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Viruses, Prokaryotes and Protists
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Non-living infectious agents
Viral replication
Eubacteria and Archaebacteria
Bacterial replication
The endosymbiotic origin hypothesis
Protists
Viruses
• Non-living
–No cell membrane
–No metabolism
–No growth or development
• But…
–Evolve!
–Reproduce! (Not by cell division)
Viral Structure
• Nucleic acid: DNA or
RNA (cellular
organisms have both)
• Capsid: Protein coat
– May be surrounded
by glycoprotein and
lipid envelope (these
usually infect
animals)
Bacteriophage
T4
Two basic capsid shapes
•Helical
•Icosahedral (20 triangular sides)
•May have both (e.g. bacteriophage)
Reproduction
• Depends on hosts replicative
machinery
• May code for some required
enzymes, e.g., reverse transcriptase
• Virus particles don’t grow or develop
–Emerge assembled, full size
• Two common replicative cycles
Lytic cycle: Lyses or ruptures cell
1. Virulent
virus binds
to cell
surface
3. Use host’s
metabolism to
synthesize
viral DNA and
proteins
2. Insert Viral
DNA & destroy
host’s DNA
5. Lyse
cell to
release
viral
particles
4. Assemble
new virions
Lysogeny
• Temperate virus
incorporates its DNA
into the host’s genome
• Prophage is replicated
when the host replicates
• Lysogenic conversion
changes host phenotype
– cholera and diphtheria
toxins result from
lysogenic conversion
of host bacteria
RNA viruses
• Must use their own enzymes – cells do not
have enzymes to make copies from RNA
• “Normal” RNA viruses produce a
complementary strand of RNA and use it
as a template to make more copies of their
RNA
• Retroviruses use “reverse transcriptase" to
make DNA from RNA, then insert this DNA
into the host genome
HIV a Retrovirus
• Reverse transcribes
ss DNA from RNA
• Single strand serves
as template for
complementary DNA
• ds DNA integrated
into host genome
• May later transcribe
DNA to new RNA
and make new
viruses
Prions (Prusiner – Nobel Prize)
• PROteinaceous INfectious particles
• Non-genetic information: no nucleic acid at
all, just protein
• Influence normal protein folding
• Transmissible Spongiform Encephalopathy
– Mad Cow Disease
– Creutzfeld-Jacob Disease
– Chronic Wasting Disease
– Scrapie
• Hosts produce
normal prion
protein PrPc
• Disease causing
prion protein PrPsc
folded differently
• PrPsc are resistant
to degradation
and serve as
template causing
PrPc to misfold
Prokaryotes - Archaea and Bacteria
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Unicellular (some colonial)
Shapes: Bacilli, Cocci, Spirilla
No nucleus
Few/No membrane bound organelles
Circular DNA double helix
Single filament flagellum (when present)
Cell division – neither mitosis nor meiosis
Small – most 0.5 – 1.0 mm in diameter
Fig. 27.4
Most, but not all…
• Giant bacterium (left), compared to
Paramecium (right), is about 0.6mm
(600μm)
• Smallest beetles are shorter!
Here’s a fairy
wasp with a
scale bar for
comparison to
some protists!
