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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

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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

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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

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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

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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

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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

The nucleus

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Mitosis

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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

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Rough endoplasmic reticulum

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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

16nucleus RER Golgi vesicles secretion

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Internal Structures• Lysosomes

– 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

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Internal Structures

• Mitochondria

– 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

Structure of mitochondrion

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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

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Internal Structures

• Ribosomes

– Composed of rRNA and proteins

– Scattered in cytoplasm or associated with RER

– Larger than prokaryotic ribosomes

– Function in protein synthesis

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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

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Survey of Eukaryotic Microbes

• Fungi

• Algae

• Protozoa

• Parasitic worms

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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

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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

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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

Nutritional sources for fungi

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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

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Figure 5.18

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Fungal Reproduction

• Primarily through spores formed on reproductive

hyphae

• Asexual reproduction – spores are formed

through budding or mitosis; conidia or

sporangiospores

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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

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Formation of zygospores

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Production of ascospores

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Figure 5.22 Formation of basidiospores in a mushroom

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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)

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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

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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

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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

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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

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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

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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

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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

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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 free-

living, harmless

4. Apicomplexa – motility is absent except male gametes;

sexual and asexual reproduction; complex life cycle – all

parasitic

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Mastigophora

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Sarcodina

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Ciliophora

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Apicomplexa

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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.

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Entamoeba histolytica

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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

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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

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Helminths

• Acquired through ingestion of larvae or

eggs in food; from soil or water; some are

carried by insect vectors

• Afflict billions of humans

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Parasitic Flatworms

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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

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Distribution and Importance of

Parasitic Worms

• Approximately 50 species parasitize humans

• Distributed worldwide; some restricted to

certain geographic regions with higher

incidence in tropics