Enzymes And Proteins

Question 1

Cow’s milk contains the sugar lactose. Many cats are unable to digest cow’s milk because they are lactose intolerant.
Attaching lactase to the beads is a more efficient use of lactase than adding the lactase directly to cow’s milk.
Suggest three reasons why it is more efficient to attach lactase to the beads.

Answer 1

1. Lactase beads can be reused
2. No need to remove milk
3. Avoid end product inhibition

Question 2

What do these data (data including standard deviation bars) suggest about the damage caused to human cells by the toxin and by the enzyme that neutralises acid?
Explain your answer.

Answer 2

1. More cell damage when both products present (point out the obvious)
2. Some damage when either one or other product present (point out the obvious part 2)
3. No standard deviation overlap between A & B with C making difference between them real (interpret validity of conclusion by looking at representation of data)
4. Standard deviation overlap between B & C with A so no real difference (interpret validity of conclusion by looking at representation of data)

Question 3

How would an antidote to cyanide work?

Answer 3

Stops cyanide binding to enzyme

Question 4

How are trials grouped?

Answer 4

Same test object

Question 5

Compare decrease in respiration rates across two objects in the same group

Answer 5

1. Greater effect of X on…
2. Calculate mean decrease
   (3 mark question: first would be for stating fact given in question)

Question 6

Why do DNA strands point in opposite directions?

Answer 6

1. DNA has antiparallel strands
2. Shape of nucleotides differs
3. Enzymes have specific active site shapes
4. Only substrates complementary to them can bind with them

Question 7

How does ethanol prevent oxalic acid formation?

Answer 7

Ethanol has a similar shape to substrate

So behaves as a competitive inhibitor

Question 8

GRAPH Q: Y axis— RoR and X axis— Substrate conc.

Describe what the graph shows about the effect of substrate concentration on the rate of this enzyme controlled reaction

Answer 8

Increase which then plateaus

At 27 degrees

Question 9

GRAPH Q: Y axis— RoR and X axis— Substrate conc.

What limits initial RoR?

Answer 9

Substrate concentration

Proportional rate of increase between RoR and sub concentration

Question 10

Methotrexate is a drug user in the treatment of cancer. It is a competitive inhibitor and affects the enzyme folate redux tase. Explain how the drug lowers the RoR controlled by folate reductase

Answer 10

Methotrexate has similar shape to substrate

So less ES complexes can form

Question 11

GRAPH Q: Y axis— pH and X axis— time
Two curves Y and Z which finish at same point but both decline, with Y taking less time to.
Mean radius of triglyceride droplets formed with curve Y is half curve Z

Describe and explain difference between two curves using this information

Answer 11

Smaller droplets = greater SA:V ratio

More surface for lipase= faster digestion of triglycerides

So in curve Y, with fatty acids being produced quicker, pH declines quicker due to increase in presence of bile salts which are responsible for emulsifying fats

Question 12

Scientists are trying to find a way to give an enzyme to people with a disease— why can’t they give it to them as a tablet?

Answer 12

Enzymes are proteins

Will denature

Question 13

Many substances causing food stains are large, insoluble proteins. Suggest how a biological washing powder removes this type of stain

Answer 13

Hydrolysis reaction

Then washed away (soluble)

Question 14

Suggest two limitations to scientific experiments in which two objects are being compared

Answer 14

Only situations in which objects work were examined

Only one set of results

Question 15

Biological washing powders often contain a number of different enzymes. This enables them to remove a wider range of stains from clothes. Explain why a number of enzymes are required to remove a wider range of stains

Answer 15

Enzymes are specific

Stains are specific

Enzymes need to have active site specific to substrate (the stains) to form ES complexes with them so multiple active sites (thus enzymes) necessary

Question 16

Describe the induced fit model of enzyme action

Answer 16

Initially active site not complementary to substrate

So enzyme active site changes shape and ES complex can form

Placing strain on substrate bonds and lowering Ea

Question 17

Describe effect of high concentration of lipase solution on rate of pH decrease

Answer 17

Faster fall in pH AND levels off at same point

Since more enzyme = more ES complexes forming

But same volume of fatty acids will be produced

Question 18

GRAPH Q: Explain the lack of protease enzyme activity with an increase in time at high temperatures (50 and 60 degrees)

Answer 18

At both temps, enzyme denatured

Faster denaturalise at 60 degrees than 50 degrees due to more KE at 60

Which breaks hydrogen bonds in A.S.

Changing its shape and stopping its ability to form ES complexes

Question 19

Some processes are secreted as extra cellular enzymes by bacteria. Suggest one advantage to a bacterium of secreting an extra cellular protease in its natural environment

Answer 19

Digest proteins

Absorb A.A.s for growth

Question 20

Describe the action of membrane-bound dipeptidases and explain their importance

Answer 20

Hydrolyse peptide bonds

To release A.A.s which can cross cell membranes