EUKARYOTIC CELL BIOLOGY AND MICROORGANISM Advance Microbiology

Eukaryotic Cell Structure In contrast to prokaryotes, eukaryotes contain a membrane-enclosed nucleus and several other organells.

Nucleus • The nucleus is enclosed by pair of membranes, the inner • The nucleus contains the genome of the eukaryotic cell. • In eukaryotic, DNA within the nucleus is wound around histones to form nucleosomes, and from them chromosomes. • The nucleus is enclosed by pair of membranes, the inner membrane is a simple sac, while the outer membrane is in many places continuous with the endoplasmic reticulum.

• The inner and outer nuclear membranes specialize in interactions with the nucleoplasm and the cytoplasm, respectively. • The nuclear membrane also contains pores, formed from holes where the inner and outer membranes are joined. The pores allow a complex of proteins to import and export other proteins and nucleic acids into and out of the nucleus, a process called nuclear transport. • Within the nucleus, the nucleolus is the site of ribosomal RNA synthesis. Eukaryotic Cell Structure And Function

The nucleus. Electron micrograph of a yeast cell by freez-etching, showing a surface view of the nucleus.

Respiratory and Fermentative Organells: the Mithocondrion and the Hydrogenosome Mitochondria • For respiration and oxidative phosphorylation (a mechanism of ATP formation). • Can be rod-shaped or nearly spherical. • A typical animal cell can contain over 1000 mitochondria. • Surronded by two membranes. The outer membrane, composed of an equal mixture of protein and lipid, relatively permeable and contains numerous minute channels that allow passage of ions and small organic molecules. The inner membrane is more protein rich and is also less permeable. Eukaryotic Cell Structure And Function

• Mitochondria also possess a series of folded internal membranes called cristae, the sites o enzymes involved in respiration and ATP production. • The matrix contains a number of enzymes involved in the oxidation of organic compounds-in particular, enzymes of the citric acid cycle. Diagram showing the overall structure of the mitochondrion. Note inner and outermost membranes. Eukaryotic Cell Structure And Function

tissue, showing the variability in morphology. Note the cristae. Tranmission electron micrographs of mitochondria from rat tissue, showing the variability in morphology. Note the cristae. Eukaryotic Cell Structure And Function

• Some anaerobic eukaryotic microorganisms lack mitochondria The Hydrogenosome • Some anaerobic eukaryotic microorganisms lack mitochondria and contain instead a hydrogenosome. • The hydrogenosome lacks cristae and citric acid cycle. Electron micrograph of a thin section through a cell of the anaerobic flagellate, Trichomonas vaginalis. Eukaryotic Cell Structure And Function

Biochemistry of the hydrogenosome

Photosynthetic Organells: The Chloroplast • Chloroplasts are choropyll- containing organelles found in phototrophic eukaryotes- algae. • Chloroplasts have permeble outermost membrane, a much less permeable inner membrane, and an intermembrane space. • The inner membrane surrounds the lumen of the chloroplast, called the Stroma. a b Photomicrographs of algal cells showing chloroplasts. (a) Stephanodiscus, (b) Spirogyra, spiral-shaped chloroplasts

• Instead, chlorophyll and all other components needed for photosynthesis are located in a series of flattened membrane discs called thylakoids. In green algae and green plants, thylakoids are typically stacked into discrete structural units called grana. • The chloroplats stroma contains large amounts of the enzyme ribulose bisphosphate carboxylase (RubisCo), a key catalist of the calvin cycle, the series of biosynthetic reactions by which most photosynthetic organism convert CO2 into organic compound. Chloroplast Thylakoid Chloroplast of the golden brown alga Ochromonas danica. Note thylakoids.

Endosymbiosis: Relationships of Mithocondria and Chloroplasts to Bacteria 1. 2. 3. 4. 5. Mithochondria and chloroplasts contain DNA The eukaryotic nucleus contains bacterially derived genes Mitochondria and chloroplasts contain their own ribosomes 70S-same as prokaryotes ribosomes. Antibiotic specifity Several antibiotics (ex. Streptomycin) kill or inhibit bacteria. These same antbiotics also inhibit protein synthase in mitocondria and chloroplast. Molecular phylogeny Using comparative ribosomal RNA sequencing methods and oranellar genome studies have shown convincingly that the chlorolpast and mitochondrion originated from the Bacteria. Eukaryotic Cell Structure And Function

