IP Biology Notes: Molecular Genetics (Upper Sec 12)
Free IP Biology notes on DNA, genes, protein synthesis basics, and genetic engineering for Sec 3 to Sec 4.
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.
If molecular genetics is where DBQ evidence, sequence changes, or biotechnology explanations start to break down, use the IP Upper Secondary Biology tuition page for the focused Year 3-4 route.
The core idea is simple: DNA stores instructions by the order of its bases.
Use it as a working check: A gene is a DNA section that codes for a polypeptide. Base order affects amino acid order, which affects protein shape and function.
Then go one layer deeper: Example: changing one base can change one amino acid. Sometimes nothing changes, but sometimes the protein folds differently and works poorly.
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).
Base sequence reasoning checkpoint
Before writing the final effect, decide which level the question is asking about.
