5. Energy Production - Carbohydrates (b) Flashcards
How do high NADH levels regulate glycolysis?
They signal high energy levels so there is product inhibition of step 6, which inhibits glycolysis.
Define allostery.
Activator or inhibitor binds at another site.
What are the two ways in which enzymes can be inhibited?
Allostery and covalent modification.
What are the key steps affected by allosteric regulation in glycolysis?
1, 3 and 10.
How is step 1 of glycolysis regulated?
By the enzymes hexokinase. It has decreased action if glucose 6-phosphate are too high due to product inhibition.
How is step 3 of glycolysis regulated?
By the enzyme phosphofructokinase-1. In the muscles, it has decreased action, and therefore inhibits glycolysis, if the ATP:AMP ratio is high. In the liver, it has increase action, and therefore stimulates glycolysis, if there is a high insulin: glucagon ratio.
How is step 10 of glycolysis regulated?
By the enzyme pyruvate kinase. It is stimulated by a high insulin: glucagon ratio.
How could product inhibition of step 6 of glycolysis occur?
If there was no NAD+ regenerated and lots of NADH produced.
What two ways can NAD+ be regenerated?
In stage four of metabolism or by lactate dehydrogenase.
How can lactate be utilised?
NAD+ + lactate -> NADH + H+ + pyruvate.
What can raise lactate levels?
Strenuous exercise, shock or congestive heart disease.
Why does hyperlactaemia not have any affect on the blood pH but lactic acidosis does?
Because hyperlactaemia means the levels of lactate (2-5mM) are below the renal threshold, whereas with lactic acidosis, the levels of lactate (>5mM) are above the renal threshold so lowers pH.
What is the cause of fructosuria?
Absence of fructokinase.
What is the cause of fructose intolerance?
Absence of aldolase. This means fructose 1-P accumulates in the liver causing liver damage.
How can fructose intolerance be treated?
Remove fructose from the diet.