Prokaryotes
(AKA Bacteria)

Chapter 27

Domains Bacteria

&

Archaebacteria

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What should we already know about prokaryotes/bacteria?

one-celled prokaryotesdominant form of life on Earthincredibly diverse

Prokaryote

Eukaryote

double helix

Single circular chromosomehaploidnaked DNAno histone proteins~4 million base pairs~4300 genes1/1000 DNA of eukaryotereproduce asexuallymitosis/ binary fissionoffspring genetically identical to parentrapid growthgeneration every ~20 minutes108 (100 million) colony overnight!

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2 Bacteria DOMAINS

DOMAIN BACTERIA

(Eubacteria)

Contain peptidoglycan in cell wallOne type of RNA polymeraseLack introns in genomeNo histonesSensitive to antibiotics

DOMAIN ARCHAEA

(Archaebacteria)

Live in harsh environments LACK PEPTIDOGLYCAN in cell wallsMore than one RNA polymeraseHISTONES associated with DNAINTRONS in some genesResist antibiotics

EXAMPLES:
1) METHANOGENS

form CH4; require ANAEROBIC conditions (bottom of pond, landfill, sewage)

2) HALOPHILES

salt loving; require extremes in salt (> 10%)

3) THERMOACIDOPHILES

heat/acid loving; found in geothermal springs high heat/low pH

Prokaryote Structure

Unicellular3 Shapes:

Bacilli

Cocci

Spirilli

Size1/10 size of eukaryote cell1 micron (1um)Internal structureno internal compartmentsno membrane-bound organellesonly ribosomescircular, naked DNAnot wrapped around proteins

Prokaryote Cell Wall Structure

peptidoglycan = polysaccharides + amino acid chains

lipopolysaccharides = lipids + polysaccharides

Thats important for
your doctor to know!

peptide side

chains

cell wall

peptidoglycan

plasma membrane

protein

Gram-positive bacteria

Gram-negative bacteria

peptidoglycan

plasma

membrane

outer

membrane

outer membrane of
lipopolysaccharides

cell wall

Prokaryotic metabolism

How do bacteria acquire their energy & nutrients?photoautotrophsphotosynthetic bacteriachemoautotrophsoxidize inorganic compoundsnitrogen, sulfur, hydrogen heterotrophslive on plant & animal matterdecomposers & pathogens

OXYGEN REQUIREMENTS
Obligate aerobes - require oxygen
Obligate anaerobes - poisoned by oxygen
Facultative anaerobes - Use cellular respiration if has O2 can do fermentation w/o oxygen

Where does variation come from?

Spontaneous Mutation1 in every 200 bacteria has a mutation

2. Transformation (recombination)

Plasmids small supplemental circles of DNA

3. Transduction

4. Conjugation direct transfer of DNA

transposonsAll allow for rapid dissemination of new phenotypes within and between bacterial populations, allowing for rapid evolution.

#1 - Spontaneous Mutation

Spontaneous mutation is a
significant source of variation
in rapidly reproducing speciesExample: E. colihuman colon (large intestines)2 x 1010 (billion) new E. coli each day!spontaneous mutationsfor 1 gene, only ~1 mutation in 10 million replicationseach day, ~2,000 bacteria develop mutation in that genebut consider all 4300 genes, then:
4300 x 2000 = 9 million mutations per day per human host!

# 2 - Transformation

Bacteria are opportunistspick up naked foreign DNA wherever it may be hanging outhave surface transport proteins that are specialized for the uptake of naked DNA import bits of chromosomes from other bacteriaincorporate the DNA bits into their own chromosomeexpress new genes via the alteration of a bacterial cells genotype and thus phenotype transformationform of recombination

REMEMBER

Plasmids

Small supplemental circles of DNA5000 - 20,000 base pairsself-replicatingcarry extra genes2-30 genes genes for antibiotic resistancecan be exchanged between bacteriabacterial sex!!rapid evolution can be imported from
environment

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Mini-chromosomes

Plasmids & Antibiotic Resistance

Resistance is futile?1st recognized in 1950s in Japanbacterial dysentery not responding to antibioticsworldwide problem nowGenes for antibiotic resistance = R plasmidsresistant genes are on plasmids that are swapped between bacteriaR plasmids also have genes that encode for sex pili, they can be transferred from one cell to another by conjugationRole in rapid evolutionMethod for spreading antibiotic resistance

REMEMBER:

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# 3 - Transduction

Phages/viruses carry bacterial genes from one host cell to anotherTwo types:

generalized transduction, a small piece of the host cells degraded DNA is packaged within a capsid, rather than the phage genome

Specialized transduction occurs via a temperate phage

VIDEO: Transduction

# 4 Conjugation
AKA: Bacteria Sex

Direct, 1 way, transfer of DNA between 2 bacterial cells that are temporarily joinedresults from presence of F (fertility) plasmidmale (= donor = F+) extends sex pilli and attaches to female (= receiver = F-) bacteriumcytoplasmic bridge allows transfer of DNA

* built-in F factor is

called an Hfr cell

(high frequency

of recombination)

VIDEO: Conjugation

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Transposons
(Transposable elements = Jumping genes)

a piece of DNA that can move from one location to another in a cells genome = transposontarget site may be within the chromosome, from a plasmid to chromosome (or vice versa), or between plasmidscontribute to genetic shuffling in bacteriacan bring multiple copies for antibiotic resistance into a single R plasmid by moving genes to that location from different plasmids

1st described by Barbara McClintock in corn

VIDEO: Jumping Genes

Insertion Sequences & Transposons

insertion sequences:simplest transposable elementsexist only in bacteriaconsists of the transposase gene (an enzyme catalyzing movement of the insertion sequence from one site to another within the genome), flanked by a pair of inverted repeat sequences Transposons:longer and more complex than insertion sequenceshave extra genes that go along for the ride, such as genes for antibiotic resistance

Bacteria as pathogens

Disease-causing microbesplant diseaseswilts, fruit rot, blightsanimal diseasestooth decay, ulcersanthrax, botulismplague, leprosy, flesh-eating diseaseSTDs: gonorrhea, chlamydia typhoid, cholera TB, pneumonialyme disease

Antibiotics can kill bacteria by inhibiting enzyme or processes specific to bacteria are powerless again viruses, which have few or no enzymes of their own.

Discovery Video: Antibiotics

Bacteria as beneficial (& necessary)

Life on Earth is dependent on bacteriadecomposersrecycling of nutrients from dead to livingnitrogen fixationonly organisms that can fix N from atmosphereneeded for synthesis of proteins & nucleic acidsplant root noduleshelp in digestion (E. coli)digest cellulose for herbivorescellulase enzymeproduce vitamins K & B12 for humansproduce foods & medicinesfrom yogurt to insulin