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BDS year 1 - biochemistry > Glycogen metabolism > Flashcards

Glycogen metabolism Flashcards

1
Q

where is glucose stored as glycogen and why

A

liver + muscle cells
glucose osmotically active – high glucose conc –> causes water uptake or endomosis
causing cell lysis

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2
Q

Why is glucose storage needed

A

allows blood glucose conc to be constant –> constant supply of glucose to brain

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3
Q

what happens when glucose conc is high or low

A

high – glucose –> glycogen

low – glycogen –> glucose

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4
Q

what is advantage of glycogen and what does glycogen support

A

can be broken down quickly –> quick supply of glucose for energy
supports anaerobic metabolism or glycolysis

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5
Q

what can animals do with glucose

A

can convert glucose –> fat

BUT CAN’T fat –> glucose

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6
Q

describe structure of glycogen

A

polysaccharide of alpha glucose
alpha 1,4 glycosidic bond in main chain +
alpha 1,6 glycosidic bond for every 12th glucose for branching

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7
Q

what is glycogenesis

A

glucose –> glycogen in liver + muscle

glycogen metabolism

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8
Q

what cells does glucose enter and how

A

liver cells – GLUT 2

muscle cells - GLUT 4

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9
Q

How would glycogenesis occur if the futile cycle isn’t formed

A

glucose enters liver cells -GLUT 2 + muscle cells - GLUT4
glucose –> glucose-6-phosphate = catalysed by glucokinase
glucose-6-phosphate –> glycogen = catalysed by Glycogen synthase

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10
Q

What is GS and when is it used and how is it activated

A

glycogen synthase
glycogenesis - not during futile cycle
GS activated by dephosphorylation
glycogen synthesis is rate limiting step = Slowest

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11
Q

when is the futile cycle formed

A

catabolism + anabolism pathways active simultaneously in cell
formed by 1 phosphate bond broken per cycle in forming UDP cycle

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12
Q

how can futile cycle be prevented

A

GS + glycogen phosphorylase (GP) must be reciprocally regulated
by allosteric effectors + phosphorylation

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13
Q

how does the futile cycle work

draw diagram

A

glucose –> glucose-6-phosphate = hexokinase
G6P –> G1P = phosphoglucomutase
G1P + UTP–> UDP-glucose + PPi = UDP glucose phosphorylase
PPi + H20 –> 2Pi = pyrophosphatase - spontaneous + lots energy released
UDP-glucose + glycogen (n) residues –> glycogen(n+1) + UDP = Glycogen synthase

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14
Q

how does glycogen catabolism occur,

briefly describe the equations (3)

A
  1. glycogen(n) –> glycogen(n-1) + G1P
  2. G1P G6P
  3. G6P + H20 –> glucose + Pi
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15
Q

why is vitamin B6 used with pyridoxal phosphate in 1st step of glycogen catabolism

A

prosthetic group

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16
Q

how does glycogen phosphorylase become active in 1st step of glycogen catabolism

A

when phosphorylated
opposite to GS activation
involves braking alpha 1,4 glycosidic bond

17
Q

what is the 2nd step of glycogen catabolism

A 
G1P  G6P
phosphoglucomutase (Pi moved C1 --> C6)
G6P goes to glycolysis to make ATP - reversible
high conc of G1P --> forward reaction
high conc of G6P --> back reaction
18
Q

what is the 3rd step of glycogen catabolism

A

G6P + H20 –> glucose + Pi
glucose-6-phosphatase in ER
only in liver = release glucose for constant supply to brain

19
Q

how and when does glycogen debranching happen

A

when 4 glucose left in branch during catabolism
3 glucose moves to main branch
breaking alpha 1,4 glycosidic bond = alpha 1,4 transglycosylase
alpha 1,6 glycosidic bond in branched glucose broken = alpha 1,6 glucosidase

20
Q

how + when does glycogen branching happen

A

glycogen anabolism
(Amylo 1,4 –> 1,6) transglycosylase transfers segment from end of glycogen chain to hydroxyl group of C6 of glucose
forms alpha 1,6 glycosidic bond
has to be 7 glucose chain each time - specific to enzyme active site

21
Q

when is insulin produced and what does it do

A

blood glucose high

activates glycogen synthesis to convert glucose –> glycogen

22
Q

when is glucagon and adrenaline produced and what do they do

A

glucagon - blood glucose too low
adrenaline - stress
hormones activate glycogenolysis + inhibit glycogen synthesis

23
Q

what are the different ways to regulate glycogen metabolism

A

glucagon
insulin
cAMP
pKA action

24
Q

how is cAMP used to regulate glycogen metabolism

A

insulin activates phosphodiesterase which inhibits cAMP

glucagon activates cAMP

25
Q

how is cAMP made inside the cells

A
  1. hormone/1st messenger binds to G protein coupled receptors
  2. binding activates G protein
  3. G protein activates adenylate cyclase
  4. ATP converts into cAMP = catalysed adenylate cyclase
26
Q

how does insulin regulate glycogen metabolism

A
  1. insulin activates glycogen synthase phosphatase
  2. GSP catalysis dephosphorylation of GS
    Phosphate GS (inactive) + ADP –> GS + ATP
  3. insulin inhibits GS kinase3 + cAMP dependant PKA
    causing inhibition of phosphorylation of glycogen kinase A
    GS + ATP –> PGS + ADP
27
Q

draw the diagram of how glucagon helps to regulation glycogen metabolism

A

see diagram

BDS year 1 - biochemistry (14 decks)

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