Eukaryotic Cells and Microorganisms Chapter 5 Eukaryotic Cells and Microorganisms

The History of Eukaryotes They first appeared approximately 2 billion years ago Evidence suggests evolution from prokaryotic organisms by symbiosis Organelles originated from prokaryotic cells trapped inside them

Eukaryotic

External Structures Locomotor appendages flagella long, sheathed cylinder containing microtubules in a 9+2 arrangement in the shaft; and a 9+0 in the basal body covered by an extension of the cell membrane 10X thicker than prokaryotic flagella function in motility cilia similar in overall structure to flagella, but shorter and more numerous found only on a single group of protozoa and certain animal cells function in motility, feeding and filtering

External Structures Glycocalyx an outermost boundary that comes into direct contact with environment usually composed of polysaccharides appears as a network of fibers, a slime layer or a capsule functions in adherence, protection, and signal reception beneath the glycocalyx fungi and most algae have a thick, rigid cell wall protozoa, a few algae, and all animal cells lack a cell wall and have only a membrane

External Boundary Structures Cell wall rigid, provides structural support and shape Fungi have thick inner layer of polysaccharide fibers composed of chitin or cellulose and a thin layer of mixed glycans algae – varies in chemical composition; substances commonly found include cellulose, pectin, mannans, silicon dioxide, and calcium carbonate

External Boundary Structures Cytoplasmic (cell) membrane typical bilayer of phospholipids and proteins sterols confer stability serves as selectively permeable barrier in transport Eukaryotic cells also contain membrane-bound organelles that account for 60-80% of their volume

Internal Structures Nucleus compact sphere, most prominent organelle of eukaryotic cell nuclear envelope composed of two parallel membranes separated by a narrow space and is perforated with pores contains chromosomes nucleolus – dark area for rRNA synthesis and ribosome assembly

Internal Structures Endoplasmic reticulum – two types: Rough endoplasmic reticulum (RER)– originates from the outer membrane of the nuclear envelop and extends in a continuous network through cytoplasm; rough due to ribosomes; proteins synthesized and shunted into the ER for packaging and transport; first step in secretory pathway Smooth endoplasmic reticulum (SER)– closed tubular network without ribosomes; functions in nutrient processing, synthesis and storage of lipids, etc.

Internal Structures Golgi apparatus consists of a stack of flattened sacs called cisternae closely associated with ER Transitional vesicles from the ER containing proteins go to the Golgi apparatus for modification and maturation Condensing vesicles transport proteins to organelles or secretory proteins to the outside

Cis face Trans face

Internal Structures Lysosomes vesicles containing enzymes that originate from Golgi apparatus involved in intracellular digestion of food particles and in protection against invading microbes

Internal Structures Mitochondria consists of an outer membrane and an inner membrane with folds called cristae Cristae hold the enzymes and electron carriers of aerobic respiration divide independently of cell contain DNA and prokaryotic ribosomes function in energy production

Internal Structures Chloroplast found in algae and plant cells outer membrane covers inner membrane folded into sacs, thylakoids, stacked into grana larger than mitochondria contain photosynthetic pigments convert the energy of sunlight into chemical energy through photosynthesis primary producers of organic nutrients for other organisms

Internal Structures Ribosomes composed of rRNA and proteins 40S and 60S subunits form 80S ribosomes larger than prokaryotic ribosomes function in protein synthesis

Internal Structures Cytoskeleton flexible framework of proteins, microfilaments and microtubules form network throughout cytoplasm involved in movement of cytoplasm, amoeboid movement, transport, and structural support

Survey of Eukaryotic Microorganisms Fungi Algae Protozoa Parasitic worms

Kingdom Fungi 100,000 species divided into 2 groups: macroscopic fungi (mushrooms, puffballs, gill fungi) microscopic fungi (molds, yeasts) Majority are unicellular or colonial; a few have cellular specialization

Microscopic Fungi Exist in two morphologies: yeast – round ovoid shape, asexual reproduction hyphae – long filamentous fungi or molds Some exist in either form – dimorphic – characteristic of some pathogenic molds

Fungal Nutrition All are heterotrophic Majority are harmless saprobes living off dead plants and animals Some are parasites, living on the tissues of other organisms, but none are obligate; mycoses – fungal infections Growth temperature 20o-40oC Extremely widespread distribution in many habitats

Fungal Organization Most grow in loose associations or colonies Yeast – soft, uniform texture and appearance Filamentous fungi – mass of hyphae called mycelium; cottony, hairy, or velvety texture hyphae may be divided by cross walls – septate vegetative hyphae – digest and absorb nutrients reproductive hyphae – produce spores for reproduction

