Download Lecture Notes: Prokaryotes

Prokaryotes
the oldest life forms
on planet Earth
I. Bacteria Are Omnipresent
A.
Appeared apx. 3.5 billion ybp
B.
C.
The only life forms on earth for 1.5 billion yrs.
Found in all habitats - dominating the biosphere
D.
Approximately 5,000 species identified
1. however 400K - 4 million species are likely to exist
E.
Small percentage cause disease
F.
Some are decomposers
1. key organisms in life sustaining chemical rxn’s
Many form symbiotic relationships with other
prokaryotes and eukaryotes
1. bacteria in mammalian intestines produce critical vitamins
G.
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II. Morphological Diversity Of Prokaryotes
A.
B.
Cell Shape
1. cocci: spherical (most common)
2. bacilli: rod shaped
3. spirilla and spirochetes : spiral helices (smallest)
Size
1. most have diameters of 1-5 µm
(vs. eukaryotes @ 10 -100 µm)
Fig. 27.2
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III. Structure, Function, and Reproduction
A.
Living organisms are made of either prokaryotic or eukaryotic cells.
1. prokaryotes = all bacteria; eukaryotes = all non-bacterial
cells/organisms
2. structural differences distinguish the two types
B.
Prokaryotic Structural Overview
1. no true nucleus (lack nuclear membrane)
2. genetic material in nucleoid region
3. no membrane-bound organelles
4. most are unicellular
a. some aggregates/colonies feature division of labor via specialized cells
5. cell wall present in nearly all prokaryotes
a. provides physical protection - particularly in hypotonic and hypertonic conditions.
b. constructed of a special polymer of modified sugars, cross-linked with short polypeptides
c. pathogenic issues: either an external/outer membrane -or- a sticky polysaccharide layer
external to the cell wall can confer pathogeniety and/or resistance to host defenses
C.
Functional Overview
1.
bacteria function in 2 of 4 different metabolic pathways (their way of obtaining carbon and energy)
a. phototrophic - use light energy like plants
b. chemotrophic - obtain energy from chemicals
c. autotrophic - need only use CO2 as their carbon source
d. heterotrophic - use organic molecules as a source of carbon
2.
heterotrophs are assumed to be the very first prokaryotes
a. the first metabolic pathway is assumed to be glycolysis - the extraction of energy
from organic molecules to generate ATP anaerobically = absence of O2
D.
Reproductive Overview
1.
reproduction occurs asexually via binary fission
2.
fastest: every 20 minutes; typical: every 1-3 hours
3.
although meiosis does not happen, individuals can combine genes
a. transformation: “naked” DNA is absorbed from the environment
b. conjunction: direct transfer of DNA from one cell to another
c. transduction: transfer of DNA via viral infection
4.
when under stress certain bacteria can produce an endospore: a protein based capsule
containing the individual’s genome - suspended until adequate conditions return
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IV. Eukaryotic Structural Overview
A. Eukaryotic Structural Overview
1. true nucleus (membrane-bound nucleus)
2. genetic material in nucleus
3. contain membrane-bound organelles
Prokaryotic Cell pg. 573
Eukaryotic/Animal Cell pg. 100
The End
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