucose
2 ADP  2 P i
2 ATP
2 ADP  2 P i
2 ATP
Glucose
Glycolysis
Glucose
Glycolysis
2 Pyruvate 2
NAD 
2 NADH
2 CO2 2
NAD 
2 NADH 
2 H 
2 H
2 Pyruvate
Figure 9.17 Fermentation. Emphasize the similarities and differences between two different types of fermentation. Animations of each follow.
2 Ethanol
2 Acetaldehyde
2 Lactate
(a) Alcohol fermentation
(b) Lactic acid fermentation

8.   2 ADP  2 P i 2 ATP Glucose Glycolysis 2 Pyruvate 2 NAD 2 NADH
Figure 9.17a
2 ADP  2 P i
2 ATP
Glucose
Glycolysis
2 Pyruvate
2 NAD 
2 NADH
2 CO2 
2 H 
Note end product is ethanol and NAD is regenerated
2 Acetaldehyde
2 Ethanol
(a) Alcohol fermentation

9. Alcoholic Fermentation

10.   2 ADP  2 P i 2 ATP Glucose Glycolysis 2 NAD 2 NADH  2 H
Figure 9.17b
2 ADP  2 P i
2 ATP
Glucose
Glycolysis
2 NAD 
2 NADH 
2 H 
2 Pyruvate
Figure 9.17 Fermentation.
2 Lactate
(b) Lactic acid fermentation

11. Lactic Acid Fermentation
In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO2
Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt
Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce

12. Lactate Fermentation

13. Fermentation compared to Anaerobic & Aerobic Respiration
All use glycolysis (net ATP = 2) to oxidize glucose and harvest chemical energy of food
In all three, NAD+ is the oxidizing agent that accepts electrons during glycolysis
The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respiration
Cellular respiration produces 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule

14. Anaerobic Respiration
Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O2
Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration
In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes

15. Ethanol, lactate, or other products
Figure 9.18
Glucose
Glycolysis
CYTOSOL
Pyruvate
No O2 present: Fermentation
O2 present: Aerobic cellular respiration
MITOCHONDRION
Ethanol, lactate, or other products
Acetyl CoA
Pyruvate as a key juncture in catabolism.
Citric acid cycle

16. Evolutionary Significance of Glycolysis
Ancient prokaryotes are thought to have used glycolysis long before there was oxygen in the atmosphere
Very little O2 was available in the atmosphere until about 2.7 billion years ago, so early prokaryotes likely used only glycolysis to generate ATP
Glycolysis is a very ancient process
Never pass up an opportunity to connect a unit back to evolution!

17. But I eat more than sugar..
Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration
Glycolysis accepts a wide range of carbohydrates
Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle
Emphasize the literal meaning of “carbohydrate”, carbon-waters which have a generic formula of CH2O. Multiply that by 6 and you have glucose! Add bunches of those together through bunches of dehydration synthesis reactions and you have a starch.

18. Oxidative phosphorylation
Figure 9.19
Proteins
Carbohydrates
Fats
Amino acids
Sugars
Glycerol
Fatty acids
Glycolysis
Glucose
Glyceraldehyde 3- P
NH3
Pyruvate
Acetyl CoA
Figure 9.19 The catabolism of various molecules from food.
Citric acid cycle
Oxidative phosphorylation

19. Regulation of Respiration
Feedback inhibition is the most common mechanism for control
If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down
Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway
Emphasize one last time that METABOLISM is the sum of CATABOLISM (breaking down or deconstructing) + ANABOLISM (synthesizing or building up)

20. It sounds simple but…… Why do you have to eat?
What does it have to do with entropy?
Why do you have to breathe?
Can you give an AP Biology level answer to these questions?

21. Created by:
Debra Richards
Coordinator of Secondary Science Programs
Bryan ISD
Bryan, TX