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Eukaryotic Cells and
Microorganisms
Chapter 4
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The History of Eukaryotes •Evidence from paleontology indicates the first eukaryotic cells appeared approximately 2 billion years ago •Both prokaryotes and eukaryotes evolved from a precursor cell called the Last Common Ancestor
- this cell was neither prokaryotic nor eukaryotic
- gave rise to both prokaryotic and eukaryotic cells
The Theory of Endosymbiosis
1
2
3 4
5
A Pre-Eukaryotic Cell
Cell would have flexible
membrane.
Smaller Prokaryotic Cell
Nuclear
envelope
Early
endoplasmic
reticulum
Ancestral cell
Early
mitochondria
Photosynthetic bacteria
are also engulfed;
they develop into
chloroplasts.
Chloroplast
The first eukaryotic cells have
emerged.
Algae,
higher plants
Protozoa, fungi,
animals
Smaller prokaryote becomes
established in its host’s
cytoplasm and multiplies;
it can utilize aerobic
metabolism and increase
energy availability for the host.
Ancestral eukaryotic cell
develops extensive membrane
pouches that become the
endoplasmic reticulum and
nuclear envelope.
Larger cell engulfs smaller one;
smaller one survives and begins
an endosymbiotic association.
Early
nucleus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(frog): © Adam Jones/Getty Images (RF); (protozoa): © Melba Photo Agency/PunchStock (RF); (mushroom): © Tinke Hamming/Ingram Publishing (RF);
(algae): © Stephen Durr (RF); (sprout): © Digital Vision (RF)
The Extraordinary Emergence of Eukaryotic Cells •Mitochondria of eukaryotic cells resembles a prokaryotic cell
- contains a circular chromosome
- capable of independent division
- contains prokaryotic ribosomes
- have bacterial membranes that are inhibited by drugs that only affect bacteria
•Chloroplasts likely arose when endosymbiotic cyanobacteria provided their host cells with a built-in feeding mechanism
The History of Eukaryotes (cont’d) •The first primitive eukaryotes were probably single-celled and independent •Cells later began to aggregate and form colonies •Cells became specialized within colonies •Complex organisms later evolved and individual cells lost the ability to survive on their own •Only disease-causing eukaryotes will be discussed in this chapter
- protozoa
- fungi
- helminths
Structure of a Eukaryotic Cell
Prokaryotic Cell
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
In All Eukaryotes
In Some Eukaryotes
Smooth endoplasmic
reticulum
Rough endoplasmic
reticulum with
ribosomes
Nucleolus
Nucleus
Nuclear
membrane
with pores
Cell membrane
Flagellum Chloroplast Cell wall Glycocalyx Centrioles
Mitochondrion Golgi apparatus Lysosome Actin filaments Microtubule Intermediate
filament
External Structures
Structure Flowchart
Eukaryotic cell
Internal
Boundary of cell
External
Appendages
Flagella
Cilia
Glycocalyx
Capsules
Slimes
Cell wall
Cytoplasmic membrane
Cytoplasm
Nucleus
Organelles
Ribosomes
Cytoskeleton Microtubules
Intermediate filaments
Actin filaments
Chloroplasts
Mitochondria
Golgi apparatus
Endoplasmic reticulum Ribosomes
Lysosomes
Chromosomes
Nucleolus
Nuclear envelope
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Appendages for Moving: Flagella •Motility allows microorganisms to move toward nutrients and positive stimuli and away from harmful substances and stimuli
Locomotion via cilia and flagella is common in protozoa, many algae, and a few fungal and animal cells •Eukaryotic vs. prokaryotic flagella
- eukaryotic flagellum is 10x thicker
- covered by an extension of the cell membrane
- a long, sheathed cylinder containing regularly spaced microtubules in a 9+2 arrangement
- microtubules slide past each other creating a whipping motion that requires the expenditure of energy
Appendages for Moving: Cilia
• Cilia are similar in structure to flagella, but are shorter and more numerous
- only found in a single group of protozoa and in certain animal cells
- occur all over the cell surface
- beat in oar-like strokes
- also function as feeding and filtering structures
The Glycocalyx •The outermost layer that comes into direct contact with the environment •Usually composed of polysaccharides and appears as a network of fibers, a slime layer, or a capsule •Functions
