Study Notes on Anaerobic Cellular Respiration

Definition: Anaerobic cellular respiration refers to cellular respiration that occurs without the presence of oxygen.
Contrast with Aerobic Respiration: To understand anaerobic respiration, one must know aerobic respiration, which involves glycolysis, the Kreb Cycle, and the Electron Transport Chain.
Resource Link: View Mr. Andersen's video for foundational understanding.

Key Elements:
- Occurs when oxygen is absent or when mitochondria are not present.
- Involves two main processes: glycolysis and fermentation.

Starting Material: Glucose is the primary fuel source.
Glycolysis Process:
- Glucose is broken into pyruvate.
- Total energy yield from glycolysis is 2 ATP.
- Net gain is 2 ATP after initial investment.
Kreb Cycle:
- Pyruvate enters mitochondria and is converted to acetyl CoA.
- Produces an additional 2 ATP.
- Energy is stored in carriers: NADH and FADH2.
Electron Transport Chain:
- Electrons from NADH and FADH2 are transferred through the chain.
- Oxygen acts as the final electron acceptor, forming water.
- Produces 32-34 ATP, with a typical net around 38 ATP.
- Note: Controversy exists regarding exact ATP yield.

Possible Disruptions:
- Lack of glucose (rarely an issue due to abundant food supply).
- Absence of mitochondria (due to toxins or other factors).
- Lack of oxygen results in failure of electron transport.

Physical Sensation: Holding one's breath leads to a rapid oxygen depletion, causing a potential energy crisis within cells.
Resulting Pain: Accumulation of lactic acid contributes to the discomfort experienced during strenuous activities.

Glycolysis Breakdown: Converts glucose into pyruvate, generating 2 ATP and significant NADH.
NADH Limitation:
- When NADH accumulates, and if oxygen is absent, NADH cannot donate electrons, leading to a bottleneck in metabolism.

Lactic Acid Fermentation:
- Occurs in animals and some bacteria.
- Pyruvate is converted into lactate (lactic acid).
- No ATP is produced during this step, but it regenerates NAD+, enabling continuous glycolysis.
Alcoholic Fermentation:
- Primarily occurs in yeast.
- Pyruvate is converted into ethyl alcohol and carbon dioxide.
- Again, no additional ATP is produced, but NAD+ is regenerated.

Process:
- Begins with glycolysis producing pyruvate.
- Pyruvate is converted into lactate by utilizing electrons from NADH.
- Result: Regeneration of NAD+ allows glycolysis to continue effectively, yielding energy.
Example Contexts:
- Useful in situations requiring rapid energy, such as sprinting in humans or yogurt production in bacteria.

Process:
- Similar initiation with glycolysis leading to the production of pyruvate.
- Pyruvate is further converted into ethyl alcohol and carbon dioxide, losing a carbon in the process (as carbon dioxide).
- This step is critical as it also regenerates NAD+, allowing ongoing glycolysis.
Examples:
- Production of beer and wine through yeast fermentation.
Environmental Considerations:
- Yeast ferment until alcohol concentration is high enough to be toxic, leading to its own cell death.

Cultural Significance:
- Fermentation has been utilized for millennia; ancient Egyptians brewed beer using fermentation processes.

Overall Purpose: Anaerobic respiration allows organisms to survive and generate energy in the absence of oxygen or mitochondria.
Duration Limit: The capacity for anaerobic respiration is finite; prolonged absence of oxygen will ultimately constrain energy production.