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Chapter 26
Early Earth and The Origin of Life
Early history of life
• Solar system - 12 billion years
ago (bya)
• Earth - 4.5 – 6.2 bya
• Life - 3.5 to 4.0 bya
• Prokaryotes - 3.5 to 2.0 bya
stromatolites
• Oxygen accumulation - 2.7 bya
photosynthetic cyanobacteria
• Eukaryotic life - 2.1 bya
• Muticelluar eukaryotes - 1.2 bya
• Animal diversity - 543 mya
• Land colonization - 500 mya
The Origin of Life
• Spontaneous generation
vs. biogenesis (Pasteur)
• The 4-stage Origin of life
Hypothesis:
• 1- Abiotic synthesis of
organic monomers
• 2- Polymer formation
• 3- Origin of Selfreplicating molecules
• 4- Molecule packaging
(“protobionts”)
Organic monomers/polymersynthesis
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Oparin (Rus.)/Haldane (G.B.)
hypothesis (primitive earth):
volcanic vapors (reducing
atmosphere) with lightning & UV
radiation enhances complex
molecule formation (no O2)
Miller/Urey experiment:
water, hydrogen, methane,
ammonia
all 20 amino acids, nitrogen bases,
& ATP formed
Fox proteinoid formation (abiotic
polypeptides) from organic
monomers dripped on hot sand,
clay or rock
Oparin (coacervates) protobionts
(aggregate macromolecules;
abiotic) surrounded by a shell of
H2O molecules coated by a protein
membrane
Abiotic genetic replication
• First genetic material
• Abiotic production of
ribonucleotides
• Ribozymes (RNA
catalysts)
• RNA “cooperation”
• Formation of short
polypeptides
(replication enzyme?)
• RNA-DNA template?
• Viruses?
The Major Lineages of Life
Whitaker System
Classification
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Scientific Name: Genus species
3 DOMAIN SYSTEM
• Chapter 27
Prokaryotes and the
Origins of Metabolic
Diversity
Initially Archaea seem more similar to Eubacteria than to
Eukaryotes.
Archae and Eubacteria are BOTH PROKARYOTIC organisms;
they both have closed, circular DNA;
They both are transcription and translation linked; and they
both usually reproduce via binary fission.
However, there are several differences
between Archae and Eubacteria.
1. They utilize different metabolic pathways.
2. They also differ in number of ribosomal proteins and
in the size and shape of their ribosomal S unit.
3. The Eubacteria genome is almost two times larger and
they contain more plasmids than Archae.
4. Archaea are similar to Eukaryotes in that they have
several kinds of RNA polymerase, have a great
number of histone-like proteins, have DNA in the form
of nucleosomes, and contain introns.
Biochemical determination:
Archaebacteria are distinguished by cell
walls with pseudopeptidoglycan or protein
components, and cell membranes
composed of branched hydrocarbons
linked to glycerol molecules.
ALL ABOUT ARCHAEBACTERIA
• Archaea are highly diverse organisms, both
morphologically (form and structure) and
physiologically (function).
• The organisms' possible shapes include
spherical, rod-shaped, spiral, lobed, plateshaped, irregularly shaped, and pleomorphic.
There are many different types of Archaea
that live in extremely diverse environments.
• Modern-day Archaebacteria are found in
extreme environments, such as areas of
intense heat or high salt concentration.
EUBACTERIA
EUBACTERIA
Within their domains, identification of microbes
begins with their physical appearance, followed by
biochemical and genetic tests.
SHAPE is/was
the most
commonly used
physical
appearance for
determination
of species.
Sex or
conjugation Pili
for the transfer of
extrachromosomal
DNA between donor
and recipient.
Pili
Attachment Pili
or Fimbriae.
There are many and
are used for
attachment to
surfaces. Pili are
virulence factors.
Made of the protein pilin and project from the cell
surface. There are 2 types:
Gram positive bacteria
Gram negative bacteria
Have an extra layer of
peptidoglycan in their
cell wall, and retain dye.
Have a thin layer of
peptidoglycan in their cell wall.
AND have lipopolysaccharides
with protein channels in the cell
membrane. This keeps dyes
(along with antibiotics) out!
http://www.sirinet.net/~jgjohnso/monerans.html
A bacterial flagellum has 3 basic parts: a
filament, a hook, and a basal body.
• 1) The filament is the rigid, helical structure that extends
from the cell surface. It is composed of the protein
flagellin arranged in helical chains so as to form a hollow
core. During synthesis of the flagellar filament, flagellin
molecules coming off of the ribosomes are thought to be
transported through the hollow core of the filament where
they attach to the growing tip of the filament causing it to
lengthen.
• 2) The hook is a flexible coupling between the filament and the
basal body
• 3) The basal body consists of a rod and a series of rings that anchor
the flagellum to the cell wall and the cytoplasmic membrane. Unlike
eukaryotic flagella, the bacterial flagellum has no internal fibrils and
does not flex. Instead, the basal body acts as a molecular motor,
enabling the flagellum to rotate and propell the bacterium through
the surrounding fluid. In fact, the flagellar motor rotates very rapidly. (The
motor of E. coli rotates 270 revolutions per second!)
EUKARYOTIC
FLAGELLA
•
Cell Locomotion via Cilia and
Flagella
Cilia and flagella, which extend from
the plasma membrane, are composed
of microtubules, coated with plasma
membrane material. Eukaryotic cilia
and flagella have an arrangement of
microtubules, known as the 9 + 2
arrangement (9 pairs of microtubules
(doublets) around the circumference
plus 2 central microtubules). "Spokes"
radiate from the microtubules towards
the central microtubules to help
maintain the structure of the cilium or
flagellum.
