Download Brief history of life on Earth

4/6/2015
Brief history of life on Earth
4.6 Billion Years ago: Earth forms
3.6 Billion Years ago : First life on the planet (Prokaryotes = Bacteria)
2.8 Billion Years ago : First eukaryotic life (also microbial – algae/protozoa)
0.4 Billion Years ago: First animals and plants
(Fossil evidence indicates that modern humans originated in Africa about 200,000 years ago)
Fossilized stromatolite *
Stromatolites - layered rock-like structures formed in shallow water
by the trapping/binding/cementation of sedimentary grains by microbes;
Represent the most ancient records of life on Earth.
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Two types of Cellular Organization
• Eukaryotic cells
– DNA surrounded by a membrane/envelope
=>cell nucleus
• Prokaryotic cells
– DNA not surrounded by an envelope
Prokaryotic Structure
Relatively simple structure: DNA, ribosomes, cell membrane, cell wall,
plus a few other parts (not shown)
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Eukaryotic Structure
By comparison, “euks” are much more complex, containing
specialized organelles to perform particular functions
Prokaryotes and eukaryotes:
universal vs. distinct structures
Universal: Both have DNA, ribosomes (to make
proteins), and cell membranes
“EUK”
Eukaryotes have
energy organelles (mitochondria / chloroplasts), an
endomembrane system (ER/GOLGI)
to package and sort materials,
cytoskeleton (fibers that move materials around
and help with cell division),
and a nuclear membrane
“PROK”
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How did we get from prok to euk ???
• Lynn Margulis “Endosymbiotic theory”
• Euks came from proks ingesting other proks, but
instead of digesting them they began to use them
as organelles
• Evidence shows that mitochondria and
chloroplasts have bacterial origins
“TAXONOMY”
Biology attempts to catalog organisms
1. Aristotle: described 500 plants and animals
2. Linnaeus: described 1000’s of plants and animals, devised
the binomial system (Genus/Species), part of the hierarchal
system of nomenclature
3. Whittaker: 5 Kingdom system
(Animals/Plants/Fungi/Protista/Bacteria)
4. Woese: 3 Domain System
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Nomenclature gives
scientific names to organisms
•
Linnaeus’ Binomial system: everything has two names based
on genus and species (e.g. homo sapiens)
•
His groupings were based upon shared physical
characteristics.
Quoted as saying
“GOD CREATES, LINNAEUS NAMES”
Whittaker’s Five Kingdom System
1.
2.
3.
4.
Animals
Plants
Fungi
Protists
(algae/protozoa/ +
“lower fungi”)
5. Monera
(prokaryotes)
Note that 4 out of 5
are eukaryotic
organisms, only 1/5
prokaryotic
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The three-domain system places the
Monera in separate lineages
Classification is based on
differences in ribosomal RNA
(and/or the DNA genes that encode
these RNAs)
Carl Woese
Recall that all life forms have
ribosomes, so by comparing how
similar the ribosomes are to each
other we can see how closely they are
related to one another
Comparison of rRNA genes from diverse organisms
Note that certain regions of the sequences vary from each other, so that the
more similar they are, the more closely related are the organisms (more
differences = more distant relationship)
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Relationship between diverse organisms based on
sequences of rRNA genes
Organisms A and B have only 2 differences
between them, whereas both A+B have 6
differences from C: thus it is inferred that
A+B should be closer together on a family
tree than either should be to organism C
(note that “X” is the universal ancestor of all
three other organisms)
Three Domain System
THE THREE DOMAINS ARE: EUBACTERIA, ARCHAE, and
EURKARYA (thus 2/3 PROKS and 1/3 EUKS)
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Eubacteria
COMPARISON
OF Eubacteria
Archae
Eukaryotes
THIS HIGHLIGHTS THE DIFFERENCES BETWEEN THE 3 DOMAINS
Source: S. Finkel, 2002
Eubacterial vs. Archaeal cytoplasmic membranes
ARCHAE cell
membrane is much
stronger with more
molecules and tighter
bonding than
EUBACTERIA
-- this helps them to
survive extreme
environments
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Bacteria:
Shapes and Arrangements
Bacilli
Cylinder shape
Can be singles or form chains
Examples: E. coli, Shigella,
Salmonella, Anthrax, etc.
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Cocci
CUBE OF 8 = Sarcina
Examples: “Staph” infections,
Strep throat bacteria, etc.
