Enzymes Flashcards
Explain the effects of enzymes on chemical reactions.
They are catalysts that increase the rate of reaction.
They don’t alter the equilibrium of a chemical reaction.
They accelerate attainment of equilibrium.
Decreases the activation energy for a reaction - optimises the conditions for the reaction to be ale to succeed with he available energy.
Explain the role of the active site.
The active site is in clefts or crevices rather than on the surface. This prevents water from inhibiting the reactions as clefts or crevices create conditions where water can be excluded.
Active site has a complementary shape to the substrate.
Substrate is bound to enzyme by multiple weak binds - allowing it to bind quickly and the products to unbind quickly.
Describe how reaction rates vary as a function of substrate concentration
As substrate conc increases, rate of reaction also increases.
Direct correlation.
Describe how the rate varies with enzyme concentration
Increasing enzyme conc increases rate of reaction as long as there is enough substrate to bind to it.
What is the rate of enzyme activity and how is it calculated?
Vmax and V0 are rates.
1 unit = the amount of enzyme that produces 1 MICRO MOL OF PRODUCT PER MINUTR under standard conditions.
What is Km and what does it tell you?
The substrate conc at which you get 1/2 the maximum rate
Tells you abut the affinity of an enzyme for a substrate. A low Km means the enzyme requires less substrate to reach maximum activity.
What are Vmax and V0; and how do you increase Vmax?
Vmax = maximum rate of reaction.
V0 = initial rate of reaction.
Increase Vmax by increasing concentration of enzyme.
What are competitive inhibitors and how do they effect Km and Vmax.
Substances that bind to the active site, thereby reducing the proportion of enzyme molecules bound to the substrate.
No effect on Vmax as adding enough substrate will always overcome the effect of the inhibitor.
Km increases as it takes more substrate to get 1/2 maximum activity.
What are non-competitive inhibitors and how do they effect Km and Vmax?
Substances that bind to the free enzyme away from the active site (allosteric binding site). This decreases the conc of the functional enzyme. This process is reversible.
Vmax decreases as it decreases the conc of free enzyme.
No effect on Km as 1/2 max activity occurs rom same amount of substrate.
What are irreversible inhibitors and how would these effect Vmax and Km?
Substances that form a covalent bond with the enzyme.
Only tiny concs of these inhibitors are needed to wash out the ability of the enzyme.
Vmax decreases because less enzyme is available.
Km remains the same as enzyme affinity is the same.
How does each type of inhibitor alter a V against [S] plot and a Lineweaver-Burk plot?
Check notability revision sheet for plots.
What are the four major regulatory mechanisms that control enzyme activity?
- Isoenzymes (different enzyme forms that have the same function)
- Allosteric regulation (regulation at a site away from the active site
- Phosphorylation - reversible covalent modification
- Proteolytic activation - enzymes get cleaved and activated
What are isoenzymes and give an example
Enzymes that catalyse the same reaction, but have different amino acid sequence.
Hexokinase and glucokinase function to phosphorylise glucose.
Hexokinase commits glucose to the cell, preventing it from crossing the membrane. In the liver, glucokinase is the enzyme. When glucose levels are low, it breaks down glycogen and releases glucose to the body.
What is allosteric regulation and give an example
Enzymes that are regulated at a site away from the active site.
Phosphofructokinase-1 is a rate limiting enzyme in glycolysis.
What is reversible covalent modification and give an example.
Phosphorylation is an example of this. This is adding a phosphate group. There is 1 group of enzymes adding phosphate group and one group of enzymes taking it off, so it is reversible.
