Electron Transport Chain and Fermentation

Question 1

The electron transport chain

Answer 1

• A collection of molecules (mostly proteins) with active groups that pass (donate and accept) electrons
• Electrons from NADH and FADH2 pass through the electron transport chain, slowly releasing energy, which is used to drive ATP synthesis
• > in this process molecular oxygen is reduced to water
• Note that the electron transport chain does not make ATP, but this is the stage of the respiration that utilizes molecular oxygen as final acceptor of electrons, reducing it to water.

Question 2

Inhibitors to the electron transport chain

Answer 2

Inhibited by many poisons:

• Cyanide (Blocks ETC)
• Oligomycin (Blocks ATP synthase)
• DNP (abolishes H+ gradient)

Question 3

Oxidative phosphorylation (indepth)

Answer 3

1. ADP + Pi (via ATP synthase) => ATP
2. Energy is supplied by the electron transport chain in the form of an H+ gradient across the inner mitochondrial membrane. The H+ gradient and ATP are formed by chemiosmosis.
   - Chemiosmosis: the process by which ATP is produced on the inner membrane of a mitochondrion. The ETC transfers H+ from the matrix into the intermembrane space; as the H+ flow back to the matrix through the ATP synthase, the energy of their movement is used to add Pi to ADP, making ATP
   - H+ from NADH and FADH2 are removed by the ETC and pumped from the matrix across the inner membrane into the intermembrane space.
   - This creates an H+ gradient

Question 4

Location of H+ Ions

Answer 4

• Matrix (inner substance) = Low H+ ions, has NADH and FADH, where ADP turns into ATP, H+ ions move/end up here through ATP synthase.
• Intermembrane space = High H+ gradient drives ATP synthase. The inbetween of inner membrane and outer plasma membrane.

Question 5

If ATP synthesis is uncoupled from the ETC

Answer 5

• No ATP is made, but energy is released as heat
• Hibernating and newborn animals develop “brown fat.” It contains a protein called thermogenin, which uncouples ATP synthesis (makes more heat).
• If inner mitochondrial membrane is permeabilized, H+ gradient will dissipate and no ATP will be made

Question 6

During Respiration ATP is made:

Answer 6

• 10% from substrate level phosphorylation

- 90% from oxidative phosphorylation

Question 7

Cellular respiration in prokaryotes

Answer 7

• Prokaryotes (bacteria) do not have mitochondria
• They have the ETC in the plasma membrane
• They make a max of 38 ATP because they do not convert NADH to FADH2 to shuttle it across mitochondrial membrane, and therefore do not lose energy at this step.

Question 8

Fermentation

Answer 8

• Without oxygen energy is produced by fermentation in:
• > muscles when work hard and starve for O2
• > Bacteria and fungi when kept without O2
  1. No oxygen, therefore no ETC
  2. No oxidative phosphorylation
  3. Only substrate-level phosphorylation
  4. Lactate or ethanol replace O2 as final electron acceptors

Question 9

Alcohol Fermentation

Answer 9

• Occurs in yeast
• Used to make beer
• Pyruvate broken down, releasing CO2
  1. After glycolysis, pyruvate oxidizes NADH back to NAD+ instead of going to the Krebs cycle
  2. ATP is made by substrate level phosphorylation
  3. Ethanol accumulates as waste product
  4. Energy stores in pyruvate (32-34 ATP) is lost

Question 10

Lactic Acid Fermentation

Answer 10

• Occurs in muscle cells when work hard and starve for oxygen
• Lactic acid may cause muscle pain, although alternative causes (such as increased levels of K+ ions) have been suggested
• Pyruvate is not broken down; no CO2 is released
  1. After glycolysis, pyruvate oxidizes NADH back to NAD+ instead of going to the Krebs cycle
  2. ATP is made by substrate level phosphorylation
  3. Lactate accumulates as waste product
  4. Energy stored in pyruvate (32-34 ATP) is lost

Question 11

Feedback Inhibition

Answer 11

1. Less ATP
2. More AMP
3. Induction of phosphofructokinase (allosteric enzyme, induced by AMP, inhibited by ATP and citrate)
4. More ATP or citrate
5. Inhibition of phosphofructokinase
   - This regulation is used to save organic molecules for other function.