BSCI207 Unit 2

Prokaryotes

Bacteria and Archaea

Eukaryotes Groups (4)

Single celled protists

Plants

Fungi

Animals

Eukaryotes Key Processes (4)

Sexual Reproduction

Multicellularity

Development

Evolution

Key Eukaryotic Traits (6)

Flexible cell membrane (lost cell wall)

Complex Cytoskeleton

Nuclear Membrane

Digestive Vacuoles

Organelles

Sexual Reproduction (Mitosis, Meiosis/recombination)

Eukaryotic Flexible cell membrane since lost cell wall

• Cells can change shape

• Cells can move in new ways

• Cells can pinch off bit of surrounding by endocytosis or phagocytosis

• —> Cells can grow bigger + Cells can move

Eukaryotic Complex Cytoskeleton

• Flagella

Eukaryotic Nuclear Membrane

Eukaryotic Origin of nuclear membrane

Eukaryotic Digestive Vacuoles

Eukaryotic Organelles

• Mitochondria

• Chloroplast

• Diversity of energy production

Protists

• Monophyletic group

• Typically single celled

Traditional view of diversity

Divide based on feeding styles

Molds

Absorptive, fungus-like protists

Algae

Photosynthetic, plant-like protists

Protozoa

Ingestive, animal-like protists

Eukaryotes 5 super groups

• SAR

• Archaeplastida

• Excavata

• Amoebozoa

• Opisthikonta

Late Origin Hypothesis

Basal eukaryotes split off before the evolution of mitochondria in other lineages

Early Origin Hypothesis

Mitochondria arose in eukaryotic common ancestor but were lost in some groups

Mitochondria is a key Eukaryote trait. These organelles come in several forms

Evidence that Mitochondria is a key Eukaryote trait (Relics)

• Genetic: “Mitochondrial” Genes (genes with close homologs in proteobacteria) in there nuclear genomes

• Structural: Mitochondrial remnants

• —> Hydrogenosomes (H2 - generating organelles) - double membrane-bound organelles with some redox reactions but no organized ETC’s

• —> Mitosomes have double membranes

Evidence that Mitochondria is a key Eukaryote trait (Implications)

• Single origin of mitochondria at the base of the eukaryotes

• Secondary loss in some lineages of Excavates (and in a number of other groups)

Metamonda (ciliated) include…

• Diplomonads

• Parabasilids

Diplomonads

• Usually commensals in animal guts

• Some parasites - camper’s diarrhea from drinking stagnant water

Parabasalids

• Animal symbionts/parasites

• Trichonympha - eukaryotic endosymbiont in termite guts

• Bacterial endosymbionts digest cellulose

• Other bacterial ectosymbionts (spirochaetes) insereted into the “collar” to make protist mobil

Euglenozoa

Kinetoplastids

Trypanosomes

• Have mitochondria

• Cause sleeping sickness (tse-tse fly)

• May contribute to honeybee colony collapse

Euglenozoa

Euglenids

• Single celled with flagellum

• Movement takes energy/ATP: need mitochondria

• Photosynthetic but can switch to being heterotrophic

SAR

• Stramenopiles

• Two flagella - one covered with hairs

• Diatoms (Photosynthetic unicellular, O2 producer, Deposit silica in cell wall)

• Brown Algae (ex. kelp, Photosynthetic and multicellular)

• Oomycetes (ex. water molds, aquatic sap robes, heterophic absorber)

SAR

• Alveolates

• Have alveoli (sacs under cell membrane)

• Dinoflagellate (Unicellular w/ 2 flagella, Most photosynthetic, Symbionts in corals; red tide “algal” bloom

• Ciliates (Lots of cilia for movement, Heterotrophic, Paramecium)

• Apicomplexans (Heterotrophic parasites, Plasmodium falciparum = malaria)

SAR

• Rhizarians

• Cercozoans (Ameoboid or flagella “algae”, may be photosynthetic, nucleomorph)

• Foraminiferans (Heterotrophs that secrete CaCO3 forming limestone

• Radiolarians (Radically symmetric heterotrophs, glassy endoskeletons that stiffen pseudopods)

Ancestrally, organisms replicated by…

Binary fission

Amenbozoans

• Loboseans: heterotrophs that engulf food with pseudopods

• Plasmal Slime Molds

• Cellular Slime Molds

Haploids only have ___ of each chromosome

One

Diploids have ___ of each chromosome

Two

Asexual Reproduction

• Offspring are clones of parent

• Same # of chromosomes

• Haploids

Sexual Reproduction using meiosis

• Change # of chromosomes

Benefits of Sexual Reproduction

• Asexual reproduction - makes clones of self (if azure bad mutations, can’t get rid of them)

• Sexual reproduction - sex brings together new combinations of alleles (Recombination, Rescue and revitalize genotypes = phenotypes)

Why did Sexual Reproduction arise in Eukaryotes?

