Chapter 25

Question 1

what is UDP-glucose?

(uridine diphosphate glucose)

Answer 1

activated form of glucose
the glucose donor in glycogen synthesis

Question 2

what synthesizes UDP-glucose?

Answer 2

by UDP-glucose pyrophosphorylase

Question 3

what renders the synthesis of UDP-glucose irreversible?

Answer 3

the hydrolysis of pyrophosphate

Question 4

how is UDP-glucose synthesized?

Answer 4

UDP-glycose pyrophosphorylase hydrolyzes UTP and puts it in glucose

Question 5

what drives the synthesis of UDP-glucose reaction to the right?

Answer 5

the cleavage of PPi

Question 6

what does glycogen synthase do in the reaction of Glucose to UDP-glucose?

Answer 6

glycogen synthase catalyzes the transfer of glucose from UDP-glucose to a growing chain

Question 7

what does glycogen synthase do in the synthesis of glycogen?

Answer 7

it transfers a glucose moiety from UDP-glucose to the C-4 terminal residue of a glycogen chain to form an α-1,4-glycosidic bond

Question 8

what does glycogen synthase require as a primer?

Answer 8

an oligosaccharide of glucose residues

Question 9

what synthesizes the primer needed by glycogen synthase?

Answer 9

glycogenin

Question 10

what is glycogenin?

Answer 10

a dimer of two identical subunits

Question 11

what does each subunit of glycogenin do?

Answer 11

each subunit generates an oligosaccharide of glucose residues 10-20 molecules long

Question 12

what does glycogen synthase do to the primer?

Answer 12

it extends the primer

Question 13

glycogen synthase can only synthesize what kind of linkages?

Answer 13

α-1,4-linkages

Question 14

what does a branching enzyme do?

Answer 14

it generates branches allowing glycogen synthase to extend the branch polymer

Question 15

how does a branching enzyme create branches?

Answer 15

it generates branches by cleaving an α-1,4-linkage and taking a block of approximately 7 glucoses and synthesizing an α-1,6-linkage,

Question 16

what does the branching of an enzyme allow?

Answer 16

increase insolubility
increases ends for synthesis and degradation

Question 17

when is glycogen synthase inactive?

Answer 17

when in the phosphorylated b form

Question 18

when is glycogen synthase active?

Answer 18

in the unphosphorylated a form

Question 19

what is the key regulatory process of glycogen synthesis?

Answer 19

the conversion of the b form in the T state to the active R state by binding glucose 6-phosphate

Question 20

what is the difference between phosphorylation of glycogen synthase and glycogen phosphorylase?

Answer 20

it has opposite effects
glycogen phosphorylase is phosphorylated and active in a form and unphopshorylated in b form
glycogen synthase is phosphorylated in b form and unphosphorylated in a form

Question 21

Quick quiz: why is the fact that phosphorylation has opposite effects on glycogen synthesis and breakdown advantageous?

Question 22

what inhibits glycogen synthesis?

Answer 22

• phosphorylation of glycogen synthase by protein kinase A (PKA) to form glycogen synthase b
• phosphorylation by glycogen synthase kinase (GSK)

Question 23

what does insulin do to glycogen synthesis pathways?

Answer 23

it turns on pathways to store glucose

Question 24

when levels of glucagon and epinephrine GO UP do you want to turn on synthesis of glycogen or turn it off?

Question 25

what happens during the FED state?

Answer 25

there is high glucose levels

Question 26

what happens during the FASTING state?

Answer 26

there are low glucose levels

Question 27

how does the regulation of protein phosphatase 1 in muscle take place?

Answer 27

* Phosphorylation of Gm by protein kinase A dissociates the catalytic subunit from its substrates in the glycogen particle * Phosphorylation of the inhibitor subunit by protein kinase A inactivates catalytic unit of PP1

Question 28

what does protein phosphatase 1 (PP1) do to the glycogen metabolism?

