Carbohydrates 5

Question 1

What are other names for the Citric acid cycle?

Answer 1

• Krebs cycle

- Tricarboxylic acid cycle (TCA)

Question 2

What fuel molecules go through the TCA cycle?

Answer 2

All fuel molecules:

• Carbohydrates
• Fatty acids
• Amino acids

Question 3

Where does the TCA cycle occur?

Answer 3

Mitochondrial matrix

Question 4

What happens in the TCA cycle?

Answer 4

-It removes e’s and passes them on to form NADH and FADH

Question 5

Why is the TCA cycle very efficient?

Answer 5

• Cyclical in nature

- Small number of citric acid cycle molecules can make loads of NADH and FADH

Question 6

How is acetyl CoA formed?

Answer 6

• Occurs in the mitochondrial matrix
• Action of pyruvate dehydrogenase
• Pyruvate undergoes decarboxylation, oxidation and transfer of CoA complex.
• 2H are released during decarboxylation

Question 7

What are role do each of the enzyme subunits of pyruvate dehydrogenase play?

Answer 7

• E1 catalyses the first decarboxylation of pyruvate
• E2 transfers the acetyl group to coenzyme A
• E3 recycles the lipoyllysine through the reduction of FAD which is recycled by passing electrons NAD

Question 8

What happens each turn of the TCA cycle?

Answer 8

2C’s enter as acetyl CoA and 2C’s are removed as CO2

Question 9

What reaction is similar to pyruvate dehydrogenase?

Answer 9

a-ketoglutarate dehydrogenase

Question 10

How is entry into the cycle controlled?

Answer 10

• Pyruvate dehydrogenase is regulated by it’s immediate products and the end point of cellular respiration ATP
• Its regulated depending on the needs of the cell

Question 11

What is the nature of the 2 points of control of the TCA cycle?

Answer 11

They are non-reversible reactions (exergonic steps)

Question 12

What are the 2 other points of control?

Answer 12

• Isocitrate dehydrogenase

- a-ketoglutarate dehydrogenase

Question 13

Describe isocitrate dehydrogenase.

Answer 13

• As with pyruvate dehydrogenase enzyme is allosterically controlled through ATP and NADH concentrations.
• ATP and NADH will negatively regulate
• ADP positive regulates

Question 14

Describe a-ketoglutarate dehydrogenase.

Answer 14

• ATP and NADH negatively regulate

- Also succinyl CoA negatively regulates

Question 15

How do the control points allows re-direction of cellular resources?

Answer 15

• Blocking isocitrate dehydrogenase causes citrate to build up which shuttle citrate into the cytoplasm causing phosphofructokinase to stop glycolysis
• a-ketoglutaratenbuilds up when a-ketoglutarate dehydrogenase is inactive, which switches its use to production of amino acids

Question 16

What happens when the cellular energy needs are met through the TCA cycle?

Answer 16

It can produce the building blocks of nucleotide bases, haem groups and proteins

Question 17

What can the enzyme pyruvate carboxylase do?

Answer 17

Can convert pyruvate to oxaloacetate

Question 18

When is pyruvate carboxylase active?

Answer 18

It is only active when acetyl CoA is present so a build up of acetyl CoA triggers the reaction.