Gluconeogenesis

Question 1

What non-carbohydrate sources can glucose be synthesized from if it is not available from glycogen breakdown or dietary sources?

Answer 1

1) Glycolysis products
2) Lactate
3) Pyruvate
4) TCA cycle intermediates
5) Carbon skeletons of most amino acids

Question 2

Which two amino acids are broken down to acetyl-CoA instead of oxaloacetate? Can they be the precusors of glucose?

Answer 2

Leucine and Lysine; no

Question 3

What four-carbon compound are non-carbohydrate sources for glucose broken down to?

Answer 3

oxaloacetate

Question 4

True or false: Fatty acids can not serve as precursors to glucose. Why?

Answer 4

True; fatty acids are degraded to acetyl-CoA, which cannot be converted to oxaloacetate.

Question 5

True or false: Acetyl Co-A can be converted to oxaloacetate and used to synthesyze glucose.

Answer 5

False; no pathway exists to convert acetyl-CoA to glucose.

Question 6

What is the product of gluconeogenesis?

Answer 6

glucose

Question 7

Which reactions in glycolysis are not reversible?

Answer 7

1) Hexakinase
2) Phosphofructokinase
3) Pyruvate kinase

Question 8

What enzyme catalyzes the conversion of pyruvate and HCO3- to oxaloacetate?

Answer 8

Pyruvate carboxylase

Question 9

What reaction does pyruvate carboxylase catalyze?

Answer 9

Pyruvate and HCO3- to oxaloacetate

Question 10

Is the reaction from pyruvate to oxaloacetate endergonic or exergonic?

Answer 10

Endergonic

Question 11

What drives the reaction of pyruvate to oxaloacetate that is catalyzed by pyruvate carboxylase?

Answer 11

ATP hydrolysis

Question 12

True or false: Oxaloacetate is a “high energy” compound?

Answer 12

True

Question 13

What provides the energy needed to synthesized PEP (via PEP carboxykinase-PEPCK)?

Answer 13

The exergonic decarboxilation of oxaloacetate

Question 14

Which enzyme catalyzes the reaction of oxaloacetate to PEP?

Answer 14

PEP carboxykinase (PEPCK)

Question 15

Where does the phosphoryl group that is added to oxaloacetate to make it PEP come from?

Answer 15

From GTP

Question 16

What two enzymes do the reverse reaction of pyruvate kinase (i.e., take pyruvate to phosphoenolpyruvate)?

Answer 16

1) Pyruvate carboxylase

2) PEP carboxykinase (PEPCK)

Question 17

For which two pathways does oxaloacetate serve as an intermediate?

Answer 17

Gluconeogenesis and the TCA cycle

Question 18

Why is maintaining glucose levels in the body important?

Answer 18

Glucose is the only source of fuel for red blood cells and the primary source of fuel for the brain.

Question 19

How long can glycogen stores in the body supply the body with glucose during a fast?

Answer 19

About one day

Question 20

What is the major site of gluconeogenesis?

Answer 20

Liver (some also takes place in the kidneys)

Question 21

True or false: The liver, kidneys, brain, heart, and skeletal muscle are all key sites of gluconeogenesis.

Answer 21

False. Only the liver and kidneys.

Question 22

Where do the brain and muscle get glucose from when the body is in a fasting state?

Answer 22

From the blood (into which the liver and kidneys deposit the glucose derived from gluconeogenesis).

Question 23

What substrate does gluconeogenesis convert into glucose?

Answer 23

pyruvate

Question 24

What are the major non-carbohydrate precursors of glucose?

Answer 24

lactate, amino acids, and glycerol

Question 25

What enzyme in the liver converts lactate into pyruvate?

Answer 25

lactate dehydrogenase

Question 26

True or false: Animals can convert fatty acids into glucose.

Answer 26

False

Question 27

How can glycerols be converted into glucose?

Answer 27

They can be metabolized by glycolysis and then converted to glucose through gluconeogenesis.

Question 28

What molecule can glycerol be converted to that allows it to enter either the glycolytic or gluconeogenic pathway?

Answer 28

Dihydroxyacteone phosphate

Question 29

How does gluconeogenesis bypass the three irreversible steps of glycolysis?

Answer 29

1) PEP is formed from pyruvate by way of oxaloacetate.
2) F6P is formed from F-1,6-BP by hydrolysis.
3) Glucose is formed from G6P by hydrolysis.