Other Organelles and Eukaryotic Cell Structure Endoplasmic Reticulum (ER) • Is a network of membranes continuous with the nuclear membrane. • Two types: rough, which contains attached ribosomes, and smooth, which does not. • Smooth ER participates in the synthesis of lipids and in some aspects of carbohydrate metabolism. • Rough ER, through the activity of its ribosomes, is a major producer of glycoproteins and also produces new membrane material. Eukaryotic Cell Structure And Function

• Consists of a stack of membranes distinct from the ER, but Golgi Complex • Consists of a stack of membranes distinct from the ER, but which functions in concert with the ER. • In the golgi complex products of the ER are chemically modified and sorted into those destinied to secreted, for example hormones or digestive enzymes. Cell of the protozoan Toxoplasma gondii. The golgi is colored in red. Eukaryotic Cell Structure And Function

Are membrane-enclosed structures that contain various Lysosomes Are membrane-enclosed structures that contain various digestive enzymes that the cell uses to digest macromolecules such as proteins, fats, and polysacharides. Peroxisome is a membrane-enclosed structures whose function is to produce hydrogen peroxide (H2O2) from the reduction of O2 by various hydrogen donors, including alcohols and long chain fatty acids. The H2O2 produced in the peroxisome is degraded to H2O and O2 by enzyme catalase. Eukaryotic Cell Structure And Function

Microfilaments and Mirotubules • These structures form the cell cytoskeleton. • Microfilaments are about 8 nm in diameter and are polymers of the protein actin. These fibers form scaffolds throughout the cell, defining, and maintaining the shape of the cell. • Mirotubules are larger filaments, about 25 nm in diameter, and are composed of the protein tubulin. Microtubules assist microfilaments in maintaining cell structure. • They also play an important role in cell motility. Eukaryotic Cell Structure And Function

Microfilaments and eukaryotic cell architecture Eukaryotic Cell Structure And Function

• Are organelles of motility, allowing cells to move by swimming Flagella and Cilia • Are organelles of motility, allowing cells to move by swimming motility. • Cilia are essentially short flagella that beat in synchrony to propel the cell – usually quite rapidly – through the medium. • Flagella are long appendages present singly or in groups that push the cell along – typically more slowly than by cilia – through a whip-like motion. Eukaryotic Cell Structure And Function

Overview of Eukaryotic Genetic • Eukaryotic cells divided by mitosis and then undergo sexual reproduction. • From a genetic standpoint, eukaryotic cells can exist in two forms: haploid or diploid. • Mitosis is the process following DNA replication in a cell in which chromosomes condense, divide, and are separated into two sets, one for each doughter cell. • Meiosis is the process by which the conversion from the diploid to the haploid stage occurs. Eukaryotic Genetics

Mitosis, as seen in the light microscope Metaphase, chromosome are paired in the center of the cell. Anaphase, Chromosome are separating Eukaryotic Genetics

The Mating Process in Yeast: Mating Types Life cycle of a typical yeast, Sacharomyces cerevisiae. A haploid cell of S. Cerevisiae contain 16 chromosome. Eukaryotic Genetics

Eukaryotic Microbial Diversity Phylogenetic tree based on comparative 18S ribosomal RNA sequences. Note how endosymbionts (mitochondria and chloroplasts) are shown to originate in the domain Bacteria.

A phylogenetic tree based on other eukaryotic genes and proteins Eukaryotic Microbial Diversity

Characteristics of the major groups of protozoa Typical representatives Trypanosoma, Giardia, Leishmania, Trichomonas Euglena Amoeba, Entamoeba Balantidium, Paramaecium Group Mastigophora Euglenoids Sarcodina Ciliophora Common Name Flagellates Photorophic flagellates Amebas Ciliates Habitats Freshwater; parasites of animals freshmarine Freshwater and marine; animal parasites parasites; rumen Common deases African sleeping sickness, giardiasis, leishmaniasis None known Amebic dysentery (amebiasis) Dysentery Primarily animal Plasmodium, Toxoplasma parasites; insects (vector for parasitic Malaria, toxoplasmosis Apiconplexa Sporozoans deseases)

