Chapter 27

Prokaryotes and the Origins of Metabolic Diversity

Archaebacteria&Bacteria

Classification Old 5 Kingdom system

• Monera, Protists, Plants, Fungi, Animals

New 3 Domain system– reflects a greater understanding

of evolution & molecular evidence• Prokaryote: Bacteria

• Prokaryote: Archaebacteria

• Eukaryotes– Protists

– Plants

– Fungi

– Animals

Prokaryote

Eukaryote

2007-2008

Prokaryotes

Domain Bacteria

Domain Archaebacteria

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

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 membranesfor photosynthesis

like a chloroplast(thylakoids)

internal membranes

for respiration

like a mitochondrion

(cristae)

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 decomposers

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 disease

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