Topics: Bacteria, Cell, Cell wall Pages: 57 (7430 words) Published: February 18, 2013
Microorganisms and Fungi
Bacteria and Viruses


virus: A nonliving, infectious particle composed of a nucleic acid and a protein coat; it can invade and destroy a cell.

pathogen: A virus, microorganism, or other substance that causes disease; an infectious agent.

capsid: A protein sheath that surrounds the nucleic acid core in a virus.

envelope: A membrane-like layer that covers the capsids of some viruses.

glycoprotein: A protein to which carbohydrate molecules are attached.

bacteriophage: A virus that infects bacteria.

lytic: The cycle of a viral infection, replication, and cell destruction.

provirus: Viral DNA that has attached to a host cell's chromosome and that is replicated with the chromosome's DNA.

lysogenic: Viral replication cycle in which the viral genome replicates without destroying the host cell.

prion: An infectious particle that consists only of a protein and that does not contain DNA or RNA.

Direct Instruction - Running Time: 16 min 43 sec
-Composed of nucleic acids enclosed in a protein coat
-Smaller than the smallest bacterium
-Only characteristic of life is reproduction in a host cell
-Agents that cause disease
Discovery of viruses
-Tobacco mosaic virus (TMV)
-First virus identified
-Mayer, Beijerinck, Ivanovski, and Wendell Stanley
-Chemical rather than an organism
Viral structures
-Protein coat
-Envelope surrounding membranes
-Proteins with attached carbohydrates
-Viruses that infect bacteria
Viral reproduction
-Two main ways
-The lytic cycle
-The lysogenic cycle
-In both cases the virus must infect a host cell
Lytic cycle
-Cycle of viral infection, reproduction, and cell destruction Lysogenic cycle
-Virus replicates without destroying the host cells
Host cell specificity
-Viruses originated when fragments of host genes escaped or were expelled from cells -As many viruses as there are organisms
Structure of HIV
-An enveloped virus
-Composed of two molecules of single-stranded RNA
How HIV infects cells
-Glycoproteins on the surface of the virus fit human cell surface receptors (CD4) -Lymphocytes
-Certain cells in the brain
-HIV capsid comes apart and release its viral RNA and reverse transcriptase to make DNA template which integrate into the host's DNA AIDS
-After the initial infection, HIV continues to replicate and mutate -HIV glycoproteins recognize a new co-receptor
-Found on subset of lymphocytes, called T-cells
-reproduces in T-cells and destroys them
-Increases number or virus particles in the blood
-Infects other T cells that block bodies immune system
-Immune system in unable to defend against infection
Viral diseases
-Emerging viruses
-Newly recognized that have reappeared or spread to new areas -Prions
-Composed of proteins but have no nucleic acid; pathogens; mad cow disease -Viroids
-Single strand or RNA (no capsid)
-Disease agents in plants
-Cucumbers, potatoes, avocados, and oranges
Important viral diseases
-Immune system failure
-Sexual contact, contaminated blood, or contaminated needles -Common cold
-Sinus congestion, muscle aches, and coughs
-Inhalation direct contact
-High fever, uncontrollable bleeding
-Body fluids
-Hepatitis A
-Flulike symptoms, swollen liver, yellow skin
-Contaminated blood, food, or water
-Hepatitis B
-Flulike symptoms, swollen liver, painful joints, can cause liver cancer -Sexual contact, contaminated blood, contaminated needles

Journal Activity
Evaluate the argument that emerging viruses are new viruses. Emerging viruses are new viruses because they are infecting something different than the original virus and they may even do something...
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