Chapter 5

Eukaryotic Cells and Microorganisms

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The History of Eukaryotes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

• They first appeared approximately 2 billion years ago

A larger prokaryotic cell such as an archaea has a flexible outer envelope and Mesosomelike internal membranes to enclose the nucleoid.

A smaller prokaryotic cell similar to purple bacteria that can use oxygen

Nuclear envelope

The larger cell engulfs the smaller one; smaller one survives and remains surrounded by the vacuolar membrane.

Early nucleus

• Evidence suggests evolution from prokaryotic organisms by symbiosis

Smaller bacterium becomes a permanent resident of its Host’ s cytoplasm; it multiplies and is passed on during cell division. It utilizes aerobic metabolism and increases energy availability for the host. Early mitochondria

Early endoplasmic reticulum

Ancestral eukaryotic cell develops additional membrane pouches that become the endoplasmic reticulum and Golgi apparatus.

• Organelles originated from prokaryotic cells trapped inside them

Photosynthetic bacteria (similar to cyanobacteria) are also engulfed; they develop into chloroplasts. Ancestral cell

Chloroplast Cell wall

Many protozoa, animals © Image by D. J. Patterson (provided by micro*scope http://microscope.mbl.edu)

Algae, higher plants

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Ancient Eukaryotes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. y.

Chloroplasts

Cell wall © Andrew Knoll

© Andrew Knoll

(a)

(b) 3

Eukaryotic Microbes

4

The Eukaryotic Cell Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Cell wall*

Mitochondrion

Cell membrane

Golgi apparatus

Rough endoplasmic reticulum with ribosomes

Microfilaments Flagellum*

Nuclear membrane with pores Nucleus Lysosome

Nucleolus

Smooth endoplasmic reticulum

Microvilli/ Glycocalyx

Microtubules

Chloroplast* Centrioles* *Structure not present in all cell types

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Organization of the Eukaryotic Cell

Eukaryotic cell

Copyright© The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

External organelles and other structures Boundary of cell

Appendages Flagella Cilia Glycocalyx Capsules Slimes Cell wall Cell/cytoplasmic membrane Cytoplasmic matrix

Internal organelles and other contents

Nucleus

Nuclear envelope Nucleolus Chromosomes

Organelles

Endoplasmic reticulum Golgi complex Mitochondria Chloroplasts

Ribosomes Cytoskeleton

Microtubules Microfilaments

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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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. y

.

outer dynein arm

Microtubules

B subfiber of doublet

Cilium

singlet

Cell Membrane ciliary membrane short glycocalyx fringe

(a)

Courtesy Richard Allen

bb

(b)

Courtesy Richard Allen

(c) Whips back and forth and pushes in snakelike pattern

Twiddles the tip

Lashes, grabs the substrate, and pulls

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External Structures • Locomotor appendages: 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Oral groove with gullet

Macronucleus

(a)

Contractile vacuole

Micronucleus

(b)

Power stroke

Recovery stroke

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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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Boundary of the Cell • 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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Boundary of the Cell • Cytoplasmic (cell) membrane – Typical bilayer of phospholipids and proteins – Sterols confer stability – Serves as selectively permeable barrier in transport – Eukaryotic cells also contain membranebound organelles that account for 60-80% of their volume

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Internal Structures Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

• 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

Endoplasmic reticulum

Chromatin

© Don Fawcett/Visuals Unlimited

Nuclear Nuclear pore envelope (a)

Nucleolus (b)

Nucleolus Nuclear pore

Nuclear envelope

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Nuclear changes during Mitosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Centrioles Interphase (resting state prior to cell division) 1

Chromatin Cell membrane Nuclear envelope

Prophase

Nucleolus

2

Cytoplasm

Daughter cells Cleavage furrow Telophase

Spindle fibers

Chromosome

Centromere Chromosome

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Early metaphase

3

Early telophase

7 Metaphase

4

Late anaphase

6

Early anaphase

5

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Internal Structures • Endoplasmic reticulum – two types: – 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 14

Rough endoplasmic reticulum Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Nuclear envelope Nuclear pore

Polyribosomes

Polyribosomes Cisterna

(b)

Small subunit mRNA (a)

Ribosome

Large subunit

RER membrane Cisterna

Protein being synthesized

(c)

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Internal Structures • Golgi apparatus

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

– Modifies, stores, and packages proteins – Consists of a stack of flattened sacs called cisternae

Endoplasmic reticulum

Transport vesicles

Condensing vesicles Cisternae

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Internal Structures Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

• Transport Processes – 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

Nucleolus Ribosome parts

Rough endoplasmic reticulum

Nucleus

Transitional vesicles

Golgi apparatus Condensing vesicles

Cell membrane

Secretion by exocytosis

Secretory vesicle

nucleus  RER  Golgi  vesicles  secretion

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Internal Structures • Lysosomes

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– Vesicles containing enzymes that originate from Golgi apparatus – Involved in intracellular digestion of food particles and in protection against invading microbes

Food particle Lysosomes

Cell membrane Nucleus Golgi apparatus

Engulfment of food

Food vacuole

• Vacuoles – Membrane bound sacs containing particles to be digested, excreted, or stored

