Lecture VIII – Protistans – Dr. Kopeny Delivered 2/8, 2/11

Lecture VIII Protistans

Lecture Themesstructure and function; recurring evolutionary themes and unifying features

the origin of mitochondria and chloroplasts

Impact of Protists on Human Health and Welfare

“The key to understanding the protists is to recognize that a series of important innovations occurred, often repeatedly, as eukaryoites diversified.” (Freeman 2002)

surface waters teem with microscopic protists

In some near-shore areas, gigantic protists from underwater forests

Protists are particularly abundant in tidal habitats

Morphologies and lifestyles found among protists. Protists are abundant in a wide variety of aquatic habitats. In marine environments, they are found in open ocean as well as in near-shore intertidal habitats (Freeman 2002)

Source: Freeman (2002)

Eugleazoa includes both photosynthetic and heterotrophic flagellates. Most are autotrophic, but the lineage includes

Trypanosoma

Euglena

Alvoelata are unicellular, and bear a cavity called and “alveoli”. Diverse in body form.

Apicompla

dinoflagellates

Ciliates

Stramenopilan are a diverse lineage of heterotrophs and phothynthetic forms (algae). The name refers to fine hairs on the flagella of members of this lineage

water molds

diatoms

brown algae

Rhodophyta are red algae – unlike other eukaryotic algae, they lack flagella at any stage in their life history. They arethe most abundant algae in tropical coastal areas

Dulce, a large, edible red algae

Green Algae and Plants evolved from a common photoautotrophic ancestor. Over 7000 species, mostly fresh water.

Volvox colonies

Sea lettuce

Desmid

Choanoflagellida Flagellate protists. Possible ancestor to Sponges – to Animals.

Size and Structure of Eukaryotic Cells compartmentalization and differentiation makes large size possible.

Problem: transport and exchange limitations with increasing size

Solution: compartmentalization

Example: Paramecium

Eukayotic compartments; nucleus, peroxisomes, mitochondria, chloroplasts, central vacuole, golgi, rough ER, smooth ER

Paramecium, a predaceous protist that feeds on prokaryotes and other protists

Nutritional and Metabolic Diversity in Protists Ingestive Lifestyles: Predation and Scavengers

Absorbtive Lifestyles; Decomposers and Parasites

Photosynthetic Lifestyles; Producers, many of which are symbionts

Photosynthetic unicellular dinoflagellates

Giardia, a unicellular human parasitegiant kelp

Paramecium

Predation and Scavenging Parasitism

pseudopodia engulf food Ciliary currents sweepd food into gullet

host parasite

the parasite is a red algae – with nonpigmented cells

host symbionts

Green cells are dinoflagellates inside a heliozoan

Red: chlorophyll aand phycobilins

Brown: chlorophyll aand chlorophyll c Green: chlorophyll

a and chlorophyll b

Photosynthetic pigmentsSymbiosis

Many photosynthetic groups of algae are distinguished by the accessory pigments they contain, in addition to chlorophyll a. Each of these accessory pigments interecpts different wavelengths of light

Apicomplexans-most apicomplexans are parasitic

Ciliates -many predators and herbivores-some parasite/basorbers (eg cattle guts, fish gills)-some feed via symbiotic photosynthesizers

Dinoflagellates-half or so are photosynthetic, many others are parasitic

Feeding diversity in protists, like electron donor and electron acceptor diversity in prokaryotes, no doubt drove phylogeneticdiversification

Consider the diversity of feeding modes in the lineage Alveolata

Locomotion and Structures for Support and Protection

Pseudopodia

flagella

cilia

Structure of microtubules in cilia and flagella

Modes of Locomotion in Protists

2 single microtubules (red) surrounded by

nine paired microtubules (yellow)A ciliatedProtist

An Amoeboid Protist

reference: chapter 4 in textbook

A ciliated protist

Paramecium can swim in either direction relative to its long axis by beating its cilia in rhythmic, coordinated fashion that progresses from one end of the cell to the other.

Amoeba extends a pseudopodium toward a Pandorina colony. At right, the amoeba surrounds colony before engulfing it

Proposed mechanism of psuedopodial movement. In endoplasm, actin subunits are bound to regulatory proteins that keep them from assembling.

Source: Hickman et al 2001

External Structures for Support and Protection

Forams; shells are made from protein hardened with calcium carbonate

Amoeba; shell made of cemented sand grains

Radiolarians; glassy skeletons allow light penetration for photosynthetic endosymbionts

Diatoms

foraminiferan with calcium carbonate tests

diatomshave glass-like silicon containg sructures

Dinoflaggelates surrounded by cellulose plates

Sources: Purves et al (2002), Freeman (2002)

Multicellularity

Clamydomonas Gonum Pandorina Volvox

Multicellular Green Alga (Coleochaete orbiculairs)

Morphological continuum in Volvocales from unicellular to multicelluar.

