Lecture 10 - Eukaryotic Microbiology Lecture Notes PDF

Lecture 10 Eukaryotic Microbiology  The Eukaryotic Cell Cell structure much more complex Extensive subcellular compartmentalization Creates multiple environments to support various metabolic activities  The Nucleus Largest organelle - contains...

Lecture 10 Eukaryotic Microbiology  The Eukaryotic Cell Cell structure much more complex Extensive subcellular compartmentalization Creates multiple environments to support various metabolic activities  The Nucleus Largest organelle - contains genetic information (DNA) Enclosed by double layered lipid envelope Pores allow transport of various cytoplasmic Transport substancesrequires energy, provided by hydrolysis of GTP Contains nucleolus - condensed regions of chromosomes, sites of rRNA synthesis DNA organized by histones Further organized into chromatin - thread like Further condenses to chromosomes for  Mitochondria Specialized organelle - generates ATP (cellular energy), double membrane, lack sterols, much more flexible Outer membrane equal proportions of protein and lipid, very permeable, due to numerous pore complexes Inner membrane - complex folds (cristae), large surface area, much higher protein content compared to outer membrane Center is matrix, contains enzymes for TCA cycle Oxidative phosphorylation occurs across cristae membrane, generates ATP  The Hydrogenosome Some organisms lack mitochondria (Trichomonas), use hydrogenosome to generate energy Lacks cristae, uses different metabolic pathway to produce ATP Glucose converted to pyruvate through glycolysis Pyruvate converted to Acetyl CoA, liberates CO2 and H2 Acetyl CoA converted to acetate Energy release from hydrolysis of high energy bond used to produce ATP from ADP and inorganic phosphate  The Chloroplast Double membrane enclosed structure, outer membrane permeable as with mitochondria Inner membrane surrounds lumen, creates stroma, organized into flattened membrane disks Chlorophyll contained in flattened disks – thylakoids, stacks of thylakoids make grana Membranes of thylakoids impermeable to ions, used to generate proton motive force for oxidative phosphorylation Catalyzes formation Stroma contains of phosphoglyceric ribulose acid bisphosphate carboxylase - RubisCO Essential for biosynthesis of glucose, confers autotrophy  The Endosymbiotic Theory Several lines of evidence support that chloroplasts and mitochondria were once free living bacteria Contain DNA, encodes rRNA, tRNA, and electron transport genes Eukaryotic genomes contain bacterial related genes, believed to have migrated from organelle Contain bacteria like ribosomes Ribosomes sensitive to prokaryotic protein synthesis inhibitors (streptomycin) rRNA sequences related to prokaryotic rRNA genes Similar lines of evidence support theory for hydrogenosome  The Endoplasmic Reticulum Extensive network of flattened cisterns continuous with the nuclear envelope Rough ER - studded with ribosomes – Protein entry point, cotranslational – Modifications made, lipids and carbohydrates attached Smooth ER - no ribosomes – More enzymatic diversity – Synthesis of phospholipids and steroids  The Golgi Complex Receives all proteins transported from RER Mail station of the cell - all proteins sorted for transport Composed of cisterns - flattened membranous stacks Many post-translational modifications made Determines fate of protein Can be packaged into secretory vesicle Can be packaged into transport vesicle (transfer between stacks, transfer to storage vesicles)  Lysosomes Single membrane enclosed vesicles Contain many digestive enzymes Acidified environment, pH 5 Process macromolecules for metabolism Play important role in immune response White blood cells engulf bacteria Phagosome fuses with lysosome Digestive enzymes kill bacteria  Peroxisomes Similar to lysosome - smaller Form by division of preexisting peroxisomes Carries out several oxidation reactions Amino acids Alcohol - generates H2O2 Also contain catalase  Microfilaments and Microtubules Structural integrity of cell supported by cytoskeleton Cytoskeleton comprised of microfilaments and microtubules Microfilaments composed of actin, 8 nm in diameter, critical role in defining cell shape Microtubules composed of tubulin, 25 nm in diameter, assist microfilaments in maintaining cell structure Also play critical role in cell movement Important components of flagella and cilia Rearrangements essential for pseudopodal movement  Flagella and Cilia Flagella - long and few Cilia - short and many Both used for motility Both have 9+2 microtubule structure Waves but doesn’t rotate, different from bacterial flagella  Maintenance of Chromosome Ends Each round of DNA replication should shorten chromosomes Would eventually result in cellular death Require machinery to preserve chromosome length Uses specific enzyme - TELOMERASE Attaches to specific sequence at end of chromosome - TELOMERE Telomeres defined by two criterion Located at end of chromosomes  How Does Telomerase Work? Telomerase has two components Enzyme capable of synthesizing DNA RNA complementary to sequence at end of chromosome RNA base pairs with DNA telomere sequence