• Phagosome – vacuole merged with a lysosome

Formation of food vacuole

Lysosome

Merger of lysosome and vacuole Phagosome

Digestion Digestive vacuole

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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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Circular DNA strand 70S ribosomes

Matrix Cristae

Inner membrane Outer membrane

(a)

Cristae (darker lines) Matrix (lighter spaces)

19 (b)

© Don Fawcett/Visuals Unlimited

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 – Primary producers of organic nutrients for other organisms

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chloroplast envelope (double membrane) 70S ribosomes

Stroma matrix

Circular DNA strand Granum

Thylakoids

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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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Small subunit mRNA Ribosome

Large subunit

RER membrane Protein being synthesized

Cisterna 21

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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Rough endoplasmic reticulum

Cell membrane Microtubule

Ribosomes

Mitochondrion Microfilaments

(a)

Courtesy of Life Technologies, Carlsbad, CA

(b)

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Comparing Prokaryotes, Eukaryotes & Viruses

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Phylogenetic Relationships between Eukaryotes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Taxonomy Based on mRNA Analysis

Animals

Metazoa Myxozoa Choanoflagellates

Kingdom Animalia

True Fungi (Eumycota)

Zygomycota Ascomycota Basidiomycota Chytridiomycota (chytrids)

Kingdom Eumycota

Naegleria

Euglena

EVOLUTIONARY ADVANCEMENT OF THE EUKARYOTES

Plants

Zea (corn)

Eukarya

Stramenopiles (formerly heterokonts or chrysophytes)

Alveolates

Entamoebae

Kingdom Plantae Kingdom Protista Division Chlorophyta Division Rhodophyta

Golden-brown and yellow-green alga Xanthophytes Brown algae Diatoms Water molds (Oomycota)

Division Chrysophyta

Ciliates Colponema Dinoflagellates Haplosporidia Apicomplexans

Phylum Ciliophora

Division Phaeophyta Division Bacillariophyta

Division Pyrrophyta Phylum Apicomplexa

Entamoebids Phylum Sarcomastigophora Amoeboflagellates Kinetoplastids Euglenids

Lack mitochondria

(b)

Land plants Green algae Cryptomonads

Red algae

Universal Ancestor

(a)

Traditional Kingdoms and Subcategories

Parabasilids (Trichomonas) Diplomonads (Giardia) Oxymonads Microsporidia

Division Euglenophyta

Phylum Sarcomastigophora

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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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

26 © George Barron, University of Guelph, CANADA

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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Septum

Janice Carr/CDC

© Dr. Judy A. Murphy, San Joaquin Delta College, Department of Microscopy, Stocton, CA

27

Fungal Nutrition Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

• 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 • Extremely widespread distribution in many habitats

(a)

© Kathy Park Talaro

28 (b)

© New Zealand Dermatological Society

Fungal Organization • Yeast – soft, uniform texture and appearance – Reproduce through an asexual process called budding Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Bud

Bud scar Bud

Ribosomes Mitochondrion Endoplasmic reticulum

Nucleus

Bud scars

Nucleus Nucleolus

Cell wall Cell membrane Golgi apparatus

Storage vacuole (a)

Fungal (Yeast) Cell

(c)

Pseudohypha

29 (b)

Janice Carr/CDC

Fungal Organization • 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Septa

As in Penicillium

Septate hyphae

Nonseptate hyphae

Septum with pores Nucleus

Nuclei

30 As in Rhizopus

Fungal Reproduction • Primarily through spores formed on reproductive hyphae • Asexual reproduction – spores are formed through budding or mitosis; conidia or sporangiospores Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

(a) Vegetative Hyphae

(b) Reproductive Hyphae

Surface hyphae

Spores

Submerged hyphae

Rhizoids Spore Germ tube

Substrate Hypha

© George Barron, University of Guelph, CANADA

(c) Germination

(d)

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Types of Asexual Mold Spores Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

(a) Sporangiospore

(b) Conidia Arthrospores

Phialospores

Chlamydospores

Sporangium

Blastospores

Sterigma

Sporangiophore

Conidiophore

Columella 1

1

2

3

Sporangiospore Macroconidia Porospore

Microconidia 2

4

5

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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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Sporangium Asexual Phase

Stolon

– Strain Rhizoid

+ Strain Spores germinate.

Zygote Germinating zygospore

Sexual Phase

Mature zygospore

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Production of ascospores Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Zygote nuclei that undergo meiosis prior to formation of asci

Ascospores

Asci Ascogenous hyphae Fruiting body Sterile hyphae

Ascogonium (female)

Cup fungus Antheridium (male) 35

+ Hypha

– Hypha

Formation of basidiospores in a mushroom Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Basidium

Pair of nuclei fuse to form diploid nucleus. Diploid nucleus undergoes meiosis to produce four haploid nuclei.

