1.3 Anaerobic respiration

What microorganisms undergo anaerobic respiration?

-Yeast, facultative anaerobe

-Clostridium perfringens, obligate anaerobes

What animal tissues may undergo anaerobic respiration?

Muscles.

Why does glycolysis only occur in the absence of oxygen?

No oxygen to act as the final electron acceptor in the electron transport chain.

Why might the link reaction and Krebs cycle not occur, in absence of oxygen?

Reduced NAD cannot be reoxidised, oxidative phosphorylation will not take place, so yield of ATP molecules produced by anaerobic respiration is greatly reduced.

How many ATP molecules are produced by anaerobic respiration?

-Gross= 4

-Net gain of 2 as 2 are used to phosphorylate glucose.

In the absence of oxygen, for glycolysis to continue what must be regenerated?

NAD must be regenerated,

anaerobic respiration involves the reoxidation of NAD.

What acts as the hydrogen acceptor in aerobic and anaerobic respiration?

-Aerobic = Oxygen

-Anaerobic= Pyruvate

What is the main difference in anaerobic respiration for animal cells and yeast/higher plants?

-In animal cells:

Pyruvate becomes reduced and accepts the hydrogen from reduced NAD forming lactate.

-In yeast/higher plants:

Ethanal becomes reduced and accepts the hydrogen from reduced NAD to form ethanol.

What is made during anaerobic respiration in animals?

-Glucose 6C, 2ATP = 2ADP + Pi

-Hexose phosphate 6C

-Triose phosphate 3C, NAD to reduced NAD, 2ADP + Pi = 2ATP x2

-Pyruvate 3C, Reduced NAD to NAD x2

-Lactate 3C x2

What is the net gain of ATP in anaerobic respiration in animals?

2

What is made during anaerobic respiration in yeast and higher plants (fermentation)?

-Glucose 6C, 2ATP = 2ADP + Pi

-Hexose phosphate 6C

-Triose phosphate 3C, NAD to reduced NAD, 2ADP + Pi = 2ATP x2

-Pyruvate 3C, CO2 out

-Ethanal 2C, Reduced NAD to NAD

-Ethanol 2C

What is the net gain of ATP in anaerobic respiration in yeast and higher plants?

2

What does Acetyl CoA do?

Links glucose, fatty acids and amino acid metabolism.

Under certain circumstances, what can be used as a respiratory substrate?

Lipids

Proteins

Glucose

What is a respiratory substrate?

A molecule that can be oxidised through respiration to fuel the synthesis of ATP.

Give 3 roles of lipids in living organisms?

1) Energy storage eg. seeds

2) Thermal insulation under skin

3) Protection from damage, vital organs

Give 6 roles of proteins in living organisms?

1) Globular proteins, enzymes eg. amylase

2) Hormones, eg. insulin

3) Antibodies

4) Haemoglobin

5) Carrier proteins

6) Fibrous proteins, eg. keratin and collagen

Why are lipids used?

As an energy source when carbohydrate levels are low as they contain twice as much energy per unit gram as carbohydrates.

What is a lipid hydrolysed into?

Lipid = Glycerol + 3 Fatty acids

What happens to the products of lipid digestion?

-Glycerol is phosphorylated by ATP, dehydrogenated and converted into triose phosphate 3C. This is an intermediate of glycolysis so can then enter glycolysis.

-Fatty acid chains, these long hydrocarbon chains can enter the Krebs cycle as acetyl co-enzyme A.

Why are large numbers of ATP produced as a result of lipid digestion?

Each fatty acid produces many 2C fragments which means the Krebs cycle can go many times producing large numbers of reduced NAD and reduced FAD to fuel the Electron transport chain

When is protein used as a respiratory substrate?

After reserves of carbohydrates and lipids have been used up, eg. when an individual is suffering from starvation.

How are proteins used as a respiratory substrate?

-Firstly, proteins are hydrolysed into their constituent amino acids.

-Then in the liver amine group is removed from amino acids, this is called deamination.

-The removed amine group is converted to ammonia and then combines with CO2 to produce urea which travels in the bloodstream to the kidneys to be excreted in the urine.

-The rest of the amino acid residue forms a keto acid.

Where are the keto acids used?

-Some keto acids eg. pyruvate, are fed into glycolysis.

-Some keto acids are converted into Krebs cycle intermediates so fed into the Krebs cycle.