TT. Protein Sysnthesis and Meiosis test- lost marks

Question 1

What is the role of RNA polymerase in transcription? (1)

Answer 1

(i) join / attach nucleotides, to form a strand / along backbone / phosphodiester

bonds;
(reject reference to H bonds, complementary base pairing)

Question 2

Explain how each mutation may affect the polypeptide for which this section of DNA is part of the code? (4)

Answer 2

(mutation 1) (S)
no change(to sequence of amino acids);
codon for alanine / degenerate codon / same amino acid coded for

(mutation 2)
(change in sequence) x replaced by y / codon for y ;
folding / shape / tertiary structure / position of bonds may change;
(reject peptide bonds)

Question 3

Explain why some cells contain a mass of DNA between 1 and 2 units (1)

Answer 3

(DNA) replication taking place/not finished;

Question 4

MRNA is used during translation to form polypeptides

Describe how MRNA in made in the Nucleus (6)

Answer 4

1. Helicase;
2. Breaks hydrogen bonds;
3. Only one DNA strand acts as template;
4. RNA nucleotides attracted to exposed bases;
5. (Attraction) according to base pairing rule;
6. RNA polymerase joins (RNA) nucleotides together;
7. Pre-mRNA spliced to remove introns.

Question 5

Give 2 factors which might increase the frequency at which a mutation in DNA occurs

Answer 5

(c) high energy radiation / X rays / ultraviolet light / gamma rays;
high energy particles / alpha particles / beta particles;
named chemical mutagens e.g. benzene / caffeine / pesticide /
mustard gas / tobacco tar / free radicals;
(two named examples of any of the above = 2 marks)
length of time of exposure (to a mutagen);
dosage (of mutagen);

Question 6

Determine the precise nature of the two single base mutations in the DNA

Answer 6

addition and deletion (of bases / nucleotides);
thymine added;
adenine deleted;
(addition of thymine and deletion of adenine = 3 marks)
(allow addition of adenine (RNA) and deletion of uracil (RNA)
= 2 marks)

Question 7

Describe what happens to chromosome in meiosis (6)

Answer 7

1. Chromosomes shorten / thicken / condense;
2. Chromosomes associate in homologous / (described) pairs /
   formation of bivalents / tetrads;
3. Crossing-over / chiasma formation;
4. Join to spindle (fibres) / moved by spindle;(*)
5. (At) equator / middle of cell;(*)
6. (join via) centromere / kinetochore;(*)
7. (Homologous) chromosomes move to opposite poles /
   chromosomes separate / move apart; (ALLOW ‘are pulled apart’)

Question 8

The number of amino acids coded for could be fewer than your answer to part a1

Answer 8

Introns / non-coding DNA / junk DNA;
Start / stop code / triplet;
Neutral: Repeats.
Accept: ‘Introns and exons present’.
Reject: ‘Due to exons’.

Question 9

Explain how a change in the DNA base sequence for a protein may result in a change in the structure of the protein (3)

Answer 9

Change in amino acid / s / primary structure;
Change in hydrogen / ionic / disulfide bonds;
Alters tertiary structure;

Reject: ‘Different amino acid is formed’ – negates first
marking point.
Neutral: Reference to active site.

Question 10

Which type of gene mutation produced the cystic fibrosis allele
explain your answer

Answer 10

deletion;
(deletion) of three bases;
because substitution / addition would change amino acid(s);