Monday February 1, 1999
Announcements: If you did not receive an exam score it could be because your social security number was incorrect. If so talk to Mrs. Schlegel.

Lecture notes:

A virus is a noncellular infectious agent.

Contains: 1. A nucleic acid core (DNA or RNA) surrounded by a protective protein coat called a capsid.
2. Some have a lipid "envelope" outside the capsid.

Viruses can only replicate after they have infected a host cell and have taken over the host cell's metabolic machinery.

Some viruses have double stranded DNA
Some viruses have single stranded DNA
Some viruses have single stranded RNA
Some viruses have double stranded RNA!

Viruses can infect every type of living cell.

There are specific host cells for each virus…Examples: plant viruses, bacteriophages (bacterial viruses), insect viruses, etc.

Lytic: 1. Infection of the host cell.
2. Replication of viral DNA/RNA.
3. Synthesis of viral proteins.
4. Assembly of virus.
5. Release of virus: a) lysis of cell (breakage)
b) budding off.

Lysogenic: 1. Infection of host cell.
2. Viral DNA becomes integrated into host DNA.
3. Latent state.
4. "Something" might induce the virus to switch to the lytic pathway.

Retroviruses

The AIDS virus is a retrovirus. These viruses have the ability to make a DNA copy of their viral RNA with the unique enzyme reverse transcriptase. This newly made DNA incorporates itself into the host's DNA.

Viroids are RNA pieces - either linear or circular.

There is no protein coat for protection.

They can somehow infect and replicate in a host cell.

They cause disease in citrus fruits, avocadoes, seed potatoes, and coconut palms.

These are small proteins with no nucleic acid.

We are just beginning to know some details.

They are thought to cause: Scrapie in sheep, Kuru in humans, Creutzfeldt-Jakob Disease in humans, Mad Cow disease.

Bacteria are called Prokaryotes which means before the nucleus.

Eubacteria: True bacteria

Some are Photosythetic and use sunlight to make ATP.
Example: Cyanobacteria (blue-green algae)
Some are Chemosynthetic and use ammonia or nitrate to make ATP.
Example: Nitrobacter ("fixes" nitrogen in the soil)
Some are Heterotrophs (other feeders) This group includes major pathogens in humans and animals
Example: Lyme disease, Botulism, Syphilis, Gonorrhea, Clamydia/

Archaebacteria:
1. Live in very hash environments.
2. Their ribosomes are different from those in Eubacteria.
3. Their lipid membrane is very different.
4. Their DNA and RNA sequences are very different from Eubacteria.
5. Cell wall is different.

Methanogens:
1. Anerobic
2. Convert CO₂ + 2H₂-------->CH₄ +O₂ (CH₄ is methane)

Halophiles:
1. Live in extremely salty places.
Example: those that live in the Great Salt Lake or the Dead Sea.

Thermoacidophiles:
1. Live in very acidic environments and/or…
2. Live in very hot environments.
Examples: bacteria that inhabit hot springs.

* Colonize the gut
* Essential in cheese making
* Nitrogen fixation in soil
* Important in the food, chemical, and pharmaceutical industries.
* Biotechnology

Plasma membrane

1 chromosome - a piece or circular DNA.

Some bacteria have extra small pieces of circular DNA called plasmids. They can code for proteins that cause serious disease - Diphtheria - or can confer antibiotic resistance to a bacterium.

Most have a cell wall (except for mycoplasms which casue serious pnuemonias).

Some have a capsule - a thick coat of polysaccharide (usually) that protects the bacteria from an attack by the immune system.

Some have "slime layers" - similar to capsules, but looser arrangement of the molecules. Smile layers serve to attach bacteria to surfaces.

Some have flagella for movement.

Some make endospores.

Bacterial reproduction
Bacterial reproduction is called Binary fission: the DNA (1 circular chromosome) divides, then two daughter cells are formed.

Conjugation
Conjugation is not reproduction. During conjugation one bacterium with a special plasmid transfers some genetic information to another bacterium which does not have this special plasmid. The genetic information transferred is a single copy of the plasmid.

Endospores
An endospore is the resting state of some bacteria. It is very resistant to heat, dry conditions, and some radiation. Example: Clostridium botulinum which causes Botulism.