| Date | November 2010 | Marks available | 3 | Reference code | 10N.3.SL.TZ0.9 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Outline | Question number | 9 | Adapted from | N/A |
Question
Outline the differences between these two proteins.
Markscheme
a. hemoglobin is a globular protein while keratin is a fibrous protein;
b. hemoglobin folds into rounded structures while keratin remains linear;
c. hemoglobin is a soluble protein while keratin is not;
d. hemoglobin consists of four peptides/subunits while keratin does not;
e. hemoglobin has prosthetic/heme groups while keratin does not;
f. hemoglobin functions as transport molecule while keratin is a structural molecule/part of hair/nails;
Examiners report
Many candidates received 2 or 3 marks for differentiating between the globular and fibrous proteins shown as well as knowing either the differences in solubility or function. Candidates did not mention that hemoglobin consists of four polypeptides whereas keratin does not or that hemoglobin has a prosthetic/heme group while keratin does not. Many were incorrectly stating that keratin has only a secondary structure and hemoglobin has a tertiary structure which is not an accurate statement. The diagram showed links (disulphide bonds) between two alpha-helices to form the tertiary structure of keratin. Both have secondary and tertiary structure but they are different and this was not made clear.
