Glycolysis/ gluconeogenesis regulation Flashcards
order of molecules in glycolysis:
glucose
G6P
F6P
fructose-1,6-bisphosphate
GAP/DHAP
GAP
1,3-phosphoglycertae
3-phosphoglycerate
2-phosphoglycertae
Phosphoenol pyruvate (PEP)
pyruvate
4 ways glycolysis is regulated
- substrate availability
- enzyme concentration
- allosteric regulation
- covalent modification
glycolysis regulation- substrate availability
substrate is glucose, availability controlled by GLUT transporter proteins
how does glucose enter the cell by GLUT proteins (regulation of glycolysis, substrate availability)
GLUT proteins in T1 configuration - open binding site on outside
glucose binds = conformational change
T2 configuration - binding site open to inside of cell
where are GLUT1, 2 and 4 proteins located?
GLUT 1 - RBC
GLUT 2 - liver/ beta cells (pancreas)
GLUT 4 - muscle cells and adipocytes
glycolysis regulation- enzyme concentration
label specific enzymes and the hormones used to regulate them
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)
glycolysis regulation- covalent modification
what hormone controls this?
pyruvate kinase is regulated by phosphorylation
active - when dephosphorylated
inactive - when phosphorylated
(caused by glucagon - through the cAMP pathway) to slow glycolysis
glycolysis regulation- allosteric regulation of step 1 of glycolysis
hexokinase is inhibited by G6P (the product of the reaction)
what is allosteric regulation?
a small regulatory molecule binds to the allosteric site
what is the exception to the allosteric regulation of hexokinase
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
glycolysis regulation- allosteric regulation of step 10
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)
glycolysis regulation- allosteric regulation of step 3 of glycolysis?
1st way - ATP:AMP ratio
PFK1 - 2 ways
ATP:AMP ratio
At rest, ATP builds -> inhibit PFK
During exercise, AMP builds -> activate PFK
glycolysis regulation- allosteric regulation of step 3 of glycolysis?
2nd way -PFK2 activity
PFK2 catalyses fructose-6-phosphate -> fructose-2,6-bisphosphate
High glucose activates PFK2
Increases fructose-2,6-bisphosphate which activates PFK1
2 aspects of gluconeogenesis regulation?
- enzyme concentration
- allosteric regulation
gluconeogenesis regulation - enzyme concentration
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
what are the gluconeogenic enzymes
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 PEPCK
gluconeogenic regulation - allosteric regulation of fructose-1,6-bisphosphatase by ATP:AMP ratio (also regulated by PFK2 activity)
At rest, ATP build - activates FBPase (speed up gluconeogenesis)
During exercise, AMP builds - inhibits FBPase
gluconeogenic regulation - allosteric regulation of fructose-1,6-bisphosphatase by PFK2 activity (also regulated by ATP:AMP ratio)
fructose-2,6-bisphosphate inhibits FBPase (but activates PFK1 in glycolysis)
High glucose -> activates PFK2 -> increase fructose-2,6-bisphosphate -> inhibits FBPase -> slow gluconeogenesis
what reaction does PFK2 catalyse?
fructose-6-phosphate -> fructose-2,6-phosphate
3rd thing that activates fructose-2,6-bisphosphate
activated by citrate
gluconeogenesis regulation - regulation of pyruvate carboxylase
Activated by acetyl-coA (diverts pyruvate away from CAC and to gluconeogenesis)
inhibited by ADP
where are the gluconeogenic enzymes localised in the cell
pyruvate carboxylase - MT
PEP carboxykinase - cytoplasm
fructose-1,6-bisphosphate - cytoplasm
glucose-6-phosphatase -ER
overview of gluconeogenesis with respect to where each step happens?
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)
how does gluconeogenesis compare to glycolysis?
the reversible steps of glycolysis are simply reversed in gluconeogenesis
the irreversible steps (1,3, and 10) have their own gluconeogenic reactions and enzymes
how is OAA transported to cytoplasm out of mitochondria for the next step in gluconeogenesis?
OAA -> malate (by malate dehydrogenase)
malate moved to cytosol, via a transporter
malate -> OAA + NADH
NADH used for other reactions
how is glucose-6-phosphate transported to ER?
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
