Lecture 21 - gluconeogenesis and stuff

Question 1

what is gluconeogenesis

Answer 1

synth of glucose from noncarbohydrate precursors via pyruvate
(kinda the reverse of glycolysis)

Question 2

where does glyconeogenesis occur

Answer 2

liver mainly
some in kidney

Question 3

what is purpose of gluconeogenesis

Answer 3

maintains glucose levels in blood
mainly needed by muscle and brain

Question 4

which steps differ between glycolysis and gluconeogenesis

Answer 4

the irreversible steps in glycolysis
they need diff enzymes to be reversed

Question 5

gluconeogenesis: how to get from pyruvate to phosphoenolpyruvate

Answer 5

1. convert to oxoacetate via pyruvate carboxylase
2. convert that into phosphoenolpyruvate via phosphoenolpyruvate carboxykinase

Question 6

gluconeogenesis: how to get from fructose 1,6-bisphosph into fructose 6-phosph

Answer 6

Fructose 1 6 bisphosphophatase enzyme

Question 7

gluconeogenesis: how to get from glucose 6-phosphate into glucose

Answer 7

glucose 6 phsophatase

Question 8

what are the 4 non-carbohydrates that are precursors to glyconeogenesis pathway

Answer 8

lactate = pyruvate = glucose
alanine= pyruvate = glucose
aspartate = oxaloacetate = glucose
glycerol (fats) = dihydroxacetone phosphate = glucose

Question 9

wha is the prosthetic group on pyruvate carboxylase that allows CO2 to be captured and fixed onto pyruvate

Answer 9

biotin

Question 10

what activates pyruvate carboxylase

Answer 10

acetyl coA
so if aCoA is high (accumulates), then it means no more energy in form of ATP needed, and glyconeogenesis is triggered instead

Question 11

how is biotin attached to pyruvate carboxylase

Answer 11

covalently attached via a lysine side chain
(so is a prosthetic group and not a cofactor)

Question 12

how is glucose stored in plants and animals

Answer 12

plants starch
animals glycogen

Question 13

where is glycogen stored

Answer 13

• cystolic granules in liver
• muscle cells of vertebrates

Question 14

process of glycogen into glucose

Answer 14

glycogen -> G1P -> G6P (via phosphoglucomutase) ->glucose

Question 15

process of glycogen into glucose

Answer 15

glycogen -> G1P -> G6P (via phosphoglucomutase) ->glucose

Question 16

what is glycogenin

Answer 16

a protein in middle of glycgen
acts as primer for glycogen SYNTHESIS
by polymerising the first few gllucose molecules

Question 17

why would glycogen be broken down instead of glyconeogenesis

Answer 17

when quick source of glucose suddenly needed
can provide enery in absence of O2

Question 18

which enzyme catalyses removal of glucose residues

Answer 18

glycogen phosphorylase

Question 19

why is glycogen phosphorylase not suffient on its own, what else is needed

Answer 19

• stops 4 residues away from a branch point, cant go further
• “limt dextrin”
• transferase enzyme moves 3 glucoses from outer branch to the chain
• glycogen debranching enzyme removes the 1 residue left = a glucose molecule
• and a longer unbranched chain left that glycogen phsophorylase can act on again

Question 20

how does glucose get made into glycogen

Answer 20

• by glucokinase and 1ATP
• to make G6P
• then G6P turned into G1P via phosphoglucomutase
• G1P + UTP –> UDP-glucose and pyrophosphate
  via UDP glycose pyrophosphorylase
• and 2 ATP are used per glucose into glycogen

Question 21

why is pyrophosphatase formed

Answer 21

instead of UTP being split between gamma and beta
it is split between beta and alpha
so 2 Pi are left = pyrophosphotase

Question 22

what needs to happen to UDP-glucose for the the glucose to be added to glycogen chain

Answer 22

UDP is removed to leave an activated molecule