Question 19M.3.sl.TZ2.6a(ii)
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.sl.TZ2.6a(ii) |
| Level | sl | Paper | 3 | Time zone | TZ2 |
| Command term | Compare and contrast | Question number | a(ii) | Adapted from | N/A |
Proteins have structural or enzyme functions.
Compare and contrast the bonding responsible for the two secondary structures.
One similarity:
One difference:
[2]
One similarity:
hydrogen bonding
OR
attractions between C=O and N–H [✔]
One difference:
α-helix has hydrogen bonds between amino acid residues that are closer than β-pleated sheet
OR
H-bonds in α-helix parallel to helix axis AND perpendicular to sheet in β-pleated sheet
OR
α-helix has one strand AND β-pleated sheet has two «or more» strands
OR
α-helix is more elastic «since H-bonds can be broken easily» AND β-pleated sheet is less elastic «since H-bonds are difficult to break» [✔]
Note: Accept a diagram which shows hydrogen bonding between O of C=O and H of NH groups for M1.
Accept “between carbonyl/amido/amide/carboxamide” but not “between amino/amine” for M1.
The similarity in bonding between the 2 types of secondary structures was answered well but the difference was not. Most students were not descriptive enough to receive the second mark or simply repeated the idea of proteins containing an alpha-helix and beta-pleated sheets rather than describing something different about them.
