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What are the characteristics of living organisms? Characteristics of living organisms • • • • • Maintain homeostasis Reproduction Cellular organization Metabolism (use energy) Contain genetic information What about viruses? What are viruses? • ultramicroscopic infectious agent that replicates itself only within cells of living hosts; many are pathogenic. • Structure of Viruses • Have no cellular structure • No cytoplasm, organelles or cell membranes do not carry out respiration or common life processes • consist of DNA or RNA surrounded by protective coat called a capsid which protects it from attack by the host and helps the virus attach to a host cell How are Viruses Classified • Shape and size • Shape is determined by the arrangement of proteins in the capsid • Disease they cause • Human viruses inn 21 groups based on genes and method of replication How are viruses transmitted? How do viruses reproduce • • • • • Airborne Contaminated food or water Sexual contact Contaminated blood products Animal bites or vectors ? Airborne Contaminated food or water Vectors or infected animal bite Sexual contact Contaminated blood products Virus lifecycles • Lytic cycle • Retro virus Lytic Cycle • Newly formed virus burst c ell killing it • Infect t neighbouring cells and damage host Reproduction of a Virus (A.E.R.A.L.) • See virus reproduction on page 123 of the textbook. • Step 1: Attachment • Step 2: Entry (the virus injects its nucleic acid into host cell. • Step 3: Replication (the hosts metabolism replicates the viral DNA or RNA) • Step 4: Assembly (new virus particles are assembled) • Step 5: Lysis and Release:( the host cell breaks open and releases the new virus particles) Step 1: Attachment • It can enter any cell, therefore it must attach to a specific receptor site on the cell membrane of the host cell. • Proteins on the surface act as keys that fit exactly into a matching shape on the host • Attachment protein is in the capsid • Each virus has a specific shape protein and can only attach to certain cells Step 2: Entry. • the virus injects its nucleic acid into host cell • Each virus can only enter particular cells with specific receptor sites. Outside the host they are inert • Enters the cell in 2 ways a. Attaches to the host c ell the virus injects its nucleic acid into the cell called the lytic cycle. This can take about 30 mins and 200 new viruses are produced. b. If contained in an envelope the virus will attach to the ,membrane of the host this will create a vacuole. When the virus breaks out of the vacuole it releases its acid into the cell Step 3: Replication • the hosts metabolism replicates the viral DNA or RNA • Synthesis of proteins: The genetic material of the virus (DNA or RNA) instructs the cell to start making viral proteins and nucleic acids (DNA/RNA Step 4: Assembly • (new virus particles are assembled) • Assembly of a new viruses: The viral proteins and nucleic acids are brought together to make new virus particles Step 5: Lysis and Release • the host cell breaks open and releases the new virus particles • Release of new virus particles: Newly formed virus particles are released from infected cell and then host cell dies (lysis). • Some viruses that cause cancer or infect bacteria can exist within a host cell and be dormant (inactive) until activated by some sort of environmental change. • People can live with these viruses and can pass them on to other generations without ever being affected by the virus. Lytic Cycle Retrovirus • Contain an enzyme called reverse transcriptase • This enzyme causes the host to copy the viral RNA into the DNA • Do not kill the cell • Ex. HIV AIDS Retrovirus Treatment of Viruses • •Viruses are very difficult to treat. •Antibiotics are ineffective as they are specific to bacteria and not viruses •VACCINES are used to help produce an immunity to the virus •Vaccines are a dead or weakened form of the virus and act to initiate an immune response •Vaccines are injections or taken orally