Glycogenesis Flashcards

1
Q

glycogenesis

A

glucose converted to glycogen

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2
Q

why do we need glycogenesis

A

to ensure a reserve of quick energy

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3
Q

major sites of glycogen synthesis and storage

A

liver and skeletal muscle
some glycogen in kidneys and heart

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4
Q

liver glycogen unique role

A

can be broken down to glucose to reenter the bloodstream
maintains blood glucose homeostasis

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5
Q

skeletal muscle glycogen storage role

A

majority of glycogen stores bc skeletal muscle is so common

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6
Q

which tissue has the greatest concentration of glycogen?

A

liver

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7
Q

glycogen stores in muscle: problem

A

an energy source that can’t directly contribute to blood glucose levels
muscles don’t have enzyme that converts phosphorylated glucose back into free glucose

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8
Q

how does glucose enter the cell?
(step 1 of glycogenesis)

A

glucose is phosphorylated by hexokinase in muscle or glucokinase in liver to become glucose-6-phosphate

ATP to ADP

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9
Q

glycogen is made up of

A

G6P (blood glucose) + gluconeogenic precursors = glycogen

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10
Q

hexokinase type 1 and 2 location

A

muscle, brain, adipose tissue

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11
Q

glucokinase (hexokinase type 4) location

A

liver and pancreas

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12
Q

hexokinase inhibition

A

allosterically inhibited by G6P (its product)
when cell has enough G6P, glucose entry into cell is slowed

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13
Q

glucokinase inhibition

A

not inhibited by G6P

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14
Q

hexokinase Km

A

low Km
function at max velocity at fasting blood glucose concentrations

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15
Q

glucokinase Km

A

high Km
functions at max velocity only when glucose levels are high (such as following a high-carbohydrate meal)

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16
Q

hexokinase and insulin

A

not induced by insulin in normal individuals

17
Q

glucokinase and insulin in normal individuals

A

induced by insulin in normal individuals

18
Q

hexokinase and insulin in insulin-resistant individuals

A

not induced by insulin

19
Q

glucokinase and insulin in insulin-resistant individuals

A

not induced by insulin

20
Q

which form of glycogen synthase (dephosphorylated or phosphorylated) is more active

A

dephosphorylated
insulin promotes dephos

21
Q

what promotes dephosphorylation of glycogen synthase

A

insulin
this is how insulin stimulates glycogenesis

22
Q

what is induced by insulin?

A

glucokinase!

23
Q

what is an alternate source of glucose for glycogensis?

A

newly synthesized glucose from gluconeogenesis

24
Q

step 2 of glycogenesis

A

transfer phosphate from carbon 6 of glucose to carbon 1
enzyme: phosphoglucomutase

25
step 3 of glycogenesis
uridine monophosphate combined with G1P to form UDP-glucose energy from UTP to UMP (hydrolysis of anhydride bond)
26
in what form is glucose incorporated into glycogen?
UDP-glucose
27
step 4 of glycogenesis
UDP-glucose to glycogen enzyme: glycogen synthase
28
what does glycogen synthase require
preformed glycogen as a primer
29
how is initial glycogen formed
glucose residue binds to glycogenin
30
when is glycogen synthase active
when it is dephosphorylated
31
when is glycogen synthase inactive
phosphorylated
32
insulin and glycogen synthesis
insulin stimulates dephosphorylation of glycogen synthase (activates it)
33
after 6 or 7 glucose molecules are added to glycogen chain,
branching of chain
34
branching enzyme
transfers 6 or 7 glucoses to C-6-OH group forms alpha(1-6) bonds bc glycogen synthase can't
35
why is branching important
increases molecule's solubility and compactness makes nonreducing ends of chains available so glucose can be cleaved rapidly and used for energy (glycogenolysis)
36
glycogenesis energy use
consumes energy bc an ATP and UTP are consumed for each molecule of glucose introduced