HL Bio: Viruses (STARRED)

How many genes do viruses have

Can range from very little to a ton, ex 8 in flu but 100+ in HHV6

Viruses

Non cellular agents that infect cells + reproduce in them (multiple origins)

Common features of viruses

Small size, fixed size, nucleic acids as genetic material, capsid made of protein, no cytoplasm and no/few enzymes

Small size

Usually 20-300 nanometers in diameter, must be smaller than host cells, don’t have cyto and other structs

Fixed size

Do not grow, full size as assembly completes, assembled in host cell

Nucleic acid as genetic material

Genes made of DNA and RNA, proteins synthesized by nucleic acid to polypeptide transition

Capsid made of protein

Genetic material enclosed in protein coat, most viruses have several proteins in capsid, self assembly means viruses are very symmetrical

Diversity of struct in viruses

Shape and structure, no genes occur in all viruses

Diversity of genetic material

Double/single stranded, variation in length of molecule, circular/linear, how replicate gen mater and use it

Example of diversity in usage

Positive-sense RNA viruses use their genes directly as messenger RNA

Lysis

Process in which viruses burst their cells to be released

During lysis

Viruses sometimes become covered in membrane (anim cells); phslipds come from pls mem in cell and proteins come from virus

Lysogenic cycle

viral DNA becomes integrated into the bacterial DNA molecule, so new whole virus particles are not produced

Lytic cycle

virus reproduces, then bursts out of host cell, killing it

bacteriophage lambda

lytic? nonenveloped, becomes widespread quickly,

bacteriophage

DNA virus that uses either a bacterium or archea as its host

coronavirus

an RNA virus with a crown like shape that uses an animal cell as its host

retrovirus

a virus that converts its RNA genome to DNA after infecting its host

Lysogenic process

attachment, DNA entry, integration, cell division

lytic process

attachment, DNA entry, DNA replication, protein synthesis, lysis, spread

obligate parasites

must have cell to replicate/exist

evidence for several origins of viruses from other organisms

progressive hypothesis and regressive hypothesis

progressive hypothesis

viruses built up in series of steps modifying cell components, fits with retrotransposons

regressive hypothesis

viruses develop in a series of steps by loss of cell components

rapid evolution in viruses

between generations (gen time short), genetic variation (mut rate high), natural selection (EVADE THEM ANTIBODIES)

influenza virus

new strains appear frequently, replicates using RNA replicase, hemagglutinin and neuraminidase can change and be put in diff combs, creating novel strands— PANDEMIC RISK

HIV virus

retrovirus that uses reverse transcriptase, doesn’t proofread (has highest mutation rate), chronic infections, not curable