AP Biology

Lecture #46Prokaryotes

Prokaryotes

Domain BacteriaDomain Archaebacteria

2007-2008

DomainBacteria

DomainArchaea

DomainEukarya

Common ancestor

• Bacteria are classified into two kingdoms: Eubacteria (true bacteria) and Archaebacteria (Ancient Bacteria).

• BACTERIA are microscopic Prokaryotes.  (“before nucleus”)

• Adapted to living in all environments (even some extreme) – they exist EVERYWHERE

Bacteria

Bacteria live EVERYWHERE!• Bacteria live in all ecosystems

– on plants & animals– in plants & animals– in the soil– in depths of the oceans– in extreme cold– in extreme hot– in extreme salt– on the living– on the dead

Microbes alwaysfind a way tomake a living!

Bacterial diversity

Rods(bacilli) and spheres(cocci) and spirals(helical)…Oh My!

Prokaryote Structure

• Unicellular– bacilli, cocci, spirilli

• Size– 1/10 size of eukaryote cell

• 1 micron (1μm)

• Internal structure– no internal compartments

• no membrane-bound organelles• only ribosomes

– circular chromosome, naked DNA• not wrapped around proteins

prokaryotecell

eukaryote cell

Shapes of Bacteria• Coccus

– Chain = Streptoccus– Cluster = Staphylococcus

• Bacillus– Chain = Streptobacillus

• Coccobacillus• Vibrio = curved• Spirillum• Spirochete• Square• Star

Variations in Cell Interior

internal membranesfor photosynthesis

like a chloroplast(thylakoids)

internal membranes

for respiration

like a mitochondrion

(cristae)

aerobic bacterium

mitochondria

cyanobacterium(photosythetic) bacterium

chloroplast

Bacterial Structures• Flagella • Pili• Capsule• Plasma Membrane• Cytoplasm• Cell Wall• Lipopolysaccharides• Teichoic Acids• Inclusions• Spores

Bacteria Structure

Nucleoid region contains a circular loop of DNA

Plasmids are rings of DNA, used in reproduction

Ribosomes in cytoplasm synthesize proteins

Flagella is used for movement

Pilli (Fimbrae) help bacteria cling to surfaces

Prokaryotes do not have organelles or a membrane bound  nucleus!

Prokaryote Cell Wall Structurepeptide side

chains

cell wallpeptidoglycan

plasma membrane

protein

Gram-positive bacteria

Gram-negative bacteria

peptidoglycan

plasmamembrane

outermembrane

outer membrane of lipopolysaccharides

cell wall

peptidoglycan = polysaccharides + amino acid chainslipopolysaccharides = lipids + polysaccharides

That’simportant foryour doctorto know!

Motility• 1- Flagella• 2- Helical shape

(spirochetes)• 3- Slime• 4-Taxis

(movement away or toward a stimulus)

Flagella• Motility - movement• Swarming occurs with some bacteria

– Spread across Petri Dish– Proteus species most evident

• Arrangement basis for classification– Monotrichous; 1 flagella– Lophotrichous; tuft at one end– Amphitrichous; both ends– Peritrichous; all around bacteria

Form & Function

• Nucleoid region (genophore: non-eukaryotic chromosome)

• Plasmids• Asexual reproduction: binary fission

(not mitosis)• “Sexual” reproduction (not meiosis):

• transformation~ uptake of genes from surrounding environment

• conjugation~ direct gene transfer from 1 prokaryote to another transduction~ gene transfer by viruses

• Endospore: resistant cells for harsh conditions (250 million years!)

• Bacteria can reproduce sexually by conjugation or asexually by binary fission.

In bacteria, genetic recombination can occur in three ways.

a. Conjugation occurs when a bacterium passes DNA to a second bacterium through a tube (sex pilus) that temporarily joins two cells; this occurs only between bacteria in the same or closely related species.

b.Transformation involves bacteria taking up free pieces of DNA secreted by live bacteria or released by dead bacteria.

c. In transduction, bacteriophages transfer portions of bacterial DNA from one cell to another. Plasmids can carry genes for resistance to antibiotics and transfer them between bacteria by any of these processes

Genetic variation in bacteria• Mutations

– bacteria can reproduce every 20 minutes• binary fission

– error rate in copying DNA• 1 in every 200 bacteria has a mutation• you have billions of E. coli in your gut!

– lots of mutation potential!

