The document summarizes the endosymbiotic theory of the origin of mitochondria and chloroplasts. It states that mitochondria likely evolved from aerobic prokaryotes that were engulfed by early eukaryotic cells, eventually becoming specialized organelles. Similarly, chloroplasts may have evolved from photosynthetic prokaryotes that were engulfed by eukaryotic cells already containing mitochondria. This endosymbiotic theory was first proposed by Lynn Margulis and has received significant evidentiary support.

1. Theories regarding origin of
Mitochondria and Chloroplasts
prasent by
Gutti.Pavan
MSC –I Biochemistry
The Institute of Science

2. Mitochondria
 The mitochondrion (plural mitochondria) is a
double membrane-bound organelle found in
all eukaryotic organisms. Some cells in
some multicellular organisms may however lack them
(for example, mature mammalian red blood cells)

3. Chloroplast
 Chloroplasts specialized compartments,
in plant and algal cells. The main role of chloroplasts is to
conduct photosynthesis, where the photosynthetic
pigment chlorophyll captures the energy from sunlight and
converts it and stores it in the energy-storage
molecules ATP and NADPH while freeing oxygen from
water.

4. Theory of origin of mitochondria
and chloroplasts
 Mitochondria and chloroplasts likely evolved from
engulfed prokaryotes that once lived as
 independent organisms. At some point, a eukaryotic
cell engulfed an aerobic prokaryote,
 which then formed an endosymbiotic relationship
with the host eukaryote, gradually
 developing into a mitochondrion.
Eukaryotic cells containing mitochondria then
engulfed photosynthetic prokaryotes, which
 evolved to become specialized chloroplast organelles.

5. endosymbiosis

6. Theory of endosymbiosis
 First proposed by Lynn
Margulis in 1960s
 Much evidence to
support eukaryotic
cellular respiration
originated via
endosymbiosis of aerobic
purple bacteria (alpha-
proteobacteria) which
ultimately became
mitochondria.

7. Endosymbiotic origin of
mitochondria & chloroplast

8. Secondary Endosymbiosis
 Secondary endosymbiosis is when a living cell
engulfs another eukaryote cell that has already
undergone primary endosymbiosis. It has happened
often enough that it has lead to genetic diversity
among the organisms on Earth. Though it undergoes
the same process of primary endosymbiosis .

9. Multiple ingestions lead to a variety of
endosymbiotic structures

10. endosymbiosis w/s secondary
endosymbiosis

11. Evidence for endosymbiosis
 Biologist Lynn Margulis first made the case for endosymbiosis in the 1960s, but for
many years other biologists were skeptical. Although Jeon watched his amoebae
become infected with the x-bacteria and then evolve to depend upon them, no one
was around over a billion years ago to observe the events of endosymbiosis.
Membranes — Mitochondria have their own cell membranes, just like a
prokaryotic cell does.
 DNA — Each mitochondrion has its own circular DNA genome, like a bacteria's
genome, but much smaller. This DNA is passed from a mitochondrion to its
offspring and is separate from the "host" cell's genome in the nucleus.
 Reproduction — Mitochondria multiply by pinching in half — the same process
used by bacteria. Every new mitochondrion must be produced from a parent
mitochondrion in this way; if a cell's mitochondria are removed, it can't build new
ones from scratch.


12. Importance of 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 (structures like
the tail of a sperm), cilia (hair-like structures that help in
locomotion), and even the nucleus the cell's command center!
However, scientists are still actively debating whether or not
these structures evolved through endosymbiosis.