Download Lecture 3: Prokaryotes and Protists

Lecture 3: Prokaryotes and Protists
I.
Background
A.
1.
Prokaryotes are adapted to a broad range of habitats
Examples
a.
Halobacteria
i.
Live in water with 32% salt concentration
b.
Deinococcus radiodurans
i.
Can survive a radiation dose of 3,000,000 rads
ii.
1000 rads is fatal to a human
c.
Picrophilus oshimae
i.
Can grow at a pH of 0.03, acidic enough to dissolve metal
B.
1.
2.
Prokaryotes dominate the biosphere
Their collective biomass outweighs that of all eukaryotes combined by at least tenfold
More prokaryotes live on the surface of the body than the total number of people who have ever
lived
II.
Structural and functional modifications
A.
1.
General characteristics
Small
a.
0.5 – 5 µm
Unicellular
a.
Some species may aggregate transiently or permanently in colonies
Shape
a.
Spheres (cocci), rods (bacilli), and spirals
Nearly all have a cell wall external to the plasma membrane
a.
Maintains the shape of the cell, affords physical protection, and prevents the cell from
bursting in a hypotonic environment
i.
In a hypertonic environment, most prokaryotes lose water and plasmolyze
Most bacterial cell walls contain peptidoglycan
a.
Polymer of modified sugars cross-linked by short polypeptides
b.
Encloses the entire bacterium and anchors other molecules that extend from its surface
2.
3.
4.
5.
B.
1.
2.
3.
4.
Gram staining
Tool for identifying specific bacteria based on differences in their cell walls
Gram-positive bacteria
a.
Have simple cell walls with large amounts of peptidoglycans
Gram-negative bacteria
a.
Have more complex cell walls with less peptidoglycan
b.
Outer membrane on the cell wall of gram-negative cells contains lipopolysaccharides
i.
Carbohydrates bonded to lipids
ii.
Lipopolysaccharides on the walls of gram-negative bacteria are often toxic
iii.
Protects the pathogens from the defenses of their hosts
c.
Gram-negative bacteria are commonly more resistant than gram-positive species to
antibiotics
i.
Outer membrane impedes entry of the drugs
Among pathogenic bacteria, gram-negative species are generally more deadly than gram-positive
species
C.
1.
2.
3.
Capsules
An additional sticky protective layer of polysaccharide or protein outside the cell wall
Capsules allow cells to adhere to their substrate or to other individuals in a colony
Some capsules protect against dehydration, and some may increase resistance to host defenses
D.
1.
Surface appendages
Fimbriae—attachment pili
a.
Surface appendages that allow prokaryotes to adhere to one another or to the substratum
b.
Fimbriae are usually more numerous and shorter than sex pili
Sex pili
a.
Specialized for holding two prokaryote cells together long enough to transfer DNA during
conjugation
2.
E.
1.
2.
Motility
Flagella
a.
Scattered over the entire surface or concentrated at one or both ends
b.
Most common method of movement
c.
Flagella of prokaryotes differ in structure and function from those of eukaryotes
Taxis
a.
Purposeful movement toward nutrients or oxygen (positive chemotaxis) or away from a
toxic substance (negative chemotaxis)
III.
Cellular and genomic organization of prokaryotes
A.
1.
2.
3.
Differences with eukaryotes
Cells of prokaryotes are simpler than those of eukaryotes
Prokaryotic cells lack the complex compartmentalization found in eukaryotic cells
Prokaryotes use specialized infolded regions of the plasma membrane to perform many metabolic
functions
a.
Lack organelles for cellular respiration and photosynthesis
Prokaryotes have smaller, simpler genomes than eukaryotes
a.
Genome usually consists of a ring of DNA with few associated proteins
b.
Prokaryotic chromosome is located in the nucleoid region
c.
Prokaryotes may also have smaller rings of DNA called plasmids
i.
Consist of only a few genes
Similar processes for DNA replication and translation of mRNA into proteins
a.
Prokaryotic ribosomes are slightly smaller and differ in protein and RNA content
b.
Selective antibiotics bind to prokaryotic ribosomes to block protein synthesis in prokaryotes
but not in eukaryotes
4.
5.
B.
1.
2.
3.
Prokaryotes grow and adapt rapidly
Prokaryotes have the potential to reproduce quickly in a favorable environment
a.
Generation times of 1–3 hours
b.
Some species can produce a new generation in 20 minutes under optimal conditions
c.
A single cell in favorable conditions produces a large colony of offspring very quickly
Prokaryotes reproduce asexually via binary fission
a.
Synthesize DNA almost continuously
Limits on reproduction
a.
Exhaust their nutrient supply
b.
Accumulate metabolic wastes
c.
Face competition from other microbes
d.
Consumed by other organisms
C.
1.
2.
3.
4.
5.
6.
