7. Early life and The diversification of prokaryotes

Origin of life (stages)

Chemical and physical processes on early Earth may have produced very simple cells through:

1. Abiotic synthesis of small molecules into macromolecules

2. The joining of small molecules into macromolecules

3. the packaging of these molecule into protocells

4. the origin of self-replicating molecules

What are the earliest known fossils?

Stromatolites

• these are banded rocks that arise from the activities of certain prokaryotes

  • they date back at least 3.5 billion years and fossil stromatolites are similar to those observed today.

Prokaryotes

most are unicellular though some form colonies

• most are 0.5-5 micrometers, much smaller than eukaryotic cells

  • they have a variety of shapes

Prokaryotes - Shapes

1. Cocci

2. Bacilli

3. Spirilla

Cocci

spherical shaped

Bacilli

rod-shaped

Spirilla

Spiral shaped

WHat is the most important feature of prokaryotic cells?

The cell wall

• this maintains the cell shape, provides physical protection and prevents the cell from bursting in a hypotonic environment

What are eukaryotic cell walls made of?

Cellulose or chitin

What do bacterial cell walls contain?

Peptidoglycan

• this is a network of sugar polymers cross-linked by polypeptides

Gram stain

a stain scientists used to classify many bacterial species

• either into Gram Stain positive or Gram stain negative groups

Gram-Positive

These are bacteria that have peptidoglycan in their out membrane

Gram-negative

These are bacteria that have less peptidoglycan in their cell wall

• the outmembrane can be toxic and they are more likely to be antibiotic resistant

What covers many prokaryotes?

A polysaccharide or protein layer called a capsule

What are fimbriae

Fimbriae are appendages or spike looking structures

• these allow them to attach to other surfaces or other prokaryotes

How do most bacteria move?

Motile bacteria propel themselves by flagella

• the flagella are structually and functionally different from eukaryotic flagella

Porkaryotic Flagella anatomy

In a prokaryotic flagella there is a motor system of rings embedded in the cell wall and plasma membrane

• An ATP driven pomp transports protons out of the cell, while diffusion brings them back in, this process powers the motor

  • the motor rotates the curved hook attached to the filament

What do prokaryotes lack?

They usually lack complex compartmentalization

• however they do have specialized membranes that perform metabolic functions

  • e.g. aerobic prokaryote & photosynthetic prokaryote

Prokaryote genome

This has less DNA than the eukaryotic genome

• most of the genome consists of a circular chromosome

  • The typical genome is a ring of DNA that is NOT surrounded by a membrane and is located ina nucleoid region

    • aka, it is not a true nucleus

What are the smaller rings of DNA in some bacteria called?

Plasmids

Phototrophs

obtains energy from light

Chemotrophs

Obtain energy from chemicals

Autotrophs

require CO2 as a carbon source

Heterotrophs

require organic nutrient to make organic compounds

Photoautotrophy

energy from light; CO2 carbon source

Chemotrophy

Energy from chemicals; CO2 carbon source

Photoheterotrophy

energy from light; carbon from organic compounds

Chemoheterotrophy

energy and carbon from organic compounds

Prokaryote's Metabolism and Oxygen requirement

Prokaryotic metabolism varies with respect to oxygen

1. Obligate Aerobes

2. Obligate anaerobes

3. Faculative anaerobes

Obligate aerobes

require O2 for cellular respiration

Obligate anaerobes

these are poisioned by O2 and use fermentation or anaerobic respiration

Faculative anaerobes

These can survive with or without O2

Nitrogen Fixation

Where prokaryotes can metabolize nitrogen in a variety of ways

• prokaryotes will convert atmospheric nitrogen into ammonia

  • e.g. peanuts & legumes

Heterocysts

these are found in colonial prokaryotes (algae) which fix nitrogen while other cells perform photosynthesis

How do prokaryotes reproduce?

They reproduce quickly by binary fission and can divide every 1-3 hours

• this means they can evolve rapidly because of their short generation times

  • e.g. antibiotic resistence can evolve in under a day

What do prokaryotes form?

They form metabolically inactive endospores

• these can remain viable in ahrsh conditions for centuries

What are the 3 factors that contribute to Prokaryotes genetic diversity?

1. Rapid reproduction

2. Mutation

3. Genetic recombination

Rapid Reproduction

Prokaryotes reproduce by binary fission which allows them to reproduce rapidly

Mutation

Mutation rates during binary fission are low but b/c of rapid reproduction, mutations can accumalate rapidly

• high diversity from mutations allows for rapid evolution

Genetic recombination in Prokaryotes can occur by..

1. Transformation → take up foreign DNA from environment

2. Transduction → movement of genes between bacteria by viruses (bacteriophages)

3. COnjugation and plasmids → sex pilli (tube) allow cells to connect and pull together for DNA transfer (one way)

Conjugation and Plasmids

The process where genetic material is transferred between bacterial cells

• Sex pilli allow cells to connect and pull together for DNA transfer

  • a piece of DNA, F factor, is required for the production of this tube

    • F factor can exist as a separate plasmid or as DNA within the bacterial chromosome.

What 2 domains are prokaryotes divided into?

1. Archaea

2. Bacteria

Archaea

Prokaryotes in this domain share certain traits with bacteria and other traits with eukaryotes!

