4. Enzymes Section B

Question 1

pg 14 Fig. 1.1 shows two ways in which enzymes interact with their substrates, explain the difference between the two ways these enzymes interact with their substrates 2

Answer 1

Enzyme A uses “Lock & Key” hypothesis with an active site that’s complementary to the shape of its substrate

Enzyme B uses “Induced fit” hypothesis with an an active site that changes its shape to fit it’s substrate.

Question 2

Explain why the shape of an active site of an enzyme is important 2

Answer 2

Active site of an enzyme is complementary to the shape of its substrate

so the substrate can temporarily bind with R-groups of amino acids

Question 3

What is primary structure of protein made of?

Answer 3

Amino acids joined with peptide bonds

Question 4

What is secondary protein structure made of? 2

Answer 4

Alpha helices

Beta Pleated sheets

Question 5

What are Alpha Helices? 2

Answer 5

Tightly coiled structures

occur due to hydrogen bonds forming between amino acids 4 places apart

Question 6

What are Beta Pleated sheets? 2

Answer 6

Looser, straighter structure is formed

Formed when bonding occurs between parallel polypeptide chains

Question 7

What is tertiary protein structure? 2

Answer 7

Caused by bonds forming between R-groups on amino acids

that lie close to each other when chain starts to be folded & coiled

Question 8

What is quaternary structure? 3

Answer 8

Not always present

composed of more than 1 polypeptide chain

contain same levels of bonding as tertiary proteins

Question 9

2 c) i) Draw

Answer 9

Draw thibgy

Question 10

What is activation energy

Answer 10

the energy level that must be overcome before a reaction can progress

Question 11

What is Vmax?

Answer 11

The point at on y-axis which the line of enzyme reaction is horizontal

Question 12

3 Fig 2.1, Determine the Vmax

Answer 12

3.4 uM min^-1

Question 13

How do you calculate Km

Answer 13

1/2Vmax on y-axis & then find value on the X-axis

Question 14

3 a) ii) Calculate the Km

Answer 14

3.4/2 =1.7, (look on graph for x-value where y=1.7)

=0.15 mM

Question 15

3 b) fig 2.1 Describe & explain shape of curve 5

Answer 15

When substrate concentration is lower, rate of reaction is proportional to substrate concentration

This is because there are still some unoccupied active sites

At higher substrate concentrations, the increase in the rate of reaction is slower

& substrate concentration is no longer limiting factor, instead enzyme concentration is

because all active sites are occupied

Question 16

3 c) in the functioning enzyme, these 3 amino acids are close together in the active site. Explain how protein structure makes this possible 2

Answer 16

coiling of polypeptide chain brings these amino acids closer together,

this is due to tertiary structure of trypsin that is caused by bonds between amino acids

Question 17

When trypsin acts on a substrate, another substance is required as a reactant. Name this substance

Answer 17

H20

Question 18

4. a) describe the reaction catalysed by lactase, use fig 3.1 to help you & in your answer identify R & product S 4

Answer 18

The hydrolysis reaction changes disaccharides to monosaccharides

The glycosidic bond is broken

R is water & S is alpha glucose

Question 19

4 b) suggest why product inhibition is useful in K.lactis when lactase is acting as an intracellular enzyme but can be a disadvantage when extracted lactase is used free in solution for the production of lactose-free milk 2

Answer 19

It’s an advantage when the enzyme is intracellular because in high quantities, the product has no requirement for use in cell respiration

But it’s a disadvantage in solution because of loss of product

Question 20

How does immobilised lactase in a commercial application help to reduce the problem of product inhibition

Answer 20

The product and enzyme are separate and the product can be quickly removed

Question 21

For a commercial application using an enzyme, the progress of the enzyme-catalysed reaction needs to be studied. Outline how the progress of an enzyme-catalysed reaction can be investigated experimentally 4

Answer 21

Keep temperature & pH constant

Take samples of the amount of product formed at regular intervals

Plot a graph of product formation against time

Draw a tangent to determine initial rate of reaction

Question 22

what does intracellular mean?

Answer 22

It works inside the cell