Endospores
Resistant cells produced when an essential nutrient is lacking in the environment
A cell replicates its chromosome and surrounds one chromosome with a durable wall to form the
endospore
a.
Water is removed from the endospore, halting metabolism
Original cell then disintegrates to leave the endospore behind
An endospore is resistant to all sorts of trauma
a.
Most endospores can survive in boiling water
Endospores may remain dormant but viable for centuries or longer
When conditions become more hospitable, the endospore absorbs water and resumes growth
D.
1.
2.
Mutation
Major source of genetic variation in prokaryotes
Short generational times
a.
Prokaryotic populations can adapt very rapidly to environmental changes
IV.
Genetic Diversity in Prokaryotes
A.
1.
Factors affecting
Rapid reproduction, mutation, and genetic recombination
B.
1.
Binary fission
Some of the offspring differ slightly in genetic makeup due to mutation
C.
Probability of a spontaneous mutation in a given E. coli gene is only about 1 X 10 per cell
Division
There are 2 X 1010 new E. coli cells that arise each day in a single human colon
a.
Approximately 2,000 will have a mutation in that gene
When all 4,300 E. coli genes are considered, 9 million mutant E. coli cells arise per day per human
host
1.
2.
D.
1.
2.
3.
4.
5.
-7
Genetic recombination
Combining of DNA from two individuals into a single genome
Three processes: transformation, transduction, and conjugation
Transformation
a.
Foreign allele replaces the native allele in the bacterial chromosome by genetic
recombination, with an exchange of homologous DNA segments
Transduction
a.
Horizontal gene transfer that occurs when a phage carries bacterial genes from one host cell
to another
Conjugation
a.
Transfers genetic material between two bacterial cells that are temporarily joined
b.
Transfer is one-way
i.
One cell donates DNA, and its “mate” receives the genes
c.
Sex pilus from the donor initially joins the two cells and retracts to pull the two cells
together
i.
Temporary mating bridge forms between the cells
V.
Nutritional and Metabolic Adaptations
A.
1.
2.
3.
4.
Classification based on the way energy and carbon are obtained
Phototrophs obtain energy from light
Chemotrophs obtain energy from chemicals in their environment
Autotrophs only need a carbon source
Heterotrophs require at least one organic nutrient as a carbon source
B.
1.
Classification based on the combination of energy and carbon sources
Photoautotrophs are photosynthetic organisms that harness light energy to drive the synthesis of
organic compounds from CO2 or other inorganic carbon compounds such as HCO3
Chemoheterotrophs must consume organic molecules for both energy and carbon
2.
C.
1.
2.
3.
Classification based on utilization of oxygen
Obligate aerobes require O2 for cellular respiration
Facultative anaerobes use O2 if it is present but can also grow by fermentation in an anaerobic
environment
Obligate anaerobes are poisoned by O2 and use either fermentation or anaerobic respiration, in
which inorganic molecules other than O2 accept electrons from electron transport chains
VI.
Role of Prokaryotes in the Biosphere
A.
Life depends on the recycling of chemical elements between the biological and chemical
components of ecosystems
Prokaryotes play an important role in this process.
Chemoheterotrophic prokaryotes function as decomposers, breaking down corpses, dead vegetation,
and waste products and unlocking supplies of carbon, nitrogen, and other elements essential for life
Prokaryotes convert inorganic compounds into forms that can be taken up by other organisms
Autotrophic prokaryotes use CO2 to make organic compounds, which are then passed up through
food chains
Cyanobacteria produce atmospheric O2, and a number of prokaryotes fix atmospheric nitrogen (N2)
into a form that other organisms can use to make proteins and nucleic acids
Prokaryotes may act to increase or decrease the availability of key plant nutrients
a.
Have complex effects on soil nutrient concentrations
Prokaryotes often interact with other species of prokaryotes or eukaryotes with complementary
metabolisms
a.
Symbiosis
b.
Commensalism
c.
Parasitism
d.
Mutualism
1.
2.
3.
4.
5.
6.
7.
VII.
Protists
A.
1.
2.
3.
4.
Background
Earliest eukaryotic descendants of prokaryotes
Most diverse group of eukaryotes
Most are unicellular
Nutritionally diverse
a.
Autotrophic
i.
Photosynthetic
ii.
Typically algae
b.
Heterotrophic
i.
Protozoana
c.
Mixotrophic
i.
Absorptive protists
Most have flagellum or cilia
Variable life cycles
a.
Asexual
b.
Sexual
i.
Syngamy
Found in moist environments
Life styles
a.
Free living
b.
Symbiotic
i.
Mutualism to parasitism
5.
6.
7.
8.
VIII.
Phylogenetic Organization of Protists
A.
1.
2.
3.
4.
5.
Five “supergroups”
Excavata
Chromalveolata
Rhizaria
Archaeplastida
Unikonta
IX.
Excavata
A.
1.