- protection
- adherence of cells to surfaces
- reception of signals from other cells and the environment
The Cell Wall •Protozoa and helminths do not have cell walls •Cell walls of fungi
- rigid and provide structural support and shape
- different in chemical composition from prokaryotic cell walls
- thick layer of polysaccharide fibers composed of chitin or cellulose
- thin outer layer of mixed glycans
A Cross-Sectional Views of Fungal Cell Walls
Cell Wall
(b) (a)
Glycocalyx
Mixed glycans
Glycoprotein
Chitin
Cell membrane
Ce
ll w
all
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© John J. Cardamone, Jr./Biological Photo Service
The Cytoplasmic Membrane •Typical bilayer of phospholipids in which protein molecules are embedded •Contain sterols of various kinds
- relative rigidity give stability to the membrane
- important in cells that do not have a cell wall •Cytoplasmic membrane serves as a selectively permeable barrier
The Nucleus •Most prominent organelle of eukaryotic cells •Separated from the cytoplasm by the nuclear envelope
- composed of two membranes separated by a narrow space
- perforated with small, regularly spaced pores, formed at sites where the membranes unite
- macromolecules migrate through the pores to the cytoplasm and vice versa
The Nucleus (cont’d)
• Nucleolus - found in the nucleoplasm
- site of RNA synthesis
- collection area for ribosomal subunits
• Chromatin - made of DNA and histone proteins
- genetic material of the cell
The Nucleus
(a) (b) Endoplasmic
reticulum
Nuclear pores
Nuclear
envelope
Nucleolus
Nuclear
pore
Nuclear
envelope Nucleolus Endoplasmic
reticulum
Nucleus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a: © Donald Fawcett/Visuals Unlimited
Endoplasmic Reticulum •A series of microscopic tunnels used in transport and storage •Rough endoplasmic reticulum (RER)
- originates from the outer membrane of the nuclear envelope and extends in a continuous network to the cell membrane
- allows transport materials from the nucleus to the cytoplasm and ultimately to the cell’s exterior
- ribosomes are attached to its membrane surface
- proteins synthesized on the RER are transported into the lumen and held for packaging and transport
Detailed Structure of the Rough Endoplasmic Reticulum
Ribosomes
Nucleus
Rough endoplasmic
reticulum
Protein being
synthesized
RER membrane
Cistern
Large subunit
(of ribosome)
mRNA
Small subunit
(of ribosome)
Polyribosomes
Cistern
(b)
(c) (a)
Nuclear
envelope
Nuclear pore
Endoplasmic Reticulum
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© Don W. Fawcett/Photo Researchers
Endoplasmic Reticulum (cont’d) •Smooth endoplasmic reticulum
- closed tubular network without ribosomes
- nutrient processing
- storage of nonprotein macromolecules such as lipids
Golgi Apparatus •Site of protein modification and shipping •Consists of several flattened, disc-shaped sacs called cisternae •Cisternae do not form a continuous network •Always closely associated with the endoplasmic reticulum
- transitional vesicles from the endoplasmic reticulum are picked up at the face of the Golgi apparatus
- proteins are modified within the cisternae by the addition of polysaccharides and lipids
- condensing vesicles pinch off of the Golgi apparatus and are then conveyed to lysosomes or transported outside the cell
Detail of the Golgi Apparatus
Endoplasmic
reticulum
Transitional
vesicles
(b)
(a)
Golgi body
Cisternae
Condensing
vesicles
Golgi Apparatus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Transport Process
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Nucleus
Rough endoplasmic
reticulum Secretory
vesicle
Nucleolus
Golgi
apparatus
Cell membrane
Secretion by
exocytosis
Ribosome
parts
Transitional
vesicles
Condensing
vesicles
Vesicles •Lysosomes
- contain a variety of enzymes involved in the intracellular digestion of food particles and protection against invading microorganisms
- participate in the removal of cell debris and damaged tissue
•Vacuoles
- membrane bound sacs containing fluids or solid particles to be digested, excreted, or stored
