Enzymes (MP)

Question 1

Enzymes

Answer 1

-globular spherical proteins
-biological catalysts that speed up reactions
-lower activation energy needed for reactions
-unchanged during a reaction so can be reused
-soluble in water due to hydrophobic/philic R groups
-contain an active site of a specific shape complementary to a specific substrate
-the tertairy structure of a protein molecule determines the shape of the active site

Question 2

Anabolic enzymes

Answer 2

synthesise larger molecules from smaller ones

Question 3

Catabolic enzymes

Answer 3

(‘cataclysm = bad’)
when metabolites are broken down into smaller molecules and release energy

Question 4

Intracellular enzymes

Answer 4

made and retained inside the cell

Question 5

Extracellular enzymes

Answer 5

made inside the cell then secreted to act on other substrates

Question 6

Catalase (an enzyme)
Intracellular

Answer 6

breaks down hydrogen peroxide into water and oxygen inside cells

! Hydrogen peroxide is a potentially harmful by-product of many bodily reactions

Question 7

Trypsin (an enzyme)
Extracellular

Answer 7

Tripsinogen is made inside the cell, this is inactive.
When secreted outside the cell (exocytosed) it converts into Trypsin which can then actively break down proteins (by enterokinase)

! It is kept inside the cell inactively as we don’t want a protease enzyme breaking down our cells.

Question 8

Saprotrophic Nutrition
(fungi and extracellular enzymes)

Answer 8

Fungi release hydrolytic enzymes that break down proteins, carbohydrates and lipids in the soil so they can be reabsorbed by the fungi for respiration and growth.

1)hydrolytic enzymes are exocytosed from the hyphae (roots of the fungi)

2) enzymes digest polymers into monomers

3)monomers are endocytosed back into the hyphae

Question 9

Enzyme action

Answer 9

the active site is an indentation, complementary to the substrate.

-Lock and key hypothesis
-Induced fit model

Question 10

Lock and key hypothesis

Answer 10

1)substrate binds to the complementary active site creating an enzyme-substrate complex

2)the substrate is broken down into products by the enzyme

3)enzyme-product complex and then the products leave the active site

back to 1

Question 11

Induced fit model

Answer 11

1) the active site is not yet complementary

2) active site will move around to fit the substrate = enzyme-substrate complex, the active site is now complementary

3)the shape change breaks the bonds creating an enzyme-product complex

4) the products are released and the active site returns to being larger again

Question 12

Similarities and differences of the lock and key hypothesis and the induced fit model

Answer 12

Similarities:
-although the active site in induced fit does not start off as complementary both eventually have a complementary active site
-enzyme-substrate and enzyme-product complexes are formed
-both enzymes lower activation energy
-unchanged so can be re-used

Differences:
-the active site changes shape in the induced fit model to more closely fit with the substrate

Question 13

Temperature coefficient
(Q10)

Answer 13

how much the rate of a reaction or biological process changes for every 10’C increase in temperature

Question 14

calculating rates of enzyme reaction using temperature coefficient

Answer 14

Q10= rate at (T+10)’C
÷ rate at T’C

eg
temp 20’C = 231 bubble/min
temp 30’C = 397 bubble/min

Q10=rate at 30’C÷rate at 20’C
=397÷ 231
Q10= 1.7

Question 15

VMax

Answer 15

The point on an enzyme substrate graph where the line plateaus and becomes flat
No more active sites for the substrate to bind with, they are all being used.

Question 16

Effect of inhibitors on VMax

Answer 16

The line on the substrate enzyme graph is lower and less steep, reaching VMax later than without inhibitors
->the inhibitors block the active sites and slow down ROR
! non-competitive inhibitors line is very low and VMax is NEVER reached because the substrate cannot bind with the changed active site

Question 17

Inhibitors

Answer 17

chemical or biological molecules that regulate chemical reactions by slowing down or blocking them from occurring
1) competitive inhibitors
2) non-competitive inhibitors
3) end-product inhibition

Question 18

competitive inhibitors

Answer 18

have a similar but not exact shape to that of the substrate
-> they compete with the substrate for the active site, when the inhibitors are associated with the active site it BLOCKS the entry of a substrate reducing ROR

RATE OF INHIBITION
1) If inhibitor conc HIGH
-> ROI increases as more inhibitors successfully collide with active site than substrate
2) If substrate conc HIGH
->’dilutes’ the inhibitor so less likely for inhibitors to bind to active site ROI decreases

Question 19

Non-competitive inhibitors

Answer 19

attach to the allosteric site of the enzyme which is away from the active site but when bound changes the tertiary shape of the enzyme this is temporary and no enzyme-substrate complex is formed

Question 20

Both competitive and non-competitive inhibitors can be temporary or permanent

Answer 20

Inhibitors can temporarily bind using H bonds and can react when the inhibitor is gone again

Inhibitors can be bound permanently through covalent bonds preventing the enzyme from reacting at all
eg. due to cyanide

Question 21

End-product inhibition

Answer 21

after a reaction the product will bind tightly onto the allosteric site of the enzyme, this changes the active site shape and reduces the amounts of product formed from then on
-> NEGATIVE FEEDBACK LOOP

Question 22

Cofactors

Answer 22

non-protein (inorganic) substances that bind to enzymes to allow them to work
eg Mg2+, Zn2+, Cl-

! They make the active site complementary to the substrate
a cofactor that is permanently bound to to the enzyme is called a PROSTHETIC group

Question 23

Zn2+ ions

Answer 23

The prosthetic group for carbonic anhydrase

Question 24

Cl- ions

Answer 24

Cofactor for amylase

Question 25

Coenzymes

Answer 25

Often **organic** and derived from vitamins They work **together with the enzyme** but is NOT an enzyme They bind **with** or **before** the substrate on the **active site** !**Coenzymes change shape after the reaction but are continually recycled** -> in questions the changing shape could be via oxidation, or +- of a H