- Viruses are the smallest living organism 10nm-300nm
- they are v.hard to term dead or alive
- All viruses have a protein coat (capsid) that surrounds the nucleic acid
- the nucleic acid can be RNA or DNA
- there are many types of viruses including: HIV and bacteriophages
Viruses only replicate within a host cell (and thus destroying the host)
- A bacteriophage (phage) is a virus that has a DNA core
- a phage attacks bacterial cells.
- They contain DNA bounded by a protein coat
- Phages invade the bacteria, inwhich they inject viral DNA
- DNA replicates and is packed into protein coats
- bacterial cells destroyed (as new phages released)
Human Immunodeficiency Virus (HIV)
structure - HIV consists of a core of RNA bounded by a protein coat and a lipid bilayer containing glycoprotein.
HIV is retrovirus - 'any group of RNA viruses which insert a DNA copy of their genome into the host cell in order to replicate.'
- HIV viruse deliver the RNA with the enzyme reverse transcriptase into the host cell.
- The enzyme catalyses the synthesis of DNA from RNA
- host cell makes copies of viruses
What does HIV do to the body?
HIV invades a type of lymphocyte (T-helper cells) thus weakening the immune system.
HIV destroys T-cells thus damaging the body's ability to fight off invading germs and diseases. The weakened immune system is known as AIDs.
- AIDs is the result of an HIV infection, but not every1 with HIV has AIDs.
- people with HIV don't show symtoms