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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