enzymes

Question 1

what are enzymes

Answer 1

-tertiary structure proteins which catalyse reactions

Question 2

what is special about the active site of an enzyme

Answer 2

-its specific and unique in shape due to the specific folding and bonding in tertiary structure of protein
- complementary to substrate to form enzyme substrate complex

Question 3

give the chemical reaction equation

Answer 3

reactants→ products

(arrow indicates its an enzyme controlled reaction)

Question 4

when can a product form in a chemical reaction

Answer 4

-when bonds are broken and reformed
-bond breaking requires activation energy

Question 5

what is activation energy

Answer 5

the minimum energy required for a successful chemical reaction

Question 6

how do enzymes increase the rate of reaction

Answer 6

-by lowering the activation energy
-the active site stresses/weakens the bonds in substrate (reactant) when enzyme-substrate complex is formed
-this allows reactions which would usually require higher temperatures, to work at lower temps

Question 7

give an example of an enzyme-catalysed reaction

Answer 7

-in digestion enzymes allow large complex molecules POLYMERS to be broke down by hydrolysis into smaller simple molecules MONOMERS before absorption and assimilation-at body temp 37 degrees

Question 8

describe the structure of an enzyme

Answer 8

-single polypeptide of about 50 amino acids which form enzyme
-hydrogen bonds maintain its shape
-active site typically made up of less than 10 amino acid R groups

Question 9

what does the lock and key theory state

Answer 9

-the active site is specifically/fully complementary to its substrate
-active site is rigid doesn’t change shape
-the substrate bind to active sit and is an exact fit to it (they are complimentary)
-products are formed and no longer fit to active site

Question 10

what does the induced fit model state

Answer 10

-active site is not fixed/rigid, it can change shape and is slightly flexible
-when substrate binds to enzyme it ‘induces’ a change in shape of active site making it more complimentary
-enzyme can alter its tertiary structure

Question 11

describe the induced fit model of enzyme action

Answer 11

-active site and enzyme are not complimentary
-so when substrate enters the active site the active site changes shape as ESC forms -this is done by stressing or distorting the bons within substrate molecule making it more complimentary
-when substrate leaves the active site goes back to og shape

Question 12

what is the optimum temp

Answer 12

-maximum energy that can be supplied to the molecules before the hydrogen and ionic bonds start to break

Question 13

describe the effect of temp on rate of reaction

Answer 13

at start there’s low levels of KE so there’s less successful collisions and low chance of forming ESC so rate is low

temp increase- enzyme and substrate molecules increased in KE and more likely to successfully collide and react. ROR increases because more ESC form per second

temp increase-optimum temperature is when there’s max KE and highest rate

temp increase- denaturation

Question 14

what happens to enzyme when temp is too high

Answer 14

enzyme vibrate faster because they have lots of KE bonds to break which may change shape of active site, no more ESC formed as substrate is no longer complimentary

Question 15

what is rate

Answer 15

How much and how quickly

Question 16

when temps exceeds optimum why does the reaction still occur

Answer 16

there’s lots of same enzymes in given volume soreaction will occurs at a slower rate until all enzymes have been denatured

Question 17

what is pH

Answer 17

measure of H+ ions

Question 18

what happens to an enzyme if the pH is changed

Answer 18

the charge on R groups of amino acids is altered and the ionic and weak hydrogen bonds are broken so the active site changes shape and enzyme becomes denatured

Question 19

what happens to an enzyme if it has a small pH change

Answer 19

it inactivates the enzyme and may flip the charges on R groups of amino acids but its reversible as this is only a temporary change, if you put enzyme back in optimum pH it will be active again

Question 20

how does substrate concentration affect the rate of reaction

Answer 20

-as substrate concentration increases the ROR increases as more ESC are formed per second ( substrate is a limiting factor)
-however eventually the ROR plateaus since all active sites are saturated /in use (enzyme concentration is now the limiting factor)

Question 21

how do you work out reaction rate at a given point

Answer 21

draw a tangent and work out gradient

Question 22

give an example of enzyme catalysed reactions

Answer 22

-digestion (hydrolysis)
-photosynthesis
-end-product inhibition
-DNA replication

Question 23

how do you work out initial reaction rate

Answer 23

draw a tangent on curve starting at 0 and then find gradient

Question 24

how do you work out rate of reaction between 2 points

Answer 24

work out gradient

Question 25

what are inhibitors

Answer 25

substances which decrease the rate of reaction

Question 26

describe competitive inhibitors

Answer 26

-they have similar structures to substrates
-they bind to the active site and prevent substrate from binding temporarily
-so fewer products are formed per second (however some product will still be formed because some active sites can bind to substrates)
-this can be overcome by increasing substrate concentration as they’ll knock off these inhibitors

Question 27

describe non-competitive inhibitors

Answer 27

-they bind to a site which is away from active site (allosteric site)
-when they bind to an enzyme it causes a conformational change to the shape of the active site so that substrates cannot bind
-binding can be temporary or permanent
-if the inhibitor molecule detaches from enzyme it can bind to another
-fewer ESC can be formed decreasing rate of reaction
-increasing substrate con wont have an affect on this

Question 28

describe the graph for the inhibitors

Answer 28

-when there is no inhibitors maximum ROR is reached and then graph plateaus
-when there is a competitive inhibitor present the line will not be as steep but it will always level off with the no inhibitors curve
-when there is a non competitive inhibitor the ROR wont be at its maximum (usually half of it) and it’ll plateau early