• Genetic recombination– bacteria swap genes

• plasmids– small supplemental

circles of DNA

• conjugation– direct transfer of DNAconjugation

Plasmid – an extra bit of DNA, used in sexual reproduction

Plasmids are also used in genetic engineering

Some bacteria form resistant endospores in response to unfavorable environmental conditions.

Nutrition & Metabolism• Photoautotrophs: photosynthetic;

harness light to drive the synthesis of organics (cyanobacteria)

• Chemoautotrophs: oxidation of inorganics for energy; get carbon from CO2

• Photoheterotrophs: use light to generate ATP but get carbon in an organic form

• Chemoheterotrophs: consume organic molecules for both energy and carbon– saprobes- dead organic matter

decomposer– parasites- absorb nutrients from living

hosts• Oxygen relationships: obligate aerobes;

facultative anaerobes; obligate anaerobes

• Bacteria classified as heterotrophs derive energy from breaking down complex organic compounds in the environment. This includes saprobes, bacteria that feed on decaying material and organic wastes, as well as those that live as parasites, absorbing nutrients from living organisms.

Prokaryotic Nutrition  1.   Bacteria differ in their need for, and tolerance of, oxygen (O2).

a.   Obligate anaerobes are unable to grow in the presence of O2; this includes anaerobic bacteria that cause botulism, gas gangrene, and tetanus.b.   Facultative anaerobes are able to grow in either the presence or absence of gaseous O2.c.   Aerobic organisms (including animals and most prokaryotes) require a constant supply of O2 to carry out cellular respiration.

staphylococcus is a gram-positive, facultative anaerobe

2.   Autotrophic Prokaryotes

a.   Photoautotrophs are photosynthetic and use light energy to assemble the organic molecules they require.b.   Chemoautotrophs make organic molecules by using energy derived from the oxidation of inorganic compounds in the environment. (methanogens)

3.   Heterotrophic Prokaryotes

a.    Most free‑living bacteria are chemoheterotrophs that take in pre-formed organic nutrients.b.    As aerobic saprotrophs, there is probably no natural organic molecule that cannot be broken down by some prokaryotic species. c.    Detritivores (saprophytic bacteria) are critical in recycling materials in the ecosystem; they decompose dead organic matter and make it available to photosynthesizers.

Bacteria have an important role to play in breaking down materials in the environment.

Some are harmful and break down material we'd rather keep, like this image of an infection of necrotizing fasciitis (flesh-eating bacteria)

Endospore• Bacteria can survive

unfavorable conditions by producing an endospore.

Bacteria as pathogens– animal diseases

• tooth decay, ulcers• anthrax, botulism• plague, leprosy, “flesh-

eating” disease• STDs: gonorrhea,

chlamydia • typhoid, cholera • TB, pneumonia• lyme diseaseplant diseases• wilts, fruit rot, blights

opportunistic: normal residents of host; cause illness when defenses are weakened •Koch’s postulates: criteria for bacterial disease confirmation•exotoxins: bacterial proteins that can produce disease w/o the prokaryote present (botulism) •endotoxins: components of gram - membranes (Salmonella)

Crystal violet

Gram's iodine

Decolorise with acetone

Counterstain withe.g. methyl red

Gram-positives appear purple

Gram-negatives appear pink

The Gram Stain

Bacteria as beneficial (& necessary)• Life on Earth is dependent on bacteria

– decomposers• recycling of nutrients from dead to living

– nitrogen fixation• only organisms that can fix N from atmosphere

– needed for synthesis of proteins & nucleic acids– plant root nodules

– help in digestion (E. coli)• digest cellulose for herbivores

– cellulase enzyme• produce vitamins K & B12 for humans

– produce foods & medicines• from yogurt to insulin

Archaebacteria• Methane producers – anaerobic• Halophiles

–Halo = salt–Philia = love

• Thermophiles–Thermo = heat

Methanogens These Archebacteria are anaerobes. They make methane (natural gas) as a waste product. They are found in swamp sediments, sewage, and in buried landfills. In the future, they could be used to produce methane as a byproduct of sewage treatment or landfill operation.

Extreme halophiles can live in extremely salty environments. Most are photosynthetic autotrophs. The photosynthesizers in this category are purple because instead of using chlorophyll to photosynthesize, they use a similar pigment called bacteriorhodopsin that uses all light except for purple light, making the cells appear purple.

These are Archaebacteria from hot springs and other high temperature environments. Some can grow above the boiling temperature of water. They are anaerobes, performing anaerobic respiration.

Thermophiles are interesting because they contain genes for heat-stable enzymes that may be of great value in industry and medicine.