enzymes

Question 1

what do enzymes do?

Answer 1

they lower the activation rate
increase the rate of the reaction
they’re not consumed in the reaction
they don’t affect the equlibrium

Question 2

what are the stages of an enzyme-catalysed reaction?

Answer 2

the substrate enters the active site
the substrate is held in the active site by weak interactions
substrates are then converted into products
then the products are released and the active site is free for more substrates to bind

Question 3

what are the properties of an active site of an enzyme?

Answer 3

the position of the substrate is in the mouse favourable position
it’s complementary to the transition state
the amino acid side chains help to stabilise the electron distribution of the transition state
the transition state very quickly turns into products
the products have a low affinity for the active site
there are non-covalent interactions between the substrate and the amino acid side chains in the enzyme

Question 3

what are the properties of an active site of an enzyme?

Answer 3

the position of the substrate is in the mouse favourable position
it’s complementary to the transition state
the amino acid side chains help to stabilise the electron distribution of the transition state
the transition state very quickly turns into products
the products have a low affinity for the active site
there are non-covalent interactions between the substrate and the amino acid side chains in the enzyme

Question 4

what does the catalytic site do?

Answer 4

it donates/ withdraws electrons and stabilises/generates intermediates and forms temporary covalent bonds

Question 4

what does the catalytic site do?

Answer 4

it donates/ withdraws electrons and stabilises/generates intermediates and forms temporary covalent bonds

Question 5

what are the 2 ways that enzymes work?

Answer 5

lock and key
induced fit

Question 6

what features are important for binding of the enzyme to the substrate?

Answer 6

shape
conformation
charge

Question 7

what is ‘specific activity’?

Answer 7

its the activity of an enzyme/mg of total protein in the enzyme preparation (μ mol min-1 mg-1)

Question 8

what are the units of enzyme activity?

Answer 8

1 enzyme unit (EU)= 1 μ mol min-1
this is the no. of micromolecules of substrate converted per min under standard conditions

Question 9

what are co-factors?

Answer 9

they’re non-protein molecules found in enzymes
like metal groups- Mg2+

Question 10

what are coenzymes?

Answer 10

theyre tightly bound (but not covalently bound) organic molecules (like NAD)

Question 11

what are holo-enzymes?

Answer 11

theyre enzyme proteins with prosthetic groups ot co-enzymes
they’re catalytically active

Question 12

what are apoenzymes?

Answer 12

its the protein part of the holo-enzyme that doesn’t have the prosthetic group
its also catycally inactive

Question 13

what are oxidoreductases?

Answer 13

theyre enzymes involved in redox reactions

Question 14

what are dehydrogenases?

Answer 14

they remove/ add H

Question 15

what are oxidases?

Answer 15

they transfer 2 electrons to make H2O2 or H2O (if only half an O molecule is present)

Question 16

what are oxygenases?

Answer 16

they incorperate O2 into the product

Question 17

what are hydroxylases?

Answer 17

they incorperate half the O2 into the product in the form of -OH (in order to form H2O at the end

Question 18

what are peroxidases?

Answer 18

they use H2O2 as an oxygen donor to form H2O

Question 19

what are transferases?

Answer 19

they transfer the chemical group from one substrate to another

Question 20

what are kinases?

Answer 20

they transfer P from ATP onto the substrate

Question 21

what are hydrolases?

Answer 21

they cause hydrolysis to occur

Question 22

what are some examples of hydrolases?

Answer 22

esterases, proteases, phosphatases and thioesterases

Question 23

what are lysases?

Answer 23

they add molecules accross the C=C bond

Question 24

what are isomerases?

Answer 24

theyre intramolecular rearrangements

Question 25

what are synthetases?

Answer 25

they form bonds between the substrates and are often linked to using ATP

Question 26

what are the factors which affect enzyme activity?

Answer 26

pH
temperature
concentration of enzyme

Question 27

how does pH affect enzyme activity?

Answer 27

the binding of the substarte and the isonisation state of the amino acid side chains are affected
the binding of the substrate and catalyisis means its important for the proteins to be at the right pH so that they have the right conformation

Question 28

how does temperature affect enzyme activity?

Answer 28

chemical reactions happen quicker at higher temps as the molecules have a higher chance of colliding and the electrons gain energy easier
the optimum temperature depends on the time of incubation
high temperatures can also denature enzymes which leads to the loss of H bonding, then unfolding and then precipitation

Question 29

how does varying the amount of enzyme affect enzyme activity?

Answer 29

the active enzyme could disassociate low concentrations
there’s a linear increase in reaction rate when you increase the amount of enzyme present

Question 30

how do you calcukate the reaction rate?

Answer 30

Vmax= max rate / velocity of the reaction
1/2 Vmax =Km (this is the typical value to see how well en enzyme works)

Question 31

what does a low and a high Km mean?

Answer 31

high =the molecules haveing low affinities for the substrate
low = the molecules having high affinities for the substrate

Question 32

what is a sequnetial reaction?

Answer 32

its a reaction with an enzyme which has 2 substrates and the reactions happen in turn, one after another

Question 33

what is a ternary complex?

Answer 33

its a complex which has 3 different molecules in it

Question 34

what is dihydrofolate reductase?

Answer 34

this has loop and domain movements (it works on e.coli dihydrofolate reductase)

Question 35

what is a ping-pong reaction?

Answer 35

its when one substrate reacts and modifies the enzyme then the second substrate reacts with the modified enzyme and so on, it produces parallel lines on the graph because one reaction cant happen until the last one has

Question 36

what are allosteric enzymes?

Answer 36

there enzymes which have binding sites separate from the active site
the bonding of the substrate to the active site causes a conformational change and allows the next substrate to bind to the other binding sites

Question 37

what does it mean if an enzyme is sigmoidal?

Answer 37

it means that it has more than one active site in the complex

Question 38

what do enzyme inhibitors do?

Answer 38

they lower the enzymes abiltiy to bind to the substrate and lower its catalytic ability

Question 39

what do reversible inhibitors do?

Answer 39

these non-covalent bond to the enzyme
they work by blocking the binding or hindering the catalytic steps

Question 40

what are irreversible inhibitors?

Answer 40

theyre also called inactivators
they covalently bond to the inhibitor and then the transition state intermediate isn’t able to break down
its also called a suicide inhibitor

Question 41

what are competitive inhibitors?

Answer 41

they compete for binding at the active site
these can be overridden by increasing substrate concentration

Question 42

what happens to Vmax and Km in competitive reversible inhibition?

Answer 42

Vmax stays the same andq Km increases if there’s enough substrate added to overcome the inhibitor

Question 43

what are non-competive inhibitors?

Answer 43

they bind to the enzyme at a position separate from the active site and there isn’t any competition for binding with the substrate