W5 Enzymes II

Question 1

Enzyme properties

Answer 1

Increases ROR by up to 10 billion fold

Show specificity

Unchanged

Do not alter reaction eq

Facilitate reaction by decreasing the free energy of activation of the reaction

Question 2

Rate

Answer 2

Rate = K3/Km 
K3 = Vmax/[total enzyme]

Question 3

Tripesphosphate isomerase

Answer 3

Perfect enzyme
Can’t be improved by mutation

Limiting factors due to diffusion controlled parts

Question 4

Chymotrypsin v.reactive serine

Answer 4

Made in pancreas + secreted into intestine along w/trypsin (has v.reactive serine group)
Protein target bound to cleft at ser. 195
Attacks protein first
Forms intermediate
Easily hydrolysed by water

Question 5

Why serine 195 v.reactive

Answer 5

V. electronegative due to catalytic triad
Proton from HO moves to N
NH proton moves to -ve of O (aspartate side chain = so -ve)

Question 6

Elastase

Answer 6

Only cleaves if N terminal of AA residue is small because the active site pocket is narrow (valine residues make AS pocket v.small)

Question 7

Serine proteases conserved 3D structure

Answer 7

Serine proteases conserved 3D structure w/a charge-relay system

Primary structures different all have catalytic tryad conserved in many different enzymes by evolution

Question 8

ATP synthesis in MC - proton driven

Answer 8

500 MC per cell

Cytochromes (A, B, C + oxidase) combine w/O to make H2O (w/H+)

Inner membrane impermeable to protons

Energy stored due to difference in charge

Question 9

Rotary ATP synthase

Answer 9

Hole where rotor sits = stator
Core allows H+ to come through
Head is rotary system which allows ATP to be made from ADP + Pi (everytime head turns)
AS binds ADP + Pi
H+ rotate enzyme to make ATP by using a +ve current

Question 10

Evidence for rotary ATP synthase

Answer 10

Protein on microscopic slide
Add ATP to rotate in opp direction
As enzymes can work in both direction
Actin filament goes around in steps of 120 degrees

Question 11

Topoisomerase II

Answer 11

A molecular clamp-unlinks tangled CS
Takes out turns about every 10 bases (one strand around each other) risk breaking CS if loops interlocked
Dimeric structure

G segent = gate DNA inserted
Uses ATP to clamp segment from other CS
Breaks first DNA captured
Passes transported DNA into a hole on the other side
Reseals the break + releases the transported DNA