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Biochemistry > glycogen metabolism II > Flashcards

glycogen metabolism II Flashcards

1
Q

regulation of glycogen metabolism is very important to

A

maintain blood sugar and provide energy to muscles

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2
Q

rate limiting enzyme of glycogen synthesis

A

glycogen synthase

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3
Q

rate limiting enzyme of glycogen degradation

A

glycogen phosphorylase

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4
Q

glycogen synthase and glycogen phosphorylase (rate limiting enzymes of glycogen synthesis and degradation) are regulated by

A

allosteric regulators and by reversible phosphorylation (under the control of hormones)

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5
Q

glycogen synthase exists in 2 forms

A
  1. non-phosphorylated “a” form -active form

2. phosphorylated “b” form - inactive form

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6
Q

glycogen synthase is phosphorylated by ______ and dephosphorylated by ______

A

glycogen synthase kinase (GSK)

protein phosphatase

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7
Q

glycogen synthase kinase (GSK) is under the influence of

A

insulin

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8
Q

allosteric regulation - power activator of glycogen synthase

A

glucose 6-phosphate

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9
Q

glycogen phosphorylase exists in 2 forms

A
  1. phosphorylated “a” form - active form (R relaxed state) - in liver
  2. dephosphorylated “b” form - inactive form (T tense state) - in muscle
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10
Q

glycogen phosphorylase is regulated by

A

several allosteric effectors (signal energy state of the cell)

reversible phosphorylation (responsive to hormones)

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11
Q

liver and muscle forms of glycogen phosphorylase (GP) are products to 2 separate genes, they are called

A

isozymes

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12
Q 
liver and muscle forms of 
glycogen phosphorylase (GP) differ in their
A

sensitivities to regulatory molecules

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13
Q

liver glycogen phosphorylase (GP) is inactivated by

A

free glucose (indicator of blood sugar levels); unaffected by AMP

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14
Q

muscle glycogen phosphorylase (GP) is allosterically activated by

A

AMP (measure of low energy status of cell)

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15
Q

allosteric regulation of liver glycogen phosphorylase (GP):

glucose binds to active site and

when glucose levels are high, no need for

A

stabilizes conformation in the inactive T state

glycogen breakdown (which would make more glucose)

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16
Q

default form of liver glycogen phosphorylase is

A

“a” form or active form

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17
Q

allosteric regulation of muscle glycogen phosphorylase (GP):

AMP bind to active site and

ATP and glucose-6-phosphate are

under normal physiological conditions, GP is inactive because of

A

stabilizes conformation of “b” in the active R state

negative allosteric regulators

inhibitory effect of ATP and gluc-6-phosphate

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18
Q

default form of muscle glycogen phosphorylase is

A

“b” form or inactive form

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19
Q

glycogenesis is favored in fed state:

blood glucose is ______

insulin is ______

cellular ATP is ______

A

high

high

high (signal of high energy)

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20
Q

when glycogen synthesis is favored:

_______ form of glycogen synthase is dominant

_______ form of glycogen phosphorylase is dominant

A

dephosphorylated form (active)

dephosphorylated form (inactive)

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21
Q

glycogenolysis is favored in fasting state and during exercise:

blood glucose is ______

glucagon is ______

cellular calcium is ______

AMP is ______

A

low

high

high (in exercising muscles)

high (from breakdown of ATP)

22
Q

when glycogen breakdown is favored:

_______ form of glycogen synthase is dominant

_______ form of glycogen phosphorylase is dominant

A

phosphorylated form (inactive)

phosphorylated form (active)

23
Q

Regulation of glycogen metabolism by insulin: glycogen synthase activation by insulin:

insulin binds to insulin receptor (receptor tyrosine kinase in muscle and liver) –> through signaling activates _____ –> PkB phosphorylates and activates _____ while phosphorylating and inactivating ______ –> PPI dephosphorylates ______ ______ (which is now activated) to proceed with glycogenesis

A

protein kinase B (PkB)

protein phosphatase I (PPI)

glycogen synthase kinase 3 (GSK3 typically phosphorylates glycogen synthase inactivating it)

glycogen synthase

24
Q

additional function of PkB

A

responsible for insertion of GLUT4 into plasma membrane

25
Q

regulation of glycogen metabolism: glycogen phosphorylase inactivation

insulin binds to insulin receptor (receptor tyrosine kinase) through signaling activates ______ –> PkB phosphorylates and activates _______ which inactivates ______ ______ and ______ ______ –> making glycogen phosphorylase inactive (preventing glycogenolysis from occuring)

A

protein kinase B (PkB)

protein phosphatase I (PPI)

glycogen phosphorylase

phosphorylase kinase (PK)

26
Q

active protein phosphatase I (PP1) dephosphoyrlates ________ and dephosphorylates _______

