detailed ex3

That’s a full exam review—good news is it all connects, so once you see the patterns it gets way easier. I’ll walk you through it clearly but without fluff so you can actually study from this.

🧬 BASIC GENETICS TERMS

Gene – a segment of DNA that codes for a functional product (usually a protein).
Operon – a group of genes controlled together under one promoter (common in bacteria).
Chromosome – a long DNA molecule containing many genes.
Genome – all genetic material in an organism.
Plasmid – small circular DNA in bacteria, separate from chromosome (often carries antibiotic resistance).
Phenotype – observable traits (appearance, behavior, etc.).
Genotype – genetic makeup (the actual DNA/alleles).
Allele – different versions of the same gene.

🔁 CENTRAL DOGMA

The central dogma explains how genetic info flows:

DNA → RNA → Protein

  • DNA is transcribed into mRNA

  • mRNA is translated into protein

✍ TRANSCRIPTION (DNA → mRNA)

Where: nucleus (eukaryotes), cytoplasm (prokaryotes)

Key parts:

  • Promoter – start site (where RNA polymerase binds)

  • Coding sequence – actual gene

  • Terminator – stop signal

Direction:

  • DNA is read 3’ → 5’

  • mRNA is built 5’ → 3’

Steps:

1. Initiation

  • RNA polymerase binds promoter

  • Helicase activity unwinds DNA

2. Elongation

  • RNA polymerase builds mRNA by matching bases:

    • A → U

    • T → A

    • C → G

    • G → C

3. Termination

  • RNA polymerase hits terminator

  • mRNA is released

🧪 HOW TO TRANSCRIBE DNA

Example:

DNA (template):
3’ – TAC GGA TTT – 5’

mRNA:
5’ – AUG CCU AAA – 3’

🧬 TYPES OF RNA

  • mRNA – carries code from DNA

  • tRNA – brings amino acids

  • rRNA – makes up ribosome

🧱 TRANSLATION (mRNA → PROTEIN)

Where: ribosome

Ribosome structure:

  • Small subunit – binds mRNA

  • Large subunit – forms peptide bonds

Ribosome sites:

  • A site – incoming tRNA

  • P site – growing chain

  • E site – exit

Key concepts:

  • Codon – 3-base mRNA sequence

  • Anticodon – matching tRNA sequence

Steps:

1. Initiation

  • Ribosome binds mRNA at start codon (AUG)

  • tRNA brings methionine

2. Elongation

  • tRNA enters A site

  • Peptide bond forms

  • Ribosome moves (translocation) 5’ → 3’

3. Termination

  • Stop codon (UAA, UAG, UGA) reached

  • Termination factor releases protein

  • Uses hydrolysis

🧬 TRANSLATION EXAMPLE

mRNA:
AUG – GCU – UAA

Protein:
Methionine – Alanine – STOP

🧬 DEGENERATE CODE

Multiple codons = same amino acid

Example:

  • UUU & UUC → Phenylalanine

This reduces mutation impact.

🧠 GENE EXPRESSION

Gene expression – making protein from a gene

  • Constitutive genes – always ON

  • Inducible operon – OFF → ON when needed

  • Repressible operon – ON → OFF when enough product

🧬 OPERONS

Operon = promoter + operator + genes

Controls transcription in bacteria.

⚙ REGULATION LEVELS

  • Transcriptional – control mRNA formation

  • Translational – control protein making

  • Post-translational – modify protein

Example: enzyme activation by phosphorylation

🧪 LAC OPERON (INDUCIBLE)

  • OFF by default

  • Turns ON when lactose present

🧪 TRP OPERON (REPRESSIBLE)

  • ON by default

  • Turns OFF when tryptophan present

🧬 MUTATIONS

Mutation – DNA change
Mutagen – causes mutation
Spontaneous – natural error

Types:

  • Silent – no amino acid change

  • Missense – different amino acid

  • Nonsense – STOP codon early

  • Frameshift – shifts reading frame (most severe)

🦠 CORONAVIRUS PROTEIN PRODUCTION

Even though it has one +ssRNA, it makes multiple proteins by:

  • Making polyproteins that get cut

  • Using ribosomal frameshifting

🦠 VIRUS STRUCTURE

  • Capsid – protein coat

  • Capsomere – capsid subunits

  • Envelope – lipid layer

  • Spike proteins – attach to host

  • Genetic material – DNA or RNA

Typical size: 20–300 nm

🔁 BACTERIOPHAGE LIFE CYCLES

Lytic:

  • Virus replicates → cell bursts

Lysogenic:

  • Viral DNA integrates (prophage)

  • Can later enter lytic

🧬 ANIMAL VIRUS VS PHAGE

  • Animal viruses enter whole cell

  • Phages inject DNA only

🦠 LATENT VIRUSES

Examples:

  • HIV

  • Herpes viruses

⚡ INDUCTION

Trigger that switches from lysogenic → lytic

🧪 IDENTIFYING VIRUSES

  1. PCR

  2. ELISA

  3. Cell culture

🌍 TERMS

  • Endemic – constant presence

  • Epidemic – regional outbreak

  • Pandemic – global spread

  • Host range – organisms infected

  • Cell tropism – cell types infected

  • Zoonotic – animal → human

🦠 INFLUENZA

Antigenic Drift

  • Small mutations

Antigenic Shift

  • Major change → pandemics

Proteins:

  • Hemagglutinin (H) – entry

  • Neuraminidase (N) – exit

Example: H1N1

Why yearly vaccine?

Virus mutates constantly (drift + shift)

🦠 HIV LIFE CYCLE

  1. Entry (binds CD4 cells)

  2. Reverse transcription (RNA → DNA)

  3. Integration into host DNA

  4. Replication

  5. Assembly & release

🦠 CORONAVIRUS LIFE CYCLE

  1. Spike binds receptor

  2. RNA enters cell

  3. Translated immediately

  4. Replication

  5. Assembly

  6. Release

💊 HIV DRUG CATEGORIES

  • Reverse transcriptase inhibitors

  • Protease inhibitors

  • Entry inhibitors

  • Integrase inhibitors