Typical protozoa. (a) Amoeba. (b) A typical ciliate, Paramaecium. (c) A flagellate, Dunaliella (this flagellate contains chlooroplasts and thus can also be consider an alga). (d) Plasmpdium vivax, an apicomplexan sporozoan, growing in a human red blood cell. Eukaryotic Microbial Diversity

Photomicrograph of the flagellated protozoan Trypanosoma brucei, the Membrane flap Red blood cell Trypanosomes. Photomicrograph of the flagellated protozoan Trypanosoma brucei, the causative agent of African sleeping sickness, from a blood smear. Trypanosoma cell Shelled amoebae: foraminifera. Note the ornate and multilobed test. Eukaryotic Genetics

Side view of a moving amoeba, Amoeba proteus, taken from a film. The time interval from top to bottom is about 6 second. The arrows point to a fixed spot on the surface. A single cell is about 80 μm in diameter.

Paramaecium, a ciliated protozoan Yeast cell (for scale) Mouth (gullet) Eukaryotic Microbial Diversity

Slime Molds • Slime molds are microbial eukaryotes that have phenotipic similarity to both fungi and protozoa. Like fungi, slime molds undergo a life cycle and can produce spores. However, like protozoa slime molds are motile and can move across a solid surface rather rapidly. • Divided into two groups, cellular slime molds, whose vegetative forms are composed of single amoebae, and the acellular slime molds, whose vegetative forms are masses of protoplasm of indefinitife size and shape called plasmodia.

Slime molds. Plasmodia of the acellular slime mold Physarum growing on an agar surface Eukaryotic Microbial Diversity

Eukaryotic Microbial Diversity Photomicrograph of various stages in the life cycle of the celullar slime mold Dictyostellium discoideum.(a) Amoebae in preaggregation stage. (b) Aggregating amoebae. (c) Low-power view of aggregating amoebae. (d) Migrating pseudoplasmodia (slugs) moving on an agar surface and leaving trails of slime in their wake. (e,f) Early stage of fruiting body, (g) Mature fruiting body. Eukaryotic Microbial Diversity

Eukaryotic Microbial Diversity Stages in fruiting-body formation in the cellular slime mold Dictyostellium discoideum. (A-C) Aggregation of amoebae; aggregtaion is triggered by cAMP. (D-G) Migration of the slug formed from aggregated ampebae. (H-L) Culmination and formation of the fruit-ing body. (M) Mature fruiting body composed of stalk and head. Eukaryotic Microbial Diversity

Fungi Fungi include the molds and yeast. Fungi differ from protozoa by virtue of their rigid cell wall, production of spores, lack of motility, and phylogenetic position. Mushrooms are large, often edible fungi that produce fruiting bodies containing basidiospores. Eukaryotic Microbial Diversity

Filamentous Fungi: Molds • They are widespread in nature and are commonly seen on stale bread, cheese, or fruit. • Each filament grows mainly at the tip, by extension of the terminal cell. • A single filament is called hypha, a collectively called a mycelium. • Has aerial branches spores called conidia. Conidia are asexual spores. • Some molds also produce sexual spores (different type depending on the group). Sexual spores of fungi are typically resistant to drying, heating, freezing, and some chemical agents. Eukaryotic Microbial Diversity

Mold Structure and Growth Diagram of a mold life cycle. Conidia can be either wind-blown or be trasported by animals. Photomicrograph of a typical mold. Conidia are seen as the spherical structure and the ends of aerial hyphae. Eukaryotic Microbial Diversity

(a) Conidiophore and conidia of Aspergillus fumigatus. (b) Colonies of an Aspergillus species growing on an agar plate. Eukaryotic Microbial Diversity a

Characteristics and major properties of fungi Typical representati ves Neurospora, Saccharomyc es, morchella (morales) Type of Sexual spore Ascospore Common Name Sac fungi Habitats Soil, decaying plant material Common deases Dutch elm, chesnut blight, ergot, rots Group Ascomycetes Hyphae Septate Amanita (poisonous mushroom), Agaricus (edible Soil, decaying plant material Blact stem, wheat rust, corn smut Basidiomycet es Club fungi, mushrooms Septate Basidiospore mushroom) Food Mucor, Rhizopus (common bread mold) spoilage; rarely involved in parasitic Soil, decaying plant material Bread molds Coenocy tic Zygomycetes Zygospore deseases

