Genetics of Viruses

Viral Structure Virus:

– “poison” (Latin)– infectious particles

consisting of a nucleic acid in a protein coat

Capsid= viral envelope Contain DNA or RNA Bacteriophages (phages)

are the most complex

Virus Diversity

Virus Reproduction Host range

– infection of a limited range of host cells (receptor molecules on the surface of cells)

– West Nile- wide range (mosquitoes, birds, horses, humans)

– Measles- narrow range (only humans)

Lytic Cycle The lytic cycle:

– attachment– injection– hydrolyzation– assembly– release

Results in death of host cell Virulent virus (phage

reproduction only by the lytic cycle)

Lysogenic Cycle Genome replicated w/o

destroying the host cell Genetic material of virus

becomes incorporated into the host cell DNA (prophage DNA)

Temperate virus (phages capable of using the lytic and lysogenic cycle) – Phage λ

May give rise to lytic cycle

Classes of Viruses

RNA viruses Retroviruses: transcribe DNA

from an RNA template (RNADNA)

Most complicated reproductive cycle

Reverse transcriptase (catalyzing enzyme)

HIVAIDS

Reproduction of HIV

Vaccines and Emerging Viruses Vaccines

– Harmless versions of viruses

– Helps immune system to build up antibodies for certain viruses

Emerging Viruses– Appear suddenly– AIDS, Ebola, SARS,

H1N1

Viroids and Prions Viroids:

– tiny, naked circular RNA– infect plants– do not code for proteins,

but use cellular enzymes to reproduce

– stunt plant growth Prions:

– “infectious proteins” (mad cow disease)

– trigger chain reaction conversions