True multicellarity is defined functionally

Differentiation of cell function (specialization, division of labor)

Differential gene expression

Multicellularity has evolved independently multiple times in Protistan lineages

Multicelluarity confers advantages by allowing for increased size, specialization, and complexity

The initial evolution towards multicellularity begins with differentiation of gamete-producing cells, the consequence of the uniquely eukaryotic reduction division process; meiosis

Source: Freeman 2002

Reproduction, Life Cycles and Alternation of Generations

Meiosis and Sexual reproduction were important Protistan innovations

Life Cycle of Chlamydomonas

http://megasun.bch.umontreal.ca/protists/chlamy/introduction.html

http://www.ucmp.berkeley.edu/greenalgae/greenalgae.html

Life cycle of Laminaryia: an example of alternation of generations

Sporophytes of this seasweed are usually found in water just below the line of the lowest tides, attached to the rocks by branching holdfasts

In early spring, at end of the main growing season, cells on the surface of the blade develop into sporangia

sporangia produce zoosporres by meiosis

Zoospores are all structurally alike, but about half of them are capable of developing into a male gametophyte and half into a femlel gametophye. Gametophytes look nothing like the sporophytes, being short, branched filaments that grow on the surface of subtidal rocks

Male gametohytes release sperm, and female gametophytes produce eggs, which remain attached tot eh gametophyte. Eggs secrete a chemical signal that attracts sperm of the same species, thereby increasing the probability of gametic union in the ocean.

Sperm fertilize the eggs

The zygotes grow into new sprorophytes, starting life attached to the remains of the old female gametophyte

Gametophytes (n)

Sporophytes (2n)

Lines of evidence indicating mitochondria and chloroplasts arose as prokaryotic symbionts

-membranous enzymes and transport systems

-replication process

-genome

-protein translation machinery, including ribosomes, t-rna

-similarities of mitochondrial and chloroplast ribosomes to prokaryote ribosomes

Endosymbiotic Theory

2.5 um 80 um

Margulis webpagewww.bio.umass.edu/faculty/biog/margulis.html

Lynn MargulisU. Mass., Distinguished Professor and Member of the National Academy of Science – developed endosymbiotic theory

Proteobacteria Cyanobacteria

Phylogenetic analyses using small subunit RNA

Ribosomes are comprised of one small and one large subunit. The single rRNA molecule of the small subunit

Ribosomes are

Gene for small subunit r-RNA is present in all organism –good gene for determining deep branching in tree of life

Sequence comparisons show that closest prokaryote relatieves of mitochondria are altpha proteobacteria.

Sequence comparisons of plastids from various photosynthetic eukaryotes cluster with prokaryotic cyanobacteria (photosyntheitc machinery and metabolic pathways are shared as well.

Protists and Human Health:Plasmodium and Malaria

http://www.malaria.org/lifecycle.html

P. falciparum is the most widespread and dangerous of the four: untreated it can lead to fatal cerebral malaria.

Infected Red Blood Cells

The distribution of malaria varies greatly from country to country and within the countries themselves. In 1990, 75% of all recorded cases outside of Africa were concentrated in nine countries

Infected mosquito bites and infects person; sporozoites and enter liver cells After several days, undergo multiple divisions to become merozoites (specialized spore) that uses apical complex to penetrate RBC

Merozoites reproduce asexually in RBC’s and lyse cells at 48 or 72 hr intervals (species specific); coordinated lysing of cells causes periodic chills and fever.

Some merozoite infect new RBC’s, some divide to form gametocytes; gametocytes that infect a biting female mosquite compete the life cycle in her body.

Gametocytes form gametes and fertilizationoccurs in mosquito digestive tract; zygote is the only dipolid stage in the life cycle

Oocyst develops in wall of mosquito gut. Thousands of sporozoites develop in the oocyst and then migrate to mosquites salivary gland

Merozite

Apex

Red blood cell0.5 um

Plasmodium Infection InterpretationStrain Rate

cp26 Low

cp29 LowHLA-B53 binds to these proteins. Immune resonse is effective

cp26 and cp29 strains together

HighImmune response fails when these strains infect the same person

cp27 Highcp28 Average HLA-B53 does not bind to these

proteins. Immune response is not as effective

Co-evolutonary Arm RaceStrong association between HLA-B53 allele and protection against malaria found in West Africa

HLA-B53 in infected liver cells bind to particular sporozoite protein and display protein-protein complex before they produce merozoites

Recognition breaks down in people co-infected by certain strains

NS leads to iimmune system adaptations for protection – and to pathogen adaptations to overcome them

HUMAN IMMUNE-DEFENSE AGAINST PLASMODIUM

Source: Freeman 2002