🧬 Molecular Biology: One Night Revision & Cram Sheet
Give a molecular account of storage, copying, repair, readout, and regulation of genetic information, and of the principles by which the main molecular methods report those processes. Each machine is met after the chemical problem it solves. A method is treated as an argument with a limit, not as a recipe.
🌟 Core Axioms & High-Yield Golden Rules
10 Core PrinciplesNon-negotiable foundational truths frequently tested in direct conceptual and numerical exam questions. Click checkbox to mark as mastered.
DNA replication is semiconservative (Meselson-Stahl experiment) and bidirectional; synthesis occurs strictly in 5' to 3' direction with pyrophosphate release.
💡 Strict 5' to 3' synthesisDNA Polymerase III is the primary replicase in prokaryotes with 3' to 5' proofreading exonuclease; DNA Polymerase I has BOTH 3' to 5' proofreading AND 5' to 3' nick-translation exonuclease.
💡 Pol I removes primers 5' to 3'Prokaryotic RNA Polymerase core enzyme is alpha2-beta-beta'-omega; sigma factor is required for promoter recognition at -10 (Pribnow box) and -35 elements.
💡 Core + Sigma = HoloenzymeEukaryotic RNA Polymerases: RNA Pol I transcribes large rRNA (28S, 18S, 5.8S); RNA Pol II transcribes mRNA, snRNA, and miRNA; RNA Pol III transcribes tRNA and 5S rRNA.
💡 I = rRNA | II = mRNA | III = tRNAmRNA 5' capping involves 7-methylguanosine linked via unique 5'-to-5' triphosphate bridge; polyadenylation signal is AAUAAA.
💡 5'-5' Cap + AAUAAA TailSplicing occurs via two transesterification reactions: branch point adenosine (2'-OH) attacks 5' splice site, forming a lariat intermediate with a 2'-5' phosphodiester bond.
💡 Lariat has 2'-5' bondGenetic code is degenerate (61 sense codons, 3 stop codons: UAA, UAG, UGA), non-overlapping, and comma-less; AUG codes for Methionine (initiator).
💡 U Go Away, U Are Away, U Are GoneWobble hypothesis (Crick): relaxed pairing at 3rd position of codon (5' position of tRNA anticodon); Inosine in anticodon can pair with A, U, or C.
💡 Inosine pairs with A, U, CLac operon: Allolactose is the physiological inducer that binds the repressor; cAMP-CAP complex exerts positive control and binds only when glucose is low.
💡 Low glucose = High cAMP = CAP bindsTelomerase is a specialized reverse transcriptase ribonucleoprotein carrying its own RNA template to synthesize telomeric repeats (TTAGGG in humans).
💡 Telomerase carries internal RNA guide📚 Chapter-by-Chapter Rapid Cram Breakdown
12 ModulesHigh-density review of every curriculum chapter. Click any chapter title to view full in-depth lecture notes.
- Master Griffith: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Avery–MacLeod–McCarty: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Hershey–Chase: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master RNA genomes: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master DNA versus RNA: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master B-form dimensions: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master supercoiling and topoisomerases: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master nucleosomes: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master higher-order folding: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master euchromatin and heterochromatin: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
Genome organisation →
- Master Operons and split genes: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master the C-value paradox: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master repetitive DNA: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master bacterial and human genomes: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
DNA replication →
- Master Meselson–Stahl: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master origins: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master the fork: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master polymerases and the clamp: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master proofreading: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
Damage and repair →
- Master Classes of lesion: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master mismatch repair: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master base excision: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master nucleotide excision: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master homologous recombination and non-homologous end joining: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
Transcription →
- Master Bacterial polymerase and promoters: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master termination: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master three eukaryotic polymerases: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master pol II initiation and the CTD: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master enhancers and Mediator: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
RNA processing →
- Master The cap: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master splicing and the lariat: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master alternative splicing: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master cleavage and polyadenylation: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master self-splicing as a contrast: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
Translation →
- Master The code and wobble: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master charging: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master A, P, and E sites: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master bacterial and eukaryotic initiation: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master elongation and the ribozyme: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master What is left to cell biology: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Hsp70 and chaperonins: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master ubiquitin and the proteasome: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master The lac operon: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master trp attenuation: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master positive and negative control: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Remodelling: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master DNA-binding domains: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master combinatorial control: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master methylation and the word epigenetic: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master miRNA and siRNA: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Restriction cloning: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master libraries: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master PCR: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master sequencing: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master blots and reporters: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
