Characterizing and Classifying Eukaryotes
Chapter 12
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 (Endosymbiotic theory)
Endosymbiotic Theory
Eukaryotes formed from union of small aerobic prokaryotes with larger anaerobic prokaryotes
Smaller prokaryotes became internal parasites
Parasites lost ability to exist independently
Larger cell became dependent on parasites for aerobic ATP production
Aerobic prokaryotes evolved into mitochondria
Similar scenario for origin of chloroplasts
Theory is not universally accepted
Structure plan of an eukaryote
Internal
Cell envelopeExternal
Cell wallCell membrane
Glycocalyx
AppendagesCapsule
Slime layerFlagella
Cilia
Endoplasmic reticulumGolgi body
MitochondriaChloroplasts
Organelles
Cytoplasmic matrix
Nucleus Cytoskeleton
Nuclear envelopeNucleolus
Chromosomes
MicrotubulesMicrofilaments
Ribosomes
Eukaryotic Organisms
Protozoa
Fungi
Algae
Helminths (parasitic worms)
Arthropods (animal vectors of diseases)
Include both human pathogens and organisms vital for human life
Nucleolus
Cilium
Ribosomes
Cytoskeleton
Cytoplasmicmembrane
Smooth endoplasmicreticulum
Rough endoplasmicreticulum
Transport vesicles
Golgi body
Secretory vesicle
Centriole
Mitochondrion
Lysosome
Nuclear pore
Nuclear envelope
Figure 3.3
Cross section of a typical eukaryotic cell
Glycocalyces
Outermost boundary that is in direct contact with environment
Composed of polysaccharides
Not as organized as prokaryotic capsules
Help anchor animal cells to each other
Provide protection against dehydration
Function in cell-to-cell recognition and communication
FlagellaLong sheathed cylinder containing microtubules
Differ structurally from prokaryotic flagella
Covered by extension of the cytoplasmic membrane
Filaments anchored to cell by basal body; no hook
May be single or multiple; generally found at one pole of cell
Function in motility by pushing or pulling the cell body
Do not rotate but undulate rhythmically
Cilia
Shorter and more numerous than flagella
Coordinated beating propels cells through their environment
Function in motility and move substances past the surface of the cell (filtering)
Figure 3.31
Eukaryotic Cell Walls
Fungi, algae, plants, and some protozoa have cell walls
Animal cells and many protozoa do not have cell walls
Composed of :
Cellulose (plants);
Cellulose, Chitin, and/or Glucomannan (Fungi);
Polysaccharides (Algae)
Cytoplasmic membraneCell wall
Figure 3.27
All eukaryotic cells have cytoplasmic membrane
Fluid mosaic model (phospholipids and proteins)
Contain steroid lipids to help maintain fluidity
Contain regions of lipids and proteins called membrane rafts
Control movement into and out of cell
Eukaryotic Cell Memebrane
Cytoplasmicmembrane
Intercellularmatrix
Cytoplasmicmembrane
Pseudopodium
Non membranous organelles
Ribosomes
Larger than prokaryotic ribosomes (80S versus 70S)
Composed of 60S and 40S subunits
Cytoskeleton
Extensive network of fibers and tubules
Anchors organelles
Produces basic shape of the cell
Made up of tubulin microtubules, actin microfilaments, and intermediate filaments
Figure 3.32
NucleusOften largest organelle in cell containing most of the cell's DNA
Semiliquid portion called nucleoplasm
Contains chromatin
RNA synthesized in nucleoli present in nucleoplasm
Surrounded by nuclear envelope
Contains nuclear pores
Nucleolus
Nucleoplasm
Chromatin
Nuclearenvelope
Nuclear pores
Rough ER
Figure 3.34
Endoplasmic reticulum
Netlike arrangement of flattened, hollow tubules continuous with nuclear envelope
Two forms
Smooth endoplasmic reticulum (SER)
Rough endoplasmic reticulum (RER) Ribosomes
Mitochondrion
Rough endoplasmicreticulum (RER)Smooth endoplasmic
reticulum (SER)Figure 3.35
medcell.med.yale.edu
Numerous ribosomes are visible. Ribosomes are temporarily attached to the cisternae as the cell translates mRNA into protein that is destined to be membrane-bound or secreted.
