Structure of DNA
DNA nucleotides, antiparallel strands, complementary base pairing and chromosome organisation in prokaryotes and eukaryotes.
How to study Higher Biology
Move from accurate biological mechanisms to unfamiliar data, experimental evidence and justified conclusions. Use current official materials for the written, extended-response and controlled-assignment formats that this question bank does not reproduce.
Core concepts
Concept 1
Relate deoxyribose, phosphate and bases to the sugar–phosphate backbone and 3′/5′ strand direction.
Exam cue: Relate deoxyribose, phosphate and bases to the sugar–phosphate backbone and 3′/5′ strand direction.
Concept 2
Use adenine–thymine and guanine–cytosine hydrogen bonding to reason from one strand to its complement.
Exam cue: Use adenine–thymine and guanine–cytosine hydrogen bonding to reason from one strand to its complement.
Concept 3
Distinguish prokaryotic circular chromosomes and plasmids from eukaryotic nuclear, mitochondrial and chloroplast DNA.
Exam cue: Distinguish prokaryotic circular chromosomes and plasmids from eukaryotic nuclear, mitochondrial and chloroplast DNA.
Risk pitfalls and guardrails
Do not substitute ribose or uracil when describing DNA.
Guardrail: Check vocabulary, sequence, direction, compartment, units and whether the evidence supports causation or only an association.
Do not describe the two DNA strands as running in the same direction.
Guardrail: Check vocabulary, sequence, direction, compartment, units and whether the evidence supports causation or only an association.
Memory anchors
DNA nucleotide
Deoxyribose + phosphate + one base.
Antiparallel
One strand runs 5′→3′ while its partner runs 3′→5′.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
Which three components form one DNA nucleotide?
A section of one DNA strand has the base sequence 5′-AGCT-3′. Which sequence is complementary and antiparallel to it?
Answer all questions to submit.
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