3.4.1 DNA, Genes and Chromosomes

Question 1

DNA – Structure related to function (7)

Answer 1

1. stable due to numerous hydrogen bonds so can be passed on from generation to generation;
2. weak hydrogen bonds between strands are easily broken for DNA replication or protein synthesis;
3. large so can carry a lot of genetic information;
4. base pairs are contained within the helix and held in place by the strong sugar-phosphate
   backbone;
5. complementary base pairs allow the synthesis of an identical daughter molecule;
6. 2 strands so both can act as templates;
7. helical shape means that it can be coiled so compact for storage

Question 2

DNA – Degenerate and Non-overlapping (2)

Answer 2

1. Degenerate: more than one (base) triplet for each amino acid;
2. Non-overlapping: each base is part of only one triplet;

Question 3

DNA – Comparing DNA and mRNA (6)

Answer 3

1. DNA double stranded/double helix and mRNA single-stranded;
2. DNA (very) long and RNA short;
3. Thymine/T in DNA and uracil/U in RNA;
4. Deoxyribose in DNA and ribose in RNA;
5. DNA has base pairing and mRNA doesn’t/ DNA has hydrogen bonding and mRNA doesn’t;
6. DNA has introns/non-coding sequences and mRNA doesn’t;

Question 4

Comparing mRNA and tRNA (3)

Answer 4

1. mRNA longer;
2. mRNA is a straight molecule but tRNA is a folded molecule/clover-leaf shaped molecule;
3. mRNA contains no hydrogen bonds but tRNA has hydrogen bonds;

Question 5

Which two molecules are ribosomes made from?
(2)

Answer 5

1. One of RNA/ribonucleic acid(s)/nucleotide(s)/nucleic acid(s)/rRNA/ribosomal RNA/ribosomal
   ribonucleic acid;
2. One of protein(s)/polypeptide(s)/amino acid(s)/ peptide(s)/ribosomal protein

Question 6

Define the term exon.

Answer 6

Base sequence coding for polypeptide/sequence of amino acids

Question 7

Name the proteins associated with DNA

Answer 7

Histone

Question 8

Differences between prokaryotic DNA and
Eukaryotic DNA (5)

Answer 8

(eukaryote v prokaryote
1. (Associated with) histones/proteins v no histones/proteins;
2. Linear v circular;
3. No plasmids v plasmids;
Do not credit if suggestion that prokaryotic DNA only exists as plasmids.
4. Introns v no introns;
5. Long(er) v short(er);

Question 9

Transcription – Describe transcription (7)

Answer 9

1. DNA strands separate by breaking hydrogen bonds;
2. (Only) one of the strands is used as a template (to make mRNA);
3. Complementary base pairing so A to U, T to A, C to G, G to C;
4. (RNA) nucleotides joined by RNA polymerase;
5. Forms phosphodiester bonds
6. Pre-mRNA formed;
7. Splicing/ introns removed to form mRNA