New mitochondria bring risks

Generalized sexual life cycle in eukaryotes

• Meiosis: division of 1 diploid cell to generate 4 haploid cells

• Fertilization fusion of 2 haploid gametes to form the diploid zygote

• Variable cycles of mitosis in 1n or 2n stages occurs for both unicellular or multicellular

Diplontic Life Cycle

• Adult is diploid

• Gonads hold immature germ cells (which are haploid)

• Release gametes which fuse (fertilization) to produce diploid zygote

• Diploid zygote grows to diploid adult

• Humans and most animals

• Not the only choice

Haplontic Life Cycle

• Adult is haploid

• Spend significant time undergoing mitosis to replicate

• Only infrequently form gametes

• Fertilization of gametes forms zygotes

• Zygotes can survive harsh conditions

Alternation of generations

Typical protist (unicellular eukaryote) - haplontic life cycle

Evolved new gene with two alleles

• Haploid individual has either gsp or gsm so forms either + or - gamete

• Each is a transaction factor that turns on a suite of genes

gsm/gsp protiens form a heterodimer transcription factor in the zygote

• The mating type gene is a transcription factor that initiates the expression of genes to make one type of gamete

Two versions (alleles) of the mating-type locus control the entire sexual cycle

The mating type locus encodes the integrated genetic machinery that:

1. Transforms cells into two gamete types (+ and -)

2. Enables fertilization

3. In Zygote drives development of zygote

4. Enables meiosis to form 4 haploid spores

Haploid life cycles in eukaryotes result from ____

Evolution of the mating-type locus in the haploid common ancestor of eukaryotes

Key Ideas of Eukaryotes

• What are key characteristics of eukaryotes?

• How do you know that mitochondria are shared eukaryotic trait?

• How do protists differ from other eukaryotes? (Few key examples)

• How did sexual reproduction arise? (What were its original benefits, How do mitosis and meiosis differ? How do vegetative vs. reproductive cells differ?)

• What is a simple model for the evolution of sex using a mating type locus? How does it work?

When did multicellular organisms first arise?

• Stomatolites are colonies of cyanobacteria (These were discovered in Australia in protected bay, similar to those in fossil record back to 3+ BY)

History of multicellular life

Phanerozoic

• Visible life

• Fossil evidence for multicellular organisms

Paleozoic

Mesozoic

Cenozoic

Multicellularity is…

• Cooperation among cells for “good” of organism

• Close association of many cells carrying out specialized vegetative and reproductive functions

5 requirements for multicellularity

1. Extracellular environment

2. Division of labor

3. Resource allocation

4. Proliferation inhibition

5. Programmed cell death

Prevalence of cheating/cancer across life

• Cancer cells are “selfish”, act opposite of normal cells working together

Several convergent designs of multicellular eukaryotes related to their nutrition (3)

1. Photosynthetic organisms

2. Absorptive organisms

3. Ingestive Organisms (animals)

Multicellular Photosynthetic Organisms

• Convergent design - flat “leave”, tubular “stems and attaching “roots/holdfasts”

Multicellular absorptive organism

• Unicellular or filamentous vegetative stages and multicellular reproductive/dispersal stages

Multicellular Ingestive Organisms

• Multicellular ingestive organisms have specialized tissues:

• Digestive - to ingest

• Muscular - to move

• Nervous - to coordinate

Who are the closest unicellular relatives of multicellular eukaryotes? (3 of 4 major multicellular clades)

• Land Plants: Green algae

• Animals: Choanoflagellates

• Fungi: Unicellular opsthokonts (exact one still being debated)

Land Plants

• Green Algae

• Brown Algae and others also evolved multicellularity

• Multicellular green plants arose in fresh water

Volvox

• Two cell types

• Movement cells and reproductive cells

Closest relative to land plants..

