Lecture 15- Metabolism Catabolism Part 2

Anaerobic Respiration

• Organisms that use electron acceptors other than O₂ carry out glycolysis, the TCA cycle, and electron transport.

• NADH and FADH₂ still donate electrons, but ATP yield is lower since O₂ is not the terminal acceptor.

• This is common in many bacteria and archaea

Why is there Less energy production in Anaerobic respiration?

• This is because the electron acceptors are less positive than the O2.

• Results in a shorter ETC and fewer protons transported.

Consequence of using alternate electron acceptor

• Using nitrates as a final electron acceptor removes nitrates from the soil.

• Depletion results in poor crop outcome.

• Causes farmers to use nitrogen-containing soil fertilizer which can ultimately leach into well water.

Fermentation occurs in some organisms

• In these organisms, they can undergo glycolysis but can’t undergo ETC or generate an electron motive force.

• Takes place in the absence of oxygen or other electron acceptors. Those that can’t undergo respiration, do not have the proteins to complete the process.

• Without the ETC, there needs to be an alternative pathway to recycle the reduced NADH. Without oxidation of NADH, the organism will run out of NAD+ molecule to reduce during glycolysis and organism will die

• While it doesn’t generate much ATP, it is critical in recycling the reduced NADH molecules into NAD+ so that they can be act as continue to act as electron acceptors.

• Indirectly contribute to energy production by keeping glycolysis active.

butyric-butylic fermentation occurs in…

Clostridium species that cause tetanus and botulism

5 Unifying facts in all fermentation pathways

1) O2 is not used.

2) Electron acceptor is pyruvate or pyruvate derivative.

3) NADH must be oxidized to NAD+

4) Decrease in ATP yield as a result of no ETC.

5) Sugar is not completely oxidized to CO2.

Homolactic acid fermentation

• Is the simplest of the fermentations in which pyruvic acid is converted into lactic acid in the absence of O2.

Process of Homolactic acid fermentation

• In this process, NADH is oxidized into NAD+ in order to be recycle for
  future glycolysis reactions.

Where does Homolactic acid fermentation occur

• Occurs in lactobacilli (used to make cheese), in streptococci,
  mammalian muscle cells.

Alcohol Fermentation

• CO2 is released from pyruvic acid resulting acetaldehyde.

Process of Alcohol Fermentation

The acetaldehyde is reduced to ethyl alcohol using the H on NADH.
Allows the recycling of NADH.

Where does Alcohol Fermentation occur?

• Not common in bacteria, but common in yeast and used for making bread and wine.