Transcript Chapter 13 - McGraw Hill Higher Education

Essentials of
The Living World
First Edition
GEORGE B. JOHNSON
13
Evolution of
Microbial Life
PowerPoint® Lectures prepared by Johnny El-Rady
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13.1 How Cells Arose
There are three possibilities for the appearance of
the first living organisms on Earth
1. Extraterrestrial origin
Life was transferred to Earth from a distant planet
2. Special creation
Life was created by supernatural or divine forces
3. Evolution
Life may have evolved from inanimate matter, with
selection as the driving force
Only the third possibility is scientifically testable
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Earth is formed 4.5
billion years ago
Fig. 13.1 A clock
of biological time
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Forming Life’s Building Blocks
Life originated ~ 2.5 billion years ago
The Earth’s atmosphere then had no oxygen
It was rich with hydrogen-rich gases (NH3, CH4)
These simple molecules combined to form
more complex molecules
Lightning provided the energy
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Forming Life’s Building Blocks
Stanley Miller and Harold Urey reconstructed the
oxygen-free atmosphere of early Earth in their lab
Cellular building blocks form spontaneously, when
the system is subjected to lightning or UV light
They concluded that life may have evolved in a
“primordial soup” of biological molecules
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Forming Life’s Building Blocks
Concerns have been raised about the “primordial
soup” hypothesis
No oxygen => no protective ozone layer
Therefore, the UV light would have destroyed the
essential ammonia and methane gases
Louis Lerman, in 1986, proposed the bubble model
Key chemical life-building processes took place within
bubbles on the ocean’s surface
Inside the bubbles the essential gases would be
protected from UV light
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Fig. 13.2
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The First Cells
The first step may have been the formation of tiny
bubbles termed microspheres
These have cell-like properties
Those microspheres better able to incorporate
molecules and energy persisted longer than others
The first macromolecule produced was RNA
It provided a possible early mechanism of
inheritance
Later, RNA was replaced as hereditary material by
the much more stable double-stranded DNA
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13.2 The Simplest Organisms
The fossil record indicates that prokaryotes
appeared 2.5 billion years ago
Eukaryotes, on the other hand, appeared only
1.5 billion years ago
Today prokaryotes are the simplest and most
abundant form of life on earth
Prokaryotes occupy a very important place in the
web of life on earth
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The Structure of a Prokaryote
Prokaryotes are small, simply organized, single cells
that lack a nucleus
Spiral
Rod
Prokaryotes include
the bacteria and
archaea
They come in three
main shapes
Rod-shaped (bacilli)
Fig. 4.9
Spherical (cocci)
Spirally coiled (spirilla)
Spherical
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The Structure of a Prokaryote
The cell membrane of prokaryotes is encased in a
cell wall
Bacterial cell walls are composed of peptidoglycan
Network of polysaccharides linked together by
peptide cross-links
Archaeal cell walls lack peptidoglycan
They are made of proteins, sugars or both
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Bacteria can be divided into two groups based on
their cell wall architecture
Gram-positive
Have a thick peptidoglycan layer
Lack outer membrane
Gram-negative
Have a thin peptidoglycan layer
Have an outer membrane containing lipopolysaccharide
The name refers to a differential stain developed by
Hans Christian Gram
Gram-positive cells retain the primary crystal violet stain
Gram-negative cells don’t and are stained by a safranin
(red) counterstain
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Fig. 13.3 The structures of bacterial cell walls
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Many bacteria have capsules
A gelatinous layer found external to the cell wall
Many bacteria possess threadlike flagella
Long external appendages used for locomotion
Some bacteria also possess pili
Short external appendages used for attachment
In harsh conditions, a few bacteria can form
endospores
Highly-resistant structures that may germinate into
active bacteria when conditions improve
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Prokaryotes
reproduce
by binary
fission
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Fig. 7.1
Some bacteria undergo a process called conjugation
The undirectional transfer of plasmid DNA following cell-tocell contact
Fig. 13.4
Pilus connecting
the two cells
together
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Both cells contain
a complete copy
of the plasmid
13.3 Comparing Prokaryotes to
Eukaryotes
Prokaryotes differ from eukaryotes in many respects
They have very little internal organization
They are unicellular and much smaller
They possess a single chromosome
They are far more metabolically diverse
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TABLE 13.1
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TABLE 13.1
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Prokaryotic Metabolism
Prokaryotes have evolved many more ways than
eukaryotes to acquire carbon and energy
Acquisition of Carbon
Autotrophs = Use CO2 as their only carbon source
Heterotrophs = Use preformed organic compounds as
