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Monday, November 3, 2008

BACTERIAL CLASSIFICATION

• HOW DO VIRUSES REPRODUCE & CAUSE DISEASE?

• VIRAL LIFECYCLES
• VIRAL DNA MAY BECOME PART OF HOST CHROMOSOME

• Viruses are packaged genes-can only reproduce inside cells.

• Lytic cycle-viral replication cycle resulting in the release of new viruses by lysis of host cell.

• Lysogenic cycle-a bacteriophage replication cycle in which the viral genome is incorporated into the bacterial host chromosome and the host cell is not lysed unless the viral genome leaves the host chromosome.

• MANY VIRUSES CAUSE DISEASE IN ANIMALS

• Viruses that infect animal cells cause diseases.

• RNA viruses have RNA as their genetic material and responsible for flu, cold, measles, mumps, AIDS, polio.

• DNA viruses have DNA as their genetic material and cause hepatitis, chicken pox, herpes.

• Amount of damage a virus can cause depends on: how quickly our immune system responds to fight the infection and ability of the infected tissue to repair itself.

• Recover quickly from colds since respiratory tract can efficiently replace damaged cells by mitosis.

• Poliovirus attacks cause permanent damage since nerve cells don’t divide. Prevention = vaccines.

• Antibiotics for bacterial infections are futile for curing viral infections.

• Development of antiviral drugs is slow since it’s difficult to find ways to kill a virus and not its host cell.

• HIV MODEL
• AIDS VIRUS MAKES DNA ON AN RNA TEMPLATE (RETROVIRUS)

• AIDS caused by a type of RNA virus.

• HIV virus is aided by membranous envelope and glycoprotein spikes to enter and leave a host cell.

• HIV contains 2 copies of RNA instead of 1.

• HIV is a retrovirus as it synthesizes
– DNA on an RNA template by
– the help of an enzyme,
– reverse transcriptase
– (catalyzes reverse transcription).

• BEHAVIOUR OF HIV NUCLEIC ACID IN A HOST CELL
• HIV RNA uncoated in the cytoplasm of host cell.
• Reverse transcriptase uses RNA as template to make DNA strand.
• Then adds second complementary DNA strand.
• Double stranded DNA enters cell’s nucleus and inserts itself into chromosomal DNA = provirus.
• Provirus is transcribed into RNA and translated into viral proteins.
• New viruses leave the cell and infect other cells.

• DO YOU UNDERSTAND BASIC BACTERIAL NUTRITION?

• PROKARYOTES COME IN VARIETY OF SHAPE

• PROKARYOTES COME IN VARIETY OF SHAPE

• Cocci-spherical, occur in clusters, are called staphylococci. Those in chains-streptococci.
• Bacilli-rod-shaped, most occur singly but in pairs (diplobacilli) and in chains (streptobacilli).
• Curved or spiral.
• Commas called vibrios.
• Helical.
• Relatively short = spirilla.
• Longer, more flexible = spirochete.
• PROKARYOTES OBTAIN NOURISHMENT IN A VARIETY OF WAYS

• 2 main resources: carbon (for synthesizing organic compounds) and energy.

• Prokaryotes exhibit much more nutritional diversity than eukaryotes.

• THE EARLY EVOLUTION OF NUTRITION

• Chemoheterotrophs dominant prokaryotes today and may have been since dawn of life.

• First prokaryote may have had simple metabolism requiring only few enzymes.

• Its environment contained no oxygen, metabolism anaerobic.

• Unlikely that sunlight was used as energy source since complex set of enzymes needed for such use.

• Carbon and energy obtained from rich soup of molecules and ions in which they evolved.

• ARCHAEA THRIVE IN EXTREME ENVIRONMENT & IN OCEAN

• Archaeal inhabitants of extreme environments have unusual proteins and other molecular adaptations that enable effective metabolism and reproduction.

• Archaea are extremophiles-can thrive in extreme environments (too hot, too salty, too acidic for other organisms).

• Extreme halophiles
• Thrive in very salty places.

• Extreme thermophiles
• Thrive in very hot water.
• In deep-ocean vents where water 1000C.


• HOW DO BACTERIA EXPLOIT SO MANY HABITATS?

HOW ARE BACTERIA A CAUSE OF DISEASE?

• DIVERSE STRUCTURAL FEATURES AID PROKARYOTES THRIVE ALMOST EVERYWHERE

Flagella
• Enables moving towards favourable places and away from less favourable ones.

• Prokaryotic flagellum is naked protein structure that lacks microtubules unlike flagellum of eukaryotic cell.

• Rings give flagellum propeller-like rotary movement.


• PILI
• Shorter and thinner than flagella.

• Help bacteria to stick to each other and to surfaces such as rocks in streams, human intestine lining, etc.

• Sex pili required for initiating bacterial “mating”.

• ENDOSPORES

• Bacteria can survive extended periods of harsh conditions by forming specialized “resting cells”.
• Has thick, protective coat, its cytoplasm is dehydrated and it does not metabolize.
• Under harsh conditions, outer cell disintegrates but endospore survives all sorts of trauma.
• When environment favourable, endospore absorbs water and resumes growth.
• Not even boiling water can kill these.


• CYANOBACTERIA

• Blue-green colour caused by trillions of cyanobacterial cells.
• Photosynthetic bacteria.
• Common in lakes, ponds, tropical oceans.
• Extensive blooms indicate polluted water conditions usually phosphates and nitrates from agricultural run offs.
• About 3.0 to 1.5bya, ancient cyanobacteria gave earth its first greenish coat.
• SOME BACTERIA CAUSE DISEASES

• Pathogens-disease causing agents.
• Most cause disease by producing poisons, two types:

• Exotoxin-toxic proteins secreted by bacterial cells, include most of the potent poisons.

• Endotoxins-not cell secretions, but components of the cell walls of certain bacteria.
• WHY ARE BACTERIA VITAL TO THE ENVIRONMENT?
• BACTERIA CAN BE USED AS BIOLOGICAL WEAPONS-BIOTERRORISM

• Animals, plants, fungi, bacteria and viruses.

• To weaponize naturally occurring pathogens, researchers selected highly virulent strains, made them antibiotic resistant and developed formulations for effective dispersion.

• Bacillus anthracis-bioweapon since it’s easier to obtain (bacterium lives in soils in agricultural regions), easy to grow in labs and forms hardy endospores that can be stored for years.

• In bloodstream, anthrax bacteria actively metabolize and multiply-release 3 proteins that combine to form toxin that destroys body tissues and cells of the immune system.

• PROKARYOTES HELP RECYCLE CHEMICALS AND CLEAN UP ENVIRONMENT

• Restores oxygen to atmosphere.
• Some cyanobacteria convert nitrogen gas in atm to nitrogen (N) cpds (nitrates and nitrites) that plants take up and use.
• Other prokaryotes living in nodules on roots of legumes contribute large amounts of N cpds to soil.
• Decomposition of organic wastes and dead organisms to inorganic chemicals that other organisms can use.
• Prokaryote decomposers are also mainstays of our sewage treatment facilities.
• Aid in bioremediation-use of prokaryotes (or other organisms) to clean up pollution.

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