Enzymes II

Question 1

What is Vmax?

Answer 1

Maximal velocity

All of active sites are filled

Question 2

What is Km?

Answer 2

Michaelis constant

Substrate concentration where half the number of active sites are filled

Question 3

What is perfect enzyme?

Answer 3

Is an enzyme where chemistry that it carries out in its active site is now so efficient that limiting step is finding the substrate. As soon it finds a substrate + binds the chemistry is very fast

Question 4

Perfect enzymes are…..

Answer 4

Diffusion controlled

Is limited by diffusion step

Question 5

What is K3/Kcat?

Answer 5

Is catalytic rate obtained from Vmax

Is turnover number

Question 6

What is equation for Kcat?

Answer 6

Kcat= Vmax/[enz] total

Question 7

Give an example of a perfect enzyme

What reaction does it catalyse?

Answer 7

Triosephosphate isomerase (TIM) 
It catalyse the conversion of dihydroxyacetone phosphate into glyceraldehyde 3-phosphate

Question 8

What is protease?

Answer 8

Is an enzyme that hydrolyses peptide bonds
Don’t cleave very peptide bond as they have selectivity
Are therapeutic targets

Question 9

What do serine proteases contain?

Answer 9

It has very reactive serine which contain a very reactive serine which contains a very reactive OH group

Question 10

Give example of serine protease

Answer 10

Chymotrypsin and trypsin

Question 11

What is catalytic triad?

Answer 11

Serine 195, Asp 103 + His 57

Question 12

What is importance of catalytic triad?

Answer 12

It is important because it makes serine OH more electronegative

Question 13

Where is catalytic triad found in?

Answer 13

All serine proteases

Question 14

Describe the specificity of chymotrypsin?

Answer 14

It has specificity for aromatic groups Phe, Trp, Tyr so bonds will be cleaved by this enzyme because hydrophobic pocket

Question 15

Describe the specificity of trypsin for specific side chain?

Answer 15

Only cleaves positively charged residue upstream, Arg, Lys. It reaches to -vely charged pocket

Question 16

Describe the specificity of elastase for specific side chain?

Answer 16

Only cleaves peptide bonds if N terminal of cleaved bond is small side chain e.g. glycine => narrow pocket therefore only small side chains can fit

Question 17

Enzymes in catalysed reaction

Answer 17

Enzyme doesn’t use water in the first step it uses serine to attack peptide bond
OH group can attack ketone group of peptide bond
Enzyme is splitting the bond, releasing part of polypeptide chain + links to other part of chain making an ester intermediate
Ester are easier to hydrolyse than amides
Ester intermediate (called acyl-enzyme) can react with water, releasing other part of polypeptide chain
Enzyme is regenerated, unchanged

Question 18

What was discovered from structure of mitochondrion?

Answer 18

Inside inner membrane, it was loaded with lollipop (stick with round end)
Lollipop is made up of 2 very important components=> pore which is stuck into inner membrane which allows proteins to go through it, head of lollipop is rotary system which enables ATP to be made from ADP + Pi

Question 19

Rotary ATP synthase has 3 active sites activated by rotating spindle

Answer 19

Proteins are fed through basal plate
Around rotor, there is hexagonal proteins => has a hole in middle in which rotor sits called stata
There are 3 active sites which bind ADP + Pi
As protons feed through, it turns around and ATP made
Energy of protons are used to make motor turn in order to make ATP

Question 20

What is topoisomerase II?

Answer 20

A molecular clamp
Unlinks tangled chromosomes
Unlinks loops of chromosomes during mitosis to physically separate them

Question 21

Describe the structure of topoisomerase II?

Answer 21

Dimeric structure =It is made up of different subunits + looks like a clamp

Question 22

What drug is topoisomerase a target for?

Answer 22

Anti cancer drugs