3.1.4.2 Many Proteins are Enzymes

Question 1

what are enzymes alternatively referred to as?

Answer 1

biological catalysts

Question 2

how do enzymes work?

Answer 2

they speed up the rate of a reaction by lowering the activation energy by providing an alternative reaction pathway

Question 3

what are enzymes made from?

Answer 3

globular, tertiary structure proteins

Question 4

define activation energy

Answer 4

the minimum amount of energy required for a reaction to begin/take place

Question 5

why is enzyme action important?

Answer 5

a lower activation energy means that metabolic reactions can occur at lower temperatures eg. humans = 37 degrees celcius

Question 6

how are enzymes made? (4 points)

Answer 6

• enzymes are tertiary globular proteins
• the primary order of amino acids determines which hydrogen bonds form in the secondary
• and consequently which type of bonds (hydrogen, ionic and covalent,) and where they occur
• to fold and twist the chain further to achieve the 3D specific structure

Question 7

define active site

Answer 7

the functional region where substrates are held to an enzyme by temporary bonds to form an ESC

Question 8

describe the lock and key model of enzyme action (2 points)

Answer 8

• this model proposes that enzymes work in the same way as a key operates a lock.
• a substrate will only fit the active site of one particular enzyme

Question 9

outline the limitation of the lock and key model of enzyme action

Answer 9

the model suggests that enzymes have a rigid structure, but we know it to be flexible as other molecules can bind at allosteric sites

Question 10

describe the induced fit model of enzyme action (3 points)

Answer 10

• the enzyme is flexible and can mould itself around a complimentary substrate.
• as it changes shape it puts a strain on the substrate molecule
• which in turn distorts the bonds in the substrate, lowering Ea

Question 11

name the 4 factors which affect the rate of enzyme action

Answer 11

temperature, pH, concentration of substrate and concentration of enzyme

Question 12

describe how temperature affects the rate of enzyme action

Answer 12

higher temp = more energy = more kinetic energy
so therefore more ESC are being formed at a faster rate
this continues up to an optimum
after exceeding the optimum H bonds begin to break first as they are the weakest.
this can alter the shape of the active site or break it completely, reducing rate or resulting in denaturation

Question 13

define pH

Answer 13

a measure of hydrogen ion (H+) concentration of a solution

Question 14

describe how pH affects the rate of enzyme action

Answer 14

enzymes all have an optimum pH which they work at
altering the pH of an enzymes environment results in the charges on amino acids being altered
this can result in hydrogen or ionic bonds being broken
altering the shape of the active site as amino acids make it
enzyme no longer fits so no ESC formed = denaturation

Question 15

what do you need to consider when talking about the affect of enzyme/substrate concentration on enzyme acion?

Answer 15

enzyme is proportional to substrate
in order to reach Vmax you need an excess of substrate
E + S –> ESC –> E + P

Question 16

define enyzme inhibitor

Answer 16

a substance which interferes with the functioning of an enzymes active site to therefore reduce activity

Question 17

define competitive inhibitor

Answer 17

a molecule which has a SIMILAR shape to the substrate, allowing it to compete with the substrate for the active site

Question 18

give 2 key points about competitive inhibitors

Answer 18

they are not permanently bound to the active site
to reduce the effect felt by them you need to increase the concentration of substrate

Question 19

define non-competitive inhibitor

Answer 19

a molecule which doesn’t compete with the substrate for the active site, instead attaching to an allosteric site

Question 20

define allosteric site

Answer 20

a different part of an enzyme which is not the active site

Question 21

what does the attachment of a non-competitve inhibitor to an allosteric site sometimes result in?

Answer 21

the enzyme’s shape being altered and therefore substrate no longer being complimentary to the active site

Question 22

give the equation for using hydrogen ion concentration to calculate pH

Answer 22

pH = -log₁₀[H+]

Question 23

how can you measure enzyme catalysed reactions?

Answer 23

measure the amount of product formed or the amount of substrate being used up per unit time

Question 24

define rate of reaction

Answer 24

the increase in product or the decrease in reactant concentration per unit time

Question 25

when measuring enzyme catalysed reactions, how do you find the rate?

Answer 25

gradient gives rate, change in y/change in x