GI biochemistry

Question 1

What is glycogenesis?

Answer 1

Synthesis of glycogen

Question 2

What is glycogenolysis?

Answer 2

Breakdown of glycogen into glucose

Question 3

What is gluconeogenesis?

Answer 3

Synthesis of glucose from metabolic precursors

Question 4

What type of glycosidic links form between glucose molecules in glycogen?

Answer 4

α1-4 glycosidic links in the main chain

α1-6 glycosidic links in the branches

Question 5

What is glycogenin?

Answer 5

A protein attached to a glycogen primer containing 4+ glucose residues, allowing addition of glucose to glycogen chain

Question 6

In the first step of glycogenesis, glucose is turned into _____

Answer 6

Glucose-6-phosphate

Question 7

In the first step of glycogenesis, glucose-6-phosphate is formed by _____ and enzyme _____

Answer 7

ATP and hexokinase

Question 8

In the second step of glycogenesis, G-6-P is transformed into ____ by enzyme _____

Answer 8

Glucose-1-phosphate by phosphoglucomutase

Question 9

In the third step of glycogenesis, G-1-P is turned into _____ by ____ and _____

Answer 9

UDP-glucose by UDP-glucose pyrophosphorylase and UTP

Question 10

In the last step of glycogenesis, glucose is added to the glycogen chain by enzyme ____

Answer 10

Glycogen synthase

Question 11

What secondary product is made in the last step of glycogenesis?

Answer 11

UDP

Question 12

Name a rate-limiting enzyme of glycogenesis

Answer 12

Glycogen synthase

Question 13

Give the equation for glycogenolysis

Answer 13

[glucose]n + phosphate -> G-1-P + [glucose]n-1

Question 14

What rate-limiting enzyme catalyses glycogen?

Answer 14

Glycogen phosphorylase

Question 15

After glycogenolysis, G-1-P is turned into G-6-P. What happens to G-6-P in the liver?

Answer 15

G6P is de-phosphorylated, can enter the blood

Question 16

After glycogenolysis, G-1-P is turned into G-6-P. What happens to G-6-P in the skeletal muscle?

Answer 16

G6P can’t be de-phosphorylated, so used in glycolysis and TCA cycle

Question 17

When and where does gluconeogenesis occur?

Answer 17

After long periods or not eating eg overnight, occurs mostly in liver, some in kidneys

Question 18

Gluconeogenesis is an energetically ______ process

Answer 18

Expensive

Question 19

Explain the process of gluconeogenesis

Answer 19

Oxaloacetate is formed in mitochondria from precursor, which is an intermediate in the TCA cycle

Question 20

What is the Cori Cycle?

Answer 20

Lactate as a precursor for GNG:

• GNG of lactate in the liver produces glucose
• Glucose travels in blood to the muscles
• Glycolysis of lactate occurs in muscles, reforming lactate

Question 21

Name the precursors of glucose in GNG

Answer 21

Lactate
Amino acids
Glycerol

Question 22

How are glycolysis and GNG regulated?

Answer 22

By precursors and by hormones eg glucagon and insulin

Question 23

What does insulin activate/deactivate?

Answer 23

Activates glycolysis, activates glycogenesis. Deactivates gluconeogenesis