unit 1 DNA structure and replication

Question 1

Describe DNA replication (6)

Answer 1

1.DNA helicase breaks hydrogen bonds;
2. Both strands act as templates;
3. (Free DNA) nucleotides line up in complementary pairs/Adenine-Thymine and Guanine-Cytosine;
4. DNA polymerase joins nucleotides (of new strand); Reject forms hydrogen bonds/joins bases
5. Forming phosphodiester bonds;
6. Each new DNA molecule consists of one old/original/template strand and one new strand;

Question 2

Describe the structure of DNA (5)

Answer 2

1. Polymer of nucleotides; Accept ‘Polynucleotide’ Accept for ‘phosphate’. phosphoric acid
2. Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base;
3. Phosphodiester bonds (between nucleotides);
4. Double helix/2 strands held by hydrogen bonds;
5. (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine;

Question 3

Describe and explain how the structure of DNA

allows accurate replication (4)

Answer 3

1. two strands therefore semi-conservative replication (possible)
2. base pairing / hydrogen bonds holds strands together
3. hydrogen bonds weak / easily broken, allow strands to separate;
4. bases (sequence) (exposed so) act as template / can be copied;
5. A with T, C with G / complementary copy;
6. DNA one parent and one new strand;

Question 4

Describe how a phosphodiester bond is

formed between two nucleotides in a DNA

molecule. (3)

Answer 4

1. condensation reaction/loss of water 2. (between) phosphate and deoxyribose
2. (catalysed by) DNA Polymerase