Viruses Higher Human Biology

Lesson Aims To describe the structure of a virus To examine the process of viral replication

Different types of viruses Influenza virusAIDS virus

Different Shaped Viruses

Size Smaller than bacteria nanometres (nm)

Structure of a Virus A virus contains nucleic acid (DNA or RNA) Surrounded by a protective coat (capsid)

Entering the Host Cell Different viruses employ different methods of entering the host cell Process depends on antigenic sites on the virus binding with certain complementary molecules in the membrane or the specific host cell Following binding the nucleic acid is introduced into the host cell

Binding With the Host Cell

Assembly of New Viruses Once in the host cell the virus assumes control of the cell’s biochemical machinery Host cell supplies energy (ATP), nucleotides, amino acids Host then makes many identical copies of viral nucleic acid and protein coats

Release Either by LYSIS (bursting of the host cell membrane) Or BUDDING (the cell membrane pinches off containing the new viral particle)

Before and After Lysis

Budding

Smallpox

Retrovirus A retrovirus contains RNA It also contains reverse transcriptase an enzyme which produces viral DNA from viral RNA The virus can thus replicate itself

Acquired Immune Deficiency Syndrome (AIDS) AIDS is a retrovirus It attacks helper T- lymphocytes The AIDS virus attaches itself by glycoprotein on its surface to receptors on the helper T cell surface

AIDS The envelope surrounding the HIV particle fuses with the membrane of the helper T-cell and the virus enters the host cell Viral DNA becomes incorporated into the host cell’s DNA where it can remain dormant for many years Viral mRNA is transcribed and it directs synthesis of new viral particles inside the host cells These escape from the infected helper T cell by budding. The original T cell’s membrane is left perforated which causes destruction of the cell

The Facts You Need To Know page 5 from “a virus can only be seen….” to “e.g. the viral nucleic acid…”