HIV and VirusesLucyStacey Christella

Viruses Obligate parasites of living cells Can’t replicate without living host cell Due to RNApol, ribosomes, etc. are

“dumb” – can’t tell viral genes from host cell genes

Host specific – different viruses infect protozoa, plants, animals, etc.

Viruses Goal: turn cell into “virus factory”1. Virus binds to protein on surface of

host cell2. Virus injects genome into cell3. Viral proteins made by host’s

ribosomes4. Viral genome copied by host’s

enzymes5. Viruses assemble and leave cell6. Repeat

Minimal Virus Genome1. Gene for capsid protein2. Gene for replicating enzyme (if

genome isn’t ds DNA)3. Genes for proteins to release virus

from cell4. Genes to suppress host genes

Retroviruses A single-stranded RNA genome Normally: DNA -> RNA -> Protein Retroviruses: DNA <- RNA -> Protein Examples: HIV, feline leukemia virus,

etc.

Retroviruses Virus makes a DNA copy of RNA genome

(“Retro”) Virus inserts copy into host’s enzyme Therefore, virus passed to daughter

cells

HIV/AIDS HIV = virus Human Immunodeficiency Virus AIDS = loss of immune system function Acquired Immunodeficiency Syndrome

How? HIV-infected cells eventually die after

producing many viruses HIV only infects cells that have protein CD4

on surface CD4 cells = miscellaneous cells - helper T

cells and macrophages essential components of immune system

HIV present in some blood and body fluids of infected people

Therefore:

How? Without treatment: 1. immune system is disabled (AIDS)2. Uncontrolled replication of HIV3. Death from opportunistic infections

Why So Dangerous? Kills immune system so you can’t fight it Reverse transcriptase has high error

rate – many mutations in HIV genome – constantly changing virus – hard to become immune to it or make vaccine

Infectious for long time – widespread epidemic

AIDS Treatments Antibiotics for opportunistic infections (rifampin –

inhibits RNApol of prokaryotes; no effect on eukaryotic RNApol; therefore kills bacteria, but no effect on HIV)

Anti-HIV drugs targeted to parts of HIV that are not present or needed in normal human cells (therefore kill virus, but not host)

“Coctail” of many nucleoside analogs if mutation occurs

HIV protease – bind to active site and prevent enzyme from working, therefore virus doesn’t mature into active form, therefore can’t infect cells

AIDS Treatments Reverse transcriptase, HIV protease,

and immune system reduces levels of HIV significantly

Questions?