1. Chapter Viruses

2. Viruses vs. Prokaryotes
are noncellular;
cannot metabolize
cannot respond to stimuli;
multiply only within living cells by parasitizing the synthetic machinery of the infected cell
evolve by mutation and natural selection
Prokaryotes
are unicellular;
metabolize;
respond to stimuli;
Reproduce independently
evolve as a result of mutation and natural selection

3. Viruses Viruses are nonliving with varied appearance.
All viruses are infectious.
In 1884, Pasteur suspected something smaller than bacteria caused rabies; he chose Latin term for “poison.”

4. Viral Structure
Viruses are obligate intracellular parasites = cannot multiply outside a living cell.

6. Viral Reproduction
Virus relies on host enzymes, ribosomes, transfer RNA (tRNA), and ATP for its own replication.
A virus takes over the metabolic machinery of the host cell when it reproduces.

7. Viral Reproduction
Lytic Cycle
Lysogenic Cycle

9. Replication of Bacteriophages
Bacteriophages (phages) are viruses that parasitize a bacterial cell.
Lytic cycle is a bacteriophage “life” cycle of five stages where a virus takes over operation of the bacterium immediately upon entering it and then destroys the bacterium.
Attachment -capsid bind with receptors
Penetration - viral DNA enters host
Biosynthesis – viral components are synthesized
Maturation – assembly of viral components
Release – new viruses leave host cell

12. Retroviruses Retrovirus is an RNA animal virus with a DNA stage.
Retroviruses contain reverse transcriptase that carries out reverse transcription producing cDNA.
Viral cDNA is integrated into host DNA and is replicated as host DNA replicates.
Viral DNA is transcribed; new viruses are produced by biosynthesis, maturation and release by budding.
Retroviruses include the AIDS viruses (e.g., HIV) and also cause certain forms of cancer.