Flashcards in Viruses Deck (24):
Viruses are obligate parasites because...
…they require a host cell to replicate
Virus Features (3)
-Infectious non-cellular agents
-No nucleus, organelles, or cytoplasm (occasional enzymes)
-Contain either DNA or RNA (single or double stranded), but never both
-Nucleic acids of some sort in linear structure (sometimes circular)
-Capsid: protein coat consisting of capsomeres that give distinctive shapes
-Some have outer shell called an envelope made of a lipid bilayer
-Genome range from 2e3 bp to 2.4e6 bp
A virus outside of a host is called...
The capsid and nucleic acids together are called...
Envelopes are used for...
…attachment of the virus to host cell; sometimes contain spikes for attachment
A virus without an envelope is considered a...
Most viruses are… (size)
Bacteriophage Lytic Cycle (3)
1. Biosynthesis: Production of phage DNA and proteins
2. Maturation: Assembly of phage particles
3. Release: Phage lysozyme breaks cell wall
Bacteriophage Lysogenic Cycle (2)
1. Integration: phage DNA will integrate into bacterial chromosome to become a prophage
2. Exit: Under certain conditions, prophage will excise itself and go into lytic cycle
Bacteriophage Terminology (2)
-Attachment: Phage attaches by tail fibers to host cell
-Penetration: Phage lysozyme opens cell wall; tail sheath contracts to force tail core and DNA into cell
Animal Virus Multiplication (6)
-Attachement: Viruses attach to cell membrane
-Penetration by endocytosis (pinocytosis) or fusion (envelope fuses with membrane)
-Uncoating by viral or host enzymes
-Biosynthesis: Production of nucleic acids and proteins
-Maturation: Nucleic acid and capsid proteins assemble
-Release by budding (enveloped viruses) or rupture
A group of viruses sharing the same genetic information and ecological niche
-Surface glycoproteins (gp120) needed for attachment to host cell CD4 receptors
-Viral nucleocapsid that enters cell with enzymes, RT, proteases, and integrase
CD4 receptors are found on...
...macrophages and CD4+ T-cells
HIV Enzymes (4)
1. RT - RNA to DNA (high mutation rate)
2. Integrase - Integrates viral DNA into host DNA
3. RNA Polymerase - Transcribes viral DNA into viral RNA
4. Protease - Slices proteins into cores that interact with viral mRNA to form new viruses, which bud off and infect more cells
1. gp120 binds to CD4 receptors and CXCR4 in T-cells or CCR5 in macrophages
2. Virus membrane fuse with host cell
3. Nucleocapsid enters and releases viral RNA and enzymes
4. RT converts viral RNA to DNA
5. Integrase integrates viral DNA into host DNA
6. New viral RNA is used as genome and to make new viral proteins
7. Proteins and RNA move to cell surface and bud off it
6. Protease cleaves and processes viral proteins for maturation
Epidemiology of HIV
-33 million infected
-Prevalent in USA, Russia, and Southern Africa
-Uses cocktail of antiretrovials (ARVs)
Classes of ARVs (4)
1. Fusion inhibitors
2. Nucleoside RT inhibitors (NRTIs)
3. Non-nucleoside RT inhibitors (NNRTIs)
4. Protease inhibitors (PI)
HIV is difficult to treat because...
...it can "hide" from immune system in host DNA; ARVs kill free floating virus only, suppressing but not eliminating it
Early ART can...
...prevent transmission and treat HIV