2.
3.
Characteristics
Have an “excavated” feeding groove
Lack mitochondria and plastids
Evolutionarily similar to prokaryotes
B.
Example
1.
Giardia lamblia
a.
Flagellated, unicellular parasite of the human digestive tract
b.
Diplomonad
i.
Two separate haploid nuclei
ii.
Prokaryotes have haploid genomes
2.
Euglenozoa—flagellates
a.
Two groups
i.
Euglenoids
ii.
Kinetoplastids
3.
Euglenoid characteristics
a.
b.
c.
Anterior pocket with one or two flagella
Paramylum
i.
Unique glucose polymer
Varying modes of nutrition
i.
Autotrophic
ii.
Heterotrophic
iii.
Mixotrophic
4.
Kinetoplastids characteristics
a.
Single large mitochondria
b.
Kinetoplastid
i.
Unique organelle
ii,
Contains extracellular DNA
X.
Chromalveolata
A.
1.
Characteristics
Alveoli
a.
Small membrane-bound cavity under the cell surface
Groups
Dinoflagellates
a.
Photosynthetic
b.
Component of phytoplankton
c.
Red tide
d.
Produce the toxin that is accumulated in shellfish that causes paralytic shellfish poisoning
Apicomplexans (sporozoans)
B.
1.
2.
a.
b.
c.
d.
Parasites
Sporozoites are the infective cells
Complex lifestyles that include multiple hosts
Plasmodium causes malaria
3.
Ciliophorans (ciliates)
a. Use cilia to move and feed
b. Two types of nuclei—macronuclei and micronuclei
c. Macronuclei control day to day functioning and asexual reproduction
d. Micronuclei function in conjugation—sexual process of genetic exchange
XI.
Rhizaria
A.
B.
1.
Unicellular organism that moves by means of pseudopodia
Characteristics
Pseudopodia
a.
Cellular extensions
i.
Cytoplasm streams behind reorganizing microtubules and cytoskeleton
Three groups
Rhizopods (amoebas)
a.
Simple, unicellular, mostly free-living
b.
Asexual reproduction
Radiolarians
a.
Actinopods—slender form of pseudopods
b.
Bundles of microtubules surrounded by a thin layer of cytoplasm
c.
May have a thin shell of silica
Foraminiferans
a.
Porous, chambered shells hardened with calcium carbonate
C.
1.
2.
3.
XII.
Stramenopila
A.
1.
Characteristics
Stramenopila
a.
Fine, hairlike projections on the flagella
b.
Defining characteristic of this group
B.
1.
Groups
Diatoms (Bacillariophyta)
a.
Reproduction is primarily asexual
b.
Unicellular with glasslike walls of silica
c.
Components of plankton
Golden algae (Chrysophyta)
2.
a.
b.
c.
Color results from accessory pigments
i.
Carotenoids
Most are unicellular
Most are biflagellated
3.
4.
C.
Water molds and related organisms (Oomycota)
a.
Lack chloroplasts and are hetrotrophic
b.
Coencytic hyphae
i.
Fine, branching filaments
ii.
Analogous to fungal hyphae
c.
White rusts and downy mildews
Brown algae (Phaeophyta)
a.
Seaweed
b.
Multicellular
Structure of seaweed
1. Thallus
a. Body
b. Appears plantlike but lacks true roots, stems, and leaves
c. Holdfast
i. Rootlike
ii. Maintains position
d. Stipe
i. Supports blades
e. Blades
i. Leaflike
ii. Large surface area for photosynthesis
f. Float
XIII.
Archaeplastida
A.
1.
Red and green algae
Closest relatives to land plants
B.
1.
2.
3.
Characteristics
Lack flagellated life cycle stages
Primarily found in warm, tropical, marine waters
Red color is due to the accessory pigment phycoerythrin
a.
Pigment unique to red algae and cyanobacteria
XIV.
Unikonta
A.
1.
Characteristics
Resemble fungi in appearance and lifestyles
a.
Convergent evolution of filamentous body structure
i.
Filamentous body structure allows greater surface area
ii.
Enhance ability to decompose organic matter in their environments
Two groups
Amoebozoans (Plasmodial slime molds)
a.
Plasmodium—feeding stage of life cycle
i.
Amoeboid, coencytic mass
ii.
Multi-nucleated cytoplasm undivided by membranes
iii.
Plasmodia have diploid nuclei
b.
Cytoplasmic streaming distributes nutrients and oxygen
c.
Reproduction
i.
When stressed, sporangia is formed and haploid spores are formed that undergo
syngamy
Acrasiomycota (Cellular slime mold)
a.
Solitary haploid cells
i. Feeding stage of life consists of individual solitary haploid cells
b.
Reproduction
i. When food supply is depleted cells aggregate to form a mass
ii. Aggregate forms fruiting body to reproduce asexually
B.
1.
2.