Spirals and other shapes
Spirilla are thick and rigid, with a single flagellum at each
end; Spirochetes are thin and flexable, with an internal
flagella called an “axial filament” that rotates beneath the
cell wall (moves like a “cork screw”)
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Bacteria:
Structure
From the outside to the inside of the cell……………
Bacterial flagella
Provide motility
Rotate (clockwise/countercwise)
Embedded in cell wall, extend out
from there
Allow bacteria to move toward
nutrients, or away from repellants (e.g.
antibiotics, white blood cells) – this is
called “chemotaxis”
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Structure of bacterial flagella
Basal body = “motor”
embedded in the cell wall
and membrane; Rotates,
which then drives the
external filament
Bacterial motion mediated by flagella
If the flagella rotate
counterclockwise, the
bacterium moves in a
straight path (“run”)
if they rotate clockwise,
the bacterium will tend to
stay in place (“tumble”)
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“Chemotaxis”
For example: If bacteria encounter food, the organisms stay around
the same area (see “A” above). However, if food is sensed
somewhere nearby, they’ll move toward it (see “B”).
Movement of Shigella within and between cells
Note that these organisms invade intestinal cells and then move from one
cell to another, causing “water loss” = extreme diarrhea
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TYPES OF FLAGELLA
Monotrichous: one flagellum at one end
Amphitrichous: flagella at both ends
Lophotrichous: two or more flagella clustered at one end only
Peritrichous: many flagella all around the cell
Pili
Protein fibers
Help bacteria to attach to surfaces (e.g.
urethra in Urinary tract infections)
Special pili (conjugation pili) are used
for bacteria “intercourse” where they
move DNA between cells
Enhance ability to cause disease
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Binding of pili to host cells
Note that the tips of
pili contain proteins
that dock down and
lock on to receptor
molecules on host
cell surfaces
Glycocalyx
Sticky, sugary layer around cells
Not all bacteria have it, but the ones
that do are more dangerous!
Attachment is easier (sticky)
Retain water, so they don’t dry out
Repel the white blood cells of the
immune system as WBCs are keyed to
look for foreign proteins so these
sugars help hide the cell
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Two types:
Cell wall
1. Gram-positive: thick layer of peptidoglycan (surrounds cells and
protects them); also contains teichoic acid; Retains the primary (purple)
gram stain in spite of gram alcohol (destaining) treatment.
2. Gram–negative: thin layer of peptidoglycan, lose the gram stain
when gram alcohol (destainer) is applied.
** Also have an extra membrane outside the cell wall called LPS
(lipopolysaccharide) layer – contains endotoxin, an ‘internal’ poison
that makes these cells dangerous (re: septic shock)
Structure of Gram-positive cell envelope
Note the thick peptidoglycan and the Teichoic acid that
binds together the cell wall components
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Structure of gram-negative cell envelope
Note the thin peptidoglycan sandwiched between two
membranes, as well as the lack of teichoic acid
This part contains endotoxin
Cell envelope of Gram-Positive vs. Gram-Negative Bacteria
Hint: Make sure you
can compare and
contrast these two for
an exam !
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Structure of E. coli peptidoglycan
Synthesis of peptidoglycan
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b-lactam antibiotics
Prevent new cell walls from
being formed so bacs burst
apart (below) !
Cell membrane
Permeability barrier (cellular materials
separate from environment);
imports specific nutrients,
exports waste,
site of ATP production in bacs
Chemical composition:
40% phospholipids
60% embedded proteins …
Both move (Fluid mosaic model)
Action of disinfectants/drugs:
alcohols dissolve this layer;
some Anti-biotics poke holes in it
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Cytoplasm
Is the center of biochemical activity
Structures within the cytosol
--Ribosomes
--Inclusion bodies: store nutrients
(Phosphate/Sulfur/Glycogen)
--DNA: two forms
A. Chromosome(s)
B. Plasmids = molecules of DNA
separate from chromosome that can carry
genes for toxins or antibiotic resistance
Spores
Are designed for dormancy
Spore formation: when nutrients are limited
Chemical composition: chromosome + small
amount of cytoplasm surrounded by thick
layers of peptidoglycan
Resistance: little water so heat resistant;
Dipicolinic Acid stabilizes the DNA
Can survive alcohol, boiling water, etc for
many years
Many Pathogenic bacteria form spores including
Anthrax, Botulism, and Tetanus bacteria
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Bacterial Spore Formation
When nutrients are
available, the spore will
germinate back to a
normal cell again
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