Nucleic Acids | OCR A-Level Biology B (Advancing Biology) (H422)

Nucleic Acids

71 questions
4 subtopics
Biology content, examined on all three papers
Component 01, Component 02 and Component 03

Nucleic Acids is examined in all three written papers — the specification states that Components 01, 02 and 03 can each assess content from any of the five modules, so nothing is confined to one paper.

It covers nucleotides, ADP and ATP, the structure of DNA and its extraction, DNA replication and the genetic code and RNA, transcription and translation.

Sample questions from Nucleic Acids

Answer each one closed book first, then open the answer.

Nucleotides, ADP and ATP

Which base occurs in DNA but not RNA, and which occurs in RNA but not DNA?

Show the answer
Thymine occurs only in DNA and uracil only in RNA.
Nucleotides, ADP and ATP

Write a word equation for the hydrolysis of ATP.

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ATP plus water gives ADP plus inorganic phosphate, with the release of energy.
The structure of DNA and its extraction

State Chargaff's rules.

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In the DNA of any species the amount of adenine equals the amount of thymine and the amount of cytosine equals the amount of guanine, while the ratio of adenine and thymine to cytosine and guanine differs between species.
The structure of DNA and its extraction

Outline how DNA can be extracted from plant tissue such as onion.

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The tissue is broken up in a mixture containing detergent, salt and protease, filtered to remove cell debris, and then ice-cold ethanol is layered gently on top of the filtrate, where the DNA precipitates as white strands at the boundary.
DNA replication and the genetic code

Name two features of replication that keep the error rate very low.

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The specificity of complementary base pairing, and the proofreading activity of DNA polymerase, which detects and removes an incorrectly paired nucleotide before continuing.
DNA replication and the genetic code

Calculate the number of different triplets possible with four bases, and explain why a code of two bases would be insufficient.

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There are 4³ = 64 possible triplets; a two-base code would give only 4² = 16 combinations, which is fewer than the twenty amino acids that must be specified.
RNA, transcription and translation

What is the role of RNA polymerase in transcription?

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RNA polymerase unwinds the DNA and breaks the hydrogen bonds between the strands, then joins the free RNA nucleotides that have paired with the template strand into a messenger RNA molecule by forming phosphodiester bonds.
RNA, transcription and translation

How does translation begin?

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The messenger RNA binds to the small subunit of a ribosome, which moves along until it reaches the start codon, and a transfer RNA with the complementary anticodon and its amino acid binds there.

The 4 subtopics

One subtopic is one session. Work down the list.

Subtopic	What it covers	Questions
Nucleotides, ADP and ATP	Recall questions on the components of a nucleotide, ribose and deoxyribose, purine and pyrimidine bases, phosphodiester bonds and the sugar–phosphate backbone, the structure of ATP and ADP, the hydrolysis of ATP, and why ATP is the universal energy currency.	17
The structure of DNA and its extraction	Recall questions on the antiparallel double helix, base pairing and hydrogen bonds, purines pairing with pyrimidines, Chargaff's rules and base percentage calculations, why DNA suits its role, and extracting DNA from onion with detergent, salt, protease and ice-cold ethanol.	18
DNA replication and the genetic code	Recall questions on semi-conservative replication, the roles of helicase and DNA polymerase, template strands and proofreading, mutations as random changes, and the genetic code as a triplet, non-overlapping, degenerate and universal code that determines protein structure.	18
RNA, transcription and translation	Recall questions on how RNA differs from DNA, messenger, transfer and ribosomal RNA, codons and anticodons, RNA polymerase and the steps of transcription, how translation begins, extends and ends, working out template and anticodon sequences, and several ribosomes on one messenger RNA.	18

Nucleic Acids is 71 of the 2,895 questions in the guide.Get the guide, £8

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.