Eukaryotic Microbial Diversity Characteristics and major properties of fungi Typical representati ves Type of Sexual spore Common Name Habitats Common deases Group Hyphae Potato Water molds Coenocy tic blight, certain fish Oomycetes Allomyces Oospore Aquatic deseases Plant wilt, infections of animals such as ringworm, athlete’s foot, surface of systemic infections Soil, decaying plant material, surfaces of animal bodies Penicillium, Aspergillus, Candida Deuteromyce tes Fungi imperfecti Septate None known (Candida) Eukaryotic Microbial Diversity

Macroscopic Fungi: Mushrooms • Mushrooms are filamentous basidiomycetes that form large fruiting bodies. • During most of its existence, the mushroom fungus lives as a simple mycelium, growing in soil, leaf litter, or decaying logs. However, when environmental condition are favorable, usually following periods of wet and cool weather, the fruiting body develops. • Sexual spores, called basidiospores are formed, borne on the underside of the fruiting body on flat plates called gills. Eukaryotic Microbial Diversity

a b c (a) Amanita, a highly poisonous mushroom. (b) Gills on the underside of the mushroom fruiting bodycontain the spore-bearing basidia. (c ) Scanning electron micrograph of basidiospores released from mushroom basidia. Eukaryotic Microbial Diversity

Life cycle of a typical mushroom Eukaryotic Microbial Diversity

Unicellular Fungi: Yeasts • The yeasts are unicellular fungi, and most of them belong to Ascomycetes. • Yeast cells are typically spherical, oval, or cylindrical, and cell division typically takes place by budding. • In the budding process, a new cell forms as a small outgrowth of the old cell; the bud gradually enlarges and then separates. • Yeast flourish in habitats where sugars are present, such as fruits, flowers, and the bark of trees. • The most important commercial yeast are the baker’s and brewer’s yeasts, which are members of the genus Sacharomyces. Sacharomyces cerevisiae Eukaryotic Microbial Diversity

Algae • Alga are phototrophic Eukarya that contain chlorophyll and caretenoid pigments within a structure called chloroplast. The chloroplasts itself has its roots in the domain bacteria. • Most algae are either unicellular or colonial, the later existing as aggregates of cells. When the cells are arranged end-to-end, the algae is said to be filamentous. Eukaryotic Microbial Diversity

Properties of major group of algae Typical representa tives Chlamydom onas Euglena Gonyaulax Nitzschia Carbon reserve materials Starch Paramylon Strach Lipids Common Name Green algae Euglenoid s Dinoflagell ates Golden- brown algae, diatoms Cell wall cellulose No wall present Cellulose Two overlapping components made of silica Major habitats Fresh water, soils, a few marine a few marine Mainly marine, soil Algal Group Chlorophyta Euglenophyta Dinoflagellata Chrysophyta Morphology Unicellular to leafy Unicellular, flagellated Unicellular

Eukaryotic Microbial Diversity Properties of major group of algae Typical representati ves Carbon reserve materials Common Name Cell wall Major habitats Algal Group Morphology Filamentous to leafy, occasionally massive and Borwn algae Phaeophyta Laminaria Lammarin Cellulose Marine plantlike Unicellular, Filamentous to leafy Floridean starch Rhodophyta Red algae Polysiphonia Cellulose Marine Eukaryotic Microbial Diversity

b d a c (a) Micrasterias, a single cell. (b) Volvox colony, containing a large number of cells. (c) Scenedesmus. A packet of four cells. (d) Sirogyra. A filamentous algae.

Euglena Polysiphonia, a marine red alga Frustule of the marine diatom Nitschia Frustule of the marine diatom Thalassiosira Frustule of the marine diatom Asteriolampra Cell of the marine dinoflagellate, Ornithocercus magnificus

Toxic dinoflagellates. (a) “a red tide” caused by massive growth of toxin-producing dinoflagellates, such as Gonyaulax. Toxin excreted into the water and also accumulates in shelfih that feed on the dinoflagellates. (b) A toxic spores of P. piscicida. (c) Fish killed by P. piscicida c Eukaryotic Microbial Diversity

Endholitic (grow inside of rocks) Cyanobacteria. Photograph of a limestone rock from Makhtesh Gadol, Negev Desert, Israel, showing a layer of cells of the cyanobacterium Chroococcidiopsis Photomicrograph of cells of Chroococcidiopsis isolated from a sandstonerock in the Negev Desert.