Answer 28

* it shifts glycogen metabolism from the degradation mode to the synthesis mode * it removes phosphoryl groups from glycogen synthase b, converting it into the more active a form * it removes phosphoryl groups from the phosphorylase kinase and glycogen phosphorylase, inhibiting glycogen degradation?

Question 29

how does PP1 inhibit glycogen degredation?

Answer 29

it removes phosphoryl groups from phosphorylase kinase and glycogen phosphorylase

Question 30

how does insulin stimulate glycogen synthesis?

Answer 30

by activating a signal transduction pathway that results in the phosphorylation and inactivation of glycogen synthase kinase

Question 31

what does PP1 do to glycogen synthase?

Answer 31

is dephosphorylates glycogen synthase, generating the active a form of the synthase, activating it and allowing glycogen synthesis

Question 32

how does insulin facilitate glycogen synthesis?

Answer 32

by increasing the number of glucose transporters (GLUT4) in the plasma membrane

Question 33

what does insulin do to glycogen synthase kinase?

Answer 33

insulin triggers a cascade that leads to the phosphorylation and inactivation of glycogen synthase kinase and prevents the phosphorylation of glycogen synthase

Question 34

what does glycogen metabolism in the liver regulate?

Answer 34

blood-glucose levels

Question 35

how do high blood-glucose levels effect glycogen degradation and synthesis?

Answer 35

degradation in the liver is inhibited synthesis is stimulated

Question 36

what does the binding of glucose to glycogen phosphorylase do?

Answer 36

it converts glycogen phosphorylase a from the R state to the T state

Question 37

what does the conversion of glycogen phosphorylase a from R to T state by glucose cause?

Answer 37

the activation of PP1 that is associated with the phosphorylase

Question 38

what does PP1 do to the glycogen metabolism?

Answer 38

it converts the glycogen metabolism from a degradation mode to a synthesis mode

Question 39

what is the first step in glucose regulation of liver-glycogen metabolism?

Answer 39

glucose binds to glycogen phosphorylase a and inhibits it, facilitating the formation of the T state of phosphorylase a

Question 40

what does the T state of phosphorylase a cause in the liver?

Answer 40

The T state of phosphorylase a does not bind protein phosphatase 1 (PP1), leading to the dissociation of PP1 from glycogen phosphorylase a, and its activation

Question 41

what does the free PP1 do to the liver-glycogen metabolism?

Answer 41

it dephosphorylates glycogen phosphorylase a and glycogen synthase b, leading to the inactivation of glycogen breakdown and the activation of glycogen synthesis

Question 42

how does glucose regulate liver-glycogen metabolism

Answer 42

1. glucose binds glycogen phosphorylase, inhibiting it 2. inhibition of glycogen phosphorylase causes formation of T state of phosphorylase a 3. T state of phosphorylase a does not bind protein phosphatase 1 (PP1) 4. PP1 dissociates from glycogen phosphorylase a, activating it 5. free PP1 dephosphorylates glycogen phosphorylase a and glycogen synthase b 6. glycogen breakdown is inactivated 7. glycogen synthesis is activated

Question 43

what do phosphorylase and synthase activity depend on in the liver?

Answer 43

glucose

Question 44

as glucose increases, phosphorylase activity….

Answer 44

decreases

Question 45

as glucose increases, synthase activity….

Answer 45

increases

Question 46

at low glucose __ is active

Answer 46

phosphorylase

Question 47

at high glucose, ___ is active

Answer 47

synthase

Question 48

what is diabetes?

Answer 48

it is characterized by the presence of excess glucose and underutilization of the fuel

Question 49

where is excess glucose secreted in people with diabetes?

Answer 49

urine

Question 50

what is type 1 diabetes (T1D)?

Answer 50

childhood onset insulin is not produced

Question 51

how is type 1 diabetes managed?

Answer 51

injection of insulin

Question 52

what is type 2 diabetes (T2D)?

Answer 52

insulin is produced by the insulin-signaling pathway is not responsive, a condition referred to as insulin resistance

Question 53

how is type 2 diabetes managed?

Answer 53

diet