2.4.3 the mechanism of enzyme action

Question 1

which 2 models explain the mechanism of enzyme action

Answer 1

• lock & key hypothesis
• induced fit hypothesis

Question 2

why do the substrate molecules fit into the active site

Answer 2

due to the tertiary structure of the enzyme’s active site which gives it a shape complementary to the substrate molecule

Question 3

which is the lock/key in the lock-and-key hypothesis

Answer 3

lock = enzyme’s active site
key = substrate//

Question 4

describe the lock-and-key hypothesis to form smaller products

Answer 4

1. substrate molecules are complementary to enzyme molecules active site
2. substrates bind to active site & held by temporary hydrogen bonds = enzyme-substrate complex (ESC)
3. substrate molecule is broken into smaller products which leave active site

Question 5

describe the lock-and-key hypothesis to form a larger product

Answer 5

1. substrate molecules bind to active site of enzyme molecule
2. forms ESC & bonds form between substrate molecules
3. larger product molecule leaves active site

Question 6

what energy do the substrate/enzyme molecules have & what does this cause them to do

Answer 6

• kinetic energy
  –> constantly moving randomly

Question 7

what happens to the substrate molecules & what does this create

Answer 7

• broken down/built up into product molecules = enzyme-product complex (still in active site)

Question 8

what is the enzyme molecule now able to do

Answer 8

form another ESC

Question 9

how many enzyme molecules are needed to convert a large number of substrate molecules into product molecules

Answer 9

small number

Question 10

who modified the lock-and-key hypothesis (and when) - what did they suggest

Answer 10

1958 daniel koshland
–> suggested the enzyme isn’t a fixed/rigid structure but the presence of the substrate induces a shape change, providing a good fit

Question 11

describe the induced fit hypothesis - refer to koshland/his suggestions

Answer 11

• when the substrate fits into the enzyme’s active site, it changes SLIGHTLY to mould itself
• moulding allows substrate to bind more effectively

Question 12

what causes the active site to change shape

Answer 12

active site is complementary to the substrate BUT on binding, the subtle changes of the side chains (R-groups) of the amino acids (that make up active site) gives a more precise shape which exactly fits the substrate

Question 13

which forces bind the substrate molecule to the enzymes active site once an ESC is formed

Answer 13

non-covalent forces eg. hydrogen bonds, ionic attractions, van der Waals forces & hydrophobic interactions

Question 14

what’s formed when the products have been made but remain in the active site - induced fit hypothesis (still)

Answer 14

enzyme-product complex

Question 15

what do enzymes lower

Answer 15

activation energy

Question 16

what does heating chemicals during a reaction do & how

Answer 16

• provide activation required for reaction
• increases kinetic energy of molecules = move more (randomly) & more likely to successfully collide/react

Question 17

what would happen in the temp. was raised too high in a living cell

Answer 17

proteins within it would denature & lipids would melt

Question 18

how do enzymes reduce the activation energy for a reaction

Answer 18

• bring specific substrate molecules close enough to react (without need for excessive heat)
• thus, lower activation energy & speed up metabolic reactions