The document discusses four major cell organelles: the endoplasmic reticulum, Golgi apparatus, mitochondria, and chloroplasts. It describes the structure and functions of each organelle. The endoplasmic reticulum is a network of membranes that synthesizes proteins and lipids. The Golgi apparatus packages and modifies proteins and lipids. Mitochondria generate energy through ATP production. Chloroplasts conduct photosynthesis. The endosymbiotic theory proposes that mitochondria and chloroplasts originated from ancient prokaryotes living symbiotically inside cells.

1. Structure and functions of cell
organelles
By
Jayalakshmi P.S.
Dept of Botany,
Sree Sankara College, Kalady

3. Endoplasmic Reticulum (ER)
• It is a complex network of tubular membranes exclusively
present in the cytoplasm of the eukaryotic cell.
• network of membranes called cisternae.
• plays a major role in the production, processing, and transport
of proteins and lipids.
• The ER produces transmembrane proteins and lipids for its
membrane and many other cell components
including lysosomes, secretory vesicles, the Golgi apparatus,
cell membrane, and plant cell vacuoles.

4. • Endoplasmic reticulum has two major regions: Smooth
endoplasmic reticulum and Rough endoplasmic reticulum.
• Rough ER has ribosomes attached to the cytoplasmic side of
the membrane which produces proteins via translation.
• Rough ER also manufactures membranes and
secretory proteins.
• Smooth ER lacks attached ribosomes.
• function- carbohydrate and lipid synthesis.
Cholesterol and phospholipids are examples.
• also serves as a transitional area for vesicles
that transport ER products to various destinations.

5. • Rough and smooth ER are connected to one another
so that the proteins and membranes made by the
rough ER can freely move into the smooth ER for
transport to other parts of the cell.
• The space inside of the ER is called the lumen.
• The ER extends from the cell membrane through
the cytoplasm and forms a continuous connection
with the nuclear envelope.
• Since the ER is connected with the nuclear envelope,
the lumen of the ER and the space inside the nuclear
envelope are part of the same compartment.

6. Golgi body
• also known as a Golgi apparatus.
• It is a cell organelle that helps
process and package proteins and
lipid molecules, especially
proteins destined to be exported
from the cell.
• They are membrane-bound
organelle present in the cytosol of
the cell.
• Golgi apparatus is composed of
flat sacs known as cisternae.

7. • The Golgi apparatus is very polar.
• One end (cis face) acts as the "receiving"
department while the other (trans face) acts
as the "shipping" department.
• The cis face is closely associated with the
ER.
• Molecules synthesized in the ER exit via
special transport vesicles that carry their
contents to the Golgi apparatus.
• The vesicles fuse with Golgi cisternae
releasing their contents into the internal
portion of the membrane.
• The molecules are modified as they are
transported between cisternae layers.

8. • Functions of Golgi Bodies
• the main function is the packaging and secretion of
proteins.
• It receives proteins from ER and packages them into
membrane-bound vesicles, which are then transported to
various destinations, such as lysosomes, plasma membrane
or for secretion.
• They also take part in the transport of lipids and lysosome
formation.

9. • Post-translational modification and enzymatic processing
occur near the membrane surface in Golgi bodies, e.g.
phosphorylation, glycosylation, etc.
• It is the site for the synthesis of various glycolipids,
sphingomyelin, etc.
• In the plant cells, complex polysaccharides of the cell wall are
synthesized in the Golgi apparatus.

10. Mitochondria
• known as the Powerhouse of the cell.
• Main function- ATP production.
• They play a major role in breaking down nutrients and generating energy-
rich molecules for the cell.
• ‘mitochondrion’ is derived from the Greek words “mitos” = “thread” and
“chondrion” =“granules-like”,
• It was first described by a German pathologist named Richard Altmann in
1890.
• It’s a double-membraned, rod-shaped structure found in both plant
and animal cells.
• Its size ranges from 0.5 to 1.0 micrometer in diameter.

11. Structure of Mitochondria
• It has an inner and outer
membrane, with
an intermembrane space between
them.
• The area within the inner
membrane of the mitochondrion
is known as the matrix, which
contains the enzymes of
the Krebs (TCA) and fatty acid
cycles, alongside DNA, RNA,
ribosomes, and calcium granules.

12. • The outer membrane contains proteins
known as porins, which allow
movement of ions into and out of the
mitochondrion.
• The inner membrane is arranged
into cristae in order to increase the
surface area available for energy
production via oxidative
phosphorylation.
• The inner membrane contains a variety
of enzymes. It contains ATP
synthase which generates ATP in the
matrix, and transport proteins that
regulate the movement of metabolites
into and out of the matrix.

13. • Mitochondrial DNA is the small
circular chromosome found inside
mitochondria.
• They replicate by a process
called binary fission and can use this
to make multiple copies in one
mitochondrion.
• Their DNA has maternal
lineage which means their DNA is
passed from mother to child with little
change.

14. • Functions of Mitochondria
• It is the site of ATP synthesis and regulates the metabolic activity of
the cell.
• Plays an important role in apoptosis or programmed cell death;
Mitochondria release cytochrome C, which activates caspase, one of
the chief enzymes involved in destroying cells during apoptosis.
• Helps in maintaining an adequate concentration of calcium ions
within the compartments of the cell by quickly absorbing calcium ions
and holding them until they are needed.

15. • In brown adipose tissue mitochondria have an alternative
function of heat production using the electron transport chain,
a process called proton leak.
• It is also involved in various cellular activities like cellular
differentiation, cell signaling, cell senescence, controlling the
cell cycle, and also in cell growth.

16. Endosymbiont Hypothesis
• Mitochondria and chloroplasts are self-dividing structures.
• They contain their own DNA and protein-synthesizing machinery, similar
to that of prokaryotes.
• These phenomena have led to the theory that the two organelles are direct
descendants of prokaryotes that entered primitive nucleated cells.
• It could be a symbiotic association between nucleated hosts and
prokaryotic parasites.
• The hosts would provide the parasites with a
stable osmotic environment and easy access to nutrients, and the parasites
would repay the hosts by providing an oxidative ATP-producing system or
a photosynthetic energy-producing reaction.