at chromosome ends Enzyme synthesizes DNA to extend chromosome ends Generates series of repetitive DNA sequences at end of chromosome  Review of Eukaryotic Genetics Many eukaryotic organisms are diploid – 2 copies of each chromosome Some eukaryotic organisms are haploid – 1 copy of each chromosome Some eukaryotic organisms maybe either haploid or diploid depending on stage of life cycle Cellular division requires replication of DNA and segregation of replicated material to each daughter cell – mitosis – may occur in haploid or diploid cells Meiosis only occurs in diploid cells, chromosomal copy number reduced by half, requires two cellular divisions, recombination events may occur  The Yeast Life Cycle May grow as a haploid or diploid organism Haploid organisms exist as one of two mating types – a or a a or a continue to grow as haploid organisms in pure culture Reproduce through mitosis, no genetic recombination occurs If a and a mating types mixed, an a cell fuses with an a cell, generates diploid  The Yeast Life Cycle Diploid organism may continue to reproduce through mitosis May be induced to sporulate under specific conditions Meiosis accompanies sporulation, crossing over may occur Results in formation to four haploid ascospores May germinate and resume haploid life cycle  Mating Type Switching Many yeast strains switch mating type if in homogeneous population Accomplished through recombination event at MAT locus Strains contain a copy of the a and a genes, lack promoter Recombination event places either a or a gene adjacent to promoter Silent copies remain, allows for switching of mating type  mRNA Processing Eukaryotic transcripts initially exist as pre-mRNA Contains coding (exons) and non-coding (introns) sequences Introns must be removed prior to translation Accomplished in some cases by the spliceosome Contains several proteins and RNA Binds conserved sequences in intron Catalyzes removal of intron Results in formation of lariat structure  mRNA Processing Some introns possess catalytic ability to remove themselves from pre-mRNA – ribozymes Requires guanosine, hydroxyl group make nucleophilic attack at intron-exon junction Breaks the phosphodiester bond, generates a 3' hydroxyl on exon Results Ribozymein catalyzes joining of a second two nucleophilic attack using 3' hydroxyl exons on exon Intron circularizes following removal of a 15 bp fragment Intron sequences ultimately degraded  mRNA Processing Removal on introns only one level of processing Pre-mRNA also modified at the 5' and 3' ends 5' end capped with 7-methyl guanosine, bound by eIF4, essential for translation 3' end poly-adenylated Bound by poly A binding protein (PABP) PABP interacts with eIF4 Interaction essential for translation  Protozoa Eukaryotic, unicellular, chemoheterotrophic organisms Many different cellular morphologies Typically inhabit water and soil Trophozoite - feeding and growing stage Ingest bacteria and small particulate nutrients Most are non-pathogenic  Asexual Life Cycle Reproduce asexually by binary fission, budding or schizogony Binary fission - equal division of one cell into two following replication of genetic material Budding - bud forms at one pole of mother cell, grows and eventually splits off to form daughter cell following replication of genetic material Schizogony - multiple fission, nucleus divides several times, cell then divides accordingly  Protozoa Paramecium among the first organisms to demonstrate heritable information in nucleus Early model for studying life cycles and development Became evident that organisms capable of asexual reproduction - BINARY FISSION Occasionally observed two paramecium attached to each other prior to cellular division - CONJUGATION Subsequent studies revealed genetic information exchanged during conjugation Led to understanding of sexual life cycle exhibited by paramecium  The Paramecium Life Cycle Mature paramecium contain three nuclei, two micronuclei and one macronucleus Micronuclei arrested at first meiotic division Macronucleus center of transcription required for physiological function  The Paramecium Life Cycle Two cells in proximity of each other may undergo conjugation Cells physically attach, causes formation of cytoplasmic bridge Two micronuclei progress through final stages of meiosis, macronucleus disintegrates Resulting cells possess 8 haploid nuclei  The Paramecium Life Cycle Seven of the haploid micronuclei randomly degenerate Remaining micronucleus divides mitotically One micronucleus from each cell migrates through cytoplasmic bridge to other cell - MIGRATING MICRONUCLEUS Two exchanged micronuclei fuse with micronuleus retained by each cell - STATIONARY MICRONUCLEUS  The Paramecium Life Cycle Cells detach and separate from one another Resulting cells are diploid Diploid nuclei undergo mitotic division, cells do not divide One nucleus becomes micronucleus, second becomes macronucleus Micronucleus divides again to complete cycle  Mastigophora Two groups - flagellated, disk shaped mitochondria, no sexual reproduction Euglenoids - photoautotrophs, semi-rigid plasma membrane (pellicle), characteristic eyespot, preemergent flagellum