12.4 - Anaerobic Respiration Flashcards
Why can the Krebs cycle and the electron transport chain not function in the absence of oxygen?
- Oxygen is the final electron acceptor in the electron transfer chain.
- Without oxygen, NADH and FADH₂ cannot donate their electrons, so they remain in their reduced forms.
- The lack of oxidized NAD and FAD halts the Krebs cycle because these coenzymes are not regenerated.
- Consequently, only glycolysis can occur anaerobically, producing ATP.
How is NAD regenerated during anaerobic respiration, and why is this important?
- Glycolysis requires oxidized NAD to continue.
- In anaerobic conditions, pyruvate accepts hydrogen from reduced NAD:
- In animals: Pyruvate → Lactate
- In plants/yeast: Pyruvate → Ethanol + CO₂
- This reaction oxidizes NADH back to NAD, enabling glycolysis to continue.
Write the summary equation for lactate formation in animals.
- Pyruvate + Reduced NAD → Lactate + Oxidized NAD
- Occurs in muscle cells during intense exercise or oxygen deprivation.
- Lactate allows NAD regeneration but can cause pH changes, leading to enzyme inhibition and muscle fatigue.
Explain how lactate accumulation affects muscle function.
- Lactate decreases pH
- denaturing enzymes
- reducing their activity, causing muscle fatigue and cramping.
Write the summary equation for ethanol and carbon dioxide formation in plants and yeast.
- Pyruvate + Reduced NAD → Ethanol + CO₂ + Oxidized NAD
- Pyruvate is decarboxylated to produce CO₂ and then accepts hydrogen from reduced NAD to form ethanol.
- Used in brewing and baking industries.
Why is ethanol production important in brewing?
- Yeast ferments sugars under anaerobic conditions to produce ethanol
- the desired product in alcoholic beverages.
Compare the energy yield of aerobic and anaerobic respiration
- Aerobic respiration: Produces ~38 ATP per glucose molecule (glycolysis, Krebs cycle, ETC).
- Anaerobic respiration: Produces only 2 ATP per glucose molecule, solely through glycolysis.
—> Reason: Pyruvate cannot enter the Krebs cycle or ETC without oxygen.
How is lactate removed from the body after anaerobic respiration?
- Lactate is transported in the blood to the liver.
- In the liver:
1) Lactate is converted back to pyruvate, which can be oxidized or used to resynthesize glycogen.
2) Oxygen is required for this process, contributing to the “oxygen debt.”
Explain what happens to lactate after exercise ends.
Lactate is oxidised back to pyruvate or converted into glycogen in the liver using oxygen, repaying the oxygen debt.
What is substrate-level phosphorylation, and where does it occur in anaerobic respiration?
- Substrate-level phosphorylation: Direct transfer of a phosphate group to ADP to form ATP.
- Occurs in glycolysis during anaerobic respiration.
- Key Example: Phosphoenolpyruvate (PEP) transfers a phosphate to ADP to form ATP in glycolysis.
Why is the regeneration of NAD crucial for glycolysis?
- Without NAD, triose phosphate cannot be oxidized to pyruvate during glycolysis.
- Regenerating NAD ensures glycolysis continues, allowing ATP production under anaerobic conditions.
Describe the role of pyruvate in anaerobic respiration.
- Pyruvate acts as a hydrogen acceptor from reduced NAD:
—> In animals: Forms lactate.
—> In plants/yeast: Forms ethanol and CO₂. - This reaction is essential to regenerate NAD for glycolysis.
What are the survival advantages of anaerobic respiration?
- Allows ATP production when oxygen is unavailable.
- In animals, supports short bursts of intense activity (e.g., escaping predators).
- In plants, enables survival in waterlogged soils where oxygen levels are low.
Why is anaerobic respiration advantageous during short-term oxygen deprivation?
It provides a rapid but limited supply of ATP, enabling cellular activity to continue temporarily.
Only occurs in the presence of oxygen.
D
Takes place in animals.
A, C, D
Produces ATP
A,D
Is scarried out by yeast in the absence of oxygen.
A, B
Produces reduced NAD
A, D
Regenerates NAD from reduced NAD.
B, C, D
Is known as glycolysis.
A