• however archaea and eukarya share a more recent common ancestor than archaea and bacteria

Archaea - Extremophiles

Prokaryotes of this domain are called this because they live in extrem environments

• Exterme halophiles - live in highly saline environments

• Extreme thermophile - thrive in very hot environments

Archaea - Methanogens

these live in swamps and marshes and produce METHANE as a waster product

• These prokaryotes anaerobes and are poisoned by O2

Comparing the 3 domains - Nuclear envelope

• Bacteria - NE Absent

• Archaea - NE Absent

• Eukarya Present

Comparing the 3 domains - Membrane enclosed organelles

• Bacteria - MEO Absent

• Archaea - MEO Absent

• Eukarya - Present

Comparing the 3 domains - Peptidoglycan in cell wall

• Bacteria - Present

• Archaea - ABsent

• Eukarya - Absent

Comparing the 3 domains - Membrane lipids

• Bacteria - Unbranched hydrocarbons

• Archaea - Some branched hydrocarbons

• Eukarya - Unbranched hydrocarbons

Comparing the 3 domains - RNA polymerase

• Bacteria - One kind of RNA

• Archaea - Several Kinds of RNA

• Eukarya - Several kinds of RNA

Comparing the 3 domains - Initiator amino acid for protein synthesis

• Bacteria - Formyl Methionine

• Archaea - Methionine

• Eukarya - Methionine

Comparing the 3 domains - introns in genes

• Bacteria - Very Rare

• Archaea - Present in some genes

• EUkarya - Present in many genes

Comparing the 3 domains - Response to the antibiotics (streptomycin and chloramphenicol)

• Bacteria - Growth usually inhibited

• Archaea - Growth not inhibited

• EUkarya - Growth not inhibited

Comparing the 3 domains - Histones associated with DNA

• Bacteria - Histones Absent

• Arcahea - Present in some species

• Eukarya - Present

Comparing the 3 domains - Circular Chromosome

• Bacteria - Present

• Archaea - Present

• Eukarya - Absent

Comparing the 3 domains - Growth at temperature above 100

• Bacteria - No

• Archaea - Some species

• Eukarya - No

Proteobacteria

Gram-negative bacteria that include photoautotrpohs, Chemoautotrophs,, and heterotrophs.

• Some are anaerobic and others aerobic

  • e.g. helicobacter, causes stomach ulcers and stomach cancer

Chlamydias

these bacteria are parasites that live within animal cells

• e.g. Chlamydia trachomatis causes blindness and nongonococcal urethritis by sexual transmission

Spirochetes

These bacteria are helical heterotrophs

• e.g. Treponema pallidum which causes syphilis, and Borrelia burgdorferi which causes Lyme disease are parasites

Cyanobacteria

These are photoautotrophs that generate O2

• Plant chloroplasts likely evolved from cyanobacteria by the process of endosymbiosis

Gram-positive bacteria consists of..

1. Actinomycetes, which decomposes soil

2. Bacillus anthracis, the cause fo anthrax

3. Clostridium botulinum, the cause of botulism

4. some Staphylococcus and Streptococcus, which can be pathogenic

5. Mycoplasms, the smallest known cells

What do prokaryotes play a major role in?

they play a major role in the recycling of chemical elements between the living and nonliving components of ecosystems

Chemoheterotrophic prokaryotes

These prokaryotes function as decomposers

• they break down corpses, dead vegetation and waste products

Chemical Recycling - Nitrogen fixation

Nitrogen-fixing porkaryotes add usable nitrogen to the environment

• not only do they increase the availibility of nitrogen but also phosphorus and potassium for plant growth

Chemical Recylcing - Immobilize

Prokaryotes can also decrease the availability of nutrients

Symbiosis

An ecological relationship in which two species live in close contact

• consists of a larger host and a smaller symbiont

  • prokaryotes often form symbiotic relationships with larger organisms

Symbiosis - Mutualism

Where both symbiotic organisms benefit from the relationship

Symbiosis - Commensalism

Where one organism benefits while neither harming or helping the other in any significant way

Symbiosis - Parasitism

An organism called a parasite harms but does not kill it's host

• they cause disease called pathogens

Pathogenic Bacteria

Prokaryotes can sometimes be human pathogens while others have positive interactions with humans

• they cause about half of all human diseases

  • e.g. lyme disease

Pathogenic Prokaryotes

They typically cause disease by releasing exotoxins or endotoxins

Exotoxins

Cause disease even if the prokaryotes that produce them are not present

• e.g. Botulism, cholera

Endotoxins

these are rleased only when the bacteria die and their cell walls break down

• E. coli, Salmonella

How do prokaryotes help research?

Experiments that have used prokaryotes have led to important advances in DNA technology

Prokaryotes are the key agents of what?

Bioremediation

• they help remove pollutants from the environment

Botox

A purified form of botulinum exotoxin

• a potent nerve blocker

  • it temporarily paralyzes or freezes facial muscles that wrinkle from habitual use

    • takes 2-3 days to kick in and lasts 4-6 months

Other uses of prokaryotes

1. Recovery of metals from ores

2. Synthesis of vitamins

3. Production of antibiotics, hormones, and other products