2.1.4 ENZYMES

Question 1

what are enzymes?

Answer 1

-proteins that act as biological catalysts used make/break down molecules by speeding up the rate of reaction without undergoing a permanent change itself
-catalyse metabolic reactions (cellular level i.e respiration) (whole organism i.e digestion)

Question 2

what do enzymes affect?

Answer 2

structures within an organism i.e involved in collagen production
-functions i.e respiration

Question 3

Intercellular reaction

Answer 3

-enzyme action WITHIN cells
-Catalase: catalyses the breakdown of hydrogen peroxide* into water and oxygen in cells
*toxic by-product of reactions, can kill cells e.g damaging cellular components
produced in plant and animal tissues

Question 4

Extracellular reactions

Answer 4

-Enzyme actions OUTSIDE of cells
1) Amylase: secreted by salivary glands and pancreas, catalyses hydrolysis of starch into maltose in the mouth
2) Trypsin: produced in pancreas and secreted into small intestine, catalyses the hydrolysis of peptide bonds(breaks down polypeptides)

Question 5

ENZYME STRUCTURE

Answer 5

-globular
-active site determined by tertiary structure

Question 6

activation energy

Answer 6

-certain amount of energy(mostly heat) needed to be supplied before reaction
-enzymes lower activation energy so reactions can happen at a lower temp —} speeds up ROR

Question 7

how does an enzyme catalyse reaction between 2 substrate molecules?

Answer 7

-if 2 substrates need to be joined together, attaching to the enzyme holds them close together and reduces any repulsion’s between molecules
-can bond easily

Question 8

how does an enzyme catalyse a hydrolysis reaction?

Answer 8

-fitting into the active site puts a strain on bonds in the substrate
-breaks up more easily

Question 9

‘Lock and key’ model

Answer 9

-substrate has a fixed complementary shape to the enzyme & active site is specific to the substrate(forms enzyme-substrate complex)

Question 10

‘induced fit’ model

Answer 10

-active site is not completely complementary to substrate shape
-so as the substrate begins binds to the enzyme, causes a conformational change in shape to the active* to facilitate the reaction and form an enzyme-product complex
*stress on the substrate’s bond which makes them easier to break which lowers activation energy

Question 11

FACTORS AFFECTING ENZYME ACTIVITY

Question 12

Temperature

Answer 12

enzyme activity increases until reaction has reached optimum temp
-enzyme gain kinetic energy as temp increases so molecules move faster and substrate and enzymes have more successful collisions(successfully bc they have more energy) so more enzyme substrate complexes form and vice versa with low temp
decreases steeply after optimum temp
-enzyme’s molecules vibrate more at high temps which breaks the bonds between amino acids
-disrupts tertiary structure of enzyme including active site
-enzyme is denatured
(effects of high temp are reversible, effects of low temp are irreversible)

Question 13

Temp coefficient(Q10)

Answer 13

how much the rate of reaction changes when the temp is raised by 10 degrees celcius
R2(rate at higher temp)➗ R1(rate at lower temp)

Question 14

pH

Answer 14

-if pH changes from its optimum, there will be more/less OH and H ions(alters charge on amino acids)
-ionic and hydrogen bonds break in tertiary structure
-tertiary structure of protein changes including active site which means substrates cannot bind so less complexes formed
-small variations cause reversible changes to the protein structure and shape but large variations cause irreversible reactions
-enzymes become denatured
-RoR reduced

Question 15

Enzyme concentration

Answer 15

-as conc increases, the ROR increases steadily as more collisions will happen and more enzyme-substrate complexes
- UNLESS there is more enzymes than substrate(substrate conc is a limiting factor)
-conc no longer has an effect
-unless substrate conc increases too, then ROR will continue to increase steadily

Question 16

Substrate concentration

Answer 16

as the subsrate conc increases, the ROR increases steadily (more collisions, enzyme-substrate complexes and more active sites occupied)- more substrate available for this to occur
-until ‘saturation point’ or V-max(where enzymes work at max rate) after that all active sites are being used
-increasing substrate concentration no longer has an effect
(decreases over time)

Question 17

What are cofactors?

