Brenda - Glycolysis Regulation Flashcards
What type of reaction is the conversion of pyruvate to acetyl-coA?
Oxidative decarboxylation, catalysed by PDH
Give two fates of acetyl CoA
Fatty acid synthesis
Converted to ketone bodies
What happens to pyruvate in yeast?
(2)
Pyruvate is converted to ethanol and CO2
This oxidises NADH to NAD+
How does bakers yeast work?
(2)
Yeast produces CO2 by pyruvate decarboxylation which causes bread to rise
Ethanol is also produced by it evaporates during baking
Where is lactate produced in mammals?
Skeletal muscles during exercise
What happens when lactate is formed?
It is transported out of muscle cells and brought to the liver where it is converted to pyruvate
When do all tissues produce lactate?
When O2 supply is inadequate all tissue produce lactate by anaerobic glycolysis
What is lactate acidosis?
The accumulation of lactate and elevation of lactic acid in the blood
How does glucose move into cells?
(3)
Moves by passive transport
Glucose conc in cells «< blood glucose
Moves through membrane-spanning glucose transporters
What happens to glucose inside the cell?
Glucose is phosphorylated
Phosphorylated glucose cannot cross plasma membrane
Write a note on the regulation of hexokinase
(4)
G6P inhibits Hexokinase isozymes I, II, III
G6P levels up when glycolysis is inhibited
Glucokinase is not inhibited by G6P
Liver cells can form G6P by action of glucokinase when glucose is abundant
List the three major control sites for glycolysis
(enzymes)
Phosphofructokinase
Pyruvate kinase
Hexokinase
What inhibits phosphofructokinase?
(3)
ATP
Citrate
H+
How does ATP inhibit phosphofructokinase?
ATP lowers enzyme affinity for fructose-6-phosophate
How does citrate inhibit phosphofructokinase?
Citrate works by enhancing the inhibitory effect of ATP
What reverses the inhibitory action of ATP?
Increased levels of ADP -> this increases PFK activity
What activates phosphofructokinase?
(2)
AMP
F-2-6-bisP
How does F-2-6-bisP activate PFK?
F-2,6-BisP activates PFK in the liver by increasing its affinity for F6P and decreasing the inhibitory effect of ATP
What inhibits pyruvate kinase?
(2)
High ATP
Acetyl CoA
How does high ATP inhibit pyruvate kinase?
High ATP reduces the affinity of pyruvate kinase for phosphoenolpyruvate
What activates pyruvate kinase?
F 1,6-BisP
How does F 1,6-BisP activate pyruvate kinase?
It allows pyruvate kinase to keep pace with the high flux of intermediates -> feedforward action
How does F 1,6-BisP activate pyruvate kinase?
It allows pyruvate kinase to keep pace with the high flux of intermediates -> feedforward action
How is pyruvate kinase inhibited by acetyl CoA?
Acetyl CoA is a major product of fatty acid oxidation i.e. energy from B oxidation has been made, we don’t need more energy
How is pyruvate kinase inhibited by acetyl CoA?
Acetyl CoA is a major product of fatty acid oxidation i.e. energy from B oxidation has been made, we don’t need more energy
What does glucagon regulate?
(2)
Glucagon regulates (PFK2) the enzyme which synthesises F2, 6BP
Glucagon regulates the enzyme (FBPase2) which hydrolyses F2,6BP back into F6P
What does glucagon regulate?
(2)
Glucagon regulates (PFK2) the enzyme which synthesises F2, 6BP
Glucagon regulates the enzyme (FBPase2) which hydrolyses F2,6BP back into F6P
What is the overall affect of glucagon?
It causes glycolysis to slow down when blood glucose falls
PFK is inhibited by H+ ions, why is this important?
It prevents excessive formation of lactate under anaerobic conditions
Explain how HK inhibition and PKF inhibition work together to turn off glycolysis
(2)
When PKF is inhibited large amounts of G6P build up
G6P then inhibits PKF -> preventing the first step of glycolysis
