Genetics of Viruses & Bacteria

Chapter 18

VIRUSES

Viral StructureGenetic material & Protein coat

Simplified Viral Reproduction

The Lytic Cycle

Lytic and Lysogenic Cycles

Classes of Animal Viruses

Reproductive Cycles: Enveloped Virus

HIV

Emerging VirusesViruses that make a sudden appearance – they emerge and get the attention of the medical community

Not new – but have evolved and expanded their range/ host

Many come from tropics

Ebola Virus Hantavirus

PrionsInfections proteinsMisfolded protein that is normally present Misfolded protein converts normal proteins

Example – Mad Cow Disease

BACTERIA

Bacterial Genome

• Circular DNA

• No introns

• Replication– Begins at origin– Works its way around – Result – 2 circles– Happens prior to binary

fission

• Small circular pieces of DNA outside of bacterial genome

• Self-replicating

• Used in DNA technology to introduce foreign DNA into bacteria

Plasmids

Genetic Recombination in Bacteria

• Transformation– Uptake of naked DNA from environment

• Conjugation– Transfer of DNA from one bacterial cell to another– Sex pili

• Transduction– Transfer of DNA from bacteriophage to bacteria

(bacteriophage got DNA from previous host cell)

Detecting Genetic Recombination

Transduction (Layer 1)

Transduction (Layer 2)

Transduction (Layer 3)

Transduction (Layer 4)

Bacterial mating (Conjugation)

Conjugation and recombination in E. coli (Layer 1)

Conjugation and recombination in E. coli (Layer 2)

Conjugation and recombination in E. coli (Layer 3)

Conjugation and recombination in E. coli (Layer 4)

Transposons (Insertion Sequences)

• “Jumping genes”• Code for enzyme that copies and moves the transposon• Inverted repeats• May cause mutation if inserted within coding seqence

Composite Transposon

• Includes genes for insertion + functional gene– Ex: antibiotic resistance gene

Regulation of a Metabolic Pathway

Operon: on/ off switch for prokaryotic genes• trp operon - represses enzymes

– In absence of tryptophan• Operon is on• Inactive repressor

– In presence of tryptophan• Operon is off• Tryptophan activates repressor which binds operator

lac operon - Inducible Enzymes• In absence of lactose, no enzymes made• In presence of lactose,

– Lactose binds and inactivates the repressor– Enzymes to digest lactose are made

Eukaryotic Genomes

Chapter 19

Eukaryotic DNA

• Linear

• Levels of packing – Ex: chromatin, chromosomes

• Includes introns

Levels of Packing Eukaryotic DNA

Types of Repetitive DNA

Effect of Transposons

Retrotransposons

Gene regulation in eukaryotic cells

• DNA methylation

• Histone acetylation

• RNA processing

• Transport to cytoplasm

• Translation

• Protein folding

• Transport to destination

• Degradation of protein

Transcription of eukaryotic genes• Introns and exons - exons expressed• Cap and tail added

Alternate RNA Splicing

Protein degradation by a proteostome

Oncogenes & Proto-oncogenes

Signaling pathways that regulate cell growth

Development of colorectal cancer• Multiple mutations lead to carcinoma

– Loss APC gene– Activation of ras oncogene– Loss of tumor-suppressor gene DCC– Loss of tumor-suppressor gene p53– More mutations