IP Biology Notes: Molecular Genetics (Upper Sec 12)
26 Nov 2025, 00:00 Z
Reviewed by
Ezekiel Tan·Academic Advisor (Biology)
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Use this as a free IP Biology notes chapter on molecular genetics for Year 3 to Year 4. It keeps the IP pacing while reinforcing the 6093 biology foundations most schools test through DBQs, diagrams, and practical explanations.
Status: SEAB O-Level Biology 6093 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for this note.
What you must know
- DNA is a double helix of two antiparallel strands; nucleotide = deoxyribose sugar + phosphate + base (A, T, C, G); complementary pairing A–T, C–G via hydrogen bonds.
- Genes are sections of DNA on chromosomes; each gene codes for a polypeptide; base sequence determines amino acid sequence.
- Basic flow: DNA sequence → mRNA copy (concept), mRNA read to assemble amino acids into polypeptide (no detailed steps needed at this level).
- Genetic engineering: isolate target gene (e.g., human insulin), insert into vector (plasmid) using restriction enzymes and ligase, transfer to host (bacteria) to express protein. Consider benefits (medicine, crops) vs risks/ethics (allergies, escape, equity).
Detailed notes
- DNA structure: double helix, antiparallel strands, sugar-phosphate backbone outside, bases inside paired A–T, C–G via hydrogen bonds; sequence stores information.
- Gene–protein link: base triplet codes for one amino acid; order of bases → order of amino acids → protein shape/function. Mutation (base change) can alter protein (sometimes silent).
- Replication (concept): strands separate; complementary nucleotides pair; ensures identical copies before cell division.
- Genetic engineering steps (IP level): identify gene → cut with restriction enzyme → splice into plasmid vector with ligase → insert into host (e.g., bacteria) → express protein → harvest. Advantages (insulin, vaccines, resistant crops); risks (allergies, gene escape, biodiversity, access).
Worked walkthroughs
- Explain how a base substitution might change an amino acid and affect protein function (or be silent).
- Outline insulin GM production at high level: human insulin gene into plasmid → bacteria produce insulin → purified for patients.
- Describe one benefit and one risk of GM pest-resistant crops (higher yield vs possible non-target effects or resistance development).
Pitfalls and fixes
- Saying DNA bases pair randomly-must be complementary (A–T, C–G).
- Ignoring that sequence order matters; not just base types.
- Describing GM without mentioning vector/host change.
- Overstating certainty of risks/benefits-keep balanced.
