Anaerobic Respiration

Why would anaerobic respiration take place?

Without oxygen present, there isn't the final hydrogen and electron acceptor in oxidative phosphorylation, therefore NAD cannot be recycled.

This means that after glycolysis, anaerobic respiration takes place.

What does anaerobic respiration produce in mammals?

Lactate (lactic acid)

What does anaerobic respiration produce in yeast?

Ethanol + CO₂

Anaerobic Respiration in Mammals

Glucose → 2x Pyruvate → 2x Lactate

Anaerobic Respiration in Animals Process

1. Without oxygen present, there isn't the final hydrogen and electron acceptor in oxidative phosphorylation, therefore NAD cannot be recycled.

2. So instead, the pyruvate acts as the final hydrogen and electron acceptor, removing hydrogen from the reduced NAD (NADH) using the enzyme lactate dehydrogenase. The pyruvate is converted to lactate (lactic acid).

3. Pyruvate removes the hydrogen from the reduced NAD (NADH) using the enzyme lactate dehydrogenase.

   The pyruvate is converted to lactate (lactic acid).

4. This means NAD is regenerated and can be used to keep glycolysis going, so a small quantity of ATP is still synthesised.

What's the net production of ATP in anaerobic respiration in mammals?

2 ATP

Reminder: Where does glycolysis occur?

Cytoplasm of a cell.

Anaerobic Respiration in Yeast Process

1. Through glycolysis, 2x pyruvate is formed.

   This produces a net production of 2 ATP.

2. The pyruvate is then decarboxylated using the enzyme ethanal decarboxylase, to form 2 x ethanal

3. Ethanal acts as the final hydrogen and electron acceptor, accepting a hydrogen from reduced NAD.

   2x ethanal forms 2x ethanol using the enzyme ethanol dehydrogenase.

4. This also allows NAD to be recycled to be used in glycolysis.

Anaerobic Respiration vs Aerobic Respiration ATP yield

- 2 ATP made in anaerobic respiration

- 32 ATP made in aerobic respiration

Why is there a lower yield of ATP in anaerobic respiration?

• No oxygen

• No final electron acceptor

• No oxidative phosphorylation

• No Krebs cycle

• No link reaction

Details of Anaerobic Respiration in Mammals

Glucose → 2x Pyruvate → 2x Lactate

Pyruvate acts as a Hydrogen electron acceptor

Enzyme = lactate dehydrogenase

Why is lactate bad in mammals and can cause problems?

Lactate (aka lactic acid) is an acid and will impact the pH of the tissues

Details of Anaerobic Respiration in Yeast

Glucose → 2x Pyruvate → 2x Ethanal → 2x Ethanol

Ethanal acts as a hydrogen electron acceptor

Enzyme = ethanal decarboxylase, and ethanol dehydrogenase

Why is anaerobic respiration bad for yeast?

If it is in a closed environment, the buildup of alcohol will eventually kill off the yeast.

Similarities between the anaerobic respiration processes

• Both use glucose

• Reduced NAD is oxidised

Why is anaerobic respiration important?

It allows NAD to be recycled so glycolysis can continue, therefore a small number of ATP is produced