lecture 18 + 19

Question 1

muscle vs liver- what do they do with glucose?

Answer 1

The muscle uses its supply to run glycolysis, TCA, and ETS for ATP generation. The liver uses its supply to deliver glucose in the blood for all cells in the body.

Question 2

why do we need branching structure of glycogen

Answer 2

The branching structure of glycogen provides a high density of nonreducing ends from which glucose monomers are removed one at a time by the enzyme, glycogen phosphorylase.

Question 3

Glycogen phosphorylase

Answer 3

the enzyme that cuts glucose units off of the glycogen chain and adds a phosphate to them to form glucose-1-phosphate. no energy expended

Question 4

transferases

Answer 4

the enzyme in glycogen breakdown that moves a group of three glucoses near a branch point and onto a straight chain so that phosphorylase can keep going

Question 5

debranching enzyme

Answer 5

removes the sugars starting at the alpha 1,6 branch so that phosphorylase can keep chewing

Question 6

mutase

Answer 6

swaps the phosphates , turning G1P into G6P. G6P is then used for glycolysis

Question 7

how is glycogen phosphorylase regulated?

Answer 7

covalent modification via phosphate group, and allosteric regulation

Question 8

what happens in the glycogen breakdown pathway that is unique to the liver?

Answer 8

liver turns G6P into free glucose using G6 phosphatase, which hides in the Er lumen

Question 9

activated enzyme in glycogen breakdown

Answer 9

phosphorylase a. contains phosphate group. R state

Question 10

inactivated enzyme in glycogen breakdown

Answer 10

phosphorylase b. T state. no phosphate

Question 11

liver phosphorylase is always ____

Answer 11

active. always in the a state, because the liver’s job is to supply the body’s cells with glucose

Question 12

how would you turn off/slow down liver phosphorylase a?

Answer 12

allosterically bind glucose, shift to T state. still phosphorylated

Question 13

muscle phosphorylase is normally in what form?

Answer 13

inactive b form, T state. when energy is needed, as signaled by an increase in AMP, phosphorylase binds AMP, kicks enzyme into gear, shifts it into R state

Question 14

how do you shift phosphorylase b to a?

Answer 14

phosphorylase kinase adds a phosphate on to PB.

Question 15

what regulates phosphorylase kinase?

Answer 15

calcium binding (high calcium activates it) and phosphorylation

Question 16

phosphorylase kinase adds the phosphate when activated by :

Answer 16

hormones that use a g protein coupled receptor

Question 17

glycogen synthase

Answer 17

adds units of glucose to the (nonreducing ends) at the 4’ OH position of the growing glycogen chain

Question 18

where does glycogen synthase get its glucose its transferring from?

Answer 18

removes a glucose moiety from UDP-glucose onto the chain

Question 19

of glycogen synthesis and breakdown, which requires energy and of what form?

Answer 19

Glycogen synthesis requires an activated form of glucose, UDP-glucose, to drive the reaction but glycogen breakdown does not require an input of energy.

Question 20

glycogen synthase requires a primer- what is it? why is it special? what does it do?

Answer 20

glycogenin. a dimer. no reducing ends! always the center of the molecule. a glycogenin adds 8 glucose units so that glucose synthase can now extend off of it

Question 21

how does glycogen synthesis function when it needs to build a branch?

Answer 21

branching enzyme : clips off the a1,4 linkage, takes a block of 7 glucoses, moves it onto another segment in the a1,6 position

Question 22

how is glycogen synthesis regulated?

Answer 22

allosterically and covalently

Question 23

when would something inhibit/activate glycogen synthesis?

Answer 23

activated after a meal when glucose is very high

Question 24

what are the active and inactive enzymes in glycogen synthesis?

Answer 24

glycogen synthase a and b

Question 25

describe glycogen synthase a

Answer 25

activated form, no phosphate group . R state

Question 26

is glycogen synthase b phosphorylated?

Answer 26

yes

Question 27

what does protein kinase a do?

Answer 27

it puts phosphates on stuff. so it activates glycogen phosphorylase a

Question 28

what does protein phosphatase 1 “PP1” do ?

Answer 28

it removes a phosphate group; this activates glycogen synthase b (turning it into a) and inactivates glycogen phosphorylase a (turning it into b)

Question 29

what happens during exercise or fasting ? describe the cascade that occurs

Answer 29

need to synthesize more glucose from glycogen- cue glycogen breakdown process. a hormone (epinephrine in muscles, glucagon in liver) binds to G protein receptor. -> gdp to gtp, triggers adenylate cyclase, cAMP production, protein kinase a activation.
PKA activates glycogen phosphorylase b into a . this then cuts glucoses off the glycogen chain

Question 30

whats happens after a meal? describe the cascade

Answer 30

excess glucose- time to do glycogen synthesis. PP1 jumps into action, which then activates glycogen synthase a. this also inactivates phosphorylase. synthase a then builds glycogen chains