A

glycogen synthase (activates)

glycogen phosphorylase (inactivates)

27
Q

mechanism of regulation by insulin:

net result: glycogen synthesis via

A

activation of glycogen synthase and inactivation of glycogen phosphorylase

28
Q

type 2 diabetes:

called:

mutations in:

A

insulin resistance

insulin receptor and/or downstream signaling proteins

29
Q

type 2 diabetes:

down-regulation in receptor levels:

A

triggered by elevated insulin

endocytosis and degradation of the insulin receptor

defective receptors not replaced by translation

30
Q

normal blood glucose:

prediabetic/at-risk:

diabetes mellitus:

A

70-100 mg/dL (fasting) ; less than 140 (fed)

100-125 mg/dL (fasting) ; greater than 140 (fed)

greater than 126 mg/dL (fasting) ; greater than 199 (fed)

31
Q

low blood sugar levels release

A

glucagon (acts on liver)

32
Q

muscle activity releases

A

epinephrine (effects are on muscle)

33
Q

glucagon and epinephrine are mediated by what type of receptors

A

GPCRs

34
Q

epinephrine and glucagon signal

A

glycogen breakdown

35
Q

phosphorylase kinase (PK) phosphorylates

A

glycogen phosphorylase to make it active

36
Q

phosphorylase kinase (inactive) –> _______ (partly active)

A

Ca 2+ (exercising muscle)

Ca2+ actually binds to calmodulin

37
Q

phosphorylase kinase (partly active) –> ________ (fully active)

A

PKA (which is activated by glucagon and epinephrine)

phosphorylated form (phosphorylase a) (active form)

38
Q

regulation of glycogenolysis by glucagon and epinephrine: glycogen synthase inactivation

______ or ______ binds to GPCR and activates ______ ______ (which produces ______) –> cAMP activates ______ –> PkA inhibits _____ (by adding an inhibitor) and inhibits _____ (by phosphorylating) –> preventing assembling of glycogen (glycogenesis)

A

glucagon or epinephrine

adenylyl cyclase

cAMP

PkA

protein phosphatase 1 (PP1)

glycogen synthase

39
Q

regulation of glycogenolysis by glucagon and epinephrine: glycogen phosphorylase activation:

______ or ______ binds to GPCR and activates ______ (which produces _____ ) –> cAMP activates ______ –> PkA phosphorylates and activates ______ which phosphorylates ______ and allows for _____ to take place

A

glucagon or epinephrine

adenylyl cyclase

cAMP

PkA

phosphorylase kinase (PK)

glycogen phosphorylase (is now activated)

glycogenolysis

40
Q

regulation of glycogenolysis by glucagon and epinephrine:

net result:

A

glycogen breakdown (via inactivation of glycogen synthase and activation of glycogen phosphorylase)

41
Q

glucagon does not act on

A

muscle cells

42
Q

in liver, glucose 1-P converted to ______ and then to glucose by ______ which allows ______

A

glucose 6-P

glucose-6-phosphatase

free glucose to be released into blood stream

43
Q

_______ _______ is considered the glucose sensor in liver cells

A

glycogen phosphorylase

44
Q

GSD 0

defective enzyme:

pathway affected:

A

glycogen synthase

glycogenesis is affected

patients cannot synthesize glycogen

rely on glucose in diet

45
Q

GSD 1

disorder name:

defective enzyme:

pathway affected:

A

Von Gierke disease

glucose 6-phosphatase

inefficient release of free glucose into the bloodstream by the liver in gluconeogenesis and glycogenolysis

46
Q

GSD 2

disorder name:

defective enzyme:

pathway affected:

A

Pompe Disease

acid maltase (used in lysosomal glycogen degradation)

lysosomal glycogenolysis: accumulation of glycogen in lysosomes

progressive muscle weakness and myopathy (including heart and skeletal muscle)

ERT: recombinant human alpha-glucosidase delivered via IV infustion in children - effective

47
Q

GSD 3

disorder name:

defective enzyme:

pathway affected:

A

Cori disease

debranching enzyme (alpha-1,6-glucosidase)

glycogenolysis: glucose cleavage and release from branch point

48
Q

GSD 4

disorder name:

defective enzyme:

pathway affected:

A

anderson disease

glucosyl (4:6) transferase

glycogenesis: chain branching is limited

death by 5 years of age

49
Q

GSD 5

disorder name:

defective enzyme:

pathway affected:

A

McArdle Disease

muscle glycogen phosphorylase

glycogenolysis: glucose 1-P release

muscles break down (myoglobin in urine)

50
Q

GSD 6

disorder name:

defective enzyme:

pathway affected:

A

Hers disease

liver glycogen phosphorylase

glycogenolysis: glucose 1-P release

low blood glucose levels (fairly benign)

Biochemistry (32 decks)

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