Proteins exam ques

Question 1

The scientists investigated the effect of concentration of inorganic
phosphate (Pi) on ATP synthase activity.
After 2 minutes, they stopped each reaction and then measured the
concentration of ATP.
The figure below shows the scientists’ results

Suggest and explain a procedure the scientists could have used to stop
each reaction.
(2marks)

Answer 1

Boil
Denatures the enzyme
OR
Put in ice/fridge/freezer;
Lower kinetic energy so no enzyme-substrate complexes form;

Question 2

Part b to the first q
Explain the change in ATP concentration with increasing inorganic
phosphate concentration.

Answer 2

(With) increasing Pi concentration, more enzymesubstrate complexes are formed;
2. At or above 40 (mmol dm-3) all active sites occupied

Question 3

A student investigated starch hydrolysis using the enzyme amylase.
During the procedure, the student:
* treated the starch to make it soluble
* prepared 10 cm3 of different concentrations (mg dm−3
) of starch
solution
* added an identical concentration of amylase to each starch solution
* measured the time in minutes to completely hydrolyse starch.
He repeated the procedure and calculated the mean time to completely
hydrolyse starch in each concentration of starch solution.
Draw a table the student could use to record all of his results

Answer 3

1. Starch (solution) in first column;
2. Headings for starch concentration
   and time for (starch)
   hydrolysis
   with mg dm-3 and
   minutes

Question 4

When bread becomes stale, the structure of some of the starch is
changed. This changed starch is called retrograded starch.
Scientists have suggested retrograded starch is a competitive inhibitor of
amylase in the small intestine.
Assuming the scientists are correct, suggest how eating stale bread could
help to reduce weight gain.

Answer 4

Less hydrolysis of starch;
2. (To) maltose;
3. (So) less absorption (of glucose)

Question 5

Describe how the structure of a protein depends on the amino acids it
contains. (5 marks)

Answer 5

1. Structure is determined by (relative) position of amino acid/R
   group/interactions
2. Primary structure is sequence/order of amino acids;
3. Secondary structure formed by hydrogen bonding (between amino
   acids);
4. Tertiary structure formed by interactions (between R groups);
5. Creates active site in enzymes
6. Quaternary structure contains >1 polypeptide chain
   OR
   Quaternary struucture formed by interactions/bonds between
   polypeptides;

Question 6

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

Answer 6

1. Lowers activation energy;
2. Induced fit causes active site (of enzyme) to change shape;
3. (So) enzyme-substrate complex causes bonds to form/break;

Question 7

Describe how a non-competitive inhibitor can reduce the rate of an
enzyme-controlled reaction.

Answer 7

) 1. Attaches to the enzyme at a site other than the active site;
Accept ‘attaches to allosteric/inhibitor site’
2. Changes (shape of) the active site
OR
Changes tertiary structure (of enzyme);
3. (So active site and substrate) n

Question 8

The secondary structure of a polypeptide is produced by bonds between
amino acids.
Describe how.

Answer 8

Hydrogen bonds;
Between NH (group of one amino acid) and C=O (group);
OR
Forming β pleated sheets / α helix;

Question 9

Two proteins have the same number and type of amino acids but different
tertiary structures.
Explain why.

Answer 9

Different sequence of amino acids
Forms ionic / hydrogen / disulfide bonds in different places;

Question 10

Formation of an enzyme-substrate complex increases the rate of reaction.
Explain how.

Answer 10

Reduces activation energy;

2. Due to bending bonds