(cid:44)(cid:1)(cid:1)(cid:1)(cid:1)(cid:9)(cid:1)(cid:1)(cid:1)(cid:1)(cid:1)(cid:1)(cid:1)(cid:7)(cid:44)
(c) LCA10 is a different form of LCA caused by a recessive mutation in the CEP290 gene.
This gene codes for the protein CEP290, which is involved in the correct functioning of
photoreceptor cells in the retina.
The mutation in CEP290 causes an error to be made when the primary transcript is spliced to
form messenger RNA (mRNA). The abnormal mRNA that is formed has an extra sequence of
RNA nucleotides, known as exon X, between exon 26 and exon 27. Exon X contains a STOP
codon.
Fig. 3.1 compares the effect of the mutation in CEP290 with the normal gene expression.
normal LCA10
exon intron exon section of DNA exon mutation exon
of CEP290
(a) DCPIP is an indicator and can be used to determine the rate of respiration of organisms such
as yeast.
(i) State the category of indicators to which DCPIP belongs.
..................................................................................................................................... [1]
(ii) Describe the colour change that occurs in DCPIP during experiments to determine the
rate of respiration.
..................................................................................................................................... [1]
(b) An investigation was carried out to determine the effect of temperature on the rate of
respiration of yeast.
• A suspension of yeast cells was added to a test‑tube containing glucose solution.
• A further four test‑tubes were set up in the same way.
• One test‑tube was placed in a water‑bath at 10 °C for 5 minutes.
• DCPIP was added to the test‑tube and the time taken for the DCPIP to change colour
was measured.
• The experiment was repeated using the other test‑tubes at 20° C, 30 °C, 40 °C and 50 °C.
The results are shown in Fig. 6.1.