Metabolism Flashcards
Equation of the enzyme catalysis
E + S <== ==> ES <== ==> EP <== ==> E + P
Simplified in :
E + S <== ==> ES ==> E + P
What happen if the concentration of enzyme is constant ?
A high concentration of substrate will hit the maximum speed of the reaction = V(max)
What is the steady state assumption ?
The moment where the concentration of ES is constant : the formation of ES = the dissociation/loss of ES
The product rarely go back to the reactant because the reaction is thermodynamically stable.
What is the pseudo first order ?
If ES can be neglected compared to the total product :
0 order : A ==> A
1 order : A ==> B (there is only one reactant)
2 order : A + B ==> C (there are 2 reactants)
What is K(m) ?
The concentration of the substrate when the reaction is at half the maximum speed. Could equal to affinity :
Bad substrate : high K(m)
Good substrate : low K(m)
What is K(cat) ?
The maximum speed of a reaction divided by the total enzyme available or the enzyme’s turnover number (how many enzyme and substrate can turn into one product at maximum speed.
What are the characteristics of Hexokinase?
It is present in high abundance in the majority of our tissue and used during hypoglycaemia.
It has a low K(m) (==> high affinity : saturation require low concentration of substrate)
It has a low V(max) (==> slow when there is an abundance of glucose)
What are the characteristics of glucokinase ?
It is highly present in the liver and is used during hyperglycaemia.
It has high K(m) around the physiological concentration of glucose : low affinity (==> need large amount of glucose to function)
It has high V(max) : faster when glucose is in abundance.
What do glucokinase and Hexokinase do ?
They are responsible for the phosphorylation of glucose into glucose 6-phosphate. Thus preventing it to go out the cell. It’s the first reaction in glycolysis.
What are isozymes ?
= isoenzymes.
There have way to regulate the processes (of a certain molecule) in the different cells. They are difference in the proprieties of isozymes of the same process it allow our body to fine tune different pathway to meet the need of different cell.
Ex : during exercise the isozymes transporting glucose into the muscle cells need to be activate but not the one in the stomach.
Why can’t glucose enter the cell alone ?
Because glucose is a polar molecule thus even if there is a gradient of concentration on either side because the membrane isn’t polar hydrophobic, glucose molecule cannot cross.
What are the main isozymes of glucose transporters ?
There are 10 but those are the most important :
Glut-1, Glut-2, Glut-3, Glut-4 and Glut-5.
What are the characteristics of Glut-1 ?
It is responsible for the basal rate of glucose uptake (normal continuous rate). Present in all the cells of the body but mainly in the membrane of red blood cells.
They have a low K(m) (+- 1mmol) : very effective binding
What are the characteristics of Glut-2 ?
They allow the beta cells of the pancreas to detect high level of glucose in the blood thus secrete insulin to reduce it. They allow the liver to stock the excess of glucose.
Present in the pancreas, liver, basal lateral membrane of kidney and intestine.
They have a high K(m) (+- 17mmol) : only register hyperglycaemia.
What are the characteristics of Glut-3 ?
They are responsible for the basal rate of glucose uptake : the normal continuous intake of glucose.
Present in the membrane of neurons.
They have a low K(m) (+- 1mmol) : very effective binding.
