topic 4 EXAM QUESTIONS

Question 1

Describe how a gene is a code for the production of a polypeptide. Do not
include information about transcription or translation in your answer. (3 marks)

Answer 1

1. (Because) base/nucleotide sequence;
2. (In) triplet(s);
3. (Determines) order/sequence of amino acid sequence/primary
   structure (in polypeptide);

Question 2

Describe how a phosphodiester bond is formed between two nucleotides
within a DNA molecule. (2)

Answer 2

1. Condensation (reaction)/loss of water;
2. (Between) phosphate and deoxyribose;
3. (Catalysed by) DNA polymerase;

Question 3

Define ‘non-coding base sequences’ and describe where the non-coding
multiple repeats are positioned in the genome.
(2)

Answer 3

DNA that does not code for protein/polypeptides
OR
DNA that does not code for (sequences of) amino acids
OR
DNA that does not code for tRNA/rRNA;
Accept the idea of not transcribed for ‘does not
code for’.
Do not credit ‘DNA that does not code for an amino
acid’.
Ignore reference to introns.
2. (Positioned) between genes;

Question 4

The nucleus and a chloroplast of a plant cell both contain DNA.
Give three ways in which the DNA in a chloroplast is different from DNA in
the nucleus. (3)

Answer 4

In chloroplasts
1. DNA shorter;
Accept smaller
2. Fewer genes;
3. DNA circular not linear;
Accept DNA in a loop not linear
Accept no chromosomes (in chloroplast) unlike nucleus
4. Not associated with protein/histones, unlike nuclear DNA;
5. Introns absent but present in nuclear DNA;

Question 5

Some DNA nucleotides have the organic base thymine, but RNA
nucleotides do not have thymine. RNA nucleotides have uracil instead of
thymine.
Give one other difference between the structure of a DNA nucleotide and
the structure of an RNA nucleotide. (1)

Answer 5

Deoxyribose in DNA and ribose in RNA;

Question 6

Compare and contrast the DNA in eukaryotic cells with the DNA in
prokaryotic cells. (5)

Answer 6

Comparisons
1. Nucleotide structure is identical;
Accept labelled diagram or description of nucleotide
as phosphate, deoxyribose and base
2. Nucleotides joined by phosphodiester bond;
OR
Deoxyribose joined to phosphate (in sugar, phosphate backbone);
3. DNA in mitochondria / chloroplasts same / similar (structure) to DNA
in prokaryotes;
Accept shorter than nuclear DNA/is circular not
linear/is not associated with protein/histones unlike
nuclear DNA;
Contrasts
4. Eukaryotic DNA is longer;
5. Eukaryotic DNA contain introns, prokaryotic DNA does not;
6. Eukaryotic DNA is linear, prokaryotic DNA is circular;
7. Eukaryotic DNA is associated with / bound to protein / histones,
prokaryotic DNA is not;