Ch. 27 Prokaryotes

Ch. 27 ProkaryotesDomain Bacteria

Domain Archaebacteria

2007-2008

DomainBacteria

DomainArchaea

DomainEukarya

Common ancestor

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

Prokaryote Structure• Unicellular– bacilli, cocci, spirilli

• Size– 1/10 size of eukaryote cell• 1 micron (1um)

• Internal structure– no internal compartments• no membrane-bound organelles• only ribosomes

– circular chromosome, naked DNA• not wrapped around proteins

prokaryotecell

eukaryote cell

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

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)

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!)

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 DNA

conjugation

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 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)

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