Molecular Biology and Biotechnology
What the exam tests
This domain covers DNA structure and replication, transcription and translation, the genetic code, gene expression, and basic biotechnology tools such as PCR, recombinant DNA, cloning vectors, Ti plasmid, Bt crops, RNA interference, and gel electrophoresis.
Core rules and concepts
- DNA is a double helix with antiparallel strands; adenine pairs with thymine, guanine with cytosine.
- Replication is semiconservative; each new molecule has one parental and one new strand.
- Transcription uses RNA polymerase and produces RNA with uracil in place of thymine.
- Translation reads mRNA codons in triplets; AUG is the start codon; UAA, UAG, and UGA are stop codons.
- PCR uses denaturation, primer annealing, and extension with a thermostable DNA polymerase.
- Ti plasmid from Agrobacterium tumefaciens is used to transfer genes into plants.
- Bt cotton carries a cry gene from Bacillus thuringiensis.
Worked example
A DNA template strand reads 3'-TAC-5'. What mRNA codon is produced? RNA polymerase pairs A with U, T with A, and C with G using the template. The mRNA is 5'-AUG-3', which codes for methionine and acts as a start codon. The reasoning requires complementarity and antiparallel direction.
Traps that cost marks
Do not use thymine in mRNA. Do not confuse the template strand with the coding strand. PCR requires primers and a thermostable polymerase; it is not just heating and cooling. Gel electrophoresis separates by size, with smaller fragments moving farther.