In contrast to the RER, smooth endoplasmic reticulum lacks ribosomes & not involved in protein synthesis. The main functions of SER are the biosynthesis of phospholipids and cholesterol and the synthesis and repair of membranes.
Golgi apparatus
Receives, processes, and packages large molecules for export from cell
Packages molecules in secretory vesicles that fuse with cytoplasmic membrane
Consists of a stack of flattened sacs called cisternae
medcell.med.yale.edu
Protein synthesis translocation
Composed of flattened hollow sacs surrounded by phospholipid bilayer
https://youtu.be/rvfvRgk0MfA
www.hhmi.org
Lysosomes, Peroxisomes, VacuolesStore and transfer chemicals within cells
Vacuoles may store nutrients in cell
Lysosomes contain catabolic enzymes
Peroxisomes contain enzymes that degrade poisonous wastes
Cell wall
Nucleus
Central vacuole
Cytoplasm
Figure 3.37
Endocytosis(phagocytosis)
Smoothendoplasmicreticulum(SER)Transportvesicle
Lysosome
Phagolysosome
Golgi body
Secretoryvesicle
Exocytosis(elimination, secretion)
Phagosome(food vesicle)
Vesiclefuses with alysosome
Bacterium
The roles of vesicles in endocytosis and exocytosis
Figure 3.38
Have two membranes composed of phospholipid bilayer
Produce most of cell's ATP
Interior matrix contains 70S ribosomes and circular molecule of DNA
Mitochondria
Outer membrane
Inner membrane
Crista
Matrix
Ribosomes
Figure 3.39
Chloroplasts
Light-harvesting structures found in photosynthetic eukaryotes
Use light energy to produce ATP
Have two phospholipid bilayer membranes and DNA
Have 70S ribosomes
Granum
Stroma
Thylakoid
Inner bilayer membrane
Outer bilayer membrane
Thylakoidspace
Figure 3.40
Reproduction in Eukaryotes
More complicated than that in prokaryotes
Eukaryotic DNA packaged as chromosomes in the nucleus
Have variety of methods of asexual reproduction
Many reproduce sexually by forming gametes and zygotes
Algae, fungi, and some protozoa reproduce both sexually and asexually
Nuclear division
Mitosis and Meiosis (you need to know this)
Table 12.1 for summary
The Protists
1) Single celled or
multi-cellular
2) Photosynthesize
with chlorophyll a
Plant-like Animal-like
Algae Protozoa
1) Single celled, lack
tissues
2) Are like animals
because:
a) heterotrophic
nutrition;
b) motility
Protozoa• Diverse group of 65,000 species, most are harmless, free-living in a
moist habitat
• Vary in shape, lack a cell wall
• Most are unicellular; colonies are rare
• 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
• 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
Protozoa
• Classification is difficult because of diversity
• Simple grouping is based on method of motility, reproduction, and life cycle
1. Phylum Mastigophora – primarily flagellar motility, some flagellar and amoeboid; sexual reproduction
2. Phylum Sarcodina – primarily amoeba; asexual reproduction by fission; most are free-living
3. Phylum Ciliophora – cilia; trophozoites and cysts; most are free-living, harmless
4. Phylum Apicomplexa – motility is absent except male gametes; sexual and asexual reproduction; complex life cycle – all parasitic
Protozoal identification
Sarcodina
Nucleus
Food vacuoles
Contractile vacuoles
Pseudopods
• Alternates between a large trophozoite, motile by means of pseudopods and a smaller nonmotile cyst
• Trophozoite has a large nucleus and lacks most other organelles
Trophozoite
Nucleus
Red bloodcell
Cyst
Entamoeba histolytica and Amebiasis
• Asymptomatic in 90% of patients
• Ameba may secrete enzymes that dissolve tissues and penetrate deeper layers of the mucosa
• Causing dysentery, abdominal pain, fever, diarrhea, and weight loss
• Carried by 10% of world population
Amebic infections of the brain• Caused by Naegleria fowleri and Acanthamoeba
• Ordinarily inhabit standing water
• Primary acute meningoencephalitis is acquired through nasal contact with water or traumatic eye damage
• Infiltration of brain is usually fatal
Mastigophora: Giardia lamblia and Giardiasis
http://www.cdc.gov/parasites/giardia/
• Pathogenic flagellate
• Unique symmetrical heart shape with concave ventral surface that acts like a suction cup
• Cysts are small, compact, and multinucleate
• Reservoirs include beavers, cattle, coyotes, cats, and humans
• Cysts can survive for 2 months in environmenthttps://web.stanford.edu/class/humbio103/ParaSites2003/Giardia/GIARDIA2.htm
Nucleus Ventral depression
Nuclei
CystTrophozoite
Usually ingested with water and food
ID 10 to 100 cysts. Cysts enter duodenum, germinate, travel to jejunum to feed and multiply
Causes giardiasis – diarrhea, abdominal pain
Diagnosis is difficult because organism is shed in feces intermittently
Treatment: quinacrine or metronidazole
Agent is killed by boiling, ozone, and iodine
Giardia lamblia and Giardiasis
Mastigophora: Trypanosoma sp.
