| Date | May 2009 | Marks available | 3 | Reference code | 09M.3.sl.TZ1.B1 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Describe | Question number | B1 | Adapted from | N/A |
Question
Myoglobin is a globular protein found in the muscle tissue and is formed from 2-amino acids.
Describe the characteristic properties of 2-amino acids.
State the name of the bond or interaction that is responsible for linking the amino acids together in the primary structure.
State the name of the bond or interaction that is responsible for the secondary structure.
State two of the bonds or interactions responsible for the 3D shape of myoglobin.
Markscheme
isoelectric point;
zwitterion/forms neutral ion when \({{\text{H}}^ + }\) transfers from COOH to \({\text{N}}{{\text{H}}_{\text{2}}}\);
buffer action/can accept \({{\text{H}}^ + }\) and OH–;
general formula \({\text{HOOCCRHN}}{{\text{H}}_{\text{2}}}\);
peptide/amide;
hydrogen bonds;
hydrogen bonds;
disulfide bridges/bonds;
ionic interactions/bonds;
van der Waals’ forces / hydrophobic interactions / London/dispersion forces / temporary induced dipoles;
Examiners report
Apart from the general formula in (a), many candidates had difficulty providing the characteristic properties of 2 – amino acids. The characteristic properties are clearly identified in the syllabus details.
Most candidates could name the correct bond types in part (b).
Most candidates could name the correct bond types in part (b).
Most candidates could name the correct bond types in part (b).