carbon sources
Acquisition of Energy
Phototrophs = Use light as energy source
Chemotrophs = Use chemicals as energy source
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Prokaryotic Metabolism
Based on carbon and energy sources, prokaryotes
can be divided into four categories
1. Photoautotrophs
Use the energy of sunlight to build organic molecules
from CO2
Cyanobacteria
2. Chemoautotrophs
Obtain energy by oxidizing inorganic substances
Nitrifiers oxidize ammonia or nitrite
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Prokaryotic Metabolism
Based on carbon and energy sources, prokaryotes
can be divided into four categories
3. Photoheterotrophs
Use light as energy and pre-formed organic molecules
as carbon sources
Purple nonsulfur bacteria
4. Chemoheterotrophs
Use organic molecules as carbon and energy sources
Decomposers and most pathogens
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13.4 Viruses Infect Organisms
Viruses are not living organisms
Rather, they are “parasitic” chemicals that can only
reproduce within living cells
Viruses are very small
Range from 17 – 1,000 nm
Viruses occur in all organisms
In every case, the basic structure is the same
Segments of DNA or RNA wrapped in a protein coat
called the capsid
There is considerable difference, however, in the details
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Fig. 13.6 The structure of bacterial, plant, and animal viruses
Membrane-like layer
Not found in all viruses
Capsid
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The Origin of Viral Diseases
Influenza
Perhaps the most lethal virus in human history
Natural reservoirs ducks and pigs in central Asia
AIDS (HIV)
First entered humans from chimpanzees in Africa
The chimpanzee virus is called simian immunodeficiency
virus (SIV)
Ebola virus
Filamentous virus that attacks connective tissue
Natural host of the virus is unknown
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The Origin of Viral Diseases
Hantavirus
Discovered in 1993
Natural host is deer mice
SARS
Severe acute respiratory syndrome
Caused by a coronavirus
Natural host is most likely the civet
West Nile Virus
Mosquito-borne virus
Natural host is birds
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13.5 The Origin of Eukaryotic Cells
The microfossil records suggests that eukaryotic
cells appeared 1.7 billion years ago
The word eukaryote is derived from the Greek
words for “true” and “nucleus”
The endoplasmic reticulum and nucleus of
eukaryotes may have evolved from infoldings of
prokaryotic cell membranes
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Endosymbiosis
The endosymbiotic theory proposes that engulfed
bacteria gave rise to mitochondria and chloroplasts
Evidence
Organelles are surrounded by two membranes
Organelles have circular DNA
Organelles have ribosomes that resemble
those of prokaryotes
Organelles divide by binary fission
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Fig. 13.7 The theory of endosymbiosis
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13.6 General Biology of Protists
Protists are highly variable eukaryotes that share
one characteristic:
They are not fungi, plants or animals
Protists have varied types of cell surfaces
Some have cell walls
Movement is also accomplished by diverse
mechanisms
Flagella
Cilia
Pseudopodia
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Many protists form cysts
Dormant cells with resistant outer covering
Protists employ all forms of nutrition except
chemoautotrophy
Phototrophs
Heterotrophs
Phagotrophs (or holozoic feeders)
Ingest visible particles of food
Osmotrophs (or saprozoic feeders)
Ingest food in soluble form
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Protists typically reproduce asexually
Binary fission  Equal halves
Budding  Progeny cell smaller than parent cell
Schizogony  Multiple fission
Sexual reproduction occurs in times of stress
Zygotic meiosis
In the Sporozoans
Gametic meiosis
In ciliates and some flagellates
Sporic meiosis
In algae
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Multicellularity
Complex multicellular organisms
Individuals are composed of many highly
specialized cells that coordinate their activities
Three kingdoms exhibit multicellularity
Plants
Animals
Fungi
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Multicellularity
Two key characteristics distinguish between complex
multicellular and simple multicellular organisms
Cell specialization
Different cells use different genes
They therefore develop in different ways
Intercell coordination
Cells adjust their activity in response to what
other cells are doing
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Multicellularity
Colony moves by
beating of flagella
of individual cells
Colonies
Permanent association of
cells, but little or no
integration of cell activities
Volvox
Unicellular green alga
Colony is hollow ball of
cells
Fig. 13.9
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Multicellularity
Aggregates
Transient collection of cells
Cellular slime molds
Cells come together during starvation
Multicellular organisms
Individuals are composed of many interacting cells that
regulate the activities of one another
True but simple multicellularity has been achieved
by three groups of protists
Brown, green, and red algae
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13.7 Kinds of Protists
Protists are the most diverse eukaryotic kingdoms
The kingdom Protista is an artificial group
Not representative of evolutionary relationships
There is little consensus, even among experts, as to
how protists should be classified
Single, very diverse kingdom
vs.
