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Biochemistry > Lecture 23 (Exam 2) > Flashcards

Lecture 23 (Exam 2) Flashcards

1
Q

What are the two rate limiting steps of glycogen synthesis and degradation, respectively?

A

Glycogen synthase

Glycogen phosphorylase

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2
Q

Both glycogen rate limiting steps are regulated by ________ regulators and reversible __________ (under the control of hormones), but effects are in opposite directions.

A

Allosteric

Phosphorylation

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3
Q

The key enzyme of glycogen synthesis is glycogen synthase. It exists in two forms, which are…

A

Active non-phosphorylated “a” form

Inactive phosphorylated “b” form

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4
Q

Glycogen synthase is phosphorylated by…

A

Glycogen synthase kinase (GSK)

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5
Q

GSK is under the control of ________ and ________.

A

Insulin

PKA (Protein kinase A)

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6
Q

Allosteric regulation of glycogen synthase is done by __________, which is a powerful activator and stabilizes the active form.

A

Glucose 6-phosphate

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7
Q

Glycogen phosphorylase (key enzyme of glycogen breakdown) exists in 2 forms, which are…

A

Active “a” form (R relaxed state) - in liver

Inactive “b” form (T tense state) - in muscle

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8
Q

Liver and muscle forms of glycogen phosphorylase are products of separate genes, called _______. They differ in their sensitivities to regulatory molecules.

A

Isozymes

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9
Q

Liver enzyme (GP) is inactivated by free ________ (indicator of blood sugar levels), and is unaffected by ______.

A

Glucose

AMP

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10
Q

Muscle form (GP) is allosterically activated by ______ (measure of low energy status of cell).

A

AMP

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11
Q

Mutation in liver GP causes what disease?

A

Hers disease

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12
Q

Mutation in muscle GP causes what disease?

A

McArdle syndrome

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13
Q

GP is in its default “a” form or active form in the liver, and is inactivated by…

A

Glucose

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14
Q

Glucose binds to the active site of GP and stabilizes conformation in the inactive _____ state. When glucose levels are high, no need for glycogen breakdown (which will make more glucose).

A

T

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15
Q

GP is in its default “b” form or inactive form in the muscle, and is activated by…

A

AMP

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16
Q

AMP binds to the active site of GP and stabilizes the conformation of “b” into the active _____ state.

A

R

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17
Q

During muscle contraction _______ is converted to AMP by myosin and adenylate kinase signaling the GP to breakdown glycogen.

A

ATP

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18
Q

What are the negative allosteric regulators of muscle GP?

A

ATP

Glucose 6-phosphate

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19
Q

Under normal physiological conditions, GP is (ACTIVE/INACTIVE) in the muscle because of inhibitory effect of ATP and Glucose 6-phosphate.

A

Inactive

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20
Q

Glycogenesis is favored in the fed state. What three things are high?

A

Blood glucose high
Insulin high
Cellular ATP high (high energy)

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21
Q

When glycogen synthesis is favored, glycogen synthase is (PHOSPHORYLATED/DEPHOSPHORYLATED).

A

Dephosphorylated (active form)

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22
Q

When glycogen synthesis is favored, glycogen phosphorylase is (PHOSPHORYLATED/DEPHOSPHORYLATED).

A

Dephosphorylated (inactive form)

23
Q

Glycogenolysis is favored in fasting state. What is low and what is high during this?

A 
Blood glucose low
Glucagon high (makes liver from glycogen to glucose)
24
Q

Glycogenolysis is also favored during exercise. What is high during this?

A 
Cellular calcium high (in exercising muscles) 
AMP high (from breakdown of ATP)
25
Q

When glycogen breakdown is favored, glycogen synthase is (PHOSPHORYLATED/DEPHOSPHORYLATED).

A

Phosphorylated (inactive form)

26
Q

When glycogen breakdown is favored, glycogen phosphorylase is (PHOSPHORYLATED/DEPHOSPHORYLATED).

A

Phosphorylated (active form)

27
Q

High blood glucose promotes glycogen synthesis. This causes a release of insulin by the ______ of the pancreas. The insulin then binds to its receptor ______ ______, where this causes activation of a signaling cascade.

A

Beta cells

Tyrosine kinase

28
Q

What are the 4 key proteins involved in glycogen synthesis regulation by insulin?

A

GLUT4
Protein kinase B (PKB)
Protein phosphatase 1 (PP1)
Glycogen synthase kinase 3 (GSK3)

29
Q

In the mechanism of regulation by insulin, put the following steps in order –

A. Activation of PKB

B. PKB phosphorylates PP1 (activate) and GSK3 (inactivate)

C. Active PP1 dephosphorylates glycogen synthase (activate) and dephosphorylates glycogen phosphorylase (inactivate)

D. Formation of the insulin receptor complex

E. Translocation of GLUT4 to membrane

A
  1. D
  2. A
  3. E
  4. B
  5. C

***Study slide 12

30
Q

This disease is caused by reduced sensitivity to insulin, called insulin resistance. There are mutations in the insulin receptor and/or downstream signaling proteins.

A

Type 2 diabetes

31
Q

Type 2 diabetes down-regulation in receptor levels can be caused by –

    • Triggered by elevated _______
    • Endocytosis and degradation of the insulin receptor
    • Defective receptors not replaced by ________
A

Insulin

Translation

32
Q

Blood glucose criteria for –

Normal fasting and fed?
Pre diabetic/at risk fasting and fed?
Diabetes mellitus fasting and fed?

