Prokaryotes (Archaea and Bacteria) Chapter 28. 2 The First Cells Microfossils are fossilized forms of microscopic life -Oldest are 3.5 billion years old.

Prokaryotes (Archaea and Bacteria)

Chapter 28

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The First CellsMicrofossils are fossilized forms of microscopic life

-Oldest are 3.5 billion years old -Isotopic analysis and concentration of carbon-12 in fossils

suggests that carbon fixation was active as much as 3.8 BYACarbon-12 is found in higher concentrations in living vs. nonliving

things

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The Cyanobacteria

Stromatolites are mats of cyanobacterial cells that trap mineral deposits-Oldest are 2.7 billion years old

-Lipids were found in ancient rocks

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Flagella, spin like propellers Composed of the protein flagellin

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Prokaryotic FeaturesMetabolic diversity

-Two types of PHOTOSYNTHESIS

-Oxygenic = Produces oxygen (make O

by oxidizing H20)

-Anoxygenic = Nonoxygen producing

(e.g.make S by oxidizing H2S... purple sulfur bacteria)

-Chemolithotrophic prokaryotes derive energy from inorganic molecules (e.g. oxidize ammonia making nitrate, taken up by plants)

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Bacteria vs. Archaea

Plasma membrane

-Bacterial-Connected to glycerol by ester linkages

as seen in Eukarya

-Archaeal-Connected to glycerol by ether linkages

• Cell wall– All prokaryotes have cell walls– Bacteria have peptidoglycan– Archaea lack peptidoglycan

• DNA replication– Both have single replication origin– Archaeal DNA replication is more similar to

that of eukaryotes

• Gene Expression– Archaeal transcription and translation are

more similar to those of eukaryotes

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Bacteria vs. Archaea

Molecular Classification

1. Amino acid sequences of key proteins

2. Percent guanine–cytosine content

3. Nucleic acid hybridization– Closely related species will have more base

pairing

4. Gene and RNA sequencing– Especially rRNA

5. Whole-genome sequencing

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Most prokaryotes have one of 3 basic shapes

-Bacillus = Rod-shaped

-Coccus = Spherical

-Spirillum = Helical-shaped

Prokaryotic Shapes

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Maintains shape and protects the cell from swelling and rupturing

Consists of peptidoglycan

-Polysaccharides cross-linked with peptides

Cell wall is the basis of the Gram stain

The Bacterial Cell Wall

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Two main types

-Gram-positive bacteria

-Thick peptidoglycan

-Teichoic and lipoteichoic acids

-Gram-negative bacteria

-Thin peptidoglycan

-Have an outer membrane

-Contains lipopolysaccharide

The Bacterial Cell Wall

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The Bacterial Cell Wall

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The Bacterial Cell Wall

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Internal Structure

Internal membranes

-Invaginated cell membrane

-For respiration or photosynthesis

Endospores

-Highly-resistant structures

-Released upon cell lysis

-Can germinate back to normal cell

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Prokaryotic Genetics

Prokaryotes do not reproduce sexually

However, they undergo horizontal gene transfer, which is of three types

-Conjugation = Cell-to-cell contact

-Transduction = By bacteriophages

-Transformation = From the environment

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ConjugationTransfer of the F plasmid occurs through the

conjugation bridge

The end result is two F+ cells

-R (antibiotic resistance) plasmids

-Virulence plasmids (E. coli O157:H7 strain)

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Transduction

Viruses package bacterial DNA and transfer it in a subsequent infection

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Transformation

Natural transformation

-DNA that is released from a dead cell is picked up by another live cell...Horizontal gene transfer (no cell fusion so not sexual !!)

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Prokaryotic Metabolism

Acquisition of Carbon

-Autotrophs = From inorganic CO2

-Heterotrophs = From organic molecules

Acquisition of Energy

-Chemolithotrophs = From inorganic chemicals

-Phototrophs = From sunlight

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Prokaryotic MetabolismPhotoautotrophs

-Cyanobacteria (light to reduce Carbon--using C02 via oxidation of H20). Similar to plants and

algae.Chemolithoautotrophs

-Nitrifiers FOR energy (e.g. ammonia to nitrite). Can make reduced organic molecules from CO2

Photoheterotrophs -Purple and green Nonsulfur Bacteria

(e.g. light to oxidize Hydrogen. C source not from CO2)Chemoheterotrophs

-Majority of prokaryotes-Use organic molecules for C and energy

(oxidize organic carbon to C02 for energy. Aren’t anabolic from a CO2 starting point)

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Prokaryotic Metabolism

Type III secretion system

-Found in many Gram-negative bacteria

-Used to transfer virulence proteins directly into host cells

-Yersinia pestis – Bubonic plague

-Pseudomonads – Plant pathogens

-Blights, soft rot, wilts

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Human Bacterial Disease

Tuberculosis

-Mycobacterium tuberculosis

-Afflicts the respiratory system

-Mutidrug-resistant (MDR) strains are very alarming

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Human Bacterial Disease

Dental caries (tooth decay)

-Plaque consists of bacterial biofilms

-Streptococcus ferments sugar to lactic acid

-Tooth enamel degenerates

Peptic ulcers

-Helicobacter pylori is the main cause

-Treated with antibiotics

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Gonorrhea

-Neisseria gonorrhoeae

-Can pass from mom to baby via birth canal

-Can cause pelvic inflammatory disease (PID)

Chlamydia

-Chlamydia trachomatis

-Can cause PID and heart disease

Sexually transmitted diseases (STDs)

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Beneficial Prokaryotes

Prokaryotes are crucial to chemical cycles

-Decomposers release a dead organism’s atoms to the environment

-Photosynthesizers fix carbon into sugars

-Nitrogen fixers reduce N2 to NH3 (ammonia)

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Beneficial Prokaryotes

Bacteria are used for bioremediation

-Remove pollutants from water, air and soil

-Exxon Valdez oil spill