An overview of the field of molecular genetics, including the basic concepts, historical development, and its significance in understanding genetic mechanisms at the molecular level.
Introduction to Molecular Genetics – Study Notes
| Process | Molecule(s) Involved | Main Enzyme(s) | Outcome |
|---|---|---|---|
| Replication | DNA → DNA | DNA polymerases, helicase, primase, ligase | Accurate copying of the genome |
| Transcription | DNA → RNA | RNA polymerase, transcription factors | Synthesis of messenger (mRNA), ribosomal (rRNA), transfer (tRNA), and non‑coding RNAs |
| Translation | mRNA → Protein | Ribosome, tRNAs, aminoacyl‑tRNA synthetases, initiation/elongation/termination factors | Polypeptide chain assembly |
Note: Reverse transcription (RNA → DNA) and RNA editing are important exceptions.
| Feature | Description | Functional Significance |
|---|---|---|
| Double helix | Two antiparallel strands, 10.5 bp per turn | Provides stable storage of genetic information |
| Base pairing | A–T (2 H‑bonds), G–C (3 H‑bonds) | Ensures fidelity during replication & transcription |
| Chromatin | DNA wrapped around histone octamers → nucleosomes → 30 nm fiber | Compacts DNA and regulates access |
| Higher‑order structure | Loops, topologically associating domains (TADs), chromosome territories | Coordinates gene regulation and replication timing |
| Element | Location | Role |
|---|---|---|
| Promoter | Upstream of transcription start site (TSS) | Binds RNA polymerase & basal transcription factors |
| Enhancer | Can be distal (kb–Mb away) | Increases transcription via looping & transcription factor binding |
| Silencer | Similar to enhancers but represses transcription | Recruits repressors or chromatin remodelers |
| Operator (prokaryotes) | Within/near promoter | Binds repressor proteins to block transcription |
| 5′ UTR / 3′ UTR | Untranslated regions of mRNA | Influence translation efficiency, stability, localization |
| Introns / Exons | Eukaryotic genes | Introns removed by splicing; exons encode protein sequence |
| Poly‑A signal | 3′ end of pre‑mRNA | Directs cleavage and polyadenylation, stabilizing mRNA |