| Date | May 2017 | Marks available | 2 | Reference code | 17M.3.hl.TZ1.15 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Outline | Question number | 15 | Adapted from | N/A |
Question
Analysis of amino acid and protein concentration is a key area of biological research.
The titration curve of aqueous glycine zwitterions with aqueous sodium hydroxide is shown from pH 6.0 to 13.0. Refer to section 33 of the data booklet.
Deduce the pH range in which glycine is an effective buffer in basic solution.
Enzymes are biological catalysts.
The data shows the effect of substrate concentration, [S], on the rate, v, of an enzyme-catalysed reaction.
Determine the value of the Michaelis constant (Km) from the data. A graph is not required.
Outline the action of a non-competitive inhibitor on the enzyme-catalysed reaction.
The sequence of nitrogenous bases in DNA determines hereditary characteristics.
Calculate the mole percentages of cytosine, guanine and thymine in a double helical DNA structure if it contains 17% adenine by mole.
Markscheme
«pH range» 8.6–10.6
Accept any value between 8.2 and 11.0.
[1 mark]
«Km =» 0.67 «mmol dm–3»
Do not penalize if a graph is drawn to determine the value.
[1 mark]
does not compete for active site
OR
binds to allosteric site/away from «enzyme» active site
OR
alters shape of enzyme
reduces rate/Vmax
[2 marks]
«% cytosine + % guanine = 100% – 17% – 17% = 66%»
Cytosine: 33 «%» AND Guanine: 33 «%»
Thymine: 17 «%»
[2 marks]
