1. Viruses

3. What are Viruses?
A virus is a non-cellular particle made up of genetic material and protein that can invade living cells.

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Size of Viruses
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5. Are Viruses Living or Non-living?
Viruses are both and neither
They have some properties of life but not others
For example, viruses can be killed, even crystallized like table salt
However, they can’t maintain a constant internal state (homeostasis).

6. Characteristics: acellular somewhere between living & nonliving
smaller than almost all living organisms
structure : protein coat called a capsid &
nucleic acid (DNA or RNA)
no growth or metabolism, no cytoplasm, no cell membrane
they do reproduce, but only by using a living host cell

7. T4 Bacteriophage

8. Characteristics Identified by shape: each depends on capsid
arrangement and composition
1) many-sided (polyhedral) ex: adenovirus
2) rod ex: TMV (tobacco mosaic virus)
3) combination of 1 & 2 ex: bacteriophage
4) filovirus ex: ebola

10. Ebola

11. Reproduction
Lytic cycle – performed by virulent viruses Steps: 1) adsorption – attachment of virus to host cell 2) entry – viral nucleic acid enters host cell 3) replication – viral nucleic acid chops up host DNA & makes viral nucleic acid (NA) & viral proteins 4) assembly – viral capsids & NA combine 5) release – viruses lyse (break open) host cell and are released to infect new cells

12. Reproduction
Lysogenic cycle – performed by temperate viruses Steps: 1) adsorption – attachment of virus to host cell 2) entry – viral nucleic acid enters host cell *viral NA integrates into host DNA as a prophage (in prokaryote) or provirus (in eukaryote) *may remain as prophage indefinitely or may be triggered to break out and complete steps like the lytic cycle (replication, assembly, release) triggers: stress, increased temperature

13. Viral Reproduction

14. retrovirus – a virus containing RNA that makes DNA off of RNA using reverse transcriptase (an enzyme) that does transcription in reverse
ex: HIV