- formed in phagocytic cells in response to food and other substances that have been engulfed
- contents of a food vacuole are digested through a merger of a vacuole and a lysosome
The Origin and Action of Lysosomes in Phagocytosis
1
2
3
4 Digestion
Digestive vacuole
Merger of lysosome
and vacuole
Formation of food
vacuole
Mitochondria
Cell membrane
Engulfment of food
Nucleus
Lysosomes
Food particle
Golgi apparatus
Food vacuole
Lysosome
Phagosome
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Mitochondria •Generate energy for the cell •Appear as round or elongated particles scattered throughout the cytoplasm •Composed of a smooth, continuous outer membrane •Inner membrane has tubular inner folds called cristae
- hold the enzymes and electron carriers of aerobic respiration
- extracts chemical energy contained in nutrient molecules and stores it as ATP
•Unique organelles
- divide independently of the cell
- contain circular strands of DNA
- have prokaryotic-sized 70S ribosomes
General Structure of a Mitochondrion
Mitochondria
(a) Cristae
(darker lines)
Matrix
(lighter spaces)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© Donald Fawcett/Visuals Unlimited
Outer membrane
(b)
Cristae
Inner membrane Matrix
DNA strand
70S ribosomes
Chloroplasts •Found in algae and plant cells •Capable of converting energy from sunlight into chemical energy through photosynthesis •Produce oxygen gas as a byproduct of photosynthesis •Resemble mitochondria but are larger, contain special pigments, and are more varied in shape
Ribosomes •Numerous, tiny particles that give a “dotted” appearance to the cytoplasm •Distributed throughout the cell
- scattered freely in the cytoplasm and cytoskeleton
- intimately associated with rough endoplasmic reticulum
- inside mitochondria and chloroplasts •Can be found in short chains of polyribosomes •Size and structure
- large and small subunits of ribonucleoprotein
- eukaryotic ribosome is 80S, a combination of 60S and 40S subunits
•Staging areas for protein synthesis
The Cytoskeleton
•A flexible framework of molecules criss-crossing the cytoplasm •Functions
- anchoring organelles
- moving RNA and vesicles
- permitting shape changes
- movement
The Cytoskeleton (cont’d)
•Actin filaments - long, thin protein strands, about 7 nm in diameter
- found throughout the cell, but most highly concentrated just inside the cell membrane
- responsible for cellular movements such as contraction, crawling, pinching, and formation of cellular extensions
The Cytoskeleton (cont’d) •Microtubules
- long hollow tubes
- maintain the shape of eukaryotic cells without cell walls
- transport substances from one part of the cell to another
- spindle fibers play a role in mitosis
•Intermediate filaments
- rope-like structures 10 nm in diameter
- structural support to the cell and organelles
Fluorescence emission intensity from a
culture of Indian Muntjac cells that were
labeled with phalloidin conjugated to Alexa
Fluor 488 for the intracellular actin
cytoskeletal
http://www.microscopyu.com/articles/fluorescence/filtercubes/blue/b2e/b2emu
ntjacactinlarge.html Figure 11.2.1 Human mesenchymal stem cell labeled with CellLight Tubulin-GFP (C10509, C10613) and CellLight Histone 2B-RFP (C10595) reagents
http://www.lifetechnologies.com/pr/en/home/references/molec
ular-probes-the-handbook/probes-for-cytoskeletal-
proteins/probes-for-tubulin-and-other-cytoskeletal-
proteins.reg.us.b2bcmgt.html
Image of a human cell showing microtubules in
green, chromosomes (DNA) in blue, and
kinetochores in pink
http://en.wikipedia.org/wiki/Kinetochore
A General Comparison of Prokaryotic Cells and Eukaryotic Cells and Viruses
A General Comparison of Prokaryotic and Eukaryotic Cells
The Fungi •Approximately 100,000 species of fungi •Macroscopic fungi: mushrooms, puffballs, gill fungi •Microscopic fungi: molds, yeasts •Forms
- unicellular
- colonial
- complex/multicellular (mushrooms, puffballs)
Fungal Cells •Yeasts
- round to oval shape
- asexual reproduction
- budding •Hyphae
- long, threadlike cells found in the bodies of filamentous fungi
- pseudohypha: chain of yeast cells
