FHMP 011 Enzymes and catalysis Flashcards
(26 cards)
What is an enzyme?
biological catalyst
What is Vmax of an enzyme?
The maximum rate of reaction or the rate of reaction under ideal circumstances
What is Kcat?
- the turnover number
- Vmax/[E]
- the number of substrate molecules converted into product by an enzyme molecule in a second when the enzyme is fully saturated with substrate
What is Km?
Substrate concentration at 1/2 Vmax
what 3 factors make enzymes good catalysts?
- activity at low temps
- specificity towards substrate
- specificity of reaction
what is a cofactor?
something that an enzyme requires to increase their activity/efficiency
give 3 types of cofactors
- metal = e.g. magnesium
- prosthetic group = bound to enzyme e.g. FAD
- coenzymes = e.g. ATP
what is the EC number?
- way of classifying enzymes based on the type of reaction it catalyses
- e.g. 1,2,3,4,5,6
what does EC number 1 mean?
1 = oxidoreductases = redox reactions = e.g. lactate dehydrogenase
what does EC number 2 mean?
2 = transferase = group transfer reactions e.g. DNA methyltransferase
what does EC number 3 mean?
3 = hydrolyses = hydrolysis reactions e.g. chymotrypsin
what does EC number 4 mean?
4 = lyases = addition/removal of groups to form double bonds e.g. lyases
what does EC number 5 mean?
5 = isomerases = isomerisation e.g. triose phophate isomerase
what does EC number 6 mean?
6 = ligases = ligation of 2 substrates at the expense of ATP hydrolysis e.g. aminoacyl-tRNA synthase
what is the active site?
The active site is the region on the enzyme where the substrate binds.
what factors affect enzyme activity?
temperature, pH, substrate and enzyme concentration
describe how pH effects enzyme activity
- every enzyme will have its specific optimum pH range
- the pH if outside the optimum range, the H+ or OH- ions will interact with the enzyme’s structure, thus effecting its binding ability and decreasing its activity outside the range ( enzyme denatures)
describe how temperature effects enzyme activity
- as temperature increases, they gain more energy and collide more often and increasing the activity until it reaches its optimum temperature
- when the enzyme reaches past its optimum temperature, the bonds of the enzyme will start to break down and the structure which effects its binding ability and thus decreases its activity (enzyme denatures)
what does thermolabile mean?
- a substance that is easily destroyed or denatured by heat
- mutations in an enzyme can make it more sensitive to temperature change
How does enzyme concentration affect enzyme activity?
- increasing the enzyme concentration increases the rate of reaction as it increases the availability of the active sites
- the substrate conc is the limiting factor
How does substrate concentration affect enzyme activity?
- increasing the substrate conc increases the rate of reactions as more substrate can bind to the enzymes
- the enzyme conc is the limiting factor
What is an isozyme?
Enzymes that catalyze the same reaction but have different chemical composition and different physical properties
give an example of isozymes
- lipoprotein lipase = adipose and muscle have different isozymes of this enzyme
- adipose = rate of fatty acid release is dependant on lipoprotein levels, has a high Km, after a meal when there is high lipoprotein levels, adipose LPL is highly active
- muscle = rate of fatty acid release is dependant on LPL conc as it has a low Km, so it is saturated at high lipoprotein levels, after meal, activity does not increase as already saturated
- or glucokinase/hexokinase
What is cooperativity?
a form of allosteric regulation that can amplify or decrease enzyme activity