• Two candidates (Coleochaete and Chara vulgaris)

• How to tell which? Molecular phylogeny solves mystery

• Charales is closest relative

Multicellularity is part of a series…..

Unicellular—> Colonial —> Filamentous —> Parenchymatous

Animals

• Choanoflagellates

Why would a Choanoflagellates benefit from being reversibly colonial?

• Hypothesis: Maybe it helps feeding? Colonies are induced by chemicals from bacterial food (testable)

• Experiment: Reduce bacteria in choanoflagellate cultures

• Result: Choanoflagellats only spontaneously form rosette colonies in presence of bacteria. Authors when on to isolate specific chem from one bacteria

Fungi

• Unicellular opisthokonts

Opisthokont’s dilemma

5 major fungal clades

• Chytrids

• Zygomycetes

• Glomeromycetes

• Ascomycetes

• Basidiomycetes

• Ancestor probably similar to chytrids: aquatic and flagellated

• Lile plants and animals, fungi only colonize land after becoming fairly sophisticated

How fungo “get around”

• Fungal bodies: mycelia, networks of branched hyphae

• Hyphae syncytial (no cell separations) or have only partial cell walls (septa)

Filamentous

Tissue divides along 1 axis

Parenchymatous

tissue can divide along all 3 axes

Psuedoparenchyma

Filaments that resemble parenchymatous tissue

Multicellularity Benefits

• Overcome Diffusion

• Link operate cells together by adhesion

• Task division: Cells differentiate into different types

Unicellular reproduction

Binary fussion/budding (Asexual)

Multicellular reproduction

• Can also use budding

• (Typically sexual) produce a single celled spore or gamete (typically coupled with meiosis and sex

Who gets to reproduce?

• Only some cells are sexual and replicate

• Others cede that function

• Solution: Tight control over mitotic and meiotic potential

• Does an organism need to have sex organs to have sex?

• Does an organism need to even be multicellular to have sex?

• No

• No

What does an organism need to have sex?

• Diploid phase of life cycle

• Meiosis to form haploid gametes

• Union of haploid meiotic products (“syngamy” or “fertilization”)

• Multicellular organisms use same sequences as in unicellular organisms

Sexual Lifestyles

Haplontic sex in unicellular Chlamydomonas

• A green alga

Animals have ____ sexual cycles

Diplontic

Key Ideas Multicellularity (4)

• What are 5 requirements of multicellularity?

• Multicellularity occurred in multiple lineages (Closest relatives show evolution for cells sticking together as colony, Sometimes colonial phase is reversible)

• Ultimately multicellarity becomes permanent (need to sort out which cells will be reproductive and get to pass on their genes

• Sexual reproduction can occur in single celled organisms (In many multicellular organisms, alternation of single and multicellular stages)

What are key eukaryotic trait that facilitated cell movement?

• Flexible cell membrane

• Complex cytoskeleton

How do we know that excavata once had mitochondria but lost them?

• They have homologs to proteobacterial genes in their nuclear DNA

• They have hydrogenosomes with double membranes

Which of the following are not a stramenopile?

• Dinoflagellates

• Diatoms

• Brown algae

• Oomycetes

Dinoflagellates

In Chlamydomonas, how does the mating type locus affect the zygote?

Expression of the gsp and gsm alleles together makes a heterodimer that causes a zygote to develop

Plants are composed of ___ primary parts made up of ___ tissues

• 3 primary parts: Leaf, Stem, Root

• 3 tissues: Dermal tissue, Ground tissue, Vascular tissue

Plant Primary Growth

• Small plants grow by primary growth —> which is the growth of the stem, including phloem (carries sugar and water) and xylem (carries only water)

• Herbaceous plants like flowers or grasses only undergo primary growth

• When woody plants get large enough they undergo secondary growth

Plant Secondary Growth

• Secondary growth involves adding additional tissue which greatly increases their diameter

• This includes much more xylem and phloem

• Because this tissue is added during secondary growth, we call it secondary xylem and secondary phloem

Woody plant stems have layers specialized for different tasks

• Xylem: Conducts water, supports stem

• Phloem: conducts water + sugars

• Cork: protects inner layer

Vascular Tissue

• Xylem

• Phloem

Plant Primary Body

• Formed by apical meristems in the terminal buds, axillary buds, and root tips

Plant Primary Growth

• Occurs at the tips

• Stem cells are vascular cambium

• Divide and specialize (Xylem to inside, Phloem to outside)