Chapter 5

The Eukaryotic Microorganisms

•         Membrane surrounding DNA -  nucleus

•         Internal membrane-bound organelles

•         Dimensions: 10-100 μm in diameter

•         More complex structure

•         Comprised of algae, protozoa, fungi, animals, and plants

The History of Eukaryotes - Endosymbiotic Theory

•         Eukaryotic cell evolved from an association between

–        large anaerobic prokaryote

–        oxygen requiring heterotroph (mitochondria)

–        photosynthetic prokaryote (cyanobacteria)

•         At the begging, they were undigested pray or internal parasites

•         Retained portion of DNA, ribosomes (70S), and cytoplasmic membranes

External Structures of Eukaryotic Cells

•         Flagella and Cilia - Projections used for cellular locomotion

•         Few and long

•         Filaments anchored to cell by basal body; no hook

•         May be single or multiple; generally found at one pole of cell

•         Do not rotate, but undulate rhythmically

Cilia

•      Shorter and more numerous than flagella

•      Coordinated beating propels cells through their environment

•      Also used to move substances past the surface of the cell

Internal structure of a flagellum or cilium

•         Cytoplasm containing  microtubules

•         Nine pairs of microtubules arranged in a ring  (2x9 +2)

•         Microtubules are composed of tubulin

•         Surrounded by the plasma membrane

Cell wall

Various polysaccharides

•         Algae – cellulose, silicate, agar

•         Fungi - chitin (insects)

•         Yeast - glucan and mannan

•         Protozoa - do not have a typical cell wall - flexible outer covering - pellicle

Cytoplasmic membrane

•         Similar to the plasma membrane of prokaryotes (phospholipid bilayer)

–        Functions as a selective permeable barrier

•         Differences:

–        Contain carbohydrates which serve as receptor sites in the “cell to cell” communication

–        Sterols – provide stability of the membrane

Organelles

•         Functional structures inside the cytoplasm

–        Nucleus

–        Endoplasmic reticulum

–        Golgi complex

–        Lysosomes

–        Vacuoles

–        Mitochondria

–        Chloroplasts

•         Not all the organelles are present in all cells

The Nucleus

•         The largest structure in the cell, spherical or oval

•         Contains DNA + proteins – histones

•         In non-reproducing phase DNA appears as a  threadlike mass – chromatin

•         In reproducing phase chromatin threads become shorter and thicker -  chromosomes

The Nucleus

•         Nuclear envelope - double layered membrane

•         Nuclear pores enable communication of nucleus with the cytoplasm

•         Contains nucleolus (nucleoli) - site of RNA synthesis

Endoplasmic reticulum (ER)

•         Network of flattened membranous sacks

•         Continuous to nuclear envelope

•         Transportation of substances from the nucleus to cytoplasm

Two types of ER:

•         Rough - with ribosomes

–        Synthesis and transport of proteins and phospholipids

•         Smooth - without ribosomes

–        Synthesis of phospholipids, fats, steroids

Golgi Complex

•         Complex of flattened sacks composed of phospholipid bilayer

•         Found close to the ER

•         Receives proteins packaged in transitional vesicles (budded off the ER)

•         Function: modifies, packages and delivers proteins  by secretory vesicles

•         within the cell

•         outside of cell (vesicle is fused with a cytoplasmic membrane and its content released - exocytosis)

Lysosomes

•         Membrane enclosed spheres

•         Formed from Golgi complex

•         Contain the catabolic enzymes (including lysozyme)

•         Fuses with the food vesicle - phagolysosome

•         Digest macromolecules, old cell parts, and microorganisms

Mitochondria

•         Rod-shaped or spherical structures

•         Double membrane

–        outer membrane smooth

–        inner membrane folded - forming cristea

•         Matrix - central part of a       mitochondrium

•         Cristae are the sites for many chemical reactions

•         Main role is in the ATP production (“powerhouse of the cell”)

•         Contain their own DNA, replicates independently

•         Contain 70S ribosomes

Chloroplasts

•         Membrane enclosed structure which is the site of photosynthesis

•         Inside the chloroplast there are flattened membrane sacs - thylakoids (stacked together - grana) – contain chlorophyll

•         Replication by simple division

•         Have 70S ribosomes

Contain their own DNA

Cytoplasm

•         The substance inside the plasma membrane

•         Internal structure – cytoskeleton

–        microfilaments – rods

–        microtubules - cylinders

•         Provide:

–        support and shape of the cell

–        transportation of substances throughout the cell

•         Cytoplasmic streaming - the movement of the cytoplasm

Ribosomes

•         Granular structures - sites of protein synthesis

•         They are either

–        attached to the ER or nuclear membrane

–        free in the cytoplasm

•         Larger than prokaryotic ribosomes (80S - subunites - 60S + 40S)

Survey of Eukaryotic Microorganisms

•         Fungi

•         Algae

•         Protozoa

The Kingdom of the Fungi

•         Morphology:

–        Yeast - unicellular

–        Molds - multicellular 

–        Mushrooms - macroscopic

•         Found in: water, soil, on animal or plant hosts (parasitic)

Molds

•         Body consists of filaments – hyphae

–        Septate hyphae – cross walls (septa) divide hyphae into cell-like units

–        Nonseptate hyphae –the whole hypha is one cell with many nuclei

•         Hyphae make up  mycelium

Fungal Nutrition

•         Fungi are heterotrophs – require organic compounds for their growth

–        Saprobes – on dead plants and animals

–        Parasites – on living organism

•         Fungal infection - mycosis

•         Most fungi are aerobic with exception of yeast (facultative anaerobes)

•         More resistant to osmotic pressure than bacteria

•         Can grow with a very low moisture

•         Can metabolize complex carbohydrates (cellulose, lignin)

Reproduction – formation of spores

Asexual spores

•         Formation of spores by fragmentation of hyphae

–        Conidiospores (spores not enclosed in a sac)

–        Sporangiospores – spores enclosed within a sac – sporangium

Algae

•         Eukaryotic phototrophs

•         Morphology:

–        Microscopic: unicellular, filamentous, colonial  

–        Macroscopic multicellular (seaweed) body is called thallus

•         Ecology

–        Marine and freshwater environments

–        Primary producers

–        Some algae are toxic

Protozoa (first animal)

•         Morphology:

–        Unicellular

–        Lack of cell wall (ectoplasma)

–        Some have a mouth-like opening

•         Nutrition: Heterotrotrophic or parasitic

•         Habitat: water and soil, some are parasitic

•         Reproduction:          

–        Asexual - by mitotic division

–        Sexual - conjugation

–        Encystment – Cyst enables parasitic protozoa to survive outside a host.

Medically important representatives of Protozoa

Amoebas

•         Entamoeba histolytica causes dysentery when in human intestines.

•         Transmitted between humans through ingestion of the cyst

Flagellates

•         Trichomonas vaginalis – a parasite, found in vagina and in the male urinary tract.

•         Transmitted by sexual intercourse. It does not have cysts – it is sensitive to desiccation

•         Trypanosoma brucei causes African sleeping sickness

•          Transmitted by tsetse fly