topic 1 - enzyme action

Question 1

what are enzymes

Answer 1

biological catalysts that speed up chemical reactions

Question 2

what do enzymes catalyse

Answer 2

metabolic reactions - at a cellular level and for the organism as a whole

Question 3

what can enzymes affect in an organism

Answer 3

structures and functions

Question 4

why are enzymes highly specific

Answer 4

due to their tertiary structure

Question 5

what is the enzymes active site

Answer 5

the active site has a specific shape - is the part of the enzyme where the substrate molecules bind to

Question 6

what do enzymes lower in a reaction, what does this lead to

Answer 6

the activation energy - making reactions happen at a lower temperature than they could without an enzyme, therefore speeding up the reaction

Question 7

before a reaction starts, what needs to be supplied to the chemicals

Answer 7

energy (often provided as heat)

Question 8

what is formed when a substrate fits into the enzyme’s active site

Answer 8

an enzyme substrate complex

Question 9

what lowers the activation energy

Answer 9

the enzyme substrate complex

Question 10

what are two reasons why the enzyme substate complex lowers the activation energy

Answer 10

(1) if two substrate molecules need to be joined, being attached to the enzyme holds them close together - reducing any repulsion between the molecules so they can bond easily
(2) if the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate - so substrate molecule breaks up more easily

Question 11

what is the lock and key model

Answer 11

this is where the substrate fits into the enzyme in the same way that a key fits into a lock

Question 12

why is the lock and key model not completely accurate

Answer 12

the enzyme and substrate do have to fit together in the first place, but new evidence showed that the enzyme substrate complex changed shape slightly to complete the fit - this locks the substrate even more tightly to the enzyme

Question 13

what does the induced fit model help to explain

Answer 13

why enzymes are so specific and only bond to one particular substrate

Question 14

explain what happens in the induced fit model

Answer 14

when the enzyme substrate complex occurs , due to the enzyme moulding around the substrate it puts strain on the bonds - therefore lowering activation energy -
products are then removed and the enzyme active site returns to its original shape

Question 15

explain what happens in the lock and key model

Answer 15

once the enzyme substrate complex has formed the charged groups within the active site distorts the substrate - lowering the activation energy, the products are then released and the enzyme active site is empty and ready to be reused

Question 16

what does the lock and key model suggest

Answer 16

that the enzyme active site is a fixed shape and due to random collisions the substrate can collide and attach to the enzyme - forming an enzyme substrate complex

Question 17

why can enzymes only catalyse one reaction

Answer 17

enzymes are specific as only one complementary substrate will fit into the active site

Question 18

what is the enzymes shape determined by

Answer 18

its tertiary structure (which is determined by the enzyme’s primary structure)

Question 19

what happens if the enzymes tertiary structure doesn’t match the active site

Answer 19

an enzyme substrate complex won’t be formed and the reaction won’t be catalysed since each enzyme has a different tertiary structure and so a different shaped active site

Question 20

what happens if the enzyme is altered in any way, what will this lead to

Answer 20

the shape of the active site will change - meaning the substrate wont’s fit into the active site and the enzyme substrate complex won’t be formed so the enzyme will no longer be able to carry out its function

Question 21

how may the tertiary structure of an enzyme be altered

Answer 21

by changes in the pH or temperature

Question 22

what is the primary structure of a protein be determined by

Answer 22

by a gene - if a mutation occurs in that gene it could change the tertiary structure of the enzyme produced