Viruses Chapter 19

What do you know about viruses?

Viral Characteristics Non-living Non-cellular Cannot grow or reproduce on its own No metabolism Cause disease AIDS, colds, flu, measles, mono Cause cancer Cervical, leukemia T4 bacteriophages infecting an E. coli bacteria

19.1 A virus consists of a nucleic acid surrounded by a protein coat

Viral Structure Genetic material Capsid Envelope Mode of entry DNA or RNA Capsid Protein coat surrounding nucleic acid Envelope Some; comes from host cell membrane Mode of entry Spikes, receptors, etc.

19.2 Viruses replicate only in host cells

Lytic Cycle Transduction Viral replication that rapidly kills the host cell causing it to lyse or burst Involves 5 steps Virus attaches to host cell membrane Virus injects its DNA into host cell Virus DNA inactivates host cell's DNA & uses host's raw materials & ribosomes to make viral DNA, capsids, tails, etc. New viral parts are assembled into new viruses Viral enzymes made by host lyse and release new viruses Transduction DNA from one bacteria (host) is transferred to another by a virus after a lytic cycle

Lytic Animation

Lysogenic Cycle Viral replication that allows replication of the genome without killing the host Involves 3 steps Bacteriophage infects bacteria cell and injects its DNA DNA becomes incorporated into bacterial chromosome Prophage Bacteria reproduces, making more copies of viral DNA Lytic cycle can be triggered

Lysogenic Animation

Transduction Animation

Viruses & Genetic Variation Mutations Replicate rapidly, many errors Leads to evolution (sometimes quickly, like the flu) Recombination Viruses pick up genes from each other Can allow them to infect new hosts

Retroviruses Contain RNA Reverse transcriptase enzyme uses the RNA to make DNA Normal flow of information is DNA  RNA  Protein Especially prone to errors in replication Use the host cell's ribosomes & raw materials to make viral proteins Cause some cancers & AIDS

Retrovirus Animation

HIV Infection