Deck 21: Glycogen Metabolism

Question 1

Phosphorylase kinase becomes fully active by being phosphorylated and binding ___________.

Answer 1

calcium ions

Question 2

What liver enzyme catalyzes the hydrolysis of a phosphate group to produce glucose?

A) glucose phosphorylase
B) glucose-1-phosphatase
C) glucose-4-phosphatase
D) glucose-6-phosphatase
E) None of the answers is correct.

Answer 2

D

Question 3

What reaction cleaves a bond by the addition of orthophosphate?

A) phosphorolysis
B) phosphatase
C) transphosphorylation
D) oxidative phosphorylation
E) None of the answers is correct.

Answer 3

A

Question 4

Phosphorylase requires the coenzyme ______________________ for activity.

Question 5

The glycogen branching enzyme moves a block of __________ (or so)glucose residues to form a branch point at least four residues from a preexisting branch.

Question 6

Insulin stimulates glycogen synthase by inactivating ________________________.

Question 7

What hormone signifies the starved state?

A) insulin
B) glucagon
C) epinephrine
D) cortisol
E) None of the answers is correct.

Question 8

What type of glycosidic bond is found at the branch points of glycogen?

A) $\alpha$ -1,2
B) $\alpha$ -1,4
C) $\alpha$ -1,6
D) $\beta$ -1,4
E) $\beta$ -1,6

Question 9

Phosphoglucomutase requires the intermediate ____________________ for the interconversion of glucose-1-phosphate and glucose-6-phosphate.

Question 10

______________ markedly stimulates glycogen breakdown in muscle by initiating a cAMP signal-transduction cascade.

Question 11

The complete oxidation of a glucose residue from glycogen produces ________________ molecules of ATP in the muscle.

Question 12

In skeletal muscle,the binding of ___________ converts phosphorylase b into the active form.

Question 13

The action of which of the following enzymes both activates glycogen breakdown and inhibits glycogen synthesis?

A) protein kinase A
B) protein kinase C
C) phosphorylase kinase
D) protein phosphatase 1
E) None of the answers is correct.

Question 14

What protein serves as the primer for glycogen synthase?

A) branching enzyme
B) debranching enzyme
C) glycogenin
D) calmodulin
E) None of the answers is correct.

Question 15

What is the primary glycosidic bond found in glycogen?

A) $\alpha$ -1,3
B) $\alpha$ -1,4
C) $\alpha$ -1,6
D) $\beta$ -1,4
E) $\beta$ -1,6

Question 16

Glycogen synthase catalyzes the transfer of a glucose residue from UDP-glucose to one of the _____________ ends of glycogen.

Question 17

Which of the following serves as the glucose "sensor" enzyme in liver cells?

A) glucose-6-phosphatase
B) hexokinase
C) phosphoglucomutase
D) UDP-glucose pyrophosphorylase
E) phosphorylase a

Question 18

What protein is the $\delta$ subunit of phosphorylase kinase?

A) protein kinase A
B) phosphorylase
C) adenylate cyclase
D) protein phosphatase 1
E) calmodulin

Question 19

Glycogen synthase is converted into the active form by the action of _________________.

Question 20

What is the activated form of glucose required for glycogen synthesis?

A) glucose-6-phosphate
B) glucose-1-phosphate
C) ADP-glucose
D) UDP-glucose
E) GDP-glucose

Question 21

What are the fates of the glucose-1-phosphate derived from glycogen?

Question 22

The key enzyme in regulation of glycogen degradation is

A) glycogen phosphatase.
B) glycogen phosphorylase.
C) glucose 1-phosphate synthase.
D) glycogen kinase.
E) None of the answers is correct.

Question 23

Why is the T state of glycogen phosphorylase less active?

A) The adjacent amino acids are not phosphorylated, and thus the catalysis cannot be carried out.
B) The active site is partially blocked.
C) ATP cannot be bound by the T state.
D) Glucose-1-phosphate remains bound to the active site.
E) None of the answers is correct.

Question 24

What molecule must be excluded from the active site of glycogen phosphorylase?

A) glucose
B) glucose 1-phosphate
C) water
D) phosphate
E) None of the answers is correct.

Question 25

What are the three steps in glycogen degradation?

Question 26

In muscle,the first event in the breakdown of glycogen due to binding of a hormone is _____.

A) cytoplasmic cAMP levels rise
B) protein kinase A phosphorylates phosphorylase kinase
C) adenylate cyclase is activated
D) protein kinase A is activated
E) activation of a G protein

Question 27

What enzyme(s)is (are)required to cleave $\alpha$ -1,6-glycosidic branches in glycogen?