directs motility, may be facultative chemoheterotrophs in dark Hemoflagellates - blood parasites, blood feeding insect vectors, long bodies, undulating membrane for motility, Tryanosoma, multiplies in insect by binary fission, defecation during bite causes infection  Mastigophora Eukaryotes that lack mitochondria Usually live as symbionts in digestive tracts of animals Usually spindle shaped with flagella protruding from one end - pull organism through medium Several pathogens - Trichomonas vaginalis Has undulating membrane - membrane bordered by flagella No cyst stage  Rhizopoda Also called amoeba Pseudopodal motility Entamoeba histolytica - intestinal dysentery, only intestinal pathogen Primary food source is red blood cells Follows typical fecal oral transmission  Ciliophora Cilliated protozoa - coordinately moved for motility, usher food to oral cavity May be anchored to surface Balantidium coli - rare but severe intestinal dysentery Cysts ingested by humans Trophozoites released in large intestine Feed on bacteria and fecal debris Cysts excreted with feces  Apicomplexan Non-motile in mature form Specialized organelle at apexes of cells Secrete enzymes through this organelle Contain enzymes that allow penetration of the host tissues Several pathogenic species - very complex life cycles Plasmodium - causative agent of malaria  Plasmodium Life Cycle Grows by sexual reproduction in insect vector Insects carrying infective form (sporozoite) transmit to humans Sprozoite transferred to liver - undergo schizogony - produce merozoites Merozoites enter bloodstream - infect red blood cells, differentiate into trophozoites Trophozoite progresses to ring stage - divides repeatedly, ruptures cell, waste released causes symptoms Some develop into gametocytes - not pathogenic, reenter insects  Sexual Life Cycle of Plasmodium Male and female gametocytes take up by insect vector Unite to form zygote in digestive tract Zygote develops into oocyst Cell divides repeatedly, forms sporozoites Oocyst ruptures releasing sporozoites Sporozoites migrate to salivary glands Can be transmitted to repeat cycle  Slime Molds Two classifications - cellular and plasmodial (acellular) Cellular slime molds only undergo asexual reproduction Plasmodial (acellular) slime molds undergo both sexual and asexual reproduction  Plasmodial (Acellular) Slime Molds Mass of protoplasm with many nuclei - PLASMODIUM Moves as giant amoeba engulfing organic matter and bacteria Distributes Under starvation conditions nutrients through- cytoplasmic fragments to many protoplasms streaming Each forms stalked sporangium, spores develop Nuclei undergo meiosis, spores released under favorable conditions Fuse to form diploid cells, cells fuse to make plasmodium More Complicated Life Cycles - Cellular Slime Molds Dictostelium discoideum - exhibits more complicated life cycle Oscillates between free living organisms - MYXAMOEBAE - and aggregate life form - SLUG Cells in aggregate life form chosen to differentiate into particular structures with defined functions Allows use for study of similar developmental pathways used in higher eukaryotes  D. discoideum Life Cycle Favorable conditions (abundant nutrients) allow haploid myxamoebae to feed independently Depletion of food triggers first cells starved to produce cAMP cAMP causes two changes, signals adjacent cells to migrate towards cell producing it Causes change in expression of surface proteins gp24 now produced, allows cell-cell attachment required for slug formation  D. discoideum Asexual Life Cycle gp24 necessary but not sufficient for full development Initial interaction triggers production of gp80, surface protein that further stabilizes cell-cell interaction Prior to completion of aggregation, gp150 expressed, displaces gp80, executes adhesion role during subsequent stages of development Cells continue to aggregate until slug or GREX forms Migrates toward light if in dark and moist environment Once in lighted area, developmental changes ensue  D. discoideum Asexual Life Cycle Cells in different regions of slug differentiate into different structures Cells in anterior region will ultimately form the the spore sack and spores - PRESPORE CELLS Mature Cells in stalk the posterior cells die region differentiate into the basal disk and stalk - PRESTALK CELLS Mature spore cells dormant Released under favorable conditions to produce new myxamoebae  Fungi Increased incidence of infectious disease, nosocomial infections Significant impact on agriculture industry, plant pathogens Also beneficial, decompose dead matter, recycle vital elements Most plants require symbiotic fungi (mycorrhizae) for nutrient acquisition Many forms are used as food by animals Also used in production of antibiotics  Molds and Fleshy Fungi Body called THALLUS-composed of long filaments of cells joined together called hyphae, can be very long Two classes of hyphae - septate and coenocytic SEPTATE - cross walls divide hyphae in to single uninucleate cells COENOCYTIC - lack cross walls, single multinucleate cell Hyphae grow from tip Each part capable of growth If breaks off, can form a new fungal colony  Types of Hyphae Some