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Viruses, Prokaryotes and Protists
Non-living infectious agents Viral replication Eubacteria and Archaebacteria Bacterial replication The endosymbiotic origin hypothesis Protists
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Viruses But… Non-living No cell membrane No metabolism
No growth or development But… Evolve! Reproduce! (Not by cell division)
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Viral Structure Bacteriophage T4
Nucleic acid: DNA or RNA (cellular organisms have both) Capsid: Protein coat May be surrounded by glycoprotein and lipid envelope (these usually infect animals)
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Two basic capsid shapes
Helical Icosahedral (20 triangular sides) May have both (e.g. bacteriophage)
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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
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Lytic cycle: Lyses or ruptures cell
3. Use host’s metabolism to synthesize viral DNA and proteins 5. Lyse cell to release viral particles 1. Virulent virus binds to cell surface 2. Insert Viral DNA & destroy host’s DNA 4. Assemble new virions
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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
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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
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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
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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
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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
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Prokaryotes - Archaea and Bacteria
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
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Fig. 27.4
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Most, but not all… Giant bacterium (left), compared to Paramecium (right), is about 0.6mm (600μm) Smallest beetles are shorter!
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Here’s a fairy wasp with a scale bar for comparison to some protists!
Polilov A The smallest insects evolve anucleate neurons. Arthropod Structure & Development DOI: /j.asd
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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
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Structures
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Bacterial Flagellum Single flagellin protein -- Different from tubulin flagellae of eukaryotes Rotates around axle – only biological wheel known
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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
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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
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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
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Transduction – Virus transmits bacterial DNA from one cell to another
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Transformation Bacterial cell takes up DNA from a ruptured cell
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Conjugation Cells attach via F-pili
One cell passes DNA (up to its entire genome!) to other
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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
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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!)
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Bacterial Shapes Bacilli – rods Cocci – balls Spirilla – spirals
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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
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Archaebacteria Methanogens Extremophiles – several types
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
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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
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Mitochondria Archaeal host
Aerobic a-proterobacteria engulfed but not digested
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Fig. 29.3 Infolding of plasma membrane thought to have led to nuclear envelope and endoplasmic reticulum
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Origin of organelles Mitochondria from endosymbiotic aerobic bacteria
Chloroplasts from endosymbiotic photosynthetic cyanobacteria (blue-green algae)
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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
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If the endosymbiont hypothesis is correct for chloroplasts, where would you expect chloroplast DNA to map onto this cladogram? Cyanobacteria
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Trichonympha A termite gut protist, but long hairy “flagella” are bacteria
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Chloroplasts from “Secondary” endosymbiosis
Some protists obtain a “chloroplast” by engulfing another photosynthetic protist as proposed for brown algae
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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
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Primary (green) and secondary (blue - at heads of arrows) symbiotic origins of chloroplasts
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“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
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Anatomy of Eukaryotic Cilia and Flagella: 9+2 Microtubules of tubulin protein
Fig. 4-24
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Common free-living freshwater protozoa illustrate locomotor diversity
Amoebas Pseudopodial locomotion Ciliates Ciliary locomotion Flagellates Flagellar locomotion
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Pseudopodia Temporary extensions of cell membrane and cytoplasm
May be used for locomotion or food gathering Top: Foraminiferan, Bottom: Amoeba
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Paramecium: a Typical Ciliate
Uses cilia to swim and feed Micronucleus for sex Macronucleus for daily operation Contractile vacuole for osmotic balance
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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
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Reproduction Highly Variable
Asexual, by binary fission Sexual – Conjugation – exchange of haploid nuclei only Ciliates end up being Identical Twins after sex!!!
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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
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Life Cycles Ancestral state
(for gametic reproduction) is for diploid zygote to undergo meiosis immediately No alternation of generations (only one multicellular stage)
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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
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Isogamous Reproduction: Chlamydomonas
1n flagellated cells very similar (-) and (+) mating types Fuse to form 2n tough-walled spore-like zygote Undergoes meiosis Releases four 1n vegetative cells
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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.
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Oogamous reproduction: Laminaria
Motile sperm swim to large non-motile eggs which lack flagellum
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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
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Protist! Protists Fungi Animals Protists “Plants” Protists Protists Protists ^
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The future of eukaryote phylogeny:
Eight monophyletic groups of eukaryotes → 10 kingdoms – or more?!
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Still much disagreement among authorities on names and even some details of branching patterns
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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
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Origins of Multicellularity
Many simple colonial protists Brown algae all multicellular, some reach 75m! Some differentiation at tissue level, but no true organs Choanoflagellates closest relatives to animals Green algae closest relatives to plants
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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
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Viruses, Prokaryotes and Protists
Non-living infectious agents Viral replication Eubacteria and Archaebacteria Bacterial replication The endosymbiotic origin hypothesis Protists
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