Glycolysis/ gluconeogenesis regulation

Question 1

order of molecules in glycolysis:

Answer 1

glucose
G6P
F6P
fructose-1,6-bisphosphate
GAP/DHAP
GAP
1,3-phosphoglycertae
3-phosphoglycerate
2-phosphoglycertae
Phosphoenol pyruvate (PEP)
pyruvate

Question 2

4 ways glycolysis is regulated

Answer 2

• substrate availability
• enzyme concentration
• allosteric regulation
• covalent modification

Question 3

glycolysis regulation- substrate availability

Answer 3

substrate is glucose, availability controlled by GLUT transporter proteins

Question 4

how does glucose enter the cell by GLUT proteins (regulation of glycolysis, substrate availability)

Answer 4

GLUT proteins in T1 configuration - open binding site on outside
glucose binds = conformational change
T2 configuration - binding site open to inside of cell

Question 5

where are GLUT1, 2 and 4 proteins located?

Answer 5

GLUT 1 - RBC
GLUT 2 - liver/ beta cells (pancreas)
GLUT 4 - muscle cells and adipocytes

Question 6

glycolysis regulation- enzyme concentration

label specific enzymes and the hormones used to regulate them

Answer 6

The only rate limiting enzymes are the ones controlling the irreversible steps (step 1, 3 and 10)

step 1 -hexokinase
step 3 - phosphofructokinase 1 (PFK1)
step 10- pyruvate kinase

Hormones:
insulin - upregulate these hormones (increase glycolysis)
glucagon -downregulate these hormones (decrease glycolysis)

Question 7

glycolysis regulation- covalent modification

what hormone controls this?

Answer 7

pyruvate kinase is regulated by phosphorylation

active - when dephosphorylated
inactive - when phosphorylated
(caused by glucagon - through the cAMP pathway) to slow glycolysis

Question 8

glycolysis regulation- allosteric regulation of step 1 of glycolysis

Answer 8

hexokinase is inhibited by G6P (the product of the reaction)

Question 9

what is allosteric regulation?

Answer 9

a small regulatory molecule binds to the allosteric site

Question 10

what is the exception to the allosteric regulation of hexokinase

Answer 10

Hexokinase IV Liver (AKA glucokinase) is not inhibited by G6P
Instead:
High glucose - glucokinase is free in cytosol
Low glucose - glucokinase sequestered in nucleus as bound to regulatory protein

(links to regulation of futile cycle)

Question 11

glycolysis regulation- allosteric regulation of step 10

Answer 11

pyruvate kinase
activated -fructose-1,6-bisphosphate
(feedforward mechanism, since its produced before pyruvate kinase is needed)
Inhibited - by ATP and acetyl coA

ATP produced by the reaction (lots of ATP, enzyme inhibited and reaction slows)

Question 12

glycolysis regulation- allosteric regulation of step 3 of glycolysis?

1st way - ATP:AMP ratio

Answer 12

PFK1 - 2 ways
ATP:AMP ratio
At rest, ATP builds -> inhibit PFK
During exercise, AMP builds -> activate PFK

Question 13

glycolysis regulation- allosteric regulation of step 3 of glycolysis?

2nd way -PFK2 activity

Answer 13

PFK2 catalyses fructose-6-phosphate -> fructose-2,6-bisphosphate

High glucose activates PFK2
Increases fructose-2,6-bisphosphate which activates PFK1

Question 14

2 aspects of gluconeogenesis regulation?

Answer 14

• enzyme concentration
• allosteric regulation

Question 15

gluconeogenesis regulation - enzyme concentration

Answer 15

rate limiting enzymes are the irreversible reactions

Gluconeogenesis has specific enzymes that catalyse the reverse of steps 1, 3 and 10 of glycolysis

glucagon -upregulates gluconeogenic enzymes
insulin - downregulates

Question 16

what are the gluconeogenic enzymes

Answer 16

enzymes that catalyse the reverse of the irreversible steps of glycolysis

reverse of step 1 - glucose-6-phosphatase
reverse of step 3 - fructose-1,6-bisphosphatase
reverse of step 10 - pyruvate carboxylase and PEP carboxykinase

Question 17

gluconeogenic regulation - allosteric regulation of fructose-1,6-bisphosphatase by ATP:AMP ratio (also regulated by PFK2 activity)

Answer 17

At rest, ATP build - activates FBPase (speed up gluconeogenesis)

During exercise, AMP builds - inhibits FBPase

Question 18

gluconeogenic regulation - allosteric regulation of fructose-1,6-bisphosphatase by PFK2 activity (also regulated by ATP:AMP ratio)

Answer 18

fructose-2,6-bisphosphate inhibits FBPase (but activates PFK1 in glycolysis)

High glucose -> activates PFK2 -> increase fructose-2,6-bisphosphate -> inhibits FBPase -> slow gluconeogenesis

Question 19

what reaction does PFK2 catalyse?

Answer 19

fructose-6-phosphate -> fructose-2,6-phosphate

Question 20

3rd thing that activates PFK2

Answer 20

activated by citrate

Question 21

gluconeogenesis regulation - regulation of pyruvate carboxylase

Answer 21

Activated by acetyl-coA (diverts pyruvate away from CAC and to gluconeogenesis)
inhibited by ADP

Question 22

where are the gluconeogenic enzymes localised in the cell

Answer 22

pyruvate carboxylase - MT
PEP carboxykinase - cytoplasm
fructose-1,6-bis phosphatase - cytoplasm
glucose-6-phosphatase -ER

Question 23

overview of gluconeogenesis with respect to where each step happens?

Answer 23

pyruvate enters MT for carboxylation, forming OAA
second step occurs in cytoplasm (OAA must be transported out)
steps continue in cytoplasm until glucose-6-phosphate forms (where it moves to ER by a transporter)

Question 24

how does gluconeogenesis compare to glycolysis?

Answer 24

the reversible steps of glycolysis are simply reversed in gluconeogenesis
the irreversible steps (1,3, and 10) have their own gluconeogenic reactions and enzymes

Question 25

how is OAA transported to cytoplasm out of mitochondria for the next step in gluconeogenesis?

Answer 25

OAA -> malate (by malate dehydrogenase) OAA + NADH + H+ <=> malate + NAD+ malate moved to cytosol, via a transporter malate + NAD+ -> OAA + NADH + H+ NADH used for other reactions

Question 26

how is glucose-6-phosphate transported to ER?

Answer 26

by T1 of transporter G6Pase (in ER membrane) catalyses reaction: H2O + G6P -> Pi + glucose T2 transports Pi, T3 transports glucose out of ER into cytosol