4.4

Question 1

Anaerobic Pathway without O2

Answer 1

Various oxygen-poor env. that DO
NOT support aerobic processes
* Human gut
* Swamps and waterlogged soils
* Deep underground
* Deep in oceans
* Landfills

Biological productivity in these
env. are LOW b/c energy yields of
anaerobic respiration are much
lower than aerobic

Question 2

2 ANAEROBIC PROCESSES TO GENERATE ATP

Answer 2

Fermentation
- Does not use ETC
- Uses an organic molecule as final electron acceptor

Anaerobic Respiration
- Uses ETC
- Uses inorganic molecule as final electron acceptor

Question 3

Fermentation

Answer 3

In the absence of O2, cells can take in glucose and use Glycolysis

to make ATP

• NADH is produced in Glycolysis, but since NO ETC, we need a away to
  oxidize it back to NAD+
• Eukaryotes use 2 forms of Fermentation:
  1. Alcohol (ethanol) Fermentation
  2. Lactate (lactic acid) Fermentation

Question 4

Alcohol (ethanol) fermentation

Answer 4

• Occurs in certain bacteria and yeast
• Pyruvate is decarboxlated–> acetylaldehyde—-> used to oxidisze NADH to NAD
• 2 CO2, 2 ethanol, 2 NAD+, 2 ATP

Question 5

Applications

Answer 5

• bakers use yeast to make bread dough rise
• brew masters use yeast to make beer and wine
• Alcohol Fermentation also occurs naturally
  in the env.
• over-ripe/rotting fruits starts to ferment

Question 6

Lactate Fermentation

Answer 6

• Used as primary energy pathway in some bacteria, but also used as a
  supplemental system in many eukaryotes in low/no O2 conditions

Ex. Occurs in muscle cells when strenuous exercise causes a demand for
ATP that exceeds the rate in which O2 can be supplied to the ETC for oxidative phosphorylation

• To maximize ATP production, Glycolysis produces 2 ATP (quickly)
  and any excess pyruvate is converted into lactate
• This pathway oxidizes NADH back to NAD+
• If high energy demands continue, lactate accumulates in cells when O2 content
  of muscle cells return to normal levels and ATP
  demands have fallen, the reaction is reversed
• Pyruvate and NADH is regenerated, which can
  be oxidized by The Citric Acid Cycle and ETC
• Lactic Acid was once believed to build up in
  muscle tissue during strenuous exercise, causing
  muscle stiffness/soreness
• NOT TRUE!
• Lactate levels return to normal

Question 7

Lactate Threshold and Debt

Answer 7

Lactate Threshold
* Point at which lactate production is TOO HIGH for transport out of muscles
* Can be increased by training

Lactate is transported from muscles to the liver, where it is oxidized back to pyruvate so
that it does not build up in muscle tissue

Question 8

Anaeobic Respiration

Answer 8

• Prokaryotes lack a mitochondria yet
  still have ETC on their plasma
  membranes
• Some use O2 as the final e- acceptor
• Others use SO4
  -2, NO3, and Fe+3