Polilov A. 2011. The smallest insects
evolve anucleate neurons. Arthropod
Structure & Development DOI:
10.1016/j.asd.2011.09.001
Optional Structures
• Polysaccharide or polypeptide
capsule
–Streptococcus pneumoniae only
pneumonia if has capsule
• Pili – “hairs”
–Neisseria gonorrhoeae, only 
disease if has pili
–F-pili used for conjugation
Structures
Bacterial
Flagellum
• Single flagellin
protein -- Different
from tubulin flagellae
of eukaryotes
• Rotates around axle
– only biological
wheel known
Plasmids
• Small circles of DNA – can be passed
on to offspring or to other cells
• Can replicate independently of the genome
or be integrated into genomic DNA
• May code for, e.g., fertility (ability to
make F-Pilus) or antibiotic resistance
• Valuable biotech tool
Bacterial Reproduction
• Binary fission without mitosis
• Synthesize DNA, but may do so faster
than rate of division
• Copies seem to attach to cell membrane
and membrane grows between attachment
points
• Cell divides with at least one copy of
DNA/cell
Genetic Recombination Possible
• 3 ways of exchanging DNA, after
which the recipient cell incorporates
the new DNA into its genome
• Differ from sexual reproduction in that
parents contribute unequally
Transduction – Virus transmits bacterial
DNA from one cell to another
Transformation
• Bacterial cell takes up DNA from
a ruptured cell
http://en.wikipedia.org/wiki/Five-second_rule
Conjugation
• Cells attach via F-pili
• One cell passes DNA (up to
its entire genome!) to other
Nutritional Modes
• Autotrophs – Can obtain energy and
carbon from inorganic compounds
• Photoautotrophs – photosynthetic -- use
solar energy and CO2 to make organic
compounds
• Chemolithoautotrophs -- chemosynthetic
– use energy from inorganic (non-carbon)
chemicals, e.g., S, N, Fe compounds
Nutritional Modes
• Heterotrophs need preformed organic
molecules, i.e., "food“, for both energy
and carbon source
• Photoheterotrophs – purple and green
nonsulfur bacteria – get energy from light,
but C from preformed organic compounds
• Chemoheterotrophs – get both energy and
carbon from preformed organic comounds
(like we do!)
Bacterial Shapes
• Bacilli – rods
• Cocci – balls
• Spirilla – spirals
Eubacteria
• Obviously – cause variety of diseases
• Also fundamental to many ecological
processes
– Carbon and Nitrogen fixation
– Decomposition
• Important symbionts
– Rhizobium, gut fauna
• Genetic engineering, biosynthesis
• Bioremediation
– Water treatment plants, oil spills
Archaebacteria
• Methanogens
– Obligate anaerobes
– Reduce CO2 to methane (CH4)
“Swamp gas” from swamps - and intestines!
• Extremophiles – several types
– Thermophiles – require hot or cold
temperatures (hot springs, glaciers)
– Halophiles
– pH tolerant
– Pressure tolerant
• Nonextreme archaea
Origin of Eukaryotes
• Endosymbiont theory
(Lynn Margulis)
• Proposes that eukaryote
mitochondria and
chloroplasts arose from
prokaryote symbionts
• Symbiosis = living
together – generally
refers to a mutualism in
which both species
benefit
Mitochondria
• Archaeal host
• Aerobic
a-proterobacteria
engulfed but not
digested
Fig. 29.3
• Infolding of
plasma
membrane
thought to
have led to
nuclear
envelope and
endoplasmic
reticulum
Origin of
organelles
• Mitochondria from
endosymbiotic
aerobic bacteria
• Chloroplasts from
endosymbiotic
photosynthetic
cyanobacteria
(blue-green algae)
Evidence?
• Many prokaryotes form symbioses – e.g.,
Trichonympha, Hatena
• Chloroplasts and mitochondria:
– are about the same size as Bacteria
– contain circular DNA
– reproduce by binary fission without mitosis
– code for some of their own proteins
– have DNA sequence similar to presumed
a-proterobacteria ancestors
– have ribosomes similar to Bacterial ribosomes
• Many antibiotics block protein synthesis by
ribosomes in organelles and prokaryotes, but not
by eukaryote ribosomes
Cyanobacteria
If the
endosymbiont
hypothesis is
correct for
chloroplasts,
where would
you expect
chloroplast
DNA to map
onto this
cladogram?
Trichonympha
• A termite gut protist, but long hairy
“flagella” are bacteria
Chloroplasts
from
“Secondary”
endosymbiosis
• Some protists
obtain a
“chloroplast” by
engulfing another
photosynthetic
protist as
proposed for
brown algae
Hatena and
Nephroselmis
Hatena even uses
Nephroselmis’s eyespot!
