Topic 17: Endosymbiosis

define symbiosis

individuals of two different species live in physical contact, often for mutual benefit

define endosymbiosis

occurs when an individual of one species lives inside an individual of another species

explain the endosymbiosis hypothesis

mitochondria originated from bacteria cell that took up residence inside another cell

developed and put forward by Lynn margulis at UMASS Amherst

Process:

1.Host cell surrounds and engulfs bacterium

2.Bacterium lives within host cell

3. Endosymbiosis: Host cell supplies bacterium with protection and carbon compounds (pyruvate and oxygen=materials for cell respiration). Bacterium supplies host cell with ATP.

Bacterium was originally engulfed for food but instead was endosymbiosis

Cyanobacteria was engulfed and a new outer membrane is made

This bacterium turns into a chloroplast

explain the evidence that endosymbiosis occurred in relation to mitochondria

double membrane bound organelle

replicate by fission

has its own circular DNA

has its own ribosomes and makes its own proteins

hosts energy-producing metabolic machinery ("powerhouse of the cell")

mitochondrial DNA is closely related to "a"(line symbol) proteobacteria

These are all bacteria traits

explain the evidence that endosymbiosis occurred in relation to chloroplasts

double membrane-bound organelles in plant lineages

replicate by fission

has its own circular DNA

genome similar to cyanobacteria (photosynthesis bacteria)

has its own ribosomes and makes its own proteins

cyanobacteria and chloroplasts are very similar looking (both have photosynthetic membranes)

explain endosymbiosis of chloroplasts

occurred once in the plantae lineage

plantae: nucleus and chloroplast with double membrane `

explain secondary endosymbiosis of chloroplasts

photosynthesis spread throughout the eukarya tree via secondary endosymbiosis because there are four membranes

eukaryotic cell engulfs another eukaryotic cell

Plantae chloroplasts have double membrane

other photosynthetic groups have chloroplasts with four plus membranes

1. Photosynthetic eukaryote is engulfed

2. Nucleus from photosynthetic eukaryote is lost, leading to organelle with four membranes

explain the four membranes

1. cyanobacteria membrane

2. original double membrane from primary endosymbiosis

3. Outside of plantae eukaryote cell

4. Secondary endosymbiotic membrane (pinched off membrane)

explain in more detail the endosymbiosis that occurred in the plantae lineage

Primary endosymbiosis occurred once in the plantae lineagge

Other organisms took in plantae cells through secondary endosymbiosis to develop the ability to photosynthesize

-red and green algal chloroplasts were transferred to other protists through secondary endosymbiosis

what was engulfed from plantae depended on the lineage

-Ex. euglenoids engulfed green algae

-Alveolata and Stramenopila engulfed red algae

-we can see this in the pigments they use for photosynthesis

*these chloroplasts were lost for some organisms through evolution

explain how photosynthesis in eukaryotes arose

photosynthesis in eukaryote likely arose once by primary endosymbiosis of cyanobacteria (in the clade plantae)

spread among lineages/clades via secondary and higher endosymbiosis

explain how mitochondria, chloroplasts, and eukaryote fit into the timeline for life on earth

Eukaryotes : 2BYA

Mitochondria: between 2 and 1.5 BYA

Chloroplasts: 1 BYA (same time as mutlicellular life)

how does lateral gene transfer relate to mitochondria and chloroplasts?

many genes transferred from chloroplasts and mitochondria to nucleus. Biggest LGT in history!

This was happening during the creation of mitochondria and chloroplasts

explain tertiary endosymbiosis

single-celled photosynthetic plankton (dinoflagellates) live inside the tissues of animals (corals)

dinoflagellates got photosynthesis from secondary endosymbiosis

given an example of primary, secondary, and tertiary endosymbiosis

primary: red algae got photosynthesis from cyanobacteria

secondary: dinoflagellates got photosynthesis from red algae

tertiary: corals got photosynthesis from dinoflagellates

explain termites in relation to endosymbiosis

termites are an example of tertiary endosymbiosis

termites eat wood, but can't digest it without help

eukaryotes (Trichonympa sp.) lives in its gut

-inside the eukaryote's cells live bacteria and archaea

-it is the bacteria/archaea doing the wood digesting