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