Week 3 - Eukaryal Microorganisms

Characteristics of eukaryal cells

1. Defined by a membrane-bound nucleus

2. Usually larger than prokaryotic cells

3. Usually contains organelles

4. May possess a cell wall

5. Complex internal cytoskeleton

Nucleus (function + interesting features)

• Contains most of a cell’s DNA, site of transcription

• Double membrane with pores, outer membrane continuous with ER

Mitochondrion (function + interesting features)

• Energy production

• Double membrane, contains DNA, independent replication

Chloroplast (function + interesting features)

• Photosynthesis

• Double membrane, contains DNA, independent replication, unique to photosynthetic organisms

Nucleolus

Non-membrane bound section within the nucleus for ribosome synthesis

Location of transcription, translation, and ribosome synthesis

Transcription: nucleus

Translation: cytoplasm

Ribosome synthesis: nucleolus

Chemiosmosis + relevant organelles

Using the electron transport chain (ETC) to produce ATP by pumping protons into the intermembrane space, then pumping them back in via ATP synthase. Creates a concentration gradient across a membrane. Done by mitochondria and chloroplasts

Chemiosmosis in chloroplasts

Happens in thylakoid membranes. Transport protons into the lumen, producing ATP in the stroma powered by sunlight.

Why are mitochondria and chloroplasts semiautonomous?

Both have their own DNA, ribosomes, and transcription machinery and can replicate independently, but most of their proteins are made in the cytoplasm (outside the organelle)

Plasma membrane structure in the 3 domains

Bacteria: phospholipid bilayer

Archaea: Bilayer or monolayer, diverse lipid composition

Eukarya: Phospholipid bilayer

Proteins in the 3 domains

Bacteria: high abundance

Archaea: high abundance

Eukarya: low abundance

Cell walls in the 3 domains (Gram ±, fungi, algae, protozoa)

Bacteria (gram-positive): thick peptidoglycan membrane with teichoic acid

Bacteria (gram-negative): thin peptidoglycan membrane + outer LPS membrane

Archaea: varied

Fungi: chitin

Algae: cellulose

Protozoa: none

Structure of cell walls in eukaryotes

Cellulose and chitin form b-1,4-glycosidic bonds for strength and rigidity

Cytoskeleton (structure + function)

• Made of microtubules, microfilaments, and intermediate filaments

• All contribute to cell shape, and some protection for the cell

Microtubules

Cytoskeletal proteins in eukaryotes for intracellular transport, separation of chromosomes, and cell motility. Homologous to tubulin-like FtsZ

Microfilaments

Cytoskeletal proteins in eukaryotes that create the cleavage furrow and assist in cell motility. Homologous to actin-like MreB

Intermediate filaments

Cytoskeletal proteins in eukaryotes that help with nuclear structure and cell-cell interactions

Sterols in plasma membranes

Help stabilize the membrane. Eukaryal version of hopanoids

Which eukarya have cell walls?

Fungi (chitin), algae (cellulose), plants (cellulose), and protozoa at certain stages of their life cycles

Small subunit (SSU) rRNA, tubulins, and heat shock proteins

Highly conserved genes that are used to create phylogenetic trees

Monophyletic groups

Originate from a common ancestor

Polyphyletic groups

Don’t share a common ancestor

Eukaryal model organism groups (4)

1. Fungi

2. Protozoa

3. Slime molds

4. Algae

Metabolism in eukaryal microorganisms

Fungi: heterotrophic

Protozoa: heterotrophic

Slime molds: heterotrophic

Algae: phototrophic

Motility in eukaryal microorganisms

Fungi: non-motile

Protozoa: varies

Slime molds: amoeboid

Algae: non-motile

Chloroplasts in eukaryal microorganisms

Fungi: no

Protozoa: no

Slime molds: no

Algae: yes

Common fungal model organism + use

• Used to study eukaryotic structures and gene expression

• Saccharomyces cerevisiae (for baking, brewing)

Common protozoan model organism + use

• Used to study cell walls, motility, and reproductive strategies

• Giardia lamblia (move via flagella)

Common slime mold model organism + use

• Used to study ecology, motility, communication, and coevolution

• Dictyostelium discoideum (form a multcellular aggregate)

Common algae model organism + uses

• Used to study eukaryal flagella and cellulose cell walls

• Chlamydomonas (ease of growth + durability)

Why do algae not form a monophyletic group?

They were originally classified based on photosynthetic ability, which did not correlate with true relatedness. Photosynthesis likely evolved independently at different times

Why are slime molds logical organisms to study cell aggregation?

