1.8- FACTORS AFFECTING ENZYME ACTION

Question 1

For an enzyme to work it must…? (2)

Answer 1

come into physical contact with its substrate

have an active site which fits the substrate

Question 2

To measure the progress of an enzyme-catalysed reaction what do we measure?

Answer 2

its time-course

Question 3

What is the time-course?

Answer 3

how long it takes for a particular event to run its course

Question 4

What two changes are most frequently measured?

Answer 4

formation of products

disappearance of substrate

Question 5

What enzyme-catalysed reaction graphs explain?

Answer 5

at first there’s a lot of substrate but no product
very easy for substrate molecules to come into contact with empty active site
all enzyme active sites filled at any given moment and substrate rapidly broken down into its products
amount of substrate decrease as it’s broken down, resulting in increase in amount of product
becomes more difficult for substrate molecules to come into contact with enzyme molecules as there are fewer substrate molecules and product molecules ‘get in the way’ of substrate molecules and prevent them reaching an active site
so takes longer for substrate molecules to be broken down by enzyme and so its rate of disappearance slows and consequently rate of formation of products slows down
rate of reaction continues to slow until there’s so little substrate that any further decrease in its concentration cannot be measures

Question 6

What does a rise in temperature increase?

Answer 6

the kinetic energy of molecules

Question 7

What happens as the kinetic energy of molecules are increased?

Answer 7

molecules move around more rapidly and collide with each other more often

Question 8

What happens in an enzyme-catalysed reaction when there’s a rise in temp?

Answer 8

enzyme and substrate molecules come together more often in a given time

more effective collisions resulting in more enzyme-substrate complexes being formed and so ROR increases

Question 9

What does the rise in temp also begin to cause?

Answer 9

hydrogen and other bonds in enzyme molecule to break

Question 10

What happens when the hydrogen and other bonds break in the enzyme?

Answer 10

enzyme, including the active site, changing shape

Question 11

what starts to happen when the enzyme changes shape?

Answer 11

substrate fits less easily into this changed active site, slowing ROR

Question 12

For many human enzymes what is the temperature that enzymes begin to change shape?

Answer 12

45°c

Question 13

At around what temperature does the enzyme stop working altogether?

Answer 13

60°c

Question 14

Why does the enzyme stop working altogether?

Answer 14

enzyme is so disrupted- denatured

Question 15

What is the definition of denaturation?

Answer 15

permanent change and, once it has occurred, enzyme does not function again

Question 16

Is the optimum temp the same for all enzymes?

Answer 16

no differs from enzyme to enzyme

Question 17

What is the approximate optimum temp for most enzymes in the human body?

Answer 17

40°c

Question 18

What temperature has our body evolved to be?

Answer 18

37°c

Question 19

Why may have our bodies evolved to be 37°c? (3)

Answer 19

although higher body temp would increase metabolic rate slightly, offset by additional energy (food) needed to maintain higher temp

other proteins may be denatured at higher temps

any further increase during illness might denature enzymes

Question 20

What is the normal body temp of many birds?

Answer 20

40°c

Question 21

Why do many birds have a normal body temp of 40°c?

Answer 21

they have a high metabolic rate for high energy requirement of flight

Question 22

What is the pH of a solution?

Answer 22

measure of its hydrogen ion concentration

Question 23

What is the formula for the pH of a solution?

Answer 23

pH = -log(small 10) (H^+)

Question 24

What does an increase or decrease in pH do?

Answer 24

reduce rate of enzyme action

Question 25

What happens when the change in pH is more extreme?

Answer 25

enzyme become denatured

Question 26

How does pH affect how an enzyme work? (2)

Answer 26

alters the charges on amino acids that make up active site- so substrate can no longer become attached to active site- enzyme-substrate complex cannot be formed

depending on how significant change in pH is, may cause bonds maintaining enzyme’s tertiary structure to break- active site changes shape

Question 27

What is the arrangement of the active site partly determined by?

Answer 27

hydrogen and ionic bonds between -NH2 and -COOH group of polypeptides that make up enzyme

Question 28

What does the H+ ions do to this bonding?

Answer 28

affect the bonding, causing active site to change shape

Question 29

Are the fluctuations in pH inside an organism usually large or small?

Answer 29

usually small

Question 30

As the fluctuation in pH in an organism in usually small, what does this mean?

Answer 30

they’re far more likely to reduce enzyme’s activity than to denature it

Question 31

How are enzymes not used up in a reaction?

Answer 31

once an active site acted on its substrate it’s free to repeat procedure on another substrate molecule

Question 32

What must there be so that an increase in amount of enzyme leads to proportionate increase in ROR?

Answer 32

excess of substrate

Question 33

What will happen if the substrate is limiting and increase in enzyme concentration?

Answer 33

no effect on ROR

Question 34

Why is there no effect on ROR when the substrate is limiting an d the enzyme conc. is increased?

Answer 34

available substrate already being used as rapidly as it can be by existing enzyme molecules

Question 35

What happens to ROR when conc. of enzyme fixed and substrate conc. slowly increased?

Answer 35

ROR increases in proportion to conc. of substrate

Question 36

Why does ROR increase when conc. of enzyme fixed and substrate conc. slowly increased?

Answer 36

because , at low substrate concentrations, enzyme molecules have only limited number of substrate molecules to collide with, and so active sites of enzymes not working to full capacity.

Question 37

What happens when more substrate is added?

Answer 37

active sites gradually become filled, until point where all of them working as fast as they can
ROR at its max

Question 38

What happens when EVEN MORE substrate added?

Answer 38

no effect on ROR