Molecular Biology and Biotechnology
What you must understand
Know the structure of DNA: double helix, sugar-phosphate backbone, complementary base pairing (A–T, G–C), hydrogen bonds between bases. Understand DNA replication (semi-conservative), transcription (DNA to mRNA in the nucleus) and translation (mRNA to protein at the ribosome, using codons and tRNA). Know the genetic code is triplet and degenerate. Understand the central dogma: DNA → RNA → protein. Know the basics of biotechnology: recombinant DNA, restriction enzymes, plasmids as vectors, gel electrophoresis, PCR, and applications such as insulin production and genetic engineering in agriculture. Be aware of ethical issues.
Traps that appear in questions
- Confusing transcription (making RNA) with translation (making protein).
- Forgetting that A pairs with T in DNA but with U in RNA.
- Thinking DNA replication is conservative - it is semi-conservative.
- Mixing up restriction enzymes (cut DNA) with ligase (joins DNA).
- Assuming all mutations change the protein - the code is degenerate, so some are silent.
Worked example
A DNA template strand reads TAC GGA. During transcription the mRNA is AUG CCU (remember U replaces T). During translation, codons AUG and CCU specify methionine and proline. Rule of thumb: read DNA → mRNA by replacing T with U and using the complementary base; read mRNA → protein in triplets from the start codon AUG.