Viruses Biology I

Characteristics Size Extremely tiny ½ to 1/100 the size of the smallest bacterial cell.

Characteristics NON-living No growth No metabolic processes Cell respiration, etc. Reproduction cannot occur outside of a host cell Host cell – cell in which a virus reproduces

Characteristics Names Different naming because they are NON-living NO latin Named for disease caused or tissue infected Rabies; polio adenoviruses Bacteriophages

Structure Inner Core of NUCLEIC ACID Virus’s genetic material DNA or RNA Genes code for making copies of virus! Outer coat Protein CAPSID Protects nucleic acid Shape is important Envelope Only in some larger viruses (animal) Human flu virus

Shape is Important to Virus’s Ability to Infect Receptor sites On cells Receive specific molecules the cell needs Protein coats of viruses designed to fit receptor sites on cells Allows virus to recognize and infect host Makes viruses specific to a cell type If the virus MUTATES, then it may be able to infect a different cell

LYTIC CYCLE Virus lands and attaches to cell Virus injects nucleic acid into cell Host cell DNA is destroyed Viral genes hijack cell and force it to make more viral DNA and capsids Viral components are assembled into new viral particles Cell undergoes LYSIS (bursts) and viruses come out Virus particles can then infect more cells 90 minutes > 200 new viruses

Lysogenic Cycle Virus infects but does NOT immediately kill cell

Lysogenic Cycle Virus attaches Virus injects genetic material Viral DNA becomes part of host cell’s OWN DNA. Every time the host cell reproduces it makes new cells containing the viral DNA (provirus) This can go on indefinitely Virus can pop out of host cell’s chromosome at any time and enter LYTIC cycle

Disease symptoms explained by Lysogenic cycle Cold sores Herpes simplex 1 Remains even after cold sore healed Cause of entering lytic cycle? Chicken Pox Shingles; nerve cells HIV Infect WBCs Small packets of virus pinch off infected cell and go to other cells of immune system Patient shows no syptoms until virus begins killing (lysis) the cells

HIV budding

RNA as Genetic Material How can it insert itself into DNA? Reverse transcriptase - enzyme coded for by virus Makes DNA from RNA DNA inserts into host chromosome Then get lysogenic cycle

Where do Viruses come from? First organisms? NO. Viruses are more closely related to the cells they infect than to each other. Viruses originate from host cells Nucleic acids that escaped from host cell Developed a way to reproduce as parasites of that same host

Vaccine Killed or damaged virus Injected into bloodstream Cannot cause disease Injected into bloodstream Immune cells learn to recognize and fight any invader that looks like this virus The REAL virus the vaccine is for You don’t get sick from exposure to real virus later

Vaccine Edward Jenner Developed 1st Vaccine Small pox Deadly Obtained pus from milkmaid suffering from cowpox Cowpox – makes people sick, but is not deadly Gave cowpox pus to a boy; he got cow pox Exposed boy to small pox Boy did not get small pox

Edward Jenner and Small Pox Vaccine

Why did it work? Cow pox was similar enough to small pox that immune cells were able to recognize and fight BOTH cow pox AND small pox viruses after they had been exposed to cow pox.

Immunity given by Vaccines LIFE LONG IMMUNITY as long as virus is stable and doesn’t MUTATE! DNA viruses are MORE STABLE than RNA viruses DNA viruses Small pox Has been eradicated RNA viruses HIV Flu Mutate often Hard to develop vaccines; flu vaccine must be redeveloped each year.

Animation Creation of a mutant virus and it’s spread – Click HERE