Viruses
What is a Virus? Non-living particle WHY? Viruses are considered non-living because they do: NOT Carry out metabolism NOT Grow or develop NOT Replicate without the help of a living cell (host).
Characteristics of Viruses Only pathogenic (causes disease). Viruses are specific to certain kinds of cells. Ex: HIV infects only Helper T cells Before a virus can replicate, it must attach to and infect a living cell, called the host cell.
Why are Viruses Pathogenic Viruses only do one thing Attach to cells Inject Genetic Material (dna/rna) Force the cell to make new viruses. Viruses do not produce anything other than parts for themselves. Do viruses make Toxins? NO
Virus Structure A virus has simple structure consisting of an inner core of genetic material (DNA or RNA) and an outer protein layer called a capsid. This structure is known as a virion.
Virus Structure Continued The two parts of a virus are: Genetic Material DNA & RNA nucleic acids which play a fundamental role in determining the structure and nature of all living things Capsid - protein shell that surrounds a virus
Virus Structure Continued Viruses Attachment to cells: Glycoproteins Projections on outside of virus used to gain access to interior of cell. VIDEO
Figure 18.2 Viral structure
Figure 18.1 Comparing the size of a virus, a bacterium, and a eukaryotic cell
Scale in Biology Virus Size and Scale Interactive
Virus Poll As you read each statement, decide whether you agree, strongly agree, disagree, OR strongly disagree and move to the appropriate corner of the room to indicate your choice. Be prepared to defend where you go!!
Do you agree, strongly agree, disagree or strongly disagree? Viruses have a cell wall.
Do you agree, strongly agree, disagree or strongly disagree? Viruses, prokaryotes and eukaryotes all contain genetic material.
Do you agree, strongly agree, disagree or strongly disagree? Viruses are much larger than prokaryotes.
Do you agree, strongly agree, disagree or strongly disagree? Viruses are surrounded by a capsid.
Do you agree, strongly agree, disagree or strongly disagree? Viruses only affect specific cells.
Do you agree, strongly agree, disagree or strongly disagree? Viruses can metabolize nutrients.
Do you agree, strongly agree, disagree or strongly disagree? Viruses rely on a host cell for reproduction.
Do you agree, strongly agree, disagree or strongly disagree? Viruses are made of cells.
Do you agree, strongly agree, disagree or strongly disagree? Viruses cannot change.
Viral Reproduction
Viruses If viruses are non-living, how do they replicate?? They need a host cell! Before a virus can replicate, it must attach to and infect a living cell. What kinds of cells? A virus is specific to a specific kind of cell.
Viral attachment Viruses are specific to certain host cells. They will only attach to a cell if the protein (projection) in its capsid or envelope matches the host cell s protein. Like an enzyme (lock and key). If a virus can t attach, it can t infect the cell.
What happens after attachment? Once a suitable host is found, the virus attaches and injects its DNA into the host. The host cell drives the production of new virus particles. The virus uses its host cell s machinery to make more copies of itself.
Viral Replication Once in a host, the virus can take one of two paths. 1. Lytic Cycle 2. Lysogenic Cycle
Two types of viral life cycles Lytic cycle The rapid reproduction of the entire virus carried out by the host eventually bursting the host cell. Remember, when in the lytic cycle the virus is TICked off so it destroys the cell.
Virus Replication-Lytic Cycle 1. Attachment 2. Insertion of DNA into host cell 3. Replication and production of viral particles 4. Lysis and release of viral particles (cell destruction)
The Lytic Cycle WATCH IT!
Two types of viral life cycles Lytic cycle The rapid reproduction of the entire virus carried out by the host eventually bursting the host cell. Lysogenic cycle Sneaky cycle The viral DNA is integrated into a host and is replicated without destroying the cell. Eventually, the virus exits the lysogenic cycle and enters the lytic cycle.
Virus Replication-Lysogenic Cycle 1. Attachment 2. Insertion of DNA into host cell 3. Integration of viral DNA into host DNA (called a provirus). 4. Viral DNA is replicated with host DNA. 6. New cells continue to replicate and divide. 5. Production of new host cell that is already infected.
Virus Replication-Lysogenic Cycle 6. New cells continue to replicate and divide. 5. Production of new host cell that is already infected. 1. Attachment 2. Insertion of DNA into host cell 4. Viral DNA is replicated with host DNA. 3. Integration of viral DNA into host DNA (called a provirus).
Virus Replication-Lysogenic Cycle 1. Attachment 2. Insertion of DNA into host cell 3. Integration of viral DNA into host DNA (called a provirus). 4. Viral DNA is replicated with host DNA. Lytic Cycle Lysogenic Cycle 5. Production of new host cell that is already infected. 8. Lysis and release of viral particles (cell destruction) 7. Replication and production of viral particles 6. New cells continue to replicate and divide.
Virus Replication-Lysogenic Cycle Each time the cell divides, the provirus also divides. Each generation results in two infected host cells. Does not destroy host cell until provirus enters the lytic cycle.
The Lysogenic Cycle WATCH IT!
Recap Video WATCH IT!