DNA structure and replicationEdexcel A-Level Biology B: Flashcards

What these 12 flashcards ask

What are the three parts of a DNA nucleotide?
Which bases are purines?
Which bases are pyrimidines?
Which bond joins nucleotides in one strand?
What holds the two DNA strands together?
How many hydrogen bonds are in an A–T pair and a G–C pair?
What is a gene?
What does semi-conservative mean?
What is the role of DNA helicase?
What is the role of DNA polymerase?
What is the role of DNA ligase?
Why is replication accurate?

Exam questions on DNA structure and replication

A scientist extracts double-stranded DNA from a bacterium and analyses its base composition. She finds that 28% of the bases are adenine.
Explain why the percentage of adenine in double-stranded DNA is equal to the percentage of thymine.2 marks
Bacteria were grown for many generations in a medium containing the heavy isotope ¹⁵N, so all the nitrogen in their DNA was ¹⁵N. They were then transferred to a medium containing only the lighter isotope ¹⁴N and allowed to divide. DNA from each generation was extracted and separated by density to show whether each molecule was heavy (both strands ¹⁵N), intermediate (one strand ¹⁵N and one ¹⁴N) or light (both strands ¹⁴N).
Explain why the result after one division in the ¹⁴N medium supports semi-conservative replication and not conservative replication.2 marks
A cell is preparing to divide. Before division, every DNA molecule in the nucleus must be copied so that each daughter cell receives a complete set of genetic information.
Describe the roles of DNA helicase, DNA polymerase and DNA ligase in DNA replication.3 marks

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).