6.1: Cellular control

Question 1

Name the enzyme that can be used to convert mRNA to single-stranded DNA.

Answer 1

reverse transcriptase

Question 2

In a colony of bees, about 5% of the workers are more adventurous than other workers. These bees are known as scout bees. They actively seek out new food sources and, if necessary, new nest sites.
Researchers investigated how gene expression differed in the brains of the scout bees
compared to the normal worker bees.
• The researchers extracted mRNA from the brain cells of normal worker bees.
• This mRNA was used to produce lengths of single-stranded DNA, which were then attached to a fluorescent dye.
• These lengths of single-stranded DNA were used as gene probes fixed onto a device known as a ‘microarray DNA chip’.
• mRNA extracted from the brain cells of
scout bees would only bind to the gene probes that matched it, causing these probes to fluoresce.
• The locations of the brightest fluorescent spots on the DNA chip revealed which genes were most active.
Explain how the locations of the fluorescent spots on the DNA chip reveal which genes
are most active.

Answer 2

1 mRNA binds to, (gene) probes/ cDNA/ ssDNA, by complementary base pairing;
2 the MORE active the gene the MORE mRNA produced;
3 during transcription;
4 MORE fluorescence indicates MORE mRNA (bound);

Question 3

The researchers found many differences in gene activity in the scout bees compared to the normal worker bees. One of these differences in activity was in a gene used to make the neurotransmitter, dopamine.
In a follow-up experiment, scout bees became less adventurous if dopamine signalling was prevented.
Use your knowledge of the DRD4 dopamine receptor in humans to comment on the findings of this research into scout bee behaviour.
(3mks) [f215-01 q2diii]

Answer 3

1 dopamine linked to, ADHD / addiction / risk-taking / 1 adventurous behaviour / hyperactivity / erratic behaviour (in humans);
2 common mechanism in bees and humans (for adventurous behaviour); [e.g. BOTH have, DRD4 /dopamine receptors; e.g. dopamine has the same effect in BOTH]
3 as they are different organisms the mechanisms may not be comparable (even though apparently similar);
4 e.g. other genes also involved in, bee / human, behaviour
[Note: ‘both have dopamine receptors which are linked to adventurous behaviour’ = 1 mk; ‘both have dopamine receptors and dopamine is linked to adventurous behaviour’ = 2 mks]

Question 4

What feature of the DNA molecule is changed as a result of mutation?

Answer 4

sequence / order, of bases / nucleotides; [base pairs]

IGNORE amino acid sequence

Question 5

Discuss the possible effects that mutation can have on the structure and function of a protein. (3mks)

Answer 5

1 different, primary / secondary / tertiary, structure; [different SEQUENCE or ORDER of amino acids/ different 3D folding or 3D shape]
2 (protein ) shorter due to, deletion / stop codon OR
longer due to, insertion / duplication;
3 protein) unchanged due to, silent mutation / non-coding DNA altered; [for ‘silent’ CREDIT ‘neutral’ or a description of more than one triplet coding for one amino acid]
4 (function is) lost / worse / better; [idea that change is harmful]