Answer 17

-non protein substances that bind to enzymes

Question 18

Inorganic cofactors

Answer 18

-inorganic molecule/ion temporarily binds to an enzyme to help form enzyme-substrate complex
-are not directly part of the reaction so aren’t used up or changed.

Question 19

Chloride ions

Answer 19

• (Cl-) are inorganic cofactors for the enzyme amylase

Question 20

Organic cofactors(coenzymes)

Answer 20

-non protein organic molecule, not permanently attached to an enzyme but are needed to allow enzyme to function
-act as carriers moving chemical groups between enzymes by binding to the active site of an enzyme
-participate in the reaction so can be changed
-continuously recycled during the process

Question 21

Vitamins as a source for coenzymes

Answer 21

-NAD comes from Vitamin B3 and is involved in repsiration

Question 22

Prosthetic groups

Answer 22

-cofactor that is tightly and permanently bound to the enzyme.
-contribute to final tertiary structure and other properties of the protein

Question 23

Zinc ions

Answer 23

(Zn2+) are a prosthetic group for carbonic anhydrase(catalyses the production of carbonic acid from water and co2 in red blood cells)

Question 24

What are enzyme inhibitors?

Answer 24

molecules that bind to the enzyme and block its process.

Question 25

Competitive inhibitors

Answer 25

-have a similar shape to substrate molecules
-compete with the substrate and binds TEMPORARILY to active site to ensure substrate cannot enter
-no reaction takes place

Question 26

how does inhibitor concentration affect this?

Answer 26

-high conc of inhibitors will take up nearly all active sites and substrate will be less likely to reach active site.

Question 27

how does substrate conc affect this?

Answer 27

-higher conc of substrate, then its chances of reaching the active site are higher before inhibitors increase
-increased ROR
(reverse effects of inhibitor)

Question 28

Irreversible inhibition

Answer 28

• bonds between the enzyme and the inhibitor are strong and covalent so the inhibitor cannot be removed easily

Question 29

Non-competitive inhibitors

Answer 29

-bind to the enzyme’s allosteric site(back of the enzyme) to change the shape of the active site so substrates can no longer bind to it.

Question 30

how are they non-competitive?

Answer 30

-increasing the concentration of substrate won’t make any difference to enzyme activity
-with non competitive, increasing substrate zinc doesn’t meet max rate of reaction

Question 31

Reversible inhibition

Answer 31

• bonds between to the enzyme and the inhibitor are weaker hydrogen bonds or weaker ionic bonds so the inhibitor can be removed easily by bonds breaking down

Question 32

End-product inhibition

Answer 32

when the final product inhibits an enzyme involved in the initial reactions of a metabolic pathway
-negative feedback control mechanism for the reaction
-excess products are not made and resources are not wasted.
non-competitive reversible inhibition when proteins produce above optimum

Question 33

work out the ROR

Answer 33

-draw tangent at t=0(or the time you’re given in the question)
calculate the gradient change in y/change in x
work our unit of rate
OR
change in conc/change in time
general formula= 1/time

Question 34

Enzyme controlled reactions: effect of temperature on amylase

Answer 34

-syringe 2cm3 of amylase into a test tube and place in water bath at 20 degrees for 5 mins
-add 2 cm3 of buffer solution into 2cm3 of starch solution
-place a drop of iodine into every well of a spotting tile
-when amylase is at 20 degrees, pour into starch solution and start timer
- every 20 seconds add a drop of amylase into each well
-stop when there is a colour change to orange-brown
-repeat for 40,60,80
-plot results on a graph

Question 35

Medicinal drugs that are inhibitors: antibiotics

Answer 35

-penicillin inhibits the enzyme transpeptidase(catalyses formation of proteins in bacteria cell walls which weakens cell wall and prevents regulation of osmotic pressure, causing cell to burst and bacterium to die)

Question 36

Metabolic poisions as enzyme inhibitors

Answer 36

-Cyanide is a non competitive, irreversible inhibitor for cytochrome C oxidase(enzyme that catalyses respiration reactions, without it, cells die)