chapter 25 - eukaryotes

Fossil record of early eukaryotes

• chemical evidence of eukaryotes have been rocked in rocks 2.7 bya

• Earliest unambiguous eukaryote fossils date back to 1.8 bya

• Multicellular eukaryotes arose around 1.3 bya

Consequence of endosymbiosis

through DNA sequences, suggests eukaryotes are combination organisims with some of their genes and cellular characteristics derived from archea and bacteria

Origins of eukaryotic features

Mostly all from archea

• mitochondria, metabolic genes and ER are from bacteria

• ER is from both

Endosymbiosis

Mitochondria and plastids were formerly small prokaryotes living in larger host cells

Endosymbioant

Cell that lives within a host cell

Serial endosymbiosis

Supposed mitochondria evolved before plastids through sequence of endosymbiotic events

• prokaryotic ancestor of mitochondria and plastids probably gained entry to host cell as undigested prey or internal parasites

Serial endosymbiosis steps

1.infolding plasma membrane

2. Engulfed aerobic bacterium

3. Cell with nucleus and Endomembrane system

4. Engulfed photosynthetic bacterium

Ancestral prokaryote →Host cell →ancestral eukaryotes→ancestral photosynthetic eukaryote

Endosymbiosis of algae

-plastid bearing lineage of protists evolved into red algae and green algae

• most likely they underwent secondary endosymbiosis, where they were ingested by a heteroeukaryote

• results in new plastids

What did evolution of eukaryotic cells allowed for

Evolution of eukaryotic cells allowed for greater rage of unicellular forms

Metazoans

Multicelllualrity evolved and gave rise to algae, plants, fungi and animals (metazoans)

• this is the second ave of diversification

Earliest multicellular eukaryotes

• were in forms of colonies (collection of connected cells but have no cellular differentiation)

What is the origin of animals

Ctenophores

• originally thought as sponges were the frist animal

Why did we believe sponges were the first animal

• morphological and molecular evidence points to chanoflagellates as closested living relative of animals

• In which sponges were made of a colony of chanoflagellates

4 supergroups of eukaryotes

1. Excavate

2. SAR

3. Archaeplastida

4. Unikota

3 types of excavata

Diplomonads, parabasalids and euglenozoans

Diplomonads and parabasalids

• Are a type of excavata that live in anaerobic environments

• Lack plastids

• Have modified mitochondria called mitosomes

• Derive energy anaerobically like glycolysis

• Have 2 equal sized nuclei and multiple flagella

• Are often parasitic

Parabasalids

• type of excavata

• Reduced mitochondria called hydrogen domes that generate some energy anaerobically

Ex. Trichomonas vaginalis, pathogen causing yeast infections

Euglenozoans

• type of excavata including predatory heterotrophs, photosynthetic autotrophs and pathogenic parasites

• Have a spiral or crystalline rod in their flagella beside their ring of microtubules

• Has 1 - 2 flagella emerging from a pocket at end of the cell

• Can be autotrophic and heterotrophic

• Has kinetoplastids and euglenids

Kinetoplastids

A clade with single mitochondrion with a mass of DNA called kinetoplast

• includes free living considers of prokaryotes in fresh water, marine and moist terrestrial ecosystems

• Includes trypanosoma

Trypanosoma

Kinetoplastid causing sleeping sickness

• transferred through kissing bugs, by taking blood meal on face and then dropping their feces

• Charles Darwin had this

3 types of SAR

1. Stramenopila

2. Alveolata

3. Rhizaria

2 major groups of stamenopila

Diatoms and brown algae

Diatoms

Unicellular algae with 2 part glass like wall of silica

• Are a type of stramenopile

• reproduce mainly asexually and sometimes sexually

• Major component of phytoplankton

• Fossilized diatom walls make up the diatomaceous earth

Brown algae

Type of stramenopiles

• multicellular and marine

• Include seaweeds

• Most complex multicellular anatomy of all algae

• form kelp forests

Brown algae strcuture

Algal body called thallus, is plantlike but lacks true roots, stems and leaves

• has a root like holdfast that anchors the stemlike stipe to support the leaflike blades

Alveolates

• clade in SAR

• Has membrane bounded sacs called alveoli under the PM

• Includes photosynthetic and heterotrophic protists

3 types of alveolates

1. Dinoflagellates

2. Apcomplexans

3. Cilliates

Dinoflagellates

• Part of alveolates

• Has characteristic shapes reinforced by internal plates of cellulose

• Aquatic mixotrophs and heterotrophs

• Abundant components of marine and fresh water phytoplankton

Red tides

Toxic dinoflagellate blooms

Apicomplexans

• part of alveolates clade

• Parasites of animals derived from algae causing serious diseases

• apex has specialized organelles to penetrate host

• Has nonphotossynthetic plastid called apicoplast

• Has sexual and asexual stages requiring 2 or more different host to complete

Apicomlexan plasmodium

Parasite causing malaria, carried by anopheles mosquitos

• needs both mosquito and human to complete life cycle

Ciliates

• part of alveolates clade

• Large and varied group of protists

• Use cilia to move and feed

• Most are predators of bacteria and other protists

Rhizarians

• part of SAR

• Includes amoebas that move and feed using pseudopodia, forams/foraminiferans for having porous multicellular shells called tests

3 types of archaeplastida

1. Red algae

2. Green algae (chlorophytes and Charophytes)

3. Plants

Red algae

• type of archaeplastida

• Is red due to pigment called phycoerythrin, that masks the green pigment chlorophyll

• Is greenish red in shallow waters and dark red in deep waters

• Multicellular and are the most abundant large algae in coastal waters in the tropics

Chlorophytes

• type of green algae

• Live in fresh water, and marine

• Unicellular, colonial and multicellular forms

• Reproduce sexually using bi flagellated gametes that have cup shaped chloroplasts

6 types of unikonta

1. Tubulinids

2. Slime molds

3. Nucelariids

4. Fungi

5. Chanoflagellates

6. Animals

Amoebozoans

• part of unikonta

• Are amoebas with lobe or tube shaped pseudopodia

• Mostly heterotrophs that eat bacteria or other protists

Opisthokonts

• type of unikonta

• Diverse group of eukaryotes including animals, fungi and several groups of protists like nucleariids

Structural and functional diversity of protists

• unicellular, colonial and multicellular forms

• Are simplest eukaryotes but are very complex at the cellular level

• Most protists are aquatic

• Many feeding behaviors (photoautrotrophs, heterotrophs, mixotrophs, etc)

Producers

Organisims that use energy from light to convert CO2 to organic compounds, forming the base of food webs

• carried out primarily by protists and photosynthetic protists in aquatic communities

What percentage of photosynthesis do protists and plants make up

30% aquatic protists, 20% photosynthetic prokaryotes and 50% plants

Examples of symbiotic protist

1. Photosynthetic dinoflagellates are food providing symbiotic partners of coral

2. Wood digesting protists inhabit the cut of many termites, allowing them to digest wood

Giardia

Protist causing beaver fever