Enzyme Activity Flashcards
What is the transition state?
The high energy intermediate that lies between the ground state (S) and the ground state (P)
What is activation energy?
The minimum amount of energy the substrate must have for a reaction to occur.
What things can increase the rate of reaction?
- Temperature- increased no of molecules with activation energy
- Concentration- Increased chance of molecular collisions.
- Enzymes- Biological catalysts that increase the rate of reaction by lowering the activation energy. They facilitate the formation of the transition state.
What are some important features of enzymes?
Highly specific Unchanged after the reaction Do not affect the reaction equilibrium Increase the rate of reaction Proteins May require associated cofactors
What is an active site?
The active site of an enzyme is the place where the substrate bonds and the chemical reaction occurs.
- The active site only occupies a small part of the enzyme. Most of the enzyme acts as a scaffold to create the active site.
- The active site is formed by amino acids from different parts of the primary sequence.
- They are clefts or crevices and they exclude water.
How do substrates bind to active sites?
- Active sites have a complementary shape to the substrate. ‘Induced fit’ hypothesis is what scientists believe now. This means that the active site only forms a complimentary shape after the binding of the substrate.
- Substrates are bound to enzymes by multiple weak bonds.
What is V0?
The initial rate of reaction
What is the Michaelis-Menten model and why is it significant?
This model proposes that a specific complex between the enzyme and the substrate is a necessary intermediate in catalysis.
V0=Vmax[S] / (Km + [S] )
It predicts that a plot of V0 versus [S] will be a rectangular hyperbola.
Not all enzymes obey this model
What is Vmax? Why is it significant?
Maximal rate when all the enzymes active sites are saturated with substrate. It is measured in amounts per unit time. It is often expressed as a standardised rate eg g/L.
THE RATE OF AN ENZYME CATALYSED REACTION IS PROPORTIONAL TO THE CONCENTRATION OF AN ENZYME. So, as the amount if enzyme doubles, so does the rate.
What is Km? Why is it significant?
The SUBSTRATE concentration that gives half the maximum velocity. (Not just half Vmax as different units).
It gives a measure of the affinity of an enzyme for its substrate. If you have a low Km, they have a high affinity for substrate and high Km means low affinity for substrate.
What is an enzyme inhibitor?
An enzyme inhibitor is a molecule that slows down or prevents an enzyme reaction, Eg drugs.
They can be IRREVERSIBLE (they bind very tightly and generally form covalent bonds. Eg nerve gases such as sarin.) or REVERSIBLE (form non covalent bonds and they can freely dissociate).
What are the two types of reversible enzyme inhibition and how do they work?
Competitive and Non-Competitive.
Competitive inhibitors bind to the active site therefore reducing the proportion of enzyme molecules that are bound to the substrate. It affect Km but not Vmax because adding enough substrate will overcome the inhibitor so not affect Vmax.
Non competitive inhibitors bind at another site on the enzyme and so affect Vmax but not Km because it decreases the number of enzymes that are able to catalyse reactions.
