I have heard it was the opinion of others that it [the plague] might be distinguished by the party's breathing upon a piece of glass, where, the breath condensing, there might living creatures be seen by a microscope, of strange, monstrous, and frightful shapes, such as dragons, snakes, serpents, and devils, horrible to behold.
-Daniel Defoe
A Journal of the Plague Year, 1721


Campbell and Reece, Chapter 18

Viruses
(Continues some material from the last lecture)
Second semester (Bio 106) starts with Diversity (the march through the kingdoms). The difficulty (previous lecture) in defining a virus as alive makes it virtually impossible for an introductory textbook to have a good place to cover viruses, so here they are.

TRANSPARENCY (Fig. 18.1) Being small (Protein and DNA) they pass through fine filters, hence an old term, "filterable"
Bacteriophage (phage-eat) protein and DNA
TRANSPARENCY Fig. 18.4 lytic cycle - bacterial cells lyse.
Viruses cause lots of disorders: measles, smallpox, chicken pox, mumps, rabies, flu = influenza, herpes, AIDS, mononucleosis, polio, colds, rubella (German measles), yellow fever, hepatitis

Some very fundamental terminology:
Antigen - non-self protein (virus coat)
Antibody to antigen made by B lymphocytes (white blood cells)

History:

Vaccines - active immunity (like disease)
memory cells of immune system
Edward Jenner 1796 "encowment" cowpox, smallpox
Smallpox is so completely eliminated that one issue is whether to get rid of lab virus.
Passive immunity - give antibodies

Flu
1918 20 million died worldwide
1957 Asian bad
1968 Hong Kong bad (70,000 died in 6 wks)
change (mutate) also exchange with birds (ducks)

TRANSPARENCY (Fig. 18.2) Structurally (and chemically) not all viruses are as simple as bacteriophage, and sometimes RNA is the hereditary material
TRANSPARENCY (Fig, 18.3) Not always does cell burst. Here you see how the virus takes over the cells machinery to make its own DNA and to make proteins etc after transcription of its DNA into RNA

TRANSPARENCY (Fig. 18.7) The retrovirus, HIV (Human Immunodeficiency Virus that leads to AIDS, acquired immunodeficiency syndrome) deserves special attention. Its hereditary material is RNA. It is called a retrovirus because it comes pre-packaged with functional reverse transcriptase enzyme to make DNA out of RNA. The DNA that is made gets incorporated into the cell's own genome.

That last phenomenon is one of the underlying themes of this chapter which in many ways is a hodge-podge - How do cells get changed genetically?

MONERA bacteria, also blue-green algae (cyanobacteria)
(algae = aquatic plants)

TRANSPARENCY Fig. 7.4
Here is a picture of E. coli (Escherichia coli), the most famous bacterium from genetics and molecular studies - this picture was found at the microbe zoo site
circular DNA
prokaryote, (karyon as in "karyotype," refers to the nucleus)
genophore - bacterial chromosome
Reproduction by fission, "Multiply and Divide"
also DNA transferred: (1) transformation (last lecture example of DNA from smooth transforming rough) , transduction (from phage TRANSPARENCY [Fig. 18.13]), conjugation (like mating, TRANSPARENCY [Fig. 18.15])
Plasmids - little circles of DNA - very useful in molecular biology and easy to identify since they carry antibiotic resistance

Fundamental story:

(relates to fundamental topic of gene regulation) lac operon - genes for enzymes for metabolism of lactose, the disaccharide in milk TRANSPARENCY (Fig. 18.21 A & B). When lactose is present, allolactose pulls repressor off of operator so that RNA polymerase can move from promoter to make mRNA for genes (lacZ, lacY and lacA) that code for their respective enzymes (beta-galactosidase, permease and transacetylase, enzymwes for lactose metabolism. The bacterium "does not bother" making lactose metabolizing enzymes unless lactose (the sugar in milk) is present. Note that one mRNA is for 3 proteins, never the case in eukaryotes.

The 1965 Nobel Prize in Physiology and Medicine was shared by FRANÇOIS JACOB and JACOUES MONOD who established the operon model.

Two other stories:

DNA is very stable, and slow mutational changes over long time periods were once thought to be the only agents of evolutionary change. Over the last few decades, and related to the idea that retroviruses can orchestrate insertions into DNA, was the idea of transposons TRANSPARENCY (Fig. 18.16). In the lab (or in nature) genes (or hunks of DNA) can insert. For instance, in fruit flies, genes can be inserted to make new transgenic Drosophila. If the "jumping gene" inadvertently jumps into the middle of another gene, it will ruin it.

The 1983 Nobel Prize in Physiology and Medicine went to BARBARA MC CLINTOCK for her discovery of mobile genetic elements.

Various spongiform encephalitis syndromes (where the brain degenerates) were once thought to be caused by slow viruses, but now are thought to be caused by protein without any hereditary material. Such disorders include Creutzfeld-Jacob Syndrome in humans, scrapie in sheep and bovine "mad cow disease." TRANSPARENCY (Fig. 18.10) shows how this might happen.

The 1997 Nobel Prize in Physiology and Medicine went to STANLEY B. PRUSINER for his discovery of Prions - a new biological principle of infection

For further study: Here is a site entitled "Communicable Disease Surveillance and Response (CSR)" which is of relevance to this and other chapters. And here is Disease information from the Centers for Disease Control, also relevant to several chapters, especially this one.

This page was last updated 7/23/02

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