Enzymes And Factors Affecting Enzymes

Question 1

When speeding up a reaction,
how do they lower the activation energy?

Answer 1

It lowers by substrate being attached to active site, enzymes twists substrate molecule
= easier to break bonds holding molecule together

Question 2

Give two reasons why enzymes substrate complex occur?

Answer 2

1. If substrate molecules needed joining. Attaching to enzymes molecule hold them closer together. Which reduces repulsion’s between molecules so they bond easier
2. If enzymes is catalysing breakdown reaction. Fitting into active site puts stain on bonds in substrate.
   Causing substrate molecules break down easier

Question 3

If a mutation occurs then what does it change on the enzyme produced

Answer 3

The tertiary structure

Question 4

Why does using a enzymes in reaction decrease the temperature?

Answer 4

As activation energy is often provided by heat
So as a enzyme lowers the activation energy the temperature will decrease

Question 5

Within the lock and key model what shape is the active site?

Answer 5

It is a fixed shape that is contemporary to substrate.

Question 6

Explain what happens to the rate of an enzyme-controlled reaction when the substrate concentration is increased after the saturation point.

Answer 6

The rate of reaction stays constant. All active sites are occupied so increasing the substrate concentration has no effect

Question 7

What does increasing the enzyme concentration become when effecting the rate of enzyme controlled reaction?

Answer 7

It becomes a limiting factor as the rate can’t increase so levels off.

Question 8

Why does the rate of reaction flatten (plateu) on graph

Answer 8

It flatters / plateaue when reached its saturation point. So all active sites are full / occupied.

Question 9

How do you work out the rate of enzyme activity from a table

Answer 9

Rate = 1 divided by time

Need to divide by the lowest time in table eg
6 divided by time

Units S -1

Question 10

What happens if you increase the substrate concentration of enzyme with inhibitor?

Answer 10

It won’t make a difference and enzyme will still be inhibited.

Question 11

Explain the rate of reaction at 60 degrees from graph

Answer 11

At 60 degrees more kinetic energy therefore more enzyme substrate complexes formed.
60 it denatures - high temp
Reaction stops so ac site changes shape
Different concentration of product means still substrate available when enzyme is denatured but it is not converted to product

Question 12

What do you need to remember after working out gradient

Answer 12

To include the units
eg.
g/dm-3 s-1

Question 13

When describing a rate of enzymes.
What
Do you describe

Answer 13

. The initial rate
. Increase - proportion,
Key words with temp - eg rise in temp , kinetic energy, collisions,
Enzyme substrate complex
. Platers - all substrate used up

Question 14

Explain how the active site of an enzyme causes a high rate of reaction

3 marks

Answer 14

. It lowers activation energy (1)

.Induced fit causes active site of enzyme to change shapes
(1)

. So enzyme substrate complex’s causes stress / strain on bonds (1)

= increase in rate of reaction

Question 15

Suggest a change the student could make to his procedure so that 10cm3 of oxygen would be produced in less than 6 seconds

Answer 15

Any of these:

Cut up/use discs/homogenise/increase surface area (of potato chips)

Use bigger chips

Increase temperature

Change pH;

Reject answer if the temperature is above 40°C
Ignore: more/increase heat

Question 16

Mammals have some cells that produce extracellular proteases. They also have cells with membrane-bound dipeptidases. Describe the action of these membrane-bound dipeptidases and explain their importance. 2 marks

Answer 16

Hydrolvse (peptide bonds) to release amino acids;
Amino acids can cross (cell) membrane;

Dipeptides cannot cross (cell) membrane;

Maintain concentration gradient of amino acids for absorption;

Ensure (nearly) maximum yield from protein breakdown;

Ignore references to crossing gut membranes.
Accept “there are carrier proteins for amino acids’
Accept ‘no carrier proteins for dipeptides’

Question 17

Galactose has a similar structure to part of the lactose molecule.
Explain how galactose inhibits lactase.

Answer 17

Galactose is a competitive inhibitor / attaches to the active site (of lactase);
Fewer enzyme substrate complexes formed.

Question 18

Describe the induced fit model of enzyme action and how an enzyme acts as a catalyst
3 marks

Answer 18

Substrate binds to the active site/enzyme
OR
Enzyme-substrate complex forms;
Accept for ‘binds’, fits

Active site changes shape (slightly) so it is complementary to
substrate
OR
Active site changes shape (slightly) so
distorting/breaking/forming bonds in the substrate;

3. Reduces activation energy;

Question 19

Formation of enzyme substrate complex increases rate of reaction
Explain how
3 marks

Answer 19

Reduces activation energy;
Accept ‘reduces Es.

Due to bending bonds
Or
Without enzyme, very few substrates have sufficient energy for reaction;

Accept ‘Due to stress/pressure/tension on bonds’
OR ‘Due to weakening bonds.

Question 20

Lyxose binds to the enzyme.

Suggest a reason for the diference in the resuls shown in the graph with and without lyxose

With has higher rate on graph

3 marks

Answer 20

1. Binding) alters the tertiary structure of the enzyme

if lyxose acting as an inhibitor
OR if answer linked to lower rate of reaction
OR if lyxose used an energy source/respiratory substrate

2. (This causes) active site to change (shape);
3. So) More (successful) E-S complexes form (per minute)
   OR
   E-S complexes form more quickly
   OR
   Further lowers activation energy;