At each cell division by a green
Hatena, one green daughter cell
and one colorless daughter cell
produced
Colorless one is heterotrophic
and has feeding structure lacking
in green sister until it engulfs a
Nephroselmis and turns green
Primary (green) and
secondary (blue - at
heads of arrows)
symbiotic origins of
chloroplasts
“Kingdom” Protista
• Eukaryotes – have nuclei and organelles
• Multiple linear chromosomes
• Locomotion: Flagella, cilia, pseudopodia
– Structure of flagella and cilia similar,
but differ from bacterial flagellum
– 9+2 arrangement of microtubules
– microtubules slide against one another
to cause bending, but do not rotate
about axle like bacterial flagellum
Anatomy of Eukaryotic
Cilia and Flagella: 9+2
Microtubules of
tubulin protein
Fig. 4-24
Common free-living freshwater protozoa
illustrate locomotor diversity
• Amoebas
– Pseudopodial locomotion
• Ciliates
– Ciliary locomotion
• Flagellates
– Flagellar locomotion
Pseudopodia
• Temporary
extensions of cell
membrane and
cytoplasm
• May be used for
locomotion or food
gathering
• Top:
Foraminiferan,
Bottom: Amoeba
Paramecium:
a Typical Ciliate
• Uses cilia to
swim and feed
• Micronucleus
for sex
• Macronucleus
for daily
operation
• Contractile
vacuole for
osmotic
balance
Flagellates
• Include zooflagellates as well as
• Euglenoids, which include heterotrophs and
facultatively heterotrophic autotrophs, and
• Dinoflagellates – red tide organisms
• Flagellar microstructure similar to cilia
Euglena
Reproduction Highly Variable
• Asexual, by binary fission
• Sexual – Conjugation – exchange of
haploid nuclei only
Ciliates end up being Identical Twins after sex!!!
Sexual Reproduction with Gametes
• In Protists, we see the origins of “male”
and “female” :
• Beginning with Isogamy -- two equal
sized gametes, no male vs female (but
may require different “mating types”
• Shift through Anisogamy – unequal
gametes, but both motile
• To Oogamy -- large, immobile egg and
small motile sperm
– defines male vs. female
Life Cycles
• Ancestral state
(for gametic
reproduction) is for
diploid zygote to
undergo meiosis
immediately
• No alternation of
generations (only
one multicellular
stage)
Alternation of Generations
• Shift to diploid
stage that
undergoes at least
one mitotic
division
• Result is a
multicellular
diploid stage and
a multicellular
haploid stage
Isogamous
Reproduction:
Chlamydomonas
• 1n flagellated cells
very similar
• (-) and (+) mating
types
• Fuse to form 2n
tough-walled sporelike zygote
• Undergoes meiosis
• Releases four 1n
vegetative cells
Anisogamous
Reproduction: Ulva
• Has male and female
haploid gametophytes
• These form 1n gametes
(female gamete larger)
• Gametes form 2n zygote
• Zygote develops into 2n
sporophyte
• Sporophyte forms spores
that develop into the
haploid gametophyte to
complete the life cycle.
Oogamous reproduction: Laminaria
• Motile sperm swim
to large non-motile
eggs which lack
flagellum
Protist Phylogeny in Flux
Old School:
Grouping Based on Trophic Modes
• Algae – Photoautotrophs
• Protozoa – Heterotrophs
• Slime molds and water molds –
Fungus-like, absorptive heterotrophs
with mycelium-like structure
NOT monophyletic groups
Protists Fungi Animals Protists
^
“Plants”
Protists Protists
Protists
The future of eukaryote phylogeny:
Eight monophyletic groups of eukaryotes
→ 10 kingdoms – or more?!
Still much disagreement among
authorities on names and even some
details of branching patterns
Main thing to
recognize is that as
a kingdom, Protista
is not a good
monophyletic group,
but is paraphyletic,
because of
unchallenged
locations of origins
of kingdoms Plantae,
Fungi, and Animalia.
Domain Eukarya remains monophyletic
Origins of Multicellularity
• Many simple colonial
protists
• Brown algae all
multicellular, some reach
75m!
• Some differentiation at
tissue level, but no true
organs
• Choanoflagellates
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closest relatives to animals
• Green algae closest
relatives to plants
Benefits of Multicellularity
• Division of labor
– Differentiation of specialized cells for feeding,
reproduction, etc
• Larger size
– Predation and defense
– Efficiency – lower mass-specific metabolic rate
• Surface:volume ratio limits size of single cell
– Needs depend on volume
– Supply rate depends on surface area
– Can increase S:V ratio by flattening, lengthening,
or convoluting surface
Viruses, Prokaryotes and Protists
•
•
•
•
•
•
Non-living infectious agents
Viral replication
Eubacteria and Archaebacteria
Bacterial replication
The endosymbiotic origin hypothesis
Protists