VirusesViruses

Where do they fit?Where do they fit?

What are Viruses?What are Viruses?

bacteria and viruses cause many diseases for all kingdoms; however, bacteria are classified as living while viruses are not.

Why?? – viruses: have no cellular structure, cytoplasm,

organelles, or cell membrane, and they do not carry out respiration or other life processes.

they consist of strands of DNA/RNA surrounded by a protective protein coat called a capsid

there are 160 major groups which differ in size and shape ( Fig. 4.20 page 122 )

viruses do multiply but not on their own. They infect other cells and depend on the metabolism of the ‘host’ cell to multiply the viral information

refer to the Life Cycle of the “T4" virus ( Fig.4.21 page 123 )

Viral ReproductionViral Reproduction

There are 2 well identified routes There are 2 well identified routes that a viral unit can enter a cell and that a viral unit can enter a cell and reproduce.reproduce. EntryEntry

1. A capsid can bind to a specific region of 1. A capsid can bind to a specific region of the host cell and inject the viral DNA/RNA the host cell and inject the viral DNA/RNA into the cell.into the cell.

2. A enveloped virus will bind to the host 2. A enveloped virus will bind to the host cells’ membrane and be taken into the cell cells’ membrane and be taken into the cell as a vacuole.as a vacuole.

Types of ReproductionTypes of Reproduction

Lytic Cycle :Lytic Cycle : virus injects its’ viral DNA/RNA into the virus injects its’ viral DNA/RNA into the

hosthost virus takes over the cells’ metabolism virus takes over the cells’ metabolism

and reproductive organelles creating viral and reproductive organelles creating viral DNA/RNA and capsids and assembling DNA/RNA and capsids and assembling them togetherthem together

the host cell eventually bursts open the host cell eventually bursts open releasing hundreds of newly created releasing hundreds of newly created viruses to spread, killing the original host.viruses to spread, killing the original host.

Reproduction movieReproduction movie

Retrovirus and Provirus (HIV)Retrovirus and Provirus (HIV) Retrovirus – Retrovirus – a retrovirus is a virus that a retrovirus is a virus that

does not kill the host immediately (if does not kill the host immediately (if ever)ever) The virus contains The virus contains reverse transcriptase reverse transcriptase

(enzyme) (enzyme) which converts RNA (viral) into which converts RNA (viral) into DNA that replicates as the cell carries out DNA that replicates as the cell carries out it’s normal cellular division.it’s normal cellular division.

Provirus – Provirus – splices into the hosts’ genome splices into the hosts’ genome (DNA), lying in wait, being passed on to (DNA), lying in wait, being passed on to daughter cells during normal cellular daughter cells during normal cellular division. An unknown trigger causes the division. An unknown trigger causes the viral DNA to come out of the host’s DNA viral DNA to come out of the host’s DNA and then go through the lytic cycle.and then go through the lytic cycle.

Viruses and BiotechnologyViruses and Biotechnology

Viruses can be very helpful in Viruses can be very helpful in producing numerous copies of a producing numerous copies of a desired gene.desired gene.

A ‘gene’ can be spliced into the viral A ‘gene’ can be spliced into the viral DNA DNA (recombinant DNA)(recombinant DNA) and and allowed to then infect a cell to create allowed to then infect a cell to create the desired gene product.the desired gene product.

HIVHIV