They can aggregate in response to certain cues and behave like complex multicellular organisms

What are classification schemes for eukaryal microorganisms based on?

Molecular marker data, morphology, and structure

Purpose of haploid/diploid stages of reproduction

Better survival and genetic variation by reproducing sexually or asexually

Ascus

A sac-like cell that stores haploid spore gametes in fungi

Budding off yeast

Reproduce via smaller yeast cells budding off larger cells. Asymmetric cytokinesis

Fission yeast

Reproduce via fission of identically sized cells. Cytokinesis occurs symmetrically.

Life cycle of Chlamydomonas

Exists in a motile haploid state. Haploid cells fuse into a diploid, hardier spore form in unfavourable conditions

Life cycle of Dictyostelium

Exists in a haploid unicellular form. Under bad conditions, a multicellular “slug” is formed with a stalk and fruiting body, which releases haploid spores. Spores fuse into a diploid macrocyst, which undergoes meiosis to generate more haploid cells.

Mitosis

Forms two identical cells from one original cell via one round of DNA replication and one round of cell division

Meiosis + associated phenomena

Forms 4 n cells from one 2n cell via one round of DNA replication and two rounds of cell division. Allows for genetic recombination, ensuring each haploid cell is genetically distinct

Endosymbiotic theory

A progenitor eukaryal cell ingested a bacterial cell (early mitochondria + chloroplasts) in two separate events, forming a symbiosis.

Evidence for the endosymbiotic theory (3)

1. Mitochondria/chloroplasts have their own DNA that is more similar to bacterial DNA than eukaryal DNA, suggesting chloroplasts came from cyanobacteria and mitochondria came from alpha-proteobacterium

2. Double, lipid membranes

3. Resemble bacteria in size and shape

Amoebas and x-bacteria

Formed a symbiotic relationship via amoebas ingesting bacteria, an example of endosymbiosis in modern cells

Paramecium and algae

Formed a symbiotic relationship via paramecium ingesting algae and using them for photosynthesis, an example of endosymbiosis in modern cells

Plasmodium falciparum

Causes malaria, is a protozoa

Trypanosoma brucei

Causes sleeping sickness, is a protozoa

Giardia lamblia

Causes diarrheal disease, is a protozoa

Toxoplasma gondii

Causes toxoplasmosis, is a protozoa

Epidermophyton

Causes ring worm, athlete’s foot, and jock itch, is a fungi

Candida albicans

Causes oral thrush and vaginal yeast infections, is a fungi

Phytophtora infestans

Causes potato blight, is fungi-like

Why is it difficult to treat infections by eukaryal microbes?

Eukaryal microbes produce enzymes/have cell structures similar to our cells, so potential drugs may target our own enzymes/cells

Ophiocordyceps unilateralis

Zombie fungus that infects insects

Examples of beneficial roles of eukaryal microorganisms (3)

• Photosynthetic algae generate oxygen

• Fungi break down dead waste

• Eukaryal organisms feed on bacteria, reducing rampant growth

Example of an insect-borne disease caused by eukaryal microbes

Malaria

What are the two lines of evidence supporting the Endosymbiotic Theory?

Mitochondria + chloroplasts divide by binary fission and contain DNA

What bacteria did chloroplasts originate from?

Cyanobacteria

What is the slime-mold Dictyostelium discoideum commonly used to study?

Evolution of multicellularity

What is chitin composed of?

Acetyl-glucosamine

Are the cells that emerge from the Chlamydomonas cyst genetically identical to those that entered it?

None will have the same genetic makeup as the cells that began the adaptive cycle. Meiosis within the cyst causes haploid cells to be genetically distinct

The appearance of mitochondria within eukaryal cells is defined as an evolutionary Big Bang. Which landmark ability might have preceded it?

Evolution of phagocytosis

What are the key features of members of Eukarya?

Nucleus and organelles

When did eukaryal cells first emerge?

2 billion years ago

Which alga is commonly used as a model eukaryal organism to study flagellar operation?

Chlamydomonas reinhardtii

Name 2 things that contribute to eukaryal species diversity

Mutation and meiotic cell division

Amitochondriates

Eukaryal cells that don’t contain mitochondria and rely on other organelles like mitosomes

Life cycle of Saccharomyces cerevisiae

Exists in both diploid or haploid phases, undergoing mitosis to reproduce asexually. Under bad conditions, diploid cells undergo meiosis to form haploid spores, being contained in the ascus. Haploid cells become diploid cells by fusing together. Haploid cells are either alpha or a mating types