12.2. Anaerobic Respiration Flashcards
Anaerobic Respiration definition
respiration without oxygen
What happens when there is no oxygen
- If oxygen is not available, oxidative phosphorylation cannot occur, because there is nothing to accept the protons and electrons at the end of the ETC
- This means that reduced NAD is not reoxidised, so the mitochondrion quickly runs out of NAD or FAD that can accept hydrogens from the Krebs Cycle reactions
- Krebs cycle and the link reactions therefore also come to a halt
- Only glycolysis is able to occur as long as the pyruvate produced at the end can be removed and the reduced NAD can be converted back to NAD
Anaerobic Respiration in Yeast
- In various microorganisms such as yeast, and in
some plant tissues, the hydrogen from reduced NAD is
passed to ethanal (CH3CHO). - This releases the NAD and allows glycolysis to continue.
- First, pyruvate is decarboxylated to ethanal; then the ethanal accepts 2H and is reduced to ethanol (C2H5OH) by the enzyme alcohol dehydrogenase.
- The conversion of glucose to ethanol is referred to as alcoholic fermentation.
Alcoholic Fermentation
The conversion of glucose to ethanol
Anaerobic Respiration in Mammals
- In other microorganisms, and in mammalian muscles when deprived of oxygen, pyruvate acts as the hydrogen acceptor and is converted to lactate by the enzyme lactate dehydrogenase (named after the reverse reaction, which it also catalyses).
- Again, the NAD is released and allows glycolysis to continue in anaerobic conditions. This pathway is known as lactic fermentation
Lactic Fermentation
The conversion of glucose into Lactate
Lactate in blood
- Lactate that is produced, diffuses into the blood and is carried in solution in the blood plasma to the liver
- Here, liver cells convert lactate back into pyruvate, but this requires oxygen
- Therefore, extra oxygen is required after exercise has finished. This extra oxygen is the oxygen debt
- When exercise has finished and oxygen is available again, some of the pyruvate in the liver cells is oxidised through Krebs cycle, Link reaction and ETC
- Some pyruvate is reconverted back into glucose in liver cells, which may be released into blood or become glycogen
What is the “extra” oxygen needed for after exercise?
- conversion of lactate to glycogen in the liver
- reoxygenation of haemoglobin in the blood
- a high metabolic rate, as many organs are operating at above resting levels.
ATP Yield in Aerobic vs Anaerobic Respiration
- only small amounts of ATP are produced when one glucose molecule undergoes anaerobic respiration due to the fact that only glycolysis is completed
- The Krebs cycle and oxidative phosphorylation, which produce most ATP, do not take place
alcoholic fermentation of glucose formula
Glucose → Ethanol + Carbon Dioxide + energy
C6H12O6 → 2C2H5OH+2CO2+energy
lactic fermentation of glucose formula
glucose (C6H12O6) → 2 lactic acid (C3H6O3) +energy
Respiratory Quotient
volume of carbon dioxide given out in unit time /
volume of oxygen taken in in unit time
Energy Levels of Respiratory Substrates
Highest
1) Lipids
2) Carbohydrates
3) Protein
Why Lipids have the highest energy level
- C-H bonds
Adaptations of Rice to wet environments
1) Stems have tissue called Aerenchyma, containing large air space
- aerenchyma allow allows oxygen from the air to diffuse into the roots
2) Cells are tolerant of high concentrations of ethanol as they have more alcohol dehydrogenase (breaks it down)
- when roots are submerged into water, less oxygen is available than when the soil contains air spaces; cells therefore respire anaerobically, producing ethanol which is toxic
3) Rice are fast growing plants and adapt fast
- leaves remain exposed to air, which facilitates gas exchange for photosynthesis and respiration
