lecture 18 + 19 Flashcards
muscle vs liver- what do they do with glucose?
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.
why do we need branching structure of glycogen
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.
Glycogen phosphorylase
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
transferases
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
debranching enzyme
removes the sugars starting at the alpha 1,6 branch so that phosphorylase can keep chewing
mutase
swaps the phosphates , turning G1P into G6P. G6P is then used for glycolysis
how is glycogen phosphorylase regulated?
covalent modification via phosphate group, and allosteric regulation
what happens in the glycogen breakdown pathway that is unique to the liver?
liver turns G6P into free glucose using G6 phosphatase, which hides in the Er lumen
activated enzyme in glycogen breakdown
phosphorylase a. contains phosphate group. R state
inactivated enzyme in glycogen breakdown
phosphorylase b. T state. no phosphate
liver phosphorylase is always ____
active. always in the a state, because the liver’s job is to supply the body’s cells with glucose
how would you turn off/slow down liver phosphorylase a?
allosterically bind glucose, shift to T state. still phosphorylated
muscle phosphorylase is normally in what form?
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
how do you shift phosphorylase b to a?
phosphorylase kinase adds a phosphate on to PB.
what regulates phosphorylase kinase?
calcium binding (high calcium activates it) and phosphorylation
phosphorylase kinase adds the phosphate when activated by :
hormones that use a g protein coupled receptor
glycogen synthase
adds units of glucose to the (nonreducing ends) at the 4’ OH position of the growing glycogen chain
where does glycogen synthase get its glucose its transferring from?
removes a glucose moiety from UDP-glucose onto the chain
of glycogen synthesis and breakdown, which requires energy and of what form?
Glycogen synthesis requires an activated form of glucose, UDP-glucose, to drive the reaction but glycogen breakdown does not require an input of energy.
glycogen synthase requires a primer- what is it? why is it special? what does it do?
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
how does glycogen synthesis function when it needs to build a branch?
branching enzyme : clips off the a1,4 linkage, takes a block of 7 glucoses, moves it onto another segment in the a1,6 position
how is glycogen synthesis regulated?
allosterically and covalently
when would something inhibit/activate glycogen synthesis?
activated after a meal when glucose is very high
what are the active and inactive enzymes in glycogen synthesis?
glycogen synthase a and b
describe glycogen synthase a
activated form, no phosphate group . R state
is glycogen synthase b phosphorylated?
yes
what does protein kinase a do?
it puts phosphates on stuff. so it activates glycogen phosphorylase a
what does protein phosphatase 1 “PP1” do ?
it removes a phosphate group; this activates glycogen synthase b (turning it into a) and inactivates glycogen phosphorylase a (turning it into b)
what happens during exercise or fasting ? describe the cascade that occurs
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
whats happens after a meal? describe the cascade
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
