IB BIO TOPIC 3.4 : DNA REPLICATION

Question 1

Explain why DNA replication is semi-conservative

Answer 1

• semi-conservative = when the double helix replicates, each of the two daughter molecules will have one old strand, derived from the parent molecule
• and one newly made strand, from free nucleotides in solution, using the parent strands as templates, and base pairing rules (A=T, G≡C) to match newly synthesized strands complementary to parental strands

Question 2

Explain the unwinding double helix

Answer 2

• helicase controls unwinding of coiled DNA

Question 3

Explain the separation of strands by helicase

Answer 3

• helicase separates complementary strands of DNA, producing a replication fork
• single strand binding proteins keep the two strands of DNA separate

Question 4

Explain the formation of complementary strands by DNA polymerase

Answer 4

• DNA polymerase uses a single parent strand of DNA as a template, adding free nucleotides from solution to the parent/template strand according to the complementary base pairing rules (A=T, G≡C)

Question 5

Explain: significance of complementary base pairing in conservation of base sequence (PART 1)

Answer 5

• DNA polymerase uses a single parent strand of DNA as a template, adding free nucleotides from solution to the parent/template strand according to the complementary base pairing rules (A=T, G≡C)
• the 2 parent strands in the double helix of DNA can be represented as A and A’
• when the 2 strands separate, each acts as a template for DNA synthesis

Question 6

Explain: significance of complementary base pairing in conservation of base sequence (PART 2)

Answer 6

• using strand A as a template, DNA polymerase, using complementary base pairing rules, adds a newly synthesised A’ strand, thus producing A - A’ double-stranded DNA identical to the parent DNA
• using strand A’ as a template, DNA polymerase, using complementary base pairing rules, adds a newly synthesised A strand, thus producing A - A’ double-stranded DNA identical to the parent DNA
• therefore, 2 DNA molecules, each A - A’ are produced