•Some fungal cells are considered dimorphic and can take either form depending on growth conditions
Hyphal Structure
(a)
Septum
Septate Hyphae
(b)
Nonseptate Hyphae
as in Rhizopus
(c)
as in Penicillium
Septa
a,b: Courtesy of Dr. Judy A. Murphy, Murphy Consuitancy Microscopy & Digital Imaging, Stockton, CA
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Microscopic Morphology of Yeasts
Pseudohypha Bud scars Nucleus
(c)
Bud (b)
(a)
Bud
Bud scar
Fungal (Yeast) Cell
Ribosomes
Mitochondrion
Cell wall
Cell membrane
Endoplasmic reticulum
Nucleus
Nucleolus
Storage vacuole
Golgi apparatus
© David M. Phillips/Visuals Unlimited
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fungi and Human Disease •Primary pathogens: can sicken even healthy persons •Opportunistic pathogens: attack persons who are already weakened in some way •Mycoses (fungal infections) vary in the way the pathogen enters the body and the degree of tissue involvement
Other Harmful Effects Caused by Fungi •Harmless spores can cause opportunistic infections in AIDS patients •Fungal cell walls give off substances that cause allergies •Toxins produced by poisonous mushrooms can cause death •Aspergillus flavus produces a potentially lethal poison to animals who eat contaminated grain •A number of fungal species are pathogenic to field plants •Cause spoilage of fresh produce during shipping and storage
Beneficial Functions of Fungi •Play an essential role in decomposing organic matter •Form stable associations with plant roots and increase their ability to absorb water and nutrients •Fungi have been engineered to produce large quantities of antibiotics, alcohol, organic acids, and vitamins •Some fungi are eaten or used to impart flavoring to food
Fungal Nutrition •Heterotrophic: acquire nutrients from a wide variety of organic substrates •Saprobic: obtain nutrients from the remnants of dead plants and animals in soil or aquatic habitats •Parasitic: grow on the bodies of living animals or plants, although very few require a living host •Fungus penetrates the substrate and secretes enzymes that reduce it to small molecules that can be absorbed by cells •Thrive in nutritionally poor or adverse environments, and those with high salt or sugar content
Morphology of Fungi •Cells of most microscopic fungi grow in loose associations or colonies •Colonies of yeasts are much like bacteria; have a soft, uniform texture and appearance •Colonies of filamentous fungi have a cottony, hairy, or velvety texture
Types of Asexual Mold Spores
Porospore
(5)
(4)
Microconidia
Macroconidia
(2) (3)
Phialospores Blastospores
Chlamydospores
Conidiospores
Arthrospores
(1) (2)
(1)
Sporangiophore
Sporangiospore
Sporangiospores
Sporangium
(a)
(b)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Solar-Powered Sea Slugs. Mollusc/Algal Chloroplast Symbiosis1,2
Mary E. Rumpho * ,1,2,
Elizabeth J. Summer2 and
James R. Manhart3
Plant Physiology May 2000 vol. 123 no. 1 29-38
Elysia chlorotica
The Protozoa •Name comes from the Greek for “first animals” •65,000 species of single-celled organisms •Most are harmless, free-living inhabitants of water and soil •A few species of parasites are responsible for hundreds of millions of infections each year
Protozoan Form and Function •Single cells containing all of the major eukaryotic organelles except chloroplasts •Cytoplasm divided into two parts
- ectoplasm: clear outer layer involved in locomotion, feeding, and protection
- endoplasm: granular inner region housing the nucleus, mitochondria, and food and contractile vacuoles
Nutritional and Habitat Range •Heterotrophic, requiring food in a complex organic form •Free-living species scavenge dead plant or animal debris or graze on bacteria and algae •Some species have special feeding structures, such as oral grooves •Some protozoa absorb food directly through the cell membrane •Parasites live on fluids of their host
Nutritional and Habitat Range (cont’d) •Main limiting factor for growth is availability of moisture
- predominant habitats are fresh and marine water, soil, plants, and animals
- can survive in extremes of temperature and pH
- many protozoa can convert to a resistant, dormant stage called a cyst