hyphae involved in nutrient acquisition - VEGETATIVE HYPHAE Some hyphae involved in reproduction - AERIAL HYPHAE Project above surface of medium that fungus is growing on Hyphae can form structures that are visible to unaided eye - MYCELIUM  Zygomycota Rhizopus nigricans - black bread mold, saprophytic, coencytic hyphae Asexual spore is sporangiospore - dark structures Sporangiospore breaks open - spores released Spores germinate if conditions favorable Sexual spore called zygospore Results in fusion of nuclei of two cells  Ascomycota Sac fungi - molds with septate hyphae and some yeast, asexual spores usually conidia produced in long chains (arthrospores) Spores freely detach and disperse Sexual reproduction results in formation of ascospore Spores produced in sac like structure called ascus Therefore, called sac fungi  Basidiomycota fungi - possess septate hyphae, include mushrooms diospores form externally on base pedestal (basidium) Usually 4 basidiospores per basidium Some members of phylum reproduce asexually through conidiospores  Unicellular Fungi - Yeast Two general classes - budding and fission yeast Cell division distinguishes two classes Budding yeast do not divide evenly Fission yeast do  Budding Yeast Nonfilamentous unicellular fungi, sphere or oval shaped Two types of yeast - budding and fission Budding yeast - S. cerevisiae Divide unevenly Parent cell forms protuberance (bud) Nucleus divides and one migrates to bud Wall forms between bud and parent cell, bud breaks away Some budding yeast form pseudohypha - short chains of cells Due to lack of separation from parent cell - important for  Fission Yeast Schizosaccharomyces pombe - divide evenly to produce two new cells Parent cell elongates, nucleus divides, new cell wall forms to divide parental cell evenly Both budding and fission yeast can undergo aerobic or anaerobic respiration - facultative anaerobes Allows survival in diverse environments Will perform aerobic respiration if oxygen present Will undergo fermentation if in anaerobic environment  Dimorphic Fungi Exhibit dimorphism - two forms of growth Can undergo yeast like growth, reproduce by budding Can undergo mold like growth, producing vegetative and aerial hyphae Many pathogenic forms of fungi exhibit dimorphic growth Temperature often dictates form of growth  Algae Very diverse life form, found in many environments Can be unicellular or multicellular Most are aquatic life forms, some inhabit soil or trees if moisture sufficient Water required for all aspects of life (cellular support, reproduction, and nutrient acquisition) All photoautotrophic like plants Not classified with plants, lack many plant structures (cuticle, vascular tissues,  Diatoms Can be either unicellular or filamentous Complex cell wall - pectin and silica, two halves to shell - fit together like Petri dish Unusual energy store – oil Asexual reproduction - each daughter cell receives one of the parental shells, must synthesize the other, get smaller each generation Critical size reached - triggers sexual reproduction, shell-less gametes produced, fuse and grow substantially before forming new shell  Dinoflagellates Unicellular algae - plankton Interlocking cellulose plates embedded in plasma membrane, structural integrity Two flagella, propel by spinning through water Photosynthetic, uses conventional chlorophyll, also accessory pigment - FUCOXANTHIN - specialized carotenoid (light absorbing pigment) Some exist in endosymbiosis with jellyfish, corals and mullosks Provide food to host organism through photosynthesis, host organism protects dinoflagellate from environment, lack cellulose  Unicellular Green Algae Chlamydomonas - unicellular green algae exhibiting sexual and asexual reproduction Organisms has distinct mating types (+ and -) Both mating types are haploid Uniform population of + or - committed to asexual reproduction (binary fission) Introduction of at least one organism of opposite mating type triggers entry into sexual reproductive life cycle  Unicellular Green Algae Haploid organisms of opposite mating type attach to each other Cells physically fuse to each other Resulting diploid cell differentiates into zygote Zygote undergoes meiosis Completion of meiosis marks end of sexual reproductive life cycle Zygote germinates releasing four recombinant haploid organisms  Life Cycles of Volvox Asexual life cycle if population uniform (all + or - mating type) Organism consists of ca. 2000 somatic cells and 16 reproductive cells - GONIDIA Gonidia undergo several rounds of cell division to produce juvenile Volvox contained within mature organism Juvenile organisms produced “inside out” All cells (somatic and gonidia) on exterior of organism Flagella of somatic cells on interior of organism Must invert to form mature organism  Life Cycles of Volvox Inversion accomplished by gastrulation like mechanism Invagination followed by cell migration moves cells from exterior to interior of organism Juvenile organisms continue to develop Ultimately released from parental organism Mature in time, cycle repeats Parental organism now composed of somatic cells devoid of gonidia Undergo programmed cell death