A

70-100 mg/dL (fasting) – 140 mg/dL (fed)
100-125 mg/dL (fasting) – Greater than 140 mg/dL (fed)
126 mg/dL (fasting) – 199 mg/dL (fed)

33
Q

Hormonal control of glycogen phosphorylase —

– Low blood sugar levels release ________ (acts on liver) which are made by alpha cells of pancreas

– Muscle activity releases _______ (effects are on muscle)

A

Glucagon

Epinephrine

34
Q

The effects of both hormones (glucagon and epinephrine) are mediated via _______. They signal glycogen breakdown.

A

GPCR (G protein coupled receptors)

35
Q

The phosphorylation of a single _______ residues converts b to a. Conversion is initiated by hormones and the phosphorylating itself is carried out by _________ _________.

A 
Serine
Phosphorylase kinase (PK)
36
Q

In regulation by glucagon, blood glucose levels are low (promote glycogen breakdown). Alpha cells of the pancreas release _______, where it goes on to bind to ______ on hepatocytes. This triggers a signaling cascade.

A

Glucagon

GPCR

37
Q

What are the key enzymes and second messengers for regulation by glucagon?

A 
G protein
Adenylate cyclase (AC) and cAMP
Protein kinase (PKA)
Protein phosphatase 1 (PP1)
Phosphorylase kinase (PK)
38
Q

For regulation by glucagon, put the following steps in order –

A. PKA phosphorylates PK (activate)
B. Activates PKA
C. PKA phosphorylates an inhibitor which inactivates PP1
D. Activates AC which forms cAMP
E. Binding of glucagon to its GPCR turns on G protein
F. PKA phosphorylates glycogen synthase (inactivates)
G. Active PK phosphorylates glycogen phosphorylase (activates)

A
  1. E
  2. D
  3. B
  4. F
  5. A
  6. C
  7. G

***Study slide 18

39
Q

This hormone creates a fight or flight response. It is released by adrenal glands and promotes degradation of glycogen in a pathway similar to glucagon.

A

Epinephrine

40
Q

Epinephrine allosteric regulators –

_________ – activates glycogen synthase. Inactivates glycogen phosphorylase

_________ – inhibits glycogen phosphorylase in liver but not muscle

________ – activates glycogen phosphorylase kinase

________ – activates glycogen phosphorylase (especially relevant during periods of exercise)

A

Glucose 6-phosphate
Free glucose
Ca++
AMP

41
Q

There is an “off” switch of glycogen breakdown. It occurs when secretion of hormone stops. PK and GP are _________ and inactivated, breakdown of glycogen stops, and synthesis of glycogen is promoted.

A

Dephosphorylated

42
Q

Glucagon (DOES/DOES NOT) act on muscle.

A

Does not (only liver)

43
Q

In the liver Glu-1-P is converted to _______ and then to glucose by ______. Free glucose is then released into the blood stream.

A

Glu-6-P

Glucose-6-Phosphatase

44
Q

Myocytes in the skeletal and cardiac cycle muscle lack _________ and hence cannot hydrolyze Glu-6-P. They use it to generate energy via glycolysis and TCA cycle.

A

Glucose-6-phosphatase

45
Q

What is the glucose sensor in liver cells?

A

Glycogen phosphorylase (GP)

46
Q

Name the following glycogen storage disease based on the characteristics –

Defective – Glucose-6-phosphatase OR transport system

Organ affected – Liver and kidney

Glycogen in the affected organ – Increased amount; normal structure

A

GSD 1 – Von Gierke

47
Q

Name the following glycogen storage disease based on the characteristics –

Deficiency in glycogen synthase
Patients cannot synthesize glycogen
Have muscle cramps due to lack of glycogen in muscle
Rely on glucose in diet
Vulnerable to hypoglycemia when fasting (during sleep)
Need to eat frequently

A

GSD 0

48
Q

Name the following glycogen storage disease based on the characteristics –

Defective enzyme – alpha-1,4-Glucosidase (lysosomal)

Organ affected – all organs

Glycogen in the affected organ – Massive increase in amount; normal structure

A

GSD II – Pompe

49
Q

Name the following glycogen storage disease based on the characteristics –

Defective enzyme – Deficiency in alpha-1,6-glucosidase (debranching enzyme)

Organ affected – Muscle and liver

Glycogen in the affected organ – Increased amount; short outer branches

*Patients possess glycogen molecules with large number of short branches. Light hypoglycemia and hepatomegaly.

A

GSD III – Cori Disease

50
Q

Name the following glycogen storage disease based on the characteristics –

Patients have long chain glycogen with fewer branches

Causes enlargement of liver and spleen, scarring of liver tissue (cirrhosis)

Death by 5 years of age

A

GSD IV – Andersen Disease

51
Q

Name the following glycogen storage disease based on the characteristics –

Deficiency in muscle glycogen phosphorylase
Rate limiting step of glycogen breakdown
Patients unable to supply muscles with enough glucose
Have weakness, muscle cramps
Exercise intolerance
Myoglobinuria (myoglobin in urine)
Tolerance by reducing strenuous exercise

A

GSD V – McArdle Disease

52
Q

Name the following glycogen storage disease based on the characteristics –

Deficiency in liver glycogen phosphorylase

Prevents glycogen breakdown in liver, hence it accumulates in the liver causing hepatomegaly

Low blood glucose levels

A

GSD VI – Hers Disease

53
Q

Name the following glycogen storage disease based on the characteristics –

Defect in alpha-glucosidase
Causes accumulation of glycogen in lysosomes
Disrupts functioning of muscle and liver cells
Progressive muscle weakness and myopathy (heart and skeletal)
Children die of heart failure

A

GSD II – Pompe Disease

54
Q

Enzyme replacement therapy (ERT) for GSD II (Pompe) is done by taking recombinant _________ and delivering it via intravenous infusion in babies/young children. (Myozyme and Lumizyme, Genzyme Corporation – FDA approved)

A

alpha-glucosidase

Biochemistry (10 decks)

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