Questions
2 questions
Difficulty
Medium
Importance
High yield for core biology and biotechnology theory papers
Overview
Molecular biology is the study of the flow of genetic information within biological systems, focusing on the central dogma of DNA to RNA to protein. It is a cornerstone of university life sciences, frequently appearing in exam papers due to its fundamental role in biotechnology and medicine. Aspirants should focus on the step-by-step enzymatic processes and the regulatory mechanisms governing gene expression.
DNA Replication
DNA replication is a semi-conservative process occurring during the S-phase of the cell cycle, ensuring genetic fidelity during division. Key enzymes coordinate to unwind, stabilize, and synthesize a complementary strand using the parental template.
- Enzymes: Helicase (unwinding), Primase (RNA primer synthesis), DNA Polymerase III (elongation), DNA Ligase (joining Okazaki fragments)
- Replication direction: Always 5' to 3' on the new strand
- Leading strand: Continuous synthesis towards replication fork
- Lagging strand: Discontinuous synthesis via Okazaki fragments
- Semi-conservative nature confirmed by Meselson-Stahl experiment
Transcription
Transcription is the process of synthesizing RNA from a DNA template, acting as the bridge between genetic storage and protein synthesis. It involves the initiation, elongation, and termination phases facilitated by RNA polymerase.
- Initiation: RNA polymerase binds to the promoter sequence (TATA box)
- Elongation: Ribonucleotide triphosphates are added to the 3' end of growing RNA
- Termination: Rho-dependent or Rho-independent mechanism
- Post-transcriptional modification: Capping, Polyadenylation, and Splicing of exons
Translation & Genetic Code
Translation converts the mRNA nucleotide sequence into a polypeptide chain using ribosomes as the molecular machinery. The genetic code is the set of rules defining how codons are translated into specific amino acids.
- Genetic code properties: Triplet, Universal, Non-overlapping, Degenerate
- Ribosome sites: A (Aminoacyl), P (Peptidyl), and E (Exit) sites
- Start codon: AUG (Methionine)
- Stop codons: UAA, UAG, UGA (do not code for amino acids)
- tRNA acts as the adapter molecule carrying the anticodon and specific amino acid
Exam Tip
Always draw a labeled diagram for the replication fork or the central dogma, as examiners prioritize schematic representation over pure theoretical explanation.
Common Mistakes
- Confusing the roles of DNA Polymerase I (repair/primer removal) and DNA Polymerase III (primary synthesis).
- Failing to mention the 5' to 3' polarity constraint, which is the most critical technical detail in replication.
- Incorrectly identifying mRNA splicing as a prokaryotic process, whereas it is strictly eukaryotic.
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