TOPIC 8 MARK SCHEME SHIT

Question 1

Suggest why plasmids are inserted into the eggs of an organism rather than the organism itself (2)

Answer 1

1. Gene gets into all/most of cells of organism
2. So gets into cells that carry out function (eg. make silk)

Question 2

Explain why use same restriction enzymes on each DNA sample (2)

Answer 2

1. Cut (DNA) at same (base) sequence
2. (So) get (fragments with gene) R/required gene

Question 3

Explain why primer A3 and primer A4 only bind to specific DNA fragments (2)

Answer 3

1. They have a specific base sequence
2. That is complementary (to allele r or R)

Question 4

Biologists compared the mitochondrial DNA of the different subspecies of giraffe. They used the results from comparing this DNA to conclude that six of the nine subspecies are separate species.
Suggest how they came to this conclusion. (2)

Answer 4

1. (Compare DNA) base sequence/base pairing
2. Different in six (species)/different in different species/similar in three (subspecies)/similar in same species/subspecies

Question 5

Define epigenetics (2)

Answer 5

1. Heritable changes in gene function
2. Without changes to the base sequence of DNA

Question 6

Oestrogen, methyl groups & acetyl groups: which bind to DNA and which bind to proteins?

Answer 6

Oestrogen: protein
Methyl groups: DNA
Acetyl groups: protein

Question 7

Explain how a mutation of a tumour suppressor gene can result in the formation of a tumour (2)

Answer 7

1. gene inactivated/not able to control/slow down cell division
2. Rate of cell division too fast/out of control

Question 8

Explain how a mutation can lead to the production of a non-functional enzyme (6)

Answer 8

1. Change/mutation in base/nucleotide sequence (of DNA/gene)
2. Change in amino acid sequence/primary structure
3. Change in hydrogen/ionic/disulphide bonds
4. Change in TERTIARY structure/shape
5. Change in ACTIVE SITE
6. Substrate not complementary to enzyme/no E-S complexes form

Question 9

Explain why the DNA probe used was for an exon in target DNA and not an intron (3)

Answer 9

1. Introns not translated/not in mRNA
2. Mutations of these exons affect amino acid sequences/change tertiary structure of protein
3. So important to know if person’s exons affected, rather than any other part of DNA/introns

Question 10

Explain shape of PCR curve (number of PCR cycles on x axis, intensity of green light on y axis) (2)

Answer 10

1. DNA doubles each PCR cycle
2. So light doubles/curve steepens more and more each cycle/curve goes up exponentially

Question 11

Explain why the same restriction endonucleases were used on each DNA sample (2)

Answer 11

1. Cut DNA at same base sequence
2. So get fragments with required gene