⚖️ Must-Know Comparison & Distinction Tables
2 TablesSide-by-side matrices comparing commonly confused biological mechanisms, kinetic types, and pathways.
Eukaryotic RNA Polymerase Classes & Functions
| Polymerase | Transcripts Produced | Alpha-Amanitin Sensitivity | Promoter Elements |
|---|---|---|---|
| RNA Polymerase I | 28S, 18S, 5.8S pre-rRNA in nucleolus | Insensitive | Core element + UCE (upstream control element) |
| RNA Polymerase II | mRNA, snRNA, miRNA, lncRNA | Highly sensitive (inhibited at <1 ug/mL) | TATA box (-25), Inr (initiator), DPE, BRE |
| RNA Polymerase III | tRNA, 5S rRNA, U6 snRNA | Moderately sensitive (inhibited at high conc) | Internal promoters: Box A, Box B, Box C |
Prokaryotic vs. Eukaryotic Translation Comparison
| Feature | Prokaryotes | Eukaryotes |
|---|---|---|
| Ribosome Subunits | 70S (50S large + 30S small) | 80S (60S large + 40S small) |
| Initiation Site | Shine-Dalgarno sequence (AGGAGG) upstream of AUG | 5' cap recognition + Kozak consensus sequence (ACCAUGG) |
| Initiator Amino Acid | N-formylmethionine (fMet-tRNAfMet) | Unformylated Methionine (Met-tRNAiMet) |
| Transcription-Translation | Coupled simultaneously in cytoplasm | Uncoupled (transcription in nucleus, translation in cytoplasm) |
⚠️ Examiner Traps & Common Student Mistakes
2 PitfallsClassic trap questions designed by examiners to catch uncritical students. Don't lose easy marks here!
Confusing Direction of Template Reading vs Synthesis
Students state that DNA polymerase reads template 5' to 3'.
DNA & RNA polymerases ALWAYS synthesize new strands 5' to 3', which means they read the antiparallel template strand 3' to 5'.
Which RNA Polymerase Synthesizes 5S rRNA?
Assuming RNA Pol I transcribes all ribosomal RNAs.
RNA Pol I synthesizes 28S, 18S, and 5.8S rRNA. BUT 5S rRNA is transcribed by RNA Polymerase III outside the nucleolus.
📐 Key Formulas & Numerical Constants
3 FormulasDNA Melting Temperature (Wallace Rule)
Tm = 2 * (A + T) + 4 * (G + C) °CEstimates duplex melting temperature for short oligonucleotides (<20 bp).
DNA Topological Linking Number
Lk = Tw + WrLk (linking number) equals Tw (twist / helical turns) plus Wr (writhe / supercoiling). Lk is invariant in unbroken DNA.
Chargaff's Equimolar Rules
A = T and G = C; (A + G) / (C + T) = 1.0Holds true strictly for double-stranded DNA; deviation indicates single-stranded DNA genome.
🏛️ Landmark Scientists & Nobel Discoveries
6 PioneersFrequently tested in historical milestone and match-the-following exam questions.
Frederick Sanger
🏅 Two Nobel Prizes in Chemistry: 1958 (Unshared, for determining the complete primary amino acid structure of insulin) and 1980 (Shared, for inventing dideoxy DNA sequencing)Major landmark discoveries
Barbara McClintock
🏅 Nobel Prize in Physiology or Medicine (1983) for her discovery of mobile genetic elementsMajor landmark discoveries
Rosalind Elsie Franklin
🏅 Tragically passed away at age 37, four years before the 1962 Nobel Prize was awarded (Nobel rules prohibit posthumous awards)Major landmark discoveries
James Watson & Francis Crick
🏅 Nobel Prize in Physiology or Medicine (1962) for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living materialMajor landmark discoveries
George Emil Palade
🏅 Nobel Prize in Physiology or Medicine (1974) for discoveries concerning the structural and functional organization of the cellMajor landmark discoveries
Susumu Tonegawa
🏅 Nobel Prize in Physiology or Medicine (1987) for his discovery of the genetic principle for generation of antibody diversityMajor landmark discoveries
🎯 Rapid-Fire Active Recall Checklist
6 QuestionsTest your memory before stepping into the exam hall. Try to answer mentally, then tap "Reveal Answer" to verify!