A) transferase
B) $\alpha$ -1,6-glucosidase
C) glycogen phosphatase
D) transferase and $\alpha$ -1,6-glucosidase
E) $\alpha$ -1,6-glucosidase and glycogen phosphatase

Question 28

What physiological conditions render phosphorylase b less active?

A) High ATP, AMP, and glucose 6-phosphate levels
B) High ATP and low calcium ion levels
C) High ATP and glucose 6-phosphate levels
D) High AMP and low ATP levels
E) None of the answers is correct.

Question 29

Which of the following occur after a carbohydrate-rich meal?

A) Blood-glucose levels increase leading to glycogen storage in the liver.
B) Blood-glucose levels increase leading to glycogen storage in the muscle.
C) Glucose uptake from the blood increases as a result of the action of insulin.
D) Glucagon is absent.
E) All of the answers are correct.

Question 30

How is phosphorylase b converted into phosphorylase a?

A) Addition of a phosphate to a serine residue
B) Dimerization, which forms the active site pocket
C) Cleavage of 10 amino acids from the N-terminal end of the protein
D) Binding of glucose, an allosteric modifier
E) None of the answers is correct.

Question 31

The key regulatory enzyme that primarily controls the rate of glycogen synthesis is

A) glycogen synthase phosphorylase.
B) glycogen synthase.
C) glycogen synthase kinase.
D) protein phosphatase-1.
E) None of the answers is correct.

Question 32

Why is glycogen branching important?

A) Branching significantly alters the melting point.
B) Branching decreases the solubility of glycogen.
C) Branching increases the rates of glycogen synthesis and degradation by increasing the potential sites of action.
D) Branching allows glycogen to be transported to other areas of the cell.
E) None of the answers is correct.

Question 33

Why is the formation of glucose-1-phosphate energetically favorable even though the ΔG°′ is very small?

Question 34

Critical hormones that signal for glycogen breakdown are

A) insulin and epinephrine.
B) glucagon and epinephrine.
C) glucagon and insulin.
D) insulin, glucagon, and epinephrine.
E) None of the answers is correct.

Question 35

Draw a structure showing the most common linkage between glucose units found in glycogen.

Question 36

What is the normal glucose concentration in blood?

A) 80-120 g/100 mL (4.4-6.7 M)
B) 8-12 g/100 mL (0.44-0.67 M)
C) 80-120 mg/100 mL (4.4-6.7 mM)
D) 80-120 $\mu$ g/100 mL (4.4-6.7 $\mu$ M)
E) None of the answers is correct.

Question 37

What are some of the advantages of having glycogen as a glucose source?

Question 38

What is the function of liver glycogen degradation?

A) For glucose export to other tissues when glucose levels are low
B) To maintain glucose levels after a large meal
C) To provide for the large energy needs of the liver
D) To allow for synthesis of lipids
E) None of the answers is correct.

Question 39

Conversion of glucose 1-phosphate to glucose 6-phosphate is carried out by the enzyme

A) phosphoglucomutase.
B) kinase 1-P.
C) phosphoglycerate mutase.
D) hexose-phosphate isomerase.
E) None of the answers is correct.

Question 40

Which of the following is a major site of glycogen storage?

A) adipose tissue
B) liver
C) pancreas
D) kidney
E) All of the answers are correct.

Question 41

What did Carl and Gerti Cori discover about the cause of von Gierke disease? Briefly explain how this information helps to explain the symptoms of the disease.

Question 42

Why does liver possess a specific enzyme that can cleave glucose 6-phosphate to form glucose and orthophosphate?

Question 43

How does insulin stimulate glycogen synthesis?

Question 44

Give the reaction catalyzed by UDP-glucose pyrophosphorylase.

Question 45

What path in addition to the cAMP-induced signal transduction is used in the liver to stimulate glycogen breakdown by epinephrine?

Question 46

Thermodynamically,the reaction glucose-1-phosphate + UTP UDP-glucose + PP_iis readily reversible.Explain why the formation of UDP-glucose from glucose-1-phosphate and UTP is essentially irreversible.

Question 47

Why can't the glucose 1-phosphate diffuse out of the cell?

Question 48

Why must glycogen control be manifested differently in muscle and liver?

Question 49

By what mechanism is phosphorylase kinase activated by Ca²⁺ levels of 1 μM?

Question 50

Compare the evolutionary history of the catalytic and regulatory features of glycogen phosphorylase.