•
Each of the microtubule doublets have
motor molecule "arms", the dynein
arms, which can grip and pull an
adjacent microtubule to generate the
sliding motion. (The protein of this
motor molecule is dynein.)
Prokaryote flagella function:
•
Flagella are the organelles of
locomotion for most of the
bacteria that are capable of
motility. Two proteins in the
flagellar motor, called MotA and
MotB, form a proton channel
through the cytoplasmic
membrane and rotation of the
flagellum is driven by a proton
gradient. This driving proton
motive force (def) occurs as
protons accumulating in the space
between the cytoplasmic
membrane and the cell wall as a
result of the electron transport
system travel through the channel
back into the bacterium's
cytoplasm.
ENDOSPORES
Under environmental stress (lack of water, nutrients
etc.) some vegetative cells produce endospores e.g.
Clostridium and Bacillus. Spores can be dormant
for many years. They can survive extreme heat,
desiccation, radiation and toxic chemicals.
However, when conditions become favorable they
revert to a vegetative state. Spore germination is
activated by heat in the presence of moistures but
the endospore must degrade the layers around the
spore.
PROKARYOTIC CELL DIVISION
Binary Fission:
• cell elongates, duplicates its chromosome
Allocation of chromosomes to daughter cells depends
on MESOSOME – an extension of the cell membrane
A diagram of the
attachment of bacterial
chromosomes,
indicating the possible
role of the mesosome.
• It ensures the distribution of the "chromosomes" in a
dividing cell.
• Upon attachment to the plasma membrane, the DNA
replicates and reattaches at separate points.
•Continued growth, to about twice the size of the cell,
gradually separates the chromosomes.
B
A
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T
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V
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S
What is an antibiotic?
Chemical substances that INHIBIT the growth
of bacteria or KILL it.
HOW:
1.
2.
3.
4.
5.
Prevent cell wall from forming properly
Prevent protein synthesis
Interfere with chromosome replication
Disrupt plasma / outer membrane
Interference with metabolism
Alexander Fleming discovers
the first antibiotic (1928)
Sir Alexander Fleming
discovers the drug
penicillin, which
counteracts harmful
bacteria. Fleming
makes the discovery
by accidentally
contaminating a
bacteria culture with a
"Penicillium notatum"
mold.
He noticed that the nontoxic mold halts the
bacteria's growth, and
later conducts
experiments to show
penicillin's
effectiveness in
combating a wide
spectrum of harmful
bacteria
ZONE OF INHIBITION
What is
antibiotic resistance?
The ability of a bacterial cell to resist the
harmful effect of an antibiotic. This could
be incorporated into the chromosome or
plasmid.
-
System to prevent entry?
To destroy the antibiotic if into cell
To block action of antibiotic
A pump system to move antibiotic out
How is antibiotic
resistance acquired?
• Consistent exposure to antibiotics
– Long-term therapy
– Farm animals
• Indiscriminate usage of antibiotics
– For example for a cold/flu
• Non-therapeutic use
– For animals to gain weight
Transfer of antibiotic resistance
genes by conjugation
CAN BACTERIA BE GOOD
FOR YOU?
• The majority is not only helpful but
necessary!
– Occupy and compete for limited nutrients
• Tough for bad bacteria to get a foothold
– Antibiotics kill both good AND bad bacteria
• Thus, good are killed and some could become
antibiotic resistant. Since there’s no good bacteria
to stop them -
– Bad strain increases in number
• Chapter 28
The Origins of Eukaryotic
Diversity
Protists
• Ingestive
(animal-like);
protozoa
• Absorptive
(fungus-like)
• Photosynthetic
(plant-like);
alga
The Endosymbionic Theory
• Mitochondria and chloroplasts were formerly
from small prokaryotes living within larger
cells (Margulis)
Protist Systematics & Phylogeny, I
• 1- Groups lacking mitochondria;
early eukaryotic link; Giardia
(human intestinal parasite;
severe diarrhea); Trichomonas
(human vaginal infection)
• 2- Euglenoids; autotrophic &
heterotrophic flagellates;
Trypanosoma (African sleeping
sickness; tsetse fly)
Protist Systematics & Phylogeny, II
• Alveolata: membrane-bound
cavities (alveoli) under cell
surfaces; dinoflagellates
(phytoplankton);
Plasmodium (malaria);
ciliates (Paramecium)
Protist Systematics & Phylogeny, III
• Stamenophila: water molds/mildews and
heterokont (2 types of flagella) algae;
numerous hair-like projections on the
flagella; most molds are decomposers and
mildews are parasites; algae include
diatoms, golden, and brown forms
Protist Systematics & Phylogeny, IV
• Rhodophyta: red
algae; no flagellated
stages; phycobilin
(red) pigment
• Chlorophyta: green
algae; chloroplasts;
gave rise to land
plants; volvox, ulva
Protist Systematics & Phylogeny, V
• Affinity uncertain:
• Rhizopods: unicellular with
pseudopodia; amoebas
• Actinopods: ‘ray foot’ (slender
pseudopodia; heliozoans,
radiolarians
Protist Systematics & Phylogeny, VI
• Mycetozoa: slime
molds (not true fungi);
use pseudopodia for
locomotion and
feeding; plasmodial
and cellular slime
molds