Gluconeogenesis: Pyruvate Carboxylase

Question 1

What is the structure of pyruvate carboxylase?

Answer 1

tetrameric protein of identitcal subunits with a Biotin prosthetic group bound to the Lys reside on each subunit

Question 2

What molecule does the Biotin prosthetic group on pyruvate carboxylase carry?

Answer 2

CO2

Question 3

What is bound to each subunit of pyruvate carboxylase?

Answer 3

Biotin prosthetic group

Question 4

What is the biotin prosthetic group of each pyruvate carboxylase subgroup covalently bound to?

Answer 4

A Lys residue

Question 5

True or false: The Biotin residue on pyruvate carboxylase is on the end of an inflexible, rigid arm.

Answer 5

False: It is on the end of a flexible arm.

Question 6

How many reaction steps does the conversion of pyruvate to oxaloacetate by pyruvate carboxylase occur in?

Answer 6

2

Question 7

What is the first step in the conversion of pyruvate to oxaloacetate by pyruvate carboxylase?

Answer 7

1) Cleavage of ATP to ADP to dehydrate bicarbonate via formation of “high energy” carboxyphosphate intermediate
2) Exergonic reaction of resulting CO2 wiht biotin
3) Biotin bound carboxy group is now activated and can be transferred without further energy input.

Question 8

What is the second step in the conversion of of pyruvate to oxaloacetate by pyruvate carboxylase?

Answer 8

The activated carboxyl group is transferred from carboxybiotin to pyruvate in a three-step process to form oxaloacetate.

Question 9

True or false: The two steps in the conversion of oxaloacetate to pyruvate carboxylase occur on the same subsite of the same enzyme.

Answer 9

False: They occur on different subsites of the same enzyme.

Question 10

What transfers biotin the biotin ring between subsites on pyruvate carboxyase?

Answer 10

The 14 angstrom long arm Lys-biotin

Question 11

For which two metabolic pathways is oxaloacetate an intermediate?

Answer 11

1) Gluconeogenesis

2) TCA cycle

Question 12

How does an increased concentration of acetyl Co-A affect pyruvate kinase?

Answer 12

It allosterically activates it, signalling that the cell has sufficient 2-carbon reserves and enhancing gluconeogenesis in order to increase the amount of oxaloacetate available to combine with acetyl CoA for the TCA cycle. This also signals not to make any more Acetyl Co-A or glucose.

Question 13

How many ATP and GTP molecules are required to take pyravate back to PEP?

Answer 13

1 ATP and 1 GDP

Question 14

Where does the carboxylation of pyruvate to oxaloacetate take place?

Answer 14

In the mitochondria

Question 15

What is the energy expense of converting pyruvate to oxaloactetate?

Answer 15

1 ATP

Question 16

What cofactor is required by pyruvate carboxylase?

Answer 16

biotin

Question 17

How do the biotin prosthetic group function on pyruvate carboxylase?

Answer 17

It carries activated CO2 and readily donates CO2 to other molecules.

Question 18

What must be bound to pyruvate carboxylase for biotin to be carboxylated? What kind of enzyme activator is this molecule?

Answer 18

acetyl CoA; allosteric

Question 19

What allosteric activator is required for the biotin prosthetic groups on pyruvate carboxylase to be carboxylated?

Answer 19

Acetyl CoA