Why is it important to learn about Eukaryotes in Microbiology?
Characteristics Eukaryotic Cells
• What type of cells do microbes infect?
• Are any microbes eukaryotes?
Structure of a Eukaryotic Cell
The History of Eukaryotes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
In All Eukaryotes
Golgi
apparatus
Lysosome
Cytoskeleton
Mitochondrion
Cell membrane
•Both prokaryotes and eukaryotes evolved from a precursor cell called the Last Common Ancestor
Nuclear
membrane
with pores
Nucleus
-
this cell was neither prokaryotic nor eukaryotic
-
gave rise to both prokaryotic and eukaryotic cells
Nucleolus
Rough endoplasmic
reticulum
Smooth endoplasmic
reticulum
•Endosymbiosis: the more complex cell type most likely emerged when a Last Common Ancestor cell engulfed smaller prokaryotic cells and coexisted with them
Flagellum
Chloroplast
Centrioles Cell wall
Glycocalyx
In Some Eukaryotes
The Nucleus
The Cytoplasmic Membrane
• Separated from the cytoplasm by the nuclear envelope
- composed of two membranes
- perforated with small, regularly spaced pores
• Nucleolus
- found in the nucleoplasm
- site of RNA synthesis
- collection area for ribosomal subunits
•Typical bilayer of phospholipids in which protein molecules are embedded
•Cytoplasmic membrane serves as a selectively permeable barrier
Nucleolus
Nuclear
envelope
Nuclear pores
Endoplasmic
reticulum
a: © Donald Fawcett/Visuals Unlimited
1
The Cell Wall
The Endoplasmic Reticulum
Animals (including helminths), and Protozoa do not have cell walls
•Cell walls of fungi
- rigid and provide structural support and shape
- different in chemical composition from prokaryotic cell walls
A series of microscopic tunnels used in transport and storage
•Rough endoplasmic reticulum (RER)
ribosomes are attached to its membrane surface
•Smooth endoplasmic reticulum
- without ribosomes
Polyribosomes
Cell Wall
Cistern
Ribosomes
Nucleus
Cell membrane
Rough endoplasmic
reticulum
Cell wall
Chitin
(b)
Glycoprotein
Mixed glycans
Nuclear
envelope
Nuclear pore
© Don W. Fawcett/Photo Researchers
Glycocalyx
(a)
© John J. Cardamone, Jr./Biological Photo Service
(b)
(a)
The Nucleus, Endoplasmic Reticulum, and Golgi Apparatus: The Cell’s Assembly Line
The Golgi Apparatus
• Site of protein modification and shipping
1. A segment of genetic code of DNA from the nucleus is copied onto RNA and passed through the nuclear pores to the rough endoplasmic reticulum
2. Synthesized proteins on the RER are deposited into the lumen and transported to the Golgi apparatus
3. Proteins in the Golgi apparatus are chemically modified and packaged into vesicles to be used by the cell
Golgi Apparatus
Condensing
vesicles
Rough endoplasmic
reticulum
Secretory
vesicle
Endoplasmic
reticulum
Nucleus
Secretion by
exocytosis
Condensing
vesicles
Golgi body
(a)
Transitional
vesicles
Cisternae
Ribosome
parts
Cell membrane
Golgi
apparatus
(b)
Transitional
vesicles
Nucleolus
Vesicles
Mitochondria
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
Engulfment of food
Formation of food
vacuole
Merger of lysosome
and vacuole
• Generate energy for the cell
• Composed of a smooth, continuous outer membrane
• Inner membrane has tubular inner folds called cristae
- holds the enzymes and electron carriers of aerobic respiration
- extracts chemical energy contained in nutrient molecules and makes ATP
Outer membrane
• Unique organelles
- divide independently of the cell
DNA strand
- contain circular strands of DNA
70S ribosomes
- have prokaryotic‐sized 70S ribosomes Digestion
Cristae
Matrix
Inner membrane
2
Ribosomes
•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
© Albert Tousson/PhotoTake
The Cytoskeleton
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Appendages for Moving: Flagella
• Microtubules slide past each other creating a whipping motion that requires the expenditure of energy
Cytoskeleton
Actin
filaments
• Motility allows microorganisms to move toward nutrients and positive stimuli and away from harmful substances and stimuli
Intermediate
filaments
Microtubule
(a)
(b)
© Albert Tousson/PhotoTake
Appendages for Moving: Cilia
• Cilia are similar in structure to flagella, but are shorter and more numerous
- occur all over the cell surface
- Locomotion via cilia and flagella is common in protozoa, many algae, and a few fungal and animal cells
Trypanosomiasis: Sleeping Sickness
Giardia lamblia
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
3
Prokaryotes vs. Eukaryotes: Drug Targets
If you want to target a prokaryote what structures in the prokaryote are not found in, or are different from, the eukaryote? Nucleus
Cell Membrane
Cell Wall
Endoplasmic Reticulum
Golgi
Vesicles
Mitochondria
Ribosome
Cytoskeleton
For a drug target you want to be able to target the parasite and not the host!
Evolution by Endosymbiosis •
Are mitochondria “old” bacteria that were phagocytosed by another type of cell and symbiotically evolved into present mitochondria?
