Viruses Living or Not

Virus Virus – small particle made of 1.Nucleic acids either DNA or RNA 2.Surrounded by a protein coat

Virus Viruses are smaller than the tiniest bacterium. They are not considered to be alive: 1.Don’t grow or develop 2. Don’t carry on respiration 3. They can’t reproduce on their own

Virus Structure

Virus The outer protein coat is called the capsid. This capsid gives the virus its shape. The protein arrangement determines what cell can be infected.

Virus Every virus has a specially shaped device call an attachment protein Each virus can only attach to a few kinds of cells This process is like two pieces of a jigsaw puzzle

Viral Replication Cycles A virus must infect a host cell to replicate. Once inside the virus takes over the cell metabolism.

Viral Replication Cycles 2 ways for a virus to enter a cell. 1. Virus nucleic acid is injected into the cell.

Viral Replication Cycles 2. Virus is surrounded by plasma membrane and taken into the cell cytoplasm. This vacuole will burst releasing the virus.

Lytic Cycle Once inside, the virus takes over the cell processes. The cell enzymes and energy are used to make more viruses. The cell will burst releasing the viruses. Lysis – bursting of a cell.

Lytic Cycle The new viruses infect more cells. This active process of making more viruses is called a lytic cycle

Lysogenic Cycle Lysogenic cycle – replication cycle where the viral nucleic acid is incorporated in the cell DNA. This new DNA is called a provirus

Lysogenic Cycle The cell carries out its own functions. Every time the cell replicates, it copies the viral DNA. This resting phase can last for many years.

Lysogenic cycle At any time, the provirus can be activated and enter a lytic cycle. When this happens, the virus will replicate and kill the cell. Examples: Herpes simplex I Hepatitis B Chicken pox

Retrovirus Retrovirus – a virus with RNA as its nucleic acid. It must work backwards making DNA from RNA The enzyme used is called Reverse transcriptase HIV is a retrovirus

BREAKING NEWS ! Papiloma virus causes cancer!!! HPV has been shown to cause cervical cancer Other viruses are being studied as possible causes of cancer.(that means tumors)

Illnesses caused by viruses Cold Flu Chicken Pox Measles Mumps Polio HIV AIDS