Gene Expression

Question 1

Increased methylation of tumour supressor genes

Answer 1

Prevents transcription, protein not produced that prevents cell divison, no control of mitosis

Question 2

How less oestrogen is good

Answer 2

Less, it activates tfs in breast causing cell divison.

Question 3

Difference btwn tumour and cancer

Answer 3

Tumour= mass of dividing cells
Cancer= when cells from tumour spread

Question 4

The scientists wanted to know on which chromosome the gene with alleles R and r
was located. From the flies with genotype RR, they obtained cells that were in
mitosis and added a labelled DNA probe specific for allele R. They then looked at the cells under an optical microscope.
Explain why they used cells that were in mitosis

Answer 4

in mitosis, the chromosomes are visible, so you can see which chromosomes the dna probe is attached to

Question 5

explain how alterations to a tumour supressor gene could lead to the formation of a tumour

Answer 5

alteration doesnt only mean mutation
could also mean epistasis

hypermethylation will decrease the expression of tumour supressor genes, this will lead to uncontrollable cell division leading to tumours
mutations in the tsg could also result in the production of a non functional protein which would also lead to uncontrollable cell div leading to a tumour

Question 6

2 features of diff proteins that enable them to be separated by gel electrophoresis

Answer 6

diff lengths- not size
diff charges
diff r groups
mass
number of amino acids

Question 7

Oestrogen is a hormone that affects transcription. It forms a complex with a
receptor in the cytoplasm of target cells. Explain how an activated oestrogen
receptor affects the target cell.

Answer 7

Receptor / transcription factor) binds to a promoter which stimulates

RNApolymerase / enzyme X;
Transcribes gene / increase transcription;

Question 8

To make the DNA probe, the geneticist had to find the base sequence of the normal
gene. Once he had copies of the gene, what methods would he use to find the base
sequence of the gene?

Answer 8

Restriction mapping / described;
2. DNA / base sequencing (of fragments) / description / name of method;
eg sanger method

Question 9

for pcr what does it mean if the bands travel less

Answer 9

2. (As has) high(est) band / band that travelled a short(est) distance /
   (er) so has large(st) fragment / number of CAG repeats;

Question 10

The diagram only shows part of the gel. Suggest how the scientists found the
number of CAG repeats in the bands shown on the gel

Answer 10

Run fragments of known length / CAG repeats (at the same time);

Question 11

Two bands are usually seen for each person tested. Suggest why only one
band was seen for Person L.

Answer 11

Homozygous / (CAG) fragments are the same length / size / mas

Question 12

Scientists can use protein structure to investigate the evolutionary relationships
between different species. Explain why.

Answer 12

Closer the (amino acid) sequence the closer the relationship;
2. (Protein structure) related to (DNA) base / triplet sequence

Question 13

Comparing the base sequence of genes provides more evolutionary information
than comparing the structure of proteins. Explain why.

Answer 13

Reference to base triplets / triplet code / more bases than amino acids /
longer base sequence than amino acid sequence;
Different (base) triplets code for same amino acids
Degeneracy of triplet code = 2 marks
2. Introns / non-coding DNA / degeneracy of code / more than one code for
each amino acid;

Question 14

two features of stem cells

Answer 14

kepe dividing or replicating

undifferentiated

Question 15

how smth affecting dna could cause cancer

Answer 15

affects tsg
inactivates it
rate of cell div increased and not stopped

Question 16

) Explain how this mutation leads to the formation of non-functioning PAH

3 marking points

Answer 16

change in amino acid sequence or the primary structure
change in bonds within active site changes tertiary structure
substrate no longer complementary no escs form

Question 17

Describe how urea is removed from the blood.

Answer 17

Hydrostatic pressure
Causes ultrafiltration (Allow description of ultrafiltration) at Bowman’s capsule /
glomeruli / renal capsule;
Through basement membrane;
Enabled by small size urea molecule;