• Pathogenic flagellates
• Trypanosomes – Trypanosoma
• T. brucei – African sleeping sickness
• T. cruzi – Chaga’s disease; South America
Trypanosoma brucei and African Sleeping Sickness
Spread by tsetse flies
Two variants of disease caused by 2 subspecies:
T.brucei. gambiense – Gambian strain; West Africa
T.brucei. rhodesiense – Rhodesian strain; East Africa
Biting of fly inoculates skin with trypomastigotes, which multiplies in blood and damages spleen, lymph nodes, and brain
Mastigophora: Trypanosoma cruzi, Chagas disease
Causes Chagas disease
Reduviid bug (kissing bug) is the vector
Infection occurs when bug feces is inoculated into a cutaneous portal
Local lesion, fever, and swelling of lymph nodes, spleen, and liver
http://www.cdc.gov/parasites/chagas/biology.html
Mastigophora: Trypanosoma cruzi, Chagas disease
Complications of chronic Chagas disease may include:
•heart rhythm abnormalities that can cause sudden death;
•a dilated heart that doesn’t pump blood well;
•a dilated esophagus or colon, leading to difficulties with eating or passing stool.
Mastigophora: Leishmania donovani and Leishmaniasis
• Leishmaniasis – zoonosis transmitted among mammalian hosts by female sand flies that require a blood meal to produce eggs
• Endemic to equatorial regions
Cutaneous-oriental sore, Baghdad boil –localized ulcerated sore
Systemic (visceral) – high intermittent fever; weight loss, enlarged spleen, liver, and lymph nodes
Kala azar is the most severe and fatal form if untreated
Mastigophora: Leishmania donovani and Leishmaniasis
Ciliophora
Oral cilia in groove
Gullet
Food vacuoles
Macronucleus
Micronucleus
Water vacuole
© Eric Russell, BioMEDIA ASSOCIATES
Bodies covered with cilia
Most ciliophora members are not pathogenicto humans
E.g. Paramecium
Apicomplexa
Sporozoans
Lack locomotor organelles in the trophozoite state
Alternate between sexual and asexual phases and between different animal hosts
Most form specialized infective bodies that are transmitted by arthropod vectors, food, water, or other means
Plasmodium
Toxoplasma
Cryptosporidium
Plasmodium: The agent of Malaria
• Dominant protozoan disease
• Obligate intracellular sporozoan
• 4 species: P. malariae, P. vivax, P. falciparum, and P. ovale
• Female Anopheles mosquito is the primary vector; blood transfusions, mother to fetus
• 300-500 million new cases each year and 2 million deaths each year
http://www.cdc.gov/malaria/
Apicomplexa: Toxoplasma gondii and Toxoplasmosis
Intracellular apicomplexan parasite with extensive distribution
Lives naturally in cats that harbor oocysts in the GI tract
Acquired by ingesting raw meats or substances contaminated by cat feces
Most cases of toxoplasmosis go unnoticed except in fetus and AIDS patients who can suffer brain and heart damage
http://www.cdc.gov/parasites/toxoplasmosis/index.html