Life Cycles and Reproduction •Trophozoite: motile feeding stage requiring ample food and moisture to stay active •Cyst
- dormant resting stage when conditions in the environment become unfavorable
- resistant to heat, drying, and chemicals
- can be dispersed by air currents
- important factor in the spread of disease
Life Cycles and Reproduction (cont’d) •Encystment
- trophozoite cell rounds up into a sphere
- ectoplasm secretes a tough, thick cuticle around the cell membrane
1
2
3
5
Mature cyst
(dormant, resting stage)
Cell rounds up,
loses motility Trophozoite
is reactivated
Trophozoite
(active, feeding stage)
Trophozoite
CDC/Dr. Stan Erlandsen
Early cyst
wall formation
4 Cyst wall
breaks open
Cyst
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Life Cycles and Reproduction (cont’d) •Some protozoan groups exist only in the trophozoite phase •Many alternate between trophozoite and cyst stage depending on the habitat •Trichomonas vaginalis, a common STD, does not form cysts and must be transmitted by intimate contact •Entamoeba histolytica and Giardia lamblia form cysts and are readily transmitted in contaminated water and food
Life Cycles and Reproduction (cont’d) •All protozoa reproduce by simple, asexual mitotic cell division or multiple fission •Sexual reproduction also occurs in most protozoa
- ciliates participate in conjugation in which two cells fuse and exchange micronuclei
- this results in new and different genetic combinations
Major Pathogenic Protozoa
The Helminths •Include tapeworms, flukes, and roundworms •Adult specimens are usually large enough to be seen with the naked eye •Not all flatworms and roundworms are parasites; many live free in soil and water •Parasitic helminths spend part of their lives in the gastrointestinal tract
The Helminths (cont’d) •Flatworms (Phylum Platyhelminthes)
- also called nematodes
- have a thin, often segmented body plan
- divided into cestodes (tapeworms) and nematodes (flukes)
•Roundworms (Phylum Aschelminthes)
- have an elongated, cylindrical, unsegmented body
Parasitic Flatworms
Suckers
Proglottid
Cuticle
Fertile eggs Immature eggs Excretory
bladder (b)
Testes
Uterus
Cuticle
Ventral
sucker
Esophagus
Oral sucker Pharynx
Intestine
Vas deferens
Ovary
Seminal
receptacle
(a)
Scolex
1 mm
1 cm
(liver fluke): © Arthur Siegelman/Visuals Unlimited; (tape worm): © Carol Geake/Animals Animals
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fasciola hepatica
en higado
Cortesía de Caleb Ruiz-Jiménez, Ph.D. Student, UPR_RCM
Fasciola hepatica
en hígado
Cortesía de Caleb Ruiz-Jiménez, Ph.D. Student, UPR_RCM
Parasitic Roundworm
Mouth
(b)
(a) Anus
Spicules
Cloaca
Seminal
vesicle
Testis
Sperm
duct
Ventral
nerve cord
Excretory
pore
Gut
Lateral
nerve cord
Dorsal
nerve cord
Brain
Pharynx
Cuticle
Pseudocoelom
Centers for Disease Control
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
General Worm Morphology •Multicellular animals equipped with organs and organ systems •Most developed organs are the reproductive tract •Reduction in the digestive, excretory, nervous, and muscular systems
Life Cycles and Reproduction •Complete life cycle includes the fertilized egg, larval, and adult stages •Adults derive nutrients and reproduce sexually in a host’s body •Nematodes: sexes are separate and different in appearance •Trematodes: sexes can be separate or hermaphroditic •Cestodes: generally hermaphroditic
Life Cycles and Reproduction (cont’d) •Helminth life cycle
- must transmit an infective form (egg or larva) to the body of another host
- the host in which the larva develops is known as the intermediate host
- adulthood and mating occur in the definitive host
•Sources for human infection are contaminated food, soil, and water or infected animals •Routes of infection are by oral intake or penetration of unbroken skin
Examples of Helminths and Their Modes of Transmission
The Life Cycle of the Pinworm
A n u s
Eggs transferred
to new host
(cross-infection).
Scratching
contaminates
hands.
Eggs emerge
from anus.
Swallowed
(self-infection) Copulatory
spicule
Fertile
egg
Female
Mouth
Cuticle
Mouth
Eggs Male
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.