Ch 16: Prokaryotes & Viruses

VocabularyStromatoliteArachaeaBacteriaCoccusBacillusSpirocheteBinary fissionEndosporeCyanobacteriaBioremediationPathogen

Lytic cycleLysogenic cycleRetrovirusVaccine

16.1: Early Earth• Earth is about 4.6 billion years old• Fossils resembling photosynthetic prokaryotes

have been found in dome shaped rocks called stromatolites, date back to 3.5 billion year ago.

16.1: Origin of Organic Molecules• In 1953, Miller & Urey

designed an experiment to simulate conditions on early Earth

• Under many different conditions produced all 20 amino acids, several sugars, lipids, the nitrogenous bases found in DNA & RNA and ATP

• Solutions of amino acids dropped onto the surface of hot sand, clay or rocks has resulted in the formation of polypeptides

16.1: The RNA World • A characteristic of life is the process of inheritance• Need molecules that can copy themselves.

Today: DNA RNA Protein

• How did this information flow originate?

• A popular hypothesis is that genes were originally short strands of RNA capable of replicating without enzymes

–Scientists have observed RNA molecules copying themselves in solutions containing nucleotides without enzymes or cells present– During the “RNA world”, RNA might have stored genetic information in addition to directing protein synthesis

16.1: Formation of Pre-Cells • Experiments have

shown that polypeptides can form microscopic fluid-filled spheres.

• If certain kinds of lipids are in the solution selectively permeable membranes will form.

• These “molecular packages” are referred to as pre-cells

Hypothetical 4-Stage Sequence for Origin of Life

1. Small organic molecules formed fr. simpler inorganic molecules

2. Small molecules joined into complex ones

3. Molecules that could copy themselves provided a basis for inheritance of molecular information

4. These molecules became packaged within membranes and separated from their surroundings

16.1: 1st Life is ProkaryoticARCHAEA•“archaea” = ancient•Exist in harsh habitats resembling conditions of early Earth•“Extremophiles”

– Thermophiles (heat)– Halophiles (salt)– Anaerobic (no oxygen)

•Believed to be as closely related to eukaryotes as they are to bacteria

BACTERIA•Contain diff. info. in nucleic acids•RNA polymerases differ•Lack introns (junk DNA)•Susceptible to antibiotics that do not affect archaea•Contain peptidoglycan in their cell walls

Phylogenic Tree of the Three Domains

16.2: BacteriaStructure & Function

• Cocci – spherical (Pnemonia)• Bacilli – rod-shaped (E.coli)• Spirilla – spiral shaped (siphilis)

16.2: Structure & Function of Bacteria: Cell Wall• Gram + (purple

stain): thick layer of peptidoglycan (absorbs more stain)

• Gram – (pink stain): thinner layer of peptidglycan with outer membrane

16. 2: Structure & Function of Bacteria: Motility

• Flagellum (whip)• Pilli (hair)• Slime secretion

(ooze)

Bacterial Reproduction: Binary Fission (ASEXUAL)

DNA is copied & moved to opposite ends of the cell as the cell divides; occurs almost continuously.•Rapid rate (every 20 min)

•Results in a colony of cells that are clones (unless mutations occur)

Genetic Variation in Bacteria: Conjucation

• 2 bacterial temporarily join • exchange plasmid DNA;

does not need to occur between cells of the same species/strain

not same as sex. Repro. (just involves exchange small amounts of DNA)

Genetic Variation in Bacteria: Transformation

• Fragments of foreign DNA “picked up” and incorporated into bacteria chromosome (usu. Fr. Dead bacteria cells)

Endospores

• Allow bacteria to survive periods of very harsh conditions by going into a dormant endospore form

• After copying DNA, one copy is surrounded by a thick protective coat and the outer cell disintegrates

• Can survive for years; when conditions are favorable, the endospores will absorb water and grow again.

Modes of Nutrition

16.2: Evolution of Cyanobacteria

• 250 ma• Change Earth’s environment; CO2 atmosphere O2

atmosphere; cool planet down.

16.2: The Oxygen Revolution• The evolution of photosynthetic cyanobacteria

resulted in the presence of free oxygen in oceans, lakes & the atmosphere

• O2 = toxic to many existing organisms (attacks bonds of organic molecules); Causes a mass extinction

• Some were not exposed to oxygen and remained anaerobic; their descendants still exist in similar environments today (anaerobic bacteria)

• Some were able to use the oxygen to get energy fr. Food diversify to become aerobic organisms in existence today

16.3: Beneficial Uses of Bacteria• Chemical recycling:

– Decomposers: replenish soil nutrients and release CO2 back to the atmosphere

– Nitrogen fixing bacteria: convert nitrogen gas in the atmosphere to an organic form usable by other organisms for nucleotide and amino acid formation

• Bioremediation:– Sewage treatment: decompose organic matter in sewage sludge– Oil spill clean-up: genetically modified digest oil– Clean old mining sites: detoxify by extracting lead & mercury

• Medicine/Pharmaceuticals:– Produce desired gene products: insulin, HGH– Probiotics: restore beneficical intestinal bacteria

• Food:– Cheese– Yogurt

16.4: Bacteria & DiseasePathogens = Bacteria that cause disease.Prevention: Water filtration & hand washingTreatment: Antibiotics (prevent cell wall formation)Common bacterial infections: strep throat, pneumonia, staph (wound) infections, upper respiratory infections

16.5: Viruses

• Not technically a living organism.

• Much smaller than bacteria.• Cannot reproduce on its

own; must infect and use living cells to repro.

• Consist of DNA/RNA + protein coat

16.5: Viral Structure

16.5: Viral Reproductive Cycles

Lytic cycle

(cell bursts open w/ viruses)

Lysogenic cycle

(No bursting open; viral DNA incorp. & copied)

Viruses & Disease• Different fr. bacteria• Antibiotics will not work on viruses b/c antibiotics target

bacteria cell walls.• Some examples of viral diseases include:

Influenza (RNA) Polio (RNA)

Common cold (RNA) Hepatitis (DNA)

Measles (RNA) Herpes (DNA)

Mumps (RNA) Smallpox (DNA)

AIDS (RNA) Rabies (RNA)

Retroviruses & HIV• Retroviruses reverse the

normal DNA to RNA to protein flow – In RNA viruses, the RNA

nucleotide will be translated

• Reverse transcriptase catalyzes the synthesis of DNA from an RNA template, the DNA intermingles with host DNA as a provirus making it difficult to detect

Defense Against Viral Diseases: Immunization (not antibiotics)

• Vaccines are made from pieces of virus (antigens = surface markers)

• Immune cells launch an “attack” and trigger formation of antibodies (memory cells) that will recognize that virus when it invades. When real virus enters body, body attacks virus b4 it can multiply.

• Don’t get flu fr. Vaccine b/c it is not an intact working virus.• http://apps.nlm.nih.gov/againsttheodds/exhibit/preventing_disease/zoom713.html