Anaerobic Respiration - Ms De Souza's Super Awesome IB ...
Anaerobic Respiration
- “anaerobic” = without oxygen
- a way to obtain energy from nutrients without oxygen
- this is done by repeating glycolysis and continuously making 2 net ATP (much less than aerobic respiration which makes 36 net ATP)
During glycolysis…
GLUCOSE - the cell does not directly require O2 for glycolysis,
- however, NAD+, needs to be regenerated for glycolysis to to continue.
- NADH is turned back into NAD+ when NADH gives its
electrons to the glycerol-phosphate shuttle to make
FADH2 in the matrix
2 PYRUVATE
- O2 is the final electron acceptor of the electron transport chain. It accepts electrons to make H2O
- If there is no O2 then, the ETC will become clogged with electrons because there won’t be a molecule to accept the electrons
- As a result, the ETC will not be free to oxidize the coenzymes NADH and FADH2
o Thus protons will not be pumped into the innermembrane space and thus a proton motive force will not be created to produce ATP
o and FAD will not be regenerated to pick up the electrons from the NADH made in glycolysis
o as a result, the NADH in the cytoplasm will not be turned back into NAD+, and so glycolysis won’t continue.
- Organisms have evolved a way of recycling NAD+ and continuing glycolysis without O2
- Electrons of NADH will be transferred to organic molecules instead of the ETC.
- The process is called FERMENTATION
o 1. ethanol formation
o 2. lactic acid formation
1) Ethanol Fermentation
- NADH transfers hydrogen atoms to acetaldehyde
- Acetaldehyde is converted into ethanol and in the process NADH is oxidized to NAD+ so glycolysis can continue
- In this way, 2 ATP is continuously made to meet energy needs
- Ethanol fermentation is carried out by yeast
- Yeast: unicellular fungus that is found in habitats where glucose/sugars are available
o Can undergo anaerobic or aerobic respiration.
o Used to make breads, pastries, wine, beer, liquor, soy sauce, bioethanol….
- Ex: Baking Bread
o Live yeast cells are mixed with starches (in flour) as the dough is kneaded
o Yeast will break down the glucose in start through cellular respiration
o Any oxygen in the dough will be used up in aerobic respiration
o Now without O2, the yeast ferments the glucose in starch to make CO2 and ethanol
o The CO2 produced will not be able to escape and thus will form bubbles making the bread rise
o The ethanol evaporates when bread is baked
- Ex: beer, wine making
o Yeast ferments sugars in fruit juices
o Fermentation ends when ethanol concentration is ~12% because this concentration will kill the yeast cells.
- Ex: Bioethanol
o Bioethanol: Ethanol produced by living organisms as a renewable energy source.
o Yeast can be used to produce bioethanol from sugar cane and maize
o After the ethanol is produced, it is purified by distillation and other methods to remove the water
o Bioethanol can be used as a fuel in vehicles
2.) Lactic Acid Fermentation
- during strenuous exercise, breakdown glucose faster than O2 can be supplied
- lactate fermentation takes over
- Lactic Acid Fermentation allows for ATP to be made very rapidly for a short period of time.
- NADH gives its electrons to pyruvate to make lactate (lactic acid)
- Lactic acid is actually poisonous to our cells.
- There is a limit to how much our cells can withstand which limits how much anaerobic respiration the body can do.
- The accumulation of lactic acid in muscles cause stiffness, soreness, and fatigue.
- When exercise stops, lactate is converted back to pyruvate for aerobic respiration by the liver.
VO2 Max and the Lactate Threshold
Aerobic Fitness: a measure of the ability of the heart, lungs, and blood stream to supply O2 to the cells of the body during physical activity.
- Muscle cells need ATP to contract
- ATP production should increase if more O2 absorbed
VO2 max = maximum oxygen consumption.
- It’s a measurement of the body’s capacity to generate energy required for physical activity.
- Maximum volume of O2 in mL the cells of the body can remove from the blood stream In 1 minute per kilogram of body mass.
- Individuals with a high VO2 max values are considered more aerobically fit.
- Average VO2 max for North Americans ~ 35mL/kg/min
- Average VO2 max for athletes ~70mL/kg/min
- VO2 max values may be increased with exercise and training but is also affected by genetics.
- Values with decrease with age.
- There isn’t always a correlation between VO2 max and athletic performance.
- As you exercise, lactate increases because O2 is not available for all the cells.
- As exercise intensity increases, lactate levels increase
Lactate Threshold
- Value of exercise intensity at which [blood lactate] increases sharply because lactate production is greater that lactate removal.
- Exercising below this intensity can be maintained for hours (such when someone is running a marathon)
- However, beyond this may limit duration b/c of pain, stiffness, fatigue
- Athletic training improves blood circulation an increases the efficiency of O2 delivery to body cells
- (This results in an increase in lactate production during exercise and an increase in the lactate threshold.
- ( can sustain greater exercise intensities.
- Lactate Threshold for Untrained athletes: 60% VO2 max
- Lactate Threshold for Elite athletes: 80% VO2 max
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2 NAD+
2 NADH
2 ADP
2 ATP
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