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Microorganisms and Fungi
Bacteria and Viruses
Viruses

Vocabulary

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
Viruses
-Composed of nucleic acids enclosed in a protein coat
-Smaller than the smallest bacterium
-Non'living
-Only characteristic of life is reproduction in a host cell
-Pathogens
-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
-Capsid
-Protein coat
-Envelope
-Envelope surrounding membranes
-Glycoproteins
-Proteins with attached carbohydrates
-Bacteriophage
-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
-Attachment
-Glycoproteins on the surface of the virus fit human cell surface receptors (CD4) -Lymphocytes
-Macrophages
-Certain cells in the brain
-Replication
-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
-AIDS
-Immune system failure
-Sexual contact, contaminated blood, or contaminated needles -Common cold
-Sinus congestion, muscle aches, and coughs
-Inhalation direct contact
-Ebola
-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
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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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