VIRUSES I Introduction to Viruses 1 Viruses are

  • Slides: 15
Download presentation
VIRUSES

VIRUSES

I. Introduction to Viruses 1. Viruses are very small, much smaller than bacteria. A.

I. Introduction to Viruses 1. Viruses are very small, much smaller than bacteria. A. Viruses are not living organisms 1. Do not have a cellular structure. 2. Does not metabolize food. 3. Cannot reproduce outside host cell. The SARS virus. (There are 1, 000 nm in 1 mm)

C. Viral Reproduction 1. Viruses reproduce by inserting their genetic material into a host

C. Viral Reproduction 1. Viruses reproduce by inserting their genetic material into a host cell’s DNA and forcing the cell to replicate the DNA. A virus approaches a bacterial cell The virus injects DNA into the cell

D. Viral Anatomy 1. An individual virus particle is called a phage. 2. A

D. Viral Anatomy 1. An individual virus particle is called a phage. 2. A virus is made of DNA or RNA and a protective protein coat, called a capsid. a. Some viruses also have a lipid bilayer membrane. 3. Prophage: viral DNA inserted into the host cell’s genome

E. Model Virus Anatomy 1. Bacteriophages consist of a. a head, which holds the

E. Model Virus Anatomy 1. Bacteriophages consist of a. a head, which holds the viral DNA b. a sheath c. a core, which pierces the bacteria so that DNA can enter the cell d. feet which have the binding proteins that help it attach to a bacteria cell.

II. Viruses and Disease A. Viral disease is caused by two things: 1. When

II. Viruses and Disease A. Viral disease is caused by two things: 1. When a virus takes over a cell, it can no longer perform its role in the body. Some symptoms are the result of non-functioning cells. 2. Inflammatory response: The body’s response to infection like fever, swelling, increased white blood cell production, killing infected cells, and extra mucous.

B. The Lytic Cycle 1. The virus takes over a cell causing it to

B. The Lytic Cycle 1. The virus takes over a cell causing it to make more viral DNA until the cell explodes which releases the new phages.

C. The Lysogenic Cycle 1. The virus inserts its DNA into the host cell

C. The Lysogenic Cycle 1. The virus inserts its DNA into the host cell but stays dormant. The virus DNA is replicated every time the cell divides. 2. All viruses eventually enter the lytic cycle, triggered by environmental conditions, immune response, or number of infected cells

III. Other Types of Virus A. Viroids are short sections of virus RNA that

III. Other Types of Virus A. Viroids are short sections of virus RNA that infect plants. These have a major economic impact in agriculture. B. Bacteriophages are viruses that infect bacteria. Helpful in getting rid of bacterial infections and in cloning genes.

III. Other Types of Virus C. Retroviruses are RNA viruses containing a reverse transcriptase

III. Other Types of Virus C. Retroviruses are RNA viruses containing a reverse transcriptase so that their RNA can be copied to DNA before insertion in the host cell. [Example: HIV] D. Prions are misfolded proteins that cause an organism’s proteins to misfold. How prions actually cause disease and reproduce is still a mystery. Diseases like mad cow disease are caused by prions.

Prion

Prion

IV. Virus Origins A. Scientists are unsure how viruses originated but have developed a

IV. Virus Origins A. Scientists are unsure how viruses originated but have developed a few hypotheses: 1. Viruses may have once been small cells that parasitised larger cells. Over time, genes not required by their parasitism were lost. 2. Viruses may have evolved from bits of DNA or RNA that escaped from the genes of a larger organism. Possibly from plasmids or transposons. 3. Viruses may have evolved from complex molecules of protein and nucleic acid at the same time as cells first appeared on earth.

V. Virus Evolution A. Viruses evolve quickly, because they reproduce quickly. However, virus DNA

V. Virus Evolution A. Viruses evolve quickly, because they reproduce quickly. However, virus DNA must remain short otherwise it will take too long for the cell to copy. B. Viruses mutate once every time they are replicated, so new mutations are very common. C. Viruses can adapt to changes in their environment in only a few months.

VI. Viruses and Medicine A. Anti-viral drugs mainly work to keep viruses in the

VI. Viruses and Medicine A. Anti-viral drugs mainly work to keep viruses in the lysogenic cycle. 1. Resistance to antiviral drugs appears within weeks. B. Vaccines work by introducing a virus related to a disease, or by introducing the capsid proteins, so that the immune system creates antibodies to target that virus. 1. Vaccines that target parts of the virus that rarely change, like the receptors necessary to attach to a cell, last for a long time (polio vaccine). Other viruses (cold, flu) do not.