enzymes

Question 1

what is the role of enzymes?

Answer 1

they act as biological catalysts by affecting the structure and function in an organism
they affect metabolism at both cellular and whole organism level.

Question 2

what are intracellular enzymes?

Answer 2

enzymes that work within cells

Question 3

what are extracellular enzymes?

Answer 3

enzymes that work outside of cells

Question 4

give an example of an intracellular enzyme and its function

Answer 4

catalase

works inside cells to catalyse the breakdown of hydrogen peroxide to oxygen and water

Question 5

give 2 examples of extracellular enzymes and their fucntions

Answer 5

amylase
found in the saliva and secreted into the mouth by cells in the salivary glands . they catalyse the hydrolysis of starch to maltose

trypsin
catalyses the hydrolysis of peptide bonds produced by the pancreas and secreted into the small intestine

Question 6

what is the structure of enzymes?

Answer 6

globular proteins

specific shape - active site where substrate binds

specific shape determined by tertiary structure

Question 7

describe the lock and key model

Answer 7

the enzymes active site is exactly complementary to the substrate so they fit like a lock and key

when the substrate is bound to the active site an enzyme-substrate complex forms

the substrate is held in a way that the right atom groups are close enough together to react and r groups within the enzyme interact with the substrate and put strain on bonds within the substrate

the enzyme-product complex forms and products are released

enzyme is unchanged and can take part in subsiquent reactions

Question 8

describe the induced fit model

Answer 8

recent evidence suggests that the enzyme actually changes shape slightly as the substrate enters

interactions between the enzyme and the substrate changes enzymes tertiary structure and strengthen the binding

this puts strain on the substrate molecule which can weaken a particular bond or bonds in a substrate so lowers activation energy for the reaction

Question 9

what are the 4 factors that affect enzyme activity?

Answer 9

pH
temperature
enzyme concentration
substrate concentration

Question 10

what is the effect of pH on enzyme activity?

Answer 10

all enzymes have optimum pH
at pH above or below this the H+ concentration and OH- concentration can mess up the ionic and hydrogen bonds within the enzyme which changes the enzymes tertiary structure and its active site, denaturing it

Question 11

what is the effect of temperature on enzyme activity?

Answer 11

as temperatue increases, the rate initially increases as particles gain kinetic energy and therefore successful collisions become more frequent
as temperature increase further, the bonds within the enzyme begin to vibrate and can break.
the tertiary structure and active site change shape and the enzyme is denatured

Question 12

what is the effect of enzyme concentration on enzyme activity?

Answer 12

increasing enzyme concentration increases the likelyhood that a substrate will collide so enzyme-substrate complexes form more frequently
but if the substrate concentration is limited there is a point where all substrate is in enzyme-substrate complexes so has no further effect

Question 13

what si the effect of substrate concentration on enzyme activity?

Answer 13

increasing substrate concentration increases rate of reaction and collisions become more frequent

this is true untill all active sites are being used so has a Vmax where increasing substrate concentration has no further effect

Question 14

how do cofactors work?

Answer 14

they transfer atoms or groups from one reaction to another in a multistep pathway or may form part of the active site of the enzyme

some enzymes need them to carry out their function

Question 15

what are conenzymes?

Answer 15

organic cofactors

Question 16

what are prosthetic groups?

Answer 16

prosthetic groups are tightly bound to form a permanent feature of the protein

Question 17

give an example of a cofactor

Answer 17

Cl- is a cofactor of amylase

Question 18

give an example of a prosthetic group

Answer 18

Zn2+ is a prosthetic group for carbonic anhydrase

Question 19

what is a source of coenzymes?

Answer 19

vitamins

Question 20

what are competitive inhibitors?

Answer 20

inhibitors of similar shape to the substrate that can bind to the active site of the enzyme and block it from the substrate
cannot carry out function so the enzyme is inhibited

Question 21

what is the effect of competitive inhibitor on the rate?

Answer 21

decreases the rate as substrates and inhibitor compete for the active site, however if substrate concentration is increased it outcompetes the inhibitor therefore Vmax does not change

Question 22

what is a non competitive inhibitor?

Answer 22

an inhibitor that binds to the enzyme away from the active site at the allosteric site. it changes the tertiary structure of the enzyme when it binds so changes the active site so it is no longer complementary to the substrate

increasing the substrate concentration will not overcome non-competitive inhibition

Question 23

what bonds are ususally involved with irreversible and reversible inhibitors?

Answer 23

weak hydrogen and ionic bonds in reversible inhibitors

strong covalent bonds in irreversible inhibitors

Question 24

give 2 examples of medicinal drugs that are competitive inhibitors

Answer 24

antiviral drugs such as reverse transcriptase inhibitor which inhibits the enzyme reverse transcriptase which catalyses the replication of viral DNA

anitbiotics such as penicillin inhibits transpeptidase which catalyses the formation of proteins of bacterial cell walls- weakens cell wall so it bursts

Question 25

Give an example of a metabollic poison and what it does

Answer 25

cyanide

irreversible inhibitor of cytochrome c oxidase which is an enzyme that catalyses respiration reactions

Question 26

what isproduct inhibition and why is it important?

Answer 26

a metabolic pathway is series of connected metabolic reactions . many enzymes in these pathways are inhibited by the product of the reaction they catalyse

it is important in controlling the amount of end product that gets made

always reversible so when level of product drops the level of inhibition starts to fall and enzyme fucntions again so more product is made

Question 27

what are inactive precursor enzymes?

Answer 27

enzymes that are produced in the inactive form
normally if they would cause damage to the cell they’re produced in or to tissues they are released from

they need to undergo a change in tertiary structure
to change the shape of their active site to be activated.

this can be done by a cofactor, other enzymes or change in pH or temperature

Question 28

why does pH need to be kept constant?

Answer 28

(so) charges in active site do not change ; ora
(so) hydrogen / ionic , bonds unaffected ; ora

(so) tertiary structure / 3D shape / active site ,
unaltered ; ora

(so) enzyme / tertiary structure , does not denature ;
ora

(so) substrate , fits / is complementary shape to , active
site ; ora

so the results are valid / as the rate (of reaction) will
vary if pH varies / so that only one
(independent) variable is changed

Question 29

What is Cl- to amylase?

Answer 29

It is a cofactor

Question 30

what is Zn2+ to carbonic anhydrase?

Answer 30

prosthetic group