Fungal Reproduction Primarily through spores formed on reproductive hyphae Asexual reproduction – spores are formed through budding or mitosis; conidia or sporangiospores Sexual reproduction – spores are formed following fusion of male and female strains and formation of sexual structure Sexual spores and spore-forming structures are one basis for classification

Fungal Classification The Fungi kingdom is subdivided into two subkingdoms Amastigomycota - common inhabitants of terrestrial habitats. Several of them are human pathogens Mastigomycota - primitive filamentous fungi that live primarily in water and may cause disease in potatoes and grapes

Amastigomycota Fungi that produce sexual and asexual spores (perfect) Zygomycota – zygospores; sporangiospores and some conidia Ascomycota – ascospores; conidia Basidiomycota – basidiospores; conidia Fungi that produce only asexual spores Deuteromycota – majority are yeasts and molds; no sexual spores known; conidia

Fungal Identification Isolation on specific media Macroscopic and microscopic observation of: asexual spore-forming structures and spores hyphal type colony texture and pigmentation physiological characteristics genetic makeup

Roles of Fungi Adverse impact Beneficial impact mycoses, allergies, toxin production destruction of crops and food storages Beneficial impact decomposers of dead plants and animals sources of antibiotics, alcohol, organic acids, vitamins used in making foods and in genetic studies

Kingdom Protista Algae Protozoa

Algae Photosynthetic organisms Kelps, seaweeds, euglenids, green algae, diatoms, dinoflagellates, brown algae, and red seaweeds Microscopic forms are unicellular, colonial, filamentous Macroscopic forms are colonial and multicellular Contain chloroplasts with chlorophyll and other pigments Cell wall May or may not have flagella

Algae Most are free-living in fresh and marine water – plankton Provide basis of food web in most aquatic habitats Produce large proportion of atmospheric O2 Dinoflagellates can cause red tides and give off toxins that cause food poisoning with neurological symptoms Classified according to types of pigments and cell wall Used for cosmetics, food, and medical products

Protozoa 65,000 species Vary in shape, lack a cell wall Most are unicellular; colonies are rare Most are harmless, free-living in a moist habitat Some are animal parasites and can be spread by insect vectors All are heterotrophic Feed by engulfing other microbes and organic matter

Protozoa Most have locomotor structures – flagella, cilia, or pseudopods Exist as trophozoite - motile feeding stage Many can enter into a dormant resting stage when conditions are unfavorable for growth and feeding – cyst All reproduce asexually, mitosis or multiple fission; many also reproduce sexually – conjugation

Protozoan Identification Classification is difficult because of diversity Simple grouping is based on method of motility, reproduction, and life cycle Mastigophora – primarily flagellar motility, some flagellar and amoeboid; sexual reproduction; cyst and trophozoite Sarcodina – primarily amoeba; asexual by fission; most are free-living Ciliophora – cilia; trophozoites and cysts; most are free-living, harmless Apicomplexa – motility is absent except male gametes; sexual and asexual reproduction; complex life cycle – all parasitic

Note: Entamoeba histolytica is a parasitic amoeba.

Important Protozoan Pathogens Pathogenic flagellates Trypanosomes – Trypanosoma T. brucei – African sleeping sickness (Tse-Tse fly) T. cruzi – Chaga’s disease; South America Infective amoebas Entamoeba histolytica – amoebic dysentery; worldwide

Helminths Multicellular animals, organs for reproduction, digestion, movement, protection Parasitize host tissues Have mouthparts for attachment to or digestion of host tissues Most have well-developed sex organs that produce eggs and sperm Fertilized eggs go through larval period in or out of host body Acquired though ingestion of larvae or eggs in food; from soil or water; some are carried by insect vectors

Major Groups of Parasitic Helminths Flatworms – flat, no definite body cavity; digestive tract a blind pouch; simple excretory and nervous systems cestodes (tapeworms) Trematodes or flukes, are flattened, nonsegmented worms with sucking mouthparts Roundworms (nematodes)- round, a complete digestive tract, a protective surface cuticle, spines and hooks on mouth; excretory and nervous systems poorly developed

Helminth Classification and Identification Classify according to shape, size, organ development, presence of hooks, suckers, or other special structures, mode of reproduction, hosts, and appearance of eggs and larvae Identify by microscopic detection of adult worm, larvae, or eggs

Distribution and Importance of Parasitic Worms Approximately 50 species parasitize humans Afflict billions of humans Distributed worldwide; some restricted to certain geographic regions with higher incidence in tropics