L11 & L12 - enzymes & inhibitors

Question 1

what are ribozymes

Answer 1

RNA based enzymes

Question 2

characteristics of enzymes?

Answer 2

increase ROR
selective
specific (due to active site)
stabilise transition state

Question 3

name the 6 classes of enzymes

Answer 3

1. oxidoreductases
2. transferases
3. hydrolases
4. lyases
5. isomerases
6. ligases

Question 4

function of oxidoreductases

Answer 4

add O2 or remove 2H

Question 5

function of transferases

Answer 5

transfer functional groups from one molecule to another

Question 6

function of hydrolases

Answer 6

hydrolysis reactions

Question 7

function of lyases

Answer 7

add groups to C=C bonds

catalyse cleavage of C-C / C-O / C-N

Question 8

function of isomerases

Answer 8

isomerase reactions 
(transfer of functional groups within molecule)

Question 9

function of ligases

Answer 9

form C-C / C-N bonds using ATP

Question 10

explain lock and key theory

Answer 10

substrate fits exactly into active site

Question 11

explain induced fit theory

Answer 11

enzyme can undergo shape changes when substrate binds due to weak interactions with the substrate

this bring functional groups into proper position to catalyse reaction

Question 12

what type of enzyme is chymotrypsin

Answer 12

serine protease

Question 13

what component of chymotrypsin makes it specific

Answer 13

hydrophobic pocket

Question 14

why is chymotrypsin a ‘serine protease’

Answer 14

because it contains a serine in the catalytic triad (responsible for its catalytic activity)

Question 15

regarding michelis menten equation, what does it mean when [s]»Km

Answer 15

[E] is rate limiting factor

Question 16

regarding michelis Menten equation, what does it mean when [s]

Answer 16

[S] is rate limiting factor

Question 17

what is the Lineweaver Burk plot

Answer 17

reciprocal of the michelis menten equation , which gives the format Y = M x + c

Question 18

what shape is MM plot

Answer 18

hyperbola
x = [S]
y = velocity (V)

Question 19

what shape is lineweaver burk plot

Answer 19

linear
X= 1/[s]
Y = 1/V

Question 20

when may a lineweaver burk plot be used

Answer 20

when [s] cant be measured experimentally

Question 21

what is the X intercept on a lineweaver burk plot

Answer 21

Km

Question 22

disadvantage of lineweaver burk plot

Answer 22

relies on extrapolation

can be influenced by poor data distribution

Question 23

advantage of lineweaver burk plot

Answer 23

allows clearer identification of Vmax and Km

clear way of identifying different types of inhibition

Question 24

why can Km be used as indication of affinity of enzyme for substrate

Answer 24

K2 is much slower than K-1 ,
so
Km ~ K-1 / K1

Question 25

is K1 , K-1 or K2 the rate determining step

Answer 25

K2

Question 26

what does a higher Km indicate?

Answer 26

lower affinity of E for S | ES breaks down quicker than its formed

Question 27

what does a lower Km indicate

Answer 27

higher affinity of E for S

Question 28

how is enzyme action regulated?

Answer 28

1. environmental (pH , temp ) 2. inhibitors 3. allosteric binding sites

Question 29

effect of temp on enzyme action?

Answer 29

increases until certain point where enzymes denature

Question 30

what is a reversible inhibitor

Answer 30

binds to enzyme but can dissociate again and enzyme activity will restore to normal

Question 31

what is a reversible inhibitor

Answer 31

inhibitor binds and inactivates enzyme permanently

Question 32

what is a competitive inhibitor

Answer 32

inhibitor that competes with S for active site

Question 33

what is a non competitive inhibitor

Answer 33

an inhibitor that binds to the allosteric site of an enzyme altering its tertiary structure and distorting the active site

Question 34

what is an uncompetitive inhibitor

Answer 34

an inhibitor that only binds to ES complex | prevents production of products

Question 35

what effect does a competitive inhibitor have on Vmax and Km

Answer 35

doesn't affect Vmax | increases Km

Question 36

how can the inhibition effects of a competitive inhibitor be overcome?

Answer 36

increasing [S]

Question 37

what effect does a non-competitive inhibitor have on Vmax and Km

Answer 37

reduces Vmax | doesn't affect Km

Question 38

how does a competitive inhibitor affect lineweaver burk plot?

Answer 38

the line will be steeper and to the left same Y intercept different X intercept

Question 39

how does a non competitive inhibitor affect lineweaver burk plot?

Answer 39

will be steeper and to the left of both other lines same X intercept as no inhibitor different y intercept

Question 40

define allosteric inhibitors

Answer 40

bind to allosteric site which causes conformational change in all active sites - enzyme works less well

Question 41

define allosteric activators

Answer 41

bind to allosteric site and cause increase in functioning of active site

Question 42

define cooperativity

Answer 42

when the substrate works as an allosteric activator, its binding activates other active sites

Question 43

what is T state?

Answer 43

less active form of enzyme

Question 44

what is R state?

Answer 44

more active form of enzyme

Question 45

why do allosteric enzymes often catalyse regulatory steps in metabolic pathways

Answer 45

1. small change in [s] causes large change in V allowing sensitive on/off control 2. rapid and reversible (no covalent bonds, can dissociate) 3. allosteric modulators can be unrelated to the E/S - one metabolic pathway can regulate another

Question 46

what shape is produced when allostery is plotted in a V / [s] graph and explain

Answer 46

sigmoidal | it is a combination of hyperbola graphs of the T and R state (pic in word doc)

Question 47

define isoenzyme

Answer 47

enzymes with different protein structures that catalyse the same reaction

Question 48

define cofactor

Answer 48

a metal ion that is required for an enzymes activity