AS Biology

Module 1 Section 1.4VirusesAS BiologySpecification

There are many different kinds of viruses

The two you need to know a bit of detail about are PHAGE and HIV (Human Immunodeficiency Virus)

You do not need to know life cycles! (so you can relax)

BacteriophageA bacteriophage (shortened to phage) is a virus that infects and replicates within a particular species of bacteria

They infect the bacteria by injecting their genome (which is either DNA or RNA based) into the cytoplasm of the bacterial cell

This genome is then assimilated by the host, and the viral genome is transcribed, viral proteins are made and more virus particles are madeBacteriophage Structure

The most well known is T4 BACTERIOPHAGE

Contains a DNA genome bounded by a protein coat

Under a microscope they look like little spaceships

HIVHIV, human immunodeficiency virus, is a disease the targets the immune system of the host

Once the immune system is depleted enough and secondary infections start to develop, people infected with HIV are then said to have AIDS (Acquired ImmunoDeficiency Syndrome)

There is currently no cure for HIV, however, combination drug treatments mean that sufferers can lead full and normal livesHIV Structure

Consists of an RNA genome bounded by a protein coat and glycoprotein containing lipid bilayer

A retrovirus; means it has an RNA genome

So it has the enzyme REVERSE TRANSCRIPTASE present to allow DNA synthesisThe phage viral life cycle (simplified)You need to learn the very basics for how phage and HIV replicate within the host bacterial cell

Phage invades the bacteria in which they replicate their genetic material

The host cell is hijacked to produce viral particles that will form new viruses

These new viruses leave the cell by bursting it open the LYTIC pathway

The HIV virus attaches to T-helper cells where the virus incorporates its DNA into the cells genome

This is done by REVERSE TRANSCRIBING the viral RNA

This leads to production of new viral particles and a destruction of white blood cells, leading to a weakening of the immune systemThe HIV viral life cycle (simplified)