A-LevelBiologyEnzymes9700/22 · Feb/Mar 2019 · Q210 Marks

In mammalian red blood cells, carbonic anhydrase has an important role in the transport of carbon dioxide. Carbonic anhydrase is an enzyme.

(a)Outline the features of an enzyme.[4]
(b)Complete Fig. 2.1 to show the reversible reaction involving carbonic anhydrase that takes place within red blood cells. [Figure 2.1] body tissues lungs[2]
(c)A ribbon structure of a molecule of carbonic anhydrase is shown in Fig. 2.2. The zinc ion is associated with the active site of the enzyme and is essential for the enzyme to function. [Figure 2.2] The molecule of carbonic anhydrase has primary, secondary and tertiary structure. Explain the extent to which Fig. 2.2 shows the primary, secondary and tertiary structure of carbonic anhydrase.[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2019). The mark or mark type is shown in brackets.

[max 4] any four from:
1 globular protein ;
A spherical / ball-shaped
I circular
2 acts as a catalyst ;
3, 4 further detail ; ;
e.g. increases the rate of a reaction (cf. to no enzyme)
A speeds up a reaction / makes the reaction go faster
does not get used up (in the reaction)
I does not take part in the reaction
A can be re-used
A is not changed (by the reaction)
does not alter the (chemical) equilibrium (between reactants and products)
5 lowers the, activation energy / energy needed for substrate to reach transition state;
6 detail;
e.g. holds substrate to place strain on bond (for bond to break)
holds substrates, in position / close, for bonds to form
facilitates transfer of, electrons / protons
7 effective in tiny quantities / AW ;
8 shows specificity / active site shape complementary to substrate / forms enzyme-substrate complex/lock and key or induced fit mechanism of action;
9 AVP;
e.g. may need, cofactor/ coenzyme / prosthetic group, to function
each has an optimum, temperature / pH
[1] carbon dioxide / CO2
[1] water / H2O
[1] carbonic acid / H2CO3;
one mark for each side of the equation
allow one mark only if, wrong way round / carbonic acid shown as proceeding to dissociate
[max 4] any four from:
primary:
sequence of amino acids not shown;
A cannot see primary structure of amino acids
secondary:
alpha/α, -helices shown;
beta / ẞ, -pleated sheets shown;
(areas of) random arrangement shown;
tertiary:
folding / coiling, (of polypeptide chain) shown / ref. to 3-D configuration;
globular shape shown ;
interactions between, R-groups / side-chains, (of amino acids) not shown ;
ref. to any two bond types not shown ;
e.g. H bonds / disulfide bridges / ionic bonds / hydrophobic interactions
folding allows presence of zinc / AW ;