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 1
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External Structures Locomotor appendages Flagella Long, sheathed cylinder containing microtubules in a 9+2 arrangement 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 5
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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 7
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 8
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 9
Nucleus Internal Structures 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 10
The nucleus 11
Mitosis 12
Internal Structures- Endoplasmic reticulum Rough endoplasmic reticulum (RER) originates from the outer membrane of the nuclear envelope 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 13
Rough endoplasmic reticulum 14
Internal Structures Golgi apparatus Modifies, stores, and packages proteins Consists of a stack of flattened sacs called cisternae 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 15
nucleus RER Golgi vesicles secretion 16
Lysosomes Internal Structures Vesicles containing enzymes that originate from Golgi apparatus Involved in intracellular digestion of food particles and in protection against invading microbes Participate in digestion Vacuoles Membrane bound sacs containing particles to be digested, excreted, or stored Phagosome vacuole merged with a lysosome 17
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Mitochondria Internal Structures Function in energy production Consist 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 19
Structure of mitochondrion 20
Internal Structures Chloroplast Convert the energy of sunlight into chemical energy through photosynthesis Found in algae and plant cells Outer membrane covers inner membrane folded into sacs, thylakoids, stacked into grana Larger than mitochondria Contain photosynthetic pigments Primary producers of organic nutrients for other organisms 21
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Ribosomes Internal Structures Composed of rrna and proteins Scattered in cytoplasm or associated with RER Larger than prokaryotic ribosomes Function in protein synthesis 23
Cytoskeleton Internal Structures Flexible framework of proteins, microfilaments and microtubules form network throughout cytoplasm Involved in movement of cytoplasm, amoeboid movement, transport, and structural support 24
Survey of Eukaryotic Microbes Fungi Algae Protozoa Parasitic worms 25
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 26
Exist in two morphologies: Microscopic Fungi Yeast round ovoid shape, asexual reproduction Hyphae long filamentous fungi or molds Some exist in either form dimorphic characteristic of some pathogenic molds 27
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 20 o -40 o C Extremely widespread distribution in many habitats 28
Nutritional sources for fungi 29
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 30
Figure 5.18 31
Fungal Reproduction Primarily through spores formed on reproductive hyphae Asexual reproduction spores are formed through budding or mitosis; conidia or sporangiospores 32
Fungal Reproduction Sexual reproduction spores are formed following fusion of two different strains and formation of sexual structure Zygospores, ascospores, and basidiospores Sexual spores and spore-forming structures are one basis for classification 33
Formation of zygospores 34
Production of ascospores 35
Figure 5.22 Formation of basidiospores in a mushroom 36
Fungal Classification Kingdom Eumycota is subdivided into several phyla based upon the type of sexual reproduction: 1. Zygomycota zygospores; sporangiospores and some conidia 2. Ascomycota ascospores; conidia 3. Basidiomycota basidiospores; conidia 4. Chytridomycota flagellated spores 5. Fungi that produce only Asexual Spores (Imperfect) 37
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 38
Roles of Fungi Adverse 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 39
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Kingdom Protista Algae - eukaryotic organisms, usually unicellular and colonial, that photosynthesize with chlorophyll a Protozoa - unicellular eukaryotes that lack tissues and share similarities in cell structure, nutrition, life cycle, and biochemistry 41
Algae Photosynthetic organisms 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 42
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 O 2 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 43
Protozoa Diverse group of 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 lack chloroplasts Cytoplasm divided into ectoplasm and endoplasm Feed by engulfing other microbes and organic matter 44
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 45
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Protozoan Identification Classification is difficult because of diversity Simple grouping is based on method of motility, reproduction, and life cycle 1. Mastigophora primarily flagellar motility, some flagellar and amoeboid; sexual reproduction 2. Sarcodina primarily amoeba; asexual by fission; most are free-living 3. Ciliophora cilia; trophozoites and cysts; most are freeliving, harmless 4. Apicomplexa motility is absent except male gametes; sexual and asexual reproduction; complex life cycle all parasitic 47
Mastigophora 48
Sarcodina 49
Ciliophora 50
Apicomplexa 51
Trypanosoma cruzi and Chagas disease The infective forms of T. cruzi are contained in the feces of the insect vectors and gain entry into its mammalian hosts through contamination. T. cruzi can also be transmitted when mammalian hosts ingest infected insects, and this mechanism of transmission may play a major role in maintaining the sylvatic cycle. 52
Entamoeba histolytica 53
Parasitic 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 54
Major Groups of Parasitic Helminths 1. 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 2. Roundworms (nematodes) round, a complete digestive tract, a protective surface cuticle, spines and hooks on mouth; excretory and nervous systems poorly developed 55
Helminths Acquired through ingestion of larvae or eggs in food; from soil or water; some are carried by insect vectors Afflict billions of humans 56
Parasitic Flatworms 57
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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 59
Distribution and Importance of Parasitic Worms Approximately 50 species parasitize humans Distributed worldwide; some restricted to certain geographic regions with higher incidence in tropics 60