This is the image of a bacterium being attacked by viral particles. You can see the contrast in size easily. In ancient Rome, ‘virus’ meant “poison” or “venomous”. This name was passed down when these extremely small particles were discovered in the late 1800’s. Find a lower-case ‘i’ on your notes page….

Section 18.1 Summary – pages Viruses are extremely small non-cellular, infectious agents composed of genetic material (DNA or RNA) enclosed in a protein coat. You will see Bacteriophages (bottom left) in many examples.... Bacteriophage VirusesFlu Viruses

Section 18.1 Summary – pages A virus has an inner core of nucleic acid, either RNA or DNA and an outer protein coat called a capsid. Capsid Nucleic acid Viral Structure

Section 18.1 Summary – pages Some larger viruses, (human flu viruses), have an additional layer surrounding their capsids, called an envelope (usually made of membrane remnants of previously infected cells). Capsid Nucleic acid Envelope

Vertebrate immune systems can detect certain viral proteins, HOWEVER the genes for viral proteins tend to mutate at very high frequencies, so viruses can often elude immune fighters For instance Influenza mutates often, that is why a new vaccine is created each year.

* viruses do not metabolize, grow, nor are they composed of cells. Also, they don’t possess a way to reproduce without a host. However, THAT is true of many parasites. All Living Things, as a species…: Are made of cells, and possess a system of organization Require, can metabolize, and use energy. Grow and develop. Reproduce. Can adapt to changing environments.

Section 18.1 Summary – pages Viruses are PATHOGENS- infectious, disease- causing agents that invade target organisms and multiply inside them or on them. Disease follows when the pathogens take over metabolic activities of other cells- damaging body tissues and interfering with their normal functioning.

Section 18.1 Summary – pages Nope, not if it can’t get in! So…how does it get into the host cell? It works like a lock and key. If the key doesn’t match a lock, you can’t open the door receptor site The “lock” of the cell is called a receptor site. If the shape of the virus does not match the host’s receptor site, the virus can not inject it’s nucleic acid or enter the cell. Virus Can a Virus Infect Any Cell?

INJECTIONENDOCYTOSIS

Steps of the Lytic Cycle: 1.Virus attaches to host 2.Virus injects nucleic acid 3.Viral nucleic acid takes over and re-programs host’s DNA 4.New viruses form 5.Lysis – cell bursts and releases new viruses Lytic Cycle Lytic Cycle : Faster cycle that quickly destroys the host.

A lysongenic cycle begins in the same way as a lytic cycle. Lysogenic Cycle Lysogenic Cycle : Slow cycle in which the viral DNA hides in the host cell Virus attaches to a host cellViral nucleic acid enters the host Viral nucleic acid integrates itself into the host’s DNA

Lysogenic Cycle Lysogenic Cycle : Slow cycle in which the viral DNA hides in the host cell This part can go on for years…. The host cell will divide, and each time it replicates it’s DNA, it also makes a copy of the viral nucleic acid. At any time, this provirus can enter the Lytic cycle….

RNA Viruses