Lecture 12: Early forms of microbial metabolism: anaerobic respiration/fermentation

Question 1

List common types of terminal e- acceptors in anaerobic respiration, and end products

Answer 1

Common types of terminal electron acceptors in anaerobic respiration:

- NO3-   (also important in nitrogen metabolism)
- SO42-  
- Fe3+
- CO2 (methanogens)

End products made from anaerobic respiration:

-CO2 (waste)
-ATP -amount depends on how much free energy was derived from electron transport NO3- = 2 ATP/NADH S = 1 ATP/NADH

Question 2

Relate amounts of ATP generated to energy released from reactions in anaerobic respiration

Answer 2

-The amount of ATP depends on the amount of free energy that was derived from the electron transport, so the more the reactions travel down the electron potential tower, the greater amount of ATP generated.

Question 3

Define substrate level phosphorylation and oxidative phosporylation for ATP synthesis, and where you find these processes in catabolism

Answer 3

ATP can be made through substrate level or oxidative phosphorylation

Substrate level:

- direct P of ADP
- can occur in glycolysis and citric acid cycle
- AND Fermentation!!
- Less efficient because it has more steps

Oxidative phosphorylation:

- ATP synthase, membrane bound
- Uses proton motive force 
- Only occurs in the ETC

Question 4

Compare and contrast anaerobic respiration and fermentation

Answer 4

Both:
-Both anaerobic

Fermentation:

• Fermentation is an anaerobic process using a pyruvate derivative as terminal e- acceptor
• Redox power comes from NAD+/NADH cycling
• It happens in the cytoplasm not in the membrane
• No redox in ETC occurs in fermentation. Thus, no oxidative phosphorylation for ATP synthesis

Products:
-ATP (Substrate level P only)

-Lactic acid (Acid fermentation)

• CO2 + EtOH (Alcoholic fermentation)
• Mixed acid fermenters can do both!
• H2

Anaerobic Respiration:

• Uses ETC
• Both substrate level phosphorylation and oxidative phosphorylation

Products:
CO2 (waste)

ATP (how much ATP depends on the terminal electron acceptor used)

Question 5

Use proper terminology for explaining the nutritional types of microorganisms

Carbon Source (Precursor metabolites)

Answer 5

Carbon source:
Autotroph: Co2

Heterotroph: organic molecules

Question 6

Use proper terminology for explaining the nutritional types of microorganisms

Electron Source (Reducing power (electrons))

Answer 6

Electron source:
Organotroph: organic molecules

Lithotroph: inorganic molecules

Question 7

Describe Fermentation.

Answer 7

Fermentation is an anaerobic process using a pyruvate derivative as terminal e- acceptor

• Redox power comes from NAD+/NADH cycling
• No redox in ETC occurs in fermentation
• Thus, no oxidative phosphorylation for ATP synthesis

Question 8

Describe Anaerobic Respiration.

Answer 8

Anaerobic Respiration is a process that utilizes both substrate level phosphorylation and oxidative phosphorylation, or only SLP. It uses a terminal electron acceptor other than oxygen, and so less ATP is produced than from Aerobic Respiration

Question 9

What are the end products of Fermentation.

Answer 9

Products:
-ATP
          Substrate level P only
          Acid fermentation
          Lactic acid
Alcoholic fermentation
          CO2 + EtOH
*Mixed acid fermenters can do both!

Question 10

What are the end products of Anaerobic Respiration.

Answer 10

Products:

CO2 and ATP (how much ATP depends on the terminal electron acceptor used)