Enzymes

Question 1

Enzymes properties and functions

Answer 1

Globular
Biological catalyst
Can be regulated
Increase rates of spontaneous reactions
Lower activation energy
Accelerate movement towards reaction equilibrium

Question 2

Ribozymes

Answer 2

catalytic RNA molecules with no protein component

Question 3

Cofactor

Answer 3

Non-protein component needed for activity

Question 4

Coenzyme

Answer 4

organic molecule produced by vitamins and is involved in the reaction

Question 5

Prosthetic Group

Answer 5

Cofactor covalently bound to enzyme or very tightly associated

Question 6

Apoenzyme

Answer 6

Component of enzyme that contains cofactor

Question 7

Holoenzyme

Answer 7

Whole enzyme

Question 8

Active site

Answer 8

Part of the enzyme in which the substrate binds and is acted upon

Question 9

Transition state

Answer 9

moment that chemical bonds are formed and broken

Question 10

How is the Michaelis Menton constant calculated

Answer 10

from the hyperbolic reaction curve as half vmax= substrate concentration at half vmax

Question 11

[S]

Answer 11

Substrate concentration

Question 12

V0

Answer 12

Initial reaction velocity

Question 13

Vmax

Answer 13

Maximum reaction velocity

Question 14

Km

Answer 14

Affinity

Question 15

Large Km

Answer 15

less stable E-S complex

Question 16

Smaller Km

Answer 16

More stable E-S complex

Question 17

Glucokinase

Answer 17

High Km, High Vmax

Question 18

Hexokinase

Answer 18

Low Km, Low Vmax

Question 19

Double displacement

Answer 19

Amino group being transferred from an amino acid

Question 20

Allosteric

Answer 20

enzyme that contains many active sites and subunits

Reversible attachment

Question 21

uncompetitive inhibitor

Answer 21

Stops enzyme carrying out reaction once substrate has bound to the enzyme
enhances the binding of substrate (so reducing Km), but the resultant enzyme-inhibitor-substrate complex only undergoes reaction to form the product slowly, so that Vmax is also reduced

Question 22

Non-competitive inhibitor

Answer 22

Binds before and changes shape of enzyme preventing the reaction taking place
Vmax is reduced
Km remains unchnaged

Question 23

2 models of allosteric enzyme kinetics

Answer 23

Concerted Model

Sequential Model

Question 24

Concerted Model

Answer 24

Each subunit consist in 2 different confirmation
Allosteric activators stabilise the open conformation
Allosteric inhibitors will stabilise the closed confirmation

Question 25

Sequential Model

Answer 25

No flipping between conformational states

Binding of first substrate causes a conformational change that allows the second substrate to bind more easily

Question 26

Covalent modification

Answer 26

Enzymes can be regulated by phosphorylation

Question 27

Enzymes that catalyse the phosphorylation of enzymes

Answer 27

Protein kinases

Protein phosphatases

Question 28

Multiple phosphorylation sites

Answer 28

allow very fine control of enzyme function, enzyme never in off state

Question 29

Proteolytic Cleavage

Answer 29

Enzymes can exist as inactive precursor proteins that are cleaved to give active enzymes such as insulin

Question 30

Irreversible inhibitors

Answer 30

Cyanide binds to Fe3+ in cytochrom C oxidase and starves the cells of ATP and disrupts terminal respiration

Question 31

Competitive inhibitors

Answer 31

Increase in Km, Vmax unchanged

Question 32

AZT

Answer 32

Nucleotide analogue
Competitive inhibition of reverse transcriptase
Mimics the ordinary DNA pre-cursor

Question 33

Feedback Inhibition

Answer 33

A build up of end product can slow down the whole pathway

Question 34

Isoenzyme

Answer 34

each of two or more enzymes with identical function but different structure

Question 35

Competetive Inhibitor

Answer 35

Increase Km by interfering with the binding of the substrate, but they do not affect Vmax because the inhibitor does not change the catalysis in ES because it cannot bind to ES

Question 36

Haem Group

Answer 36

The Fe2+ ion lies in the middle of a complex nitrogen and carbon containing (porphyrin) ring structure