endosymbiosis & cyanobacteria

“Endosymbiosis & Cyanobacteria”

Algae Seminar

Peshawa Yasin

Contents

Definition What is Endosymbiosis? How important is Endosymbiosis? Primary & Secondary endosymbiosis Endosymbiosis Hypothesis

Definition:-

Endosymbiosis (Greek: endon= "within", sym = "together" and biosis = "living").

An endosymbiont is any organism that lives within the body or cells of another organism.

What is Endosymbiosis?

The endosymbiosis theory attempts to explain the origins of organelles such as mitochondria and chloroplasts in eukaryotic cells.

According to Endosymbiosis theory:

modern eukaryotic cells evolved from simple, phagotrophic cells that ingested bacteria and cyanobacteria; the prey was not digested, and physiological processes of the endosymbionts were used by the host.

Mitochondria developed from proteobacteria,

and chloroplasts from cyanobacteria.

From prokaryote to eukaryote

How important is endosymbiosis?

Endosymbiosis explains the origin of mitochondria and chloroplasts, but could it also explain other features of the eukaryotic cell? Maybe. Endosymbiotic origins have been suggested for many structures, including flagella, cilia, and even the nucleus! However, scientists are still actively debating whether or not these structures

evolved through endosymbiosis.

Mitochondria and chloroplasts (and maybe other organelles) evolved from endosymbiotic bacteria.

Heterotrophic prokaryotes were engulfed and function as mitochondria.

Photosynthetic prokaryotes were engulfed and function as chloroplasts. Eukaryotic cell is a chimera of prokaryotic ancestors [The term chimera refers to the mixture of three prokaryotes].                                   a.  Original contributes genomeb.  One becomes mitochondrionc.  One becomes chloroplast

Primary & Secondary Endosymbiosis

Primary endosymbiosis involves the engulfment of a bacterium by another free living organism. Secondary endosymbiosis occurs when the product of primary endosymbiosis is itself engulfed and retained by another free living eukaryote. Secondary endosymbiosis has occurred several times and has given rise to extremely diverse groups of algae and other eukaryotes.

Endosymbiosis Hypothesis

A

A prokaryote ingested some aerobic bacteria. The aerobes were protected and produced energy for the prokaryote

ChloroplastsAerobic bacteria MitochondriaCyanobacteria

Prokaryote

Animal Cell

Plant cell

B C D

A

N

NN

N

B Over a long period of time the aerobes became mitochondria, no longer able to live on their own

A B C D

ChloroplastsAerobic bacteria MitochondriaCyanobacteria

Prokaryote

Animal Cell

Plant cellN

NN

N

Endosymbiosis Hypothesis

Endosymbiosis Hypothesis

C Some primitive prokaryotes also ingested cyanobacteria, which contain photosynthetic pigments

A B C D

ChloroplastsAerobic bacteria MitochondriaCyanobacteria

Prokaryote

Animal Cell

Plant cellN

NN

N

Endosymbiosis Hypothesis

D Cyanobacteria became chloroplasts, unable to live on their own

A B C D

ChloroplastsAerobic bacteria MitochondriaCyanobacteria

Prokaryote

Animal Cell

Plant cellN

NN

N

Secondary Endosymbiosis and Origin of Algal Diversity

Algae AB

Heterotroph C

N

N

Secondary endosymbiosis

N

Many membrane layers

Algae ABC

Thank you