Portion of gill covered with basidia

Basidium

Cap

Gill Annulus Stalk

Basidiospore Button

+ Basidiospore – Basidiospore

Soil, plant litter

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Fungal Classification Kingdom Eumycota is subdivided into several phyla based upon the type of sexual reproduction: 1. Phylum Zygomycota – zygospores; mostly sporangiospores and some conidia 2. Phylum Ascomycota – ascospores; conidia 3. Phylum Basidiomycota – basidiospores; conidia 4. Phylum Chytridomycota – flagellated spores 5. Fungi that produce only Asexual Spores (Imperfect)

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Diversity of Fungi Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

© George Barron, University of Guelph, CANADA

© George Barron, University of Guelph, CANADA

© Kathy Park Talaro

Chytrid cells

Diatom cell 10.0 mm © Gregory M. Filip

© Joyce E. Longcore, University of Maine

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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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Human Fungal Infections

41

The Protists Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Taxonomy Based on mRNA Analysis

Traditional Kingdoms and Subcategories

Animals

Metazoa Myxozoa Choanoflagellates

Kingdom Animalia

True Fungi (Eumycota)

Zygomycota Ascomycota Basidiomycota Chytridiomycota (chytrids)

Kingdom Eumycota

Plants EVOLUTIONARY ADVANCEMENT OF THE EUKARYOTES

• 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

Land plants Green algae Cryptomonads

Red algae

Stramenopiles (formerly heterokonts or chrysophytes)

Alveolates

Entamoebae

Kingdom Plantae Kingdom Protista Division Chlorophyta Division Rhodophyta

Golden-brown and yellow-green alga Xanthophytes Brown algae Diatoms Water molds (Oomycota)

Division Chrysophyta

Ciliates Colponema Dinoflagellates Haplosporidia Apicomplexans

Phylum Ciliophora

Division Phaeophyta Division Bacillariophyta

Division Pyrrophyta Phylum Apicomplexa

Entamoebids Phylum Sarcomastigophora Amoeboflagellates Kinetoplastids Euglenids

Lack mitochondria

Universal Ancestor

Parabasilids (Trichomonas) Diplomonads (Giardia) Oxymonads Microsporidia

Division Euglenophyta

Phylum Sarcomastigophora

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Algae Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

• 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

Ribosomes

Flagellum Mitochondrion Nucleus Nucleolus Chloroplast Golgi apparatus Cytoplasm Cell membrane Starch vacuoles Cell wall

(a)

Algal Cell

43 © Jan Hinsch/Photo Researchers, Inc

(b)

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 44

Algae Classification • 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 46

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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Trophozoite (active, feeding stage)

Trophozoite is reactivated.

Cell rounds up, loses motility.

Cyst wall breaks open. Early cyst wall formation

Mature cyst (dormant, resting stage)

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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 48

Mastigophora Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Flagellum

Ribosomes Mitochondrion Endoplasmic reticulum Nucleus Pellicle Nucleolus Cell membrane Golgi apparatus Water vacuole Centrioles

Cell membrane Glycocalyx Janice Carr/CDC

(a)

Protozoan Cell

(b)

49

Sarcodina Food vacuoles Nucleus

(a)

Pseudopods

Contractile vacuoles

© David Patterson/MBL/Biological Discovery in Woods Hole

(b)

50

Ciliophora Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Food vacuoles

Oral cilia in groove

Macronucleus Micronucleus Gullet Water vacuole (a)

© Eric Russell, BioMEDIA ASSOCIATES

© Yuuji Tsukii, Protist Information Server

(b)

51

Apicomplexa Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Cytostome

Food vacuoles

Nucleus

Cell membrane Cytostome (mouth) Food vacuole

Nucleus

Endoplasmic reticulum Mitochondrion ©

(a)

ASM

Michael Riggs et al, Infection and Immunity, Vol. 62, #5, May 1994, p. 1931

(b)

52

Pathogenic Protozoa

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Important Protozoan Pathogens Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

• Pathogenic flagellates – Trypanosomes – Trypanosoma • T. brucei – African sleeping sickness • T. cruzi – Chaga’s disease; South America

Reduviid bug

(a) Infective Trypanosome

Cycle in Human Dwellings

(b) Mode of infection Cycle in the Wild

54

Important Protozoan Pathogens Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Cysts in food, water

• Infective amoebas – Entamoeba histolytica – amebic dysentery; worldwide

(a)

Stomach Trophozoites released

Mature trophozoites

(b) (c)

Large intestine site of infection

Small intestine

Eaten

Mature cysts

Cysts exit

(d) Food, water

Feces

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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 57

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 worm, larvae, or eggs Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Oral sucker

Pharynx

Esophagus Intestine Ventral sucker Cuticle Vas deferens Uterus Cuticle

Ovary Testes

Scolex

(a)

Seminal receptacle

Proglottid

Suckers

Immature eggs

Fertile eggs

(b)

Excretory bladder

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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 • Acquired through ingestion of larvae or eggs in food; from soil or water; some are carried by insect vectors • Afflict billions of humans 59

Lifecycle of the Pinworm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Copulatory spicule Anus Mouth

Female

Eggs

Male

Selfinfection

Cuticle Mouth Fertile egg

Autoinoculation Crossinfection

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