The History of Eukaryotes
• 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 PowerPoint
- protozoa
- fungi
- helminths
Evolution by Endosymbiosis • Look at the evidence:
– Mitochondria are the same size as bacteria
– Mitochondria have one circular chromosome, just like bacteria
– Mitochondria have 70S ribosomes just like bacteria
– Mitochondria divide via binary fission just like bacteria
– Perhaps, we all carry some descendants of bacteria in all our cells as mitochondria
Fungi
• Macroscopic fungi: mushrooms, puffballs, gill fungi
• Microscopic fungi: molds, yeasts
Eukaryotes that Cause Disease
Fungi, Protozoa, and Helminthes
• Forms
- unicellular
- colonial
- complex/multicellular (mushrooms, puffballs)
• Not photosynthetic
• Can utilize a large variety of nutrients
• Fungus penetrates the substrate and secretes enzymes that reduce it to small molecules that can be absorbed by cells
4
Fungi
• Yeasts
- round to oval shape
- asexual reproduction
- Budding
- Single cell
•Hyphae
- long, threadlike cells found in the bodies of filamentous fungi
- pseudohypha: chain of yeast cells
Morphology of Fungi Mycelium: the woven, intertwining mass of hyphae that makes up the body or colony of a mold
•Septa: segments or cross walls found in most fungi that allow the flow of organelles and nutrients between adjacent compartments
•Non‐septate hyphae consist of one, long, continuous cell
•Vegetative hyphae are responsible for the visible mass of growth
Protozoa
• Name comes from the Greek for “first animals”
• 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
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
Reproductive Strategies and Spore Formation
Reproductive or fertile hyphae produce spores •Spores
- responsible for reproduction
- can be dispersed through the environment by air, water, and living things
- will germinate upon finding a favorable substrate and produce a new fungus colony in a short time
Nutritional and Habitat Range
• Heterotrophic, requiring food in a complex organic form
• Parasites live on fluids of their host
• Main limiting factor for growth is availability of moisture
- predominant habitats are fresh and marine water, soil, plants, and animals
- many protozoa can convert to a resistant, dormant stage called a cyst
5
Life Cycles and Reproduction
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 Trophozoite
•Encystment
- trophozoite cell rounds up into a sphere
-
-
resistant to heat, drying, and chemicals
-
can be dispersed by air currents
-
important factor in the spread of disease ectoplasm secretes a tough, thick cuticle around the cell membrane
Entamoeba histolytica and Giardia lamblia form cysts and are readily transmitted in contaminated water and food
•All protozoa can reproduce by simple, asexual mitotic cell division
•Sexual reproduction also occurs in most protozoa
- this results in new and different genetic combinations
Trophozoite
(active, feeding stage)
2
Cell rounds up,
loses motility
Trophozoite
is reactivated
Cyst
4
Cyst wall
breaks open
Early cyst
wall formation
3
Mature cyst
(dormant, resting stage)
CDC/Dr. Stan Erlandsen
Life Cycles and Reproduction
•Life cycle determines mode of transmission. Ex:
Trichomonas vaginalis, a common STD, does not form cysts and must be transmitted by intimate contact
5
1
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
• Most parasitic helminths spend part of their lives in the gastrointestinal tract
Parasitic Flatworms: Tapeworm
Helminths
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Flatworms
- have a thin, often segmented body plan
- divided into tapeworms and flukes
Suckers
• Roundworms
- also called nematodes - have an elongated, cylindrical, unsegmented
body
1 cm
Cuticle
Proglottid
Immature eggs Fertile eggs
(liver fluke): © Arthur Siegelman/Visuals Unlimited; (tape worm): © Carol Geake/Animals Animals
6
Parasitic Flatworms: Fluke
Parasitic Roundworm
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Mouth
Pseudocoelom
Oral sucker
Pharynx
Cuticle
Esophagus
Pharynx
Intestine
Brain
Ventral
sucker
Dorsal
nerve cord
Lateral
nerve cord
Cuticle
Gut
Vas deferens
Uterus
Sperm
duct
Excretory
Ventral
pore
nerve cord
Ovary
(b)
Testes
Testis
Seminal
receptacle
Seminal
vesicle
Cloaca
1 mm
Spicules
Excretory
bladder
(a)
Anus
(liver fluke): © Arthur Siegelman/Visuals Unlimited; (tape worm): © Carol Geake/Animals Animals
Centers for Disease Control
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
Why have they been able to decrease their dependence on their own digestive track?
Life Cycles and Reproduction
• Complete life cycle includes the fertilized egg, larval, and adult stages
• Helminth life cycle
- must transmit an infective form (egg or larva) to the body of a 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, water or infected animals
•Routes of infection are by oral intake or penetration of unbroken skin
Example of Helminthes Life Cycle: Pinworms
Life Cycles and Reproduction
• Fertilized eggs
- released to the environment
-
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Copulatory
spicule
provided with a protective shell and extra food to aid their development into larvae
Female
Swallowed
(self-infection)
Eggs transferred
to new host
(cross-infection).
Anus
Fertile
egg
Mouth
Eggs
-
vulnerable to heat, cold, drying, and predators
Male
Cuticle
Eggs emerge
from anus.
•Certain helminths can lay from 200,000 to 25 million eggs a day to assure successful completion of their life cycle
Mouth
Scratching
contaminates
hands.
7
Distribution and Importance of Parasitic Worms
• About 50 species of helminths parasitize humans
• Distributed in all areas of the world
• Higher incidence in tropical areas
• Yearly estimate of cases is in the billions and are not confined to developing countries
• Conservative estimate of 50 million helminth infections in North America alone
8