MCB Lecture 15, Allosteric regulation and Tissue specificity Flashcards
Which steps of glycolysis have Allosteric regulation?
- Glucose -> Glucose-6-phosphate
- Fructose-6-phosphate -> Fructose-1,6-bisphosphate
- Phosphoenolpyruvate-> pyruvate
Give a one sentence definition of Allosteric regulation
Allostery is the change in shape and activity of an enzyme when a regulatory molecule binds so e where else on the enzyme (not the active site)
Which is the most important control point of cellular respiration?
Fructose-6-phosphate -> Fructose-1,6-bisphosphate
What shape is the graph depicting the dependence of V0 on [S]?
Sigmoidal, it’s a combination of two Michaelis-Menten graphs
What are the T and R states?
T- inhibited state, low enzyme activity (tense state; can’t get any work done)
R- enhanced state, higher enzyme activity (relaxed state, can get work done)
What causes the enzyme to enter the R state?
What causes the enzyme to enter the T state?
Substrate binding stabilises the R state
Activators –> R state
Inhibitors –> T state
How does the V0 vs. [S] graph curve change for the T and R states?
The curves have a more M-M shape
Describe Allosteric regulation of hexokinase
Hexokinase is only allosterically changed in the muscles.
Glucose-6-phosphates acts as an inhibitor to Hexokinase
Why are there two forms of enzymes for the steps of glycolysis?
The liver and the muscles have different versions of these enzymes
What is the other name for hexokinase?
Glucokinase
Describe Allosteric regulation of Phosphofructokinase-1.
There are two different versions; one for liver, one for muscle tissue.
However, the same molecules act as activators and inhibitors
Activation: ADP, Fructose-2,6-phosphate, AMP
Inhibition: ATP, citrate, high [H]
What is the difference between Allosteric regulation of phosphofructokinase in the liver and muscles?
None, only different enzyme
Describe the Allosteric regulation of pyruvate kinase
Different enzyme in muscles and liver, however, same inhibition and activation
Activation: F-1,6-bisphosphate
Inhibition: ATP, alanine
Describe the differences in Allosteric regulation of Pyruvate Kinase in the liver and in the muscles
Only different enzyme
Describe the differences in Allosteric regulation of hexokinase in the liver and in muscle tissue
Glucose-6-phosphate acts as an inhibitor only in the muscles. No Allostery in the liver.
Different forms of the enzyme
Compare and contrast the fuel sources of the brain, muscle, liver and adipose
Brain : only glucose. Ketone bodies during starvation
Muscles : glucose, fatty acids and ketone bodies
Adipose : glucose required to synthesis triacylglycerol
Liver : glucose, amino acids, fatty acids, ketone bodies but prefers alpha keto acids (from amino acid breakdown)
Compare and contrast fuel storage in the brain, muscles, adipose and liver
Brain : none
Muscles : 75% of body’s glycogen stored here
Adipose : triacylglycerol
Liver: 25% of body’s glycogen
Compare and contract the resting state conditions in the brain, muscles, adipose and liver
Brain : uses 60% of daily glycogen
Muscle : fatty acids are main fuel source
Adipose: mainly active during starvation: breakdown of triacylglycerol
Liver: gluconeogenesis during starvation or fasting, Fatty acid oxidation for energy, and Ketone body oxidation for the brain and heart
Under starving conditions, the brain can adapt to which fuel source?
Ketone bodies
Which fuel source does the heart muscle use?
Acetoacetate in preference to glucose
