enzyme kinetics

Question 1

concept of free energy

Answer 1

energy molecules have to do useful work at a constant temperature

Question 2

how changes in free energy can be used to predict the outcome of a reaction

Answer 2

disorder always increases in a spontaneous reaction  
free energy increases 
KJ/mol
G = start - end
feasible of changeG < 0 dependant on Ea

Question 3

ATP is used as a carrier of free energy to drive energetically unfavourable reactions

Answer 3

to create order energy from env needs to be put in
hydrolysise ATP - ADP
phosphoanhydride bond is high energy, large -ve changeG - coupled with the unfavourable reaction
changeG still < 0

Question 4

explain how enzymes act as catalysts of reactions

Answer 4

Lower the Ea by weakening bonds in substrate so reactions can happen faster
transition state - atoms of molecule are rearranged both geometrically and electronically so that the reaction can proceed
bend substrates so the bonds to be broken are stressed and the substrate molecule resembles the transition state
bind molecule in AS
residues in enzymes participate in making/breaking of bonds by altering arrangement of electrons within substrate - oxidation/reduction
gain e- also gain H+ because in aq env

Question 5

Lock and key model

Answer 5

shape AS matches exactly to substrate

explains the specificity

Question 6

Induced fit model

Answer 6

substrate induce change in conformation of enzyme
result in formation of AS
degree of flexibility
crystallographic analysis proves this

Question 7

lysozyme

Answer 7

tears and nasal secretions - defence against bacteria
catalyses hydrolysis of sugar molecules in cell walls
hydrolyses alternating polysaccharide copolymers of N-acetyl glucosamine and N-acetyl muramic acid
cleaves at B(1-4) glyosidic linkage C1 from NAM to C4 of NAG

Question 8

How lysozyme works

Answer 8

Glu-35 protonates the oxygen in the glycosidic bond - breaking it
water enters and is deprotonated by Glu-35
Asp-52 stabalise +ve charge in transition state
hydroxide ion attacks remaining sugar molecule adding OH

Question 9

optimum pH of lysozyme

Answer 9

5
Asp-52 ionised
Glu-35 unionised

Question 10

Temperature and enzymes

Answer 10

rate increases with temp

temp optimum - denature

Question 11

Coenzyme

Answer 11

added to allow enz function

make shape complementary for substrate

Question 12

explain the role of the coenzyme NAD in reactions catalysed by dehydrogenases

Answer 12

dehydration reactions
dehydrogenase catalyse
NAD+ + CHRR’OH – NADH H+ + CRR’O
NAD+ catalyse by accepting hydrogen atom and 2 electrons

Question 13

lactate dehydrogenase

Answer 13

anaerobic respiration
pyruvate - lactate
generates free NAD+
lactate diffuses from muscle to blood stream - liver
NAD+ used by lactate dehydrogenase - pyruvate