Topic 2: Enzyme data and graph questions

Question 1

What are the 4 factors affecting the rate of enzyme catalysed reactions?

Answer 1

1. Enzyme concentration
2. Substrate concentration
3. Temperature
4. pH

Question 2

When carrying out an enzyme practical, one factor will be the independent variable and the other three factors should be controlled (kept the same)

1. Enzyme concentration – use the same _____ ________ to make up a set concentration e.g. 1%
2. Substrate concentration – use the same _____ ________ to make up a set concentration e.g. 1%
3. Temperature – use a ______ _____ set at the optimum temperature of the enzyme
4. pH – use a _______

Answer 2

stock solution

stock solution

water bath

buffer

Question 3

What is the formula for calculating the rate of reaction?

Answer 3

Rate = Y / X

Question 4

In an exam question, when it says “Analyse the data to explain” What should you do?
(1 point)

Answer 4

1. Both describe and explain using theory

Question 5

In an exam question, when it says “Analyse the data/describe the data” What should you do?
(2 points)

Answer 5

1. Only describe (no theory needed)

2. Follow data rules (trend, linear/non-linear, manipulate, divide data, SD bats, greatest increase etc.)

Question 6

In an exam question, when it says “Explain the data” What should you do?
(1 point)

Answer 6

1. Mostly explain, but you will probably need to state the trends that you are explaining,

NOTE: usually no marks for manipulation, greatest increase etc, - as most marks are for explanation

Question 7

Key Summary: Explain why increasing enzyme concentration increases the initial rate of reaction

As the enzyme concentration increases, the initial rate of reaction increases because … (5 steps)

Eventually reaches a plateau (graph levels off) and {there is no further increase in rate/rate becomes constant} as the substrate concentration becomes the ___________ __________.

Answer 7

1. number of enzymes (e.g. trypsin) increases
2. so number of enzyme active sites increases
3. MORE FREQUENT AND SUCCESSFUL COLLISIONS between enzyme and substrate
4. MORE ENZYME-SUBSTRATE COMPLEXES form (lowers activation energy) in a given time
5. more product forms in a given time

limiting factor

Question 8

Key Summary: Why measure the initial rate of reaction?

3 points

Answer 8

1. There needs to be enough substrate molecules to saturate the enzyme to ensure that substrate is not a limiting factor.
2. Fastest rate is at the start (initial rate) then decreases.
3. As reaction proceeds substrate concentration decreases as substrate gets used up by enzyme in the reaction.

Question 9

Key Summary: Why does increasing substrate concentration increase the rate of reaction?
(4 steps)

Answer 9

1. as the substrate concentration increases the rate of reaction increases
2. as more substrate molecules are present {they collide with the enzyme more frequently / more successful collisions} , more enzyme-substrate complexes form, so more product forms in a given time
3. eventually a maximum rate is reached - all the enzymes are involved in enzyme-substrate complexes (all active sites are {saturated with substrate/occupied})
4. if the substrate concentration carries on increasing, there is no further increase in rate of reaction

Question 10

Increasing substrate concentration increases the number of ________ __________

This means that more enzymes can convert substrate to product at the same ____ (assuming successful collisions) so product is made ______ (reaction rate increases)

___________ _________ limits rate.

Answer 10

substrate molecules

time

faster

Substrate concentration

Question 11

Eventually a point will be reached where further increases in substrate concentration will not lead to increased rate of reaction as all the enzyme active sites are in use.

__________ ___________ limits rate

Answer 11

Enzyme concentration

Question 12

At {0 degrees C /low temperature} enzymes are ______ – they lack kinetic energy so rate is slow

As temperature increases (0 - 37 degrees C), the kinetic energy, of the enzyme and substrate increase, so {they collide more often/more successful collisions}, increasing the ____

Answer 12

inactive

rate

Question 13

At temperatures above the optimum the enzyme _____ _____ become ________ and change ______, so substrate cannot fit, _______ ________ _________ cannot form, so _________ cannot form.

Answer 13

active sites

denatured

shape

enzyme substrate complexes

product

Question 14

Explain denaturation (in enzymes)
(5 steps)

Answer 14

1. increased temperature causes BONDS TO BREAK which hold together the enzyme’s tertiary structure
2. the SHAPE OF THE ENZYME changes
3. the SHAPE OF THE ACTIVE SITE changes (is denatured)
4. the SUBSTRATE WILL NOT FIT IN THE ACTIVE SITE, and no enzyme substrate complex is formed
5. the reaction rate decreases