Several different kingdoms
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There are 15 distinct phyla of protists
These are grouped into five general groups based
on shared characteristics
1.
2.
3.
4.
5.
6.
7.
8.
9.
Presence/absence of flagella/cilia
Presence and kinds of pigments
The type of mitosis
The types of cristae in mitochondria
Molecular genetics of the ribosomal “S” subunit
Types of inclusions
Overall body form
Body shell or armor
Modes of nutrition and movement
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Functional groupings
Fig. 13.10 The
major protist
groups
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Accepted taxa
TABLE 13.2
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TABLE 13.2
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13.8 A Fungus Is Not a Plant
The study of fungi is called mycology
Fungi have traditionally been included in the plant
kingdom
However, there are significant differences between
fungi and plants
Fungi are heterotrophs
Fungi have filamentous bodies
Fungi have nonmotile sperm
Fungi have cell walls made up of chitin
Fungi have nuclear mitosis
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The Body of a Fungus
Fungi exist mainly as slender filaments called
hyphae (singular, hypha)
Hyphae are strings of cells separated by septa
(singular, septum)
Pores in the septa allow for cytoplasmic
streaming between cells
Because of cytoplasmic streaming, many
nuclei may be connected by shared cytoplasm
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The main body of a fungus is not the familiar
mushroom
But rather an extensive network of hyphae
termed a mycelium (plural, mycelia)
Reproductive
structures
All parts of the
fungal body are
metabolically
active
Fig.
Morel 13.11
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Amanita
How Fungi Reproduce
Fungi reproduce both sexually and asexually
Sexual reproduction is initiated when two hyphae of
different mating types come in contact and fuse
The two nuclei do not fuse immediately
Heterokaryon
Hyphae containing nuclei derived from two
genetically different individuals
Homokaryon
Hyphae containing nuclei derived from two
genetically similar individuals
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How Fungi Reproduce
Fungi have three types of reproductive structures
Gametangia
Fig. 13.12
Form haploid gametes
that fuse to form zygote
Sporangia
Produce haploid spores
that are dispersed
Puffball
spores
Conidiophores
Produce asexual spores
Spores are a common means of fungal reproduction
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How Fungi Obtain Nutrients
Fungi obtain nutrients by external digestion
They secrete digestive enzymes into their surroundings
and absorb the resulting organic molecules
Some fungi are active
predators
Immobilizes nematodes
then eats them!
Others are even more
active predators
Snare or trap prey
Fig. 13.13 The oyster mushroom
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13.9 Kinds of Fungi
~ 74,000 species of fungi have been named so far
They are divided into four phyla
Zygomycota
Ascomycota
Basidiomycota
Chitrydiomycota
Distinguished primarily
by their mode of
sexual reproduction
A fifth group, the imperfect fungi, is artificial
It’s a “catch-all” grouping of fungi in which sexual
reproduction has not been observed yet!
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TABLE 13.3
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Ecological Roles of Fungi as Decomposers
Fungi, together with bacteria, are the principal
decomposers in the biosphere
Fungi are virtually the only organisms that can
break down lignin
Fungi cause animal diseases
Fungi are the most harmful pests of living plants
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Commercial Uses
Many commercial products are dependent on the
biochemical activities of fungi
Bread
Beer
Cheese
Soy sauce
Penicillin
Some fungi are used to convert one complex organic
molecule into another
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Fungal Associations
Two kinds of mutualistic associations between fungi
and autotrophic organisms are ecologically important
1. Mycorrhizae
Symbiotic association
between a fungus and
the roots of plants
2. Lichens
Symbiotic association
between a fungus and
a green algae or
cyanobacterium
Fig. 13.14 Lichens growing on rock
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