Cell to cell communication
Endoplasmic Reticulum
Golgi complex
➢ The study of cell communication focuses
on how a cell gives and receives messages
with its environment and with itself
➢ In multicellular organisms, cell signaling
allows for specialization of groups of cells
➢ Multiple cell types can then join together
to form tissues such as muscle, blood, and
brain tissue
Why and how do cells communicate?
Cell communication is the process by which a cell
detects and responds to signals in its environment
Most single-celled organisms can perceive changes
in nutrient availability and adapt their metabolism
as needed
Some single-celled organisms may utilize
environmental signals to locate a suitable mate;
some send signals to make their numbers known to
other members of their species
• The cells of multi-celled organisms must
communicate with one another to coordinate the
activities of the organism as a whole
• Most multi-celled organisms can utilize junctions
between cells for direct intercellular signaling
• But many forms of communication entail
binding of a signal molecule to the receptors of
target cells
• Receptor-mediated signaling can be shortrange (affecting only nearby cells) or longrange (affecting cells throughout the organism)
What is the mechanism of cell
signaling?
▪ In all cell signaling systems, the signaling molecule must bind to a
specific
receptor
this
activates
a
signal transduction pathway which produces the cellular response
▪ In the majority of signaling systems, the receptor is located within
the
plasma
membrane
Enzyme-linked receptors are very common and occur to some
extent in all known species
▪ G-protein coupled receptors are common in eukaryotic cells
▪ The ligand-gated channels that are used in membrane transport may
also serve as receptors
Transduction pathways vary in length and are
designed to refine and/or amplify the signal.
1. In bacterial cells, two-component regulatory
systems are a common form of transduction
pathway.
2. In eukaryotic cells, the transduction pathways
are usually longer and may include second
messengers; two common second messengers
are cAMP and calcium ions.
3) Signal transduction pathways allow cells
to respond differently to the same signaling
molecule
4) In another type of signaling system, the
receptors are located within the cytosol or
nucleus of the cell; this results in the
transcription of a gene
ENDOPLASMIC
RETICULUM
✓ A continuous membrane system that
forms a series of flattened sacs
within the cytoplasm of eukaryotic
cells
✓ Serves particularly in the synthesis,
folding, modification, and transport
of proteins
➢An important organelle in eukaryotic cells
➢Plays a major role in the production,
processing, and transport of proteins and
lipids
➢Produces transmembrane proteins and
lipids for its membrane and for many other
cell components including lysosomes,
secretory vesicles, the Golgi appatatus, the
cell membrane, and plant cell vacuoles.
Structure:
Morphologically divided into two structures–cisternae and
sheets
✓ Cisternae are tubular in structure, and form a threedimensional polygonal network
✓ They are about 50 nm in diameter in mammals and 30 nm
in diameter in yeast
➢ ER sheets are membrane-enclosed, two-dimensional
flattened sacs that extend across the cytoplasm.
➢ They are frequently associated with ribosomes and special
proteins called translocons that are necessary for protein
translation within the RER.
SER & RER:
The smooth endoplasmic reticulum consists of tubules, which are
located near the cell periphery. This network increases the surface
area for the storage of key enzymes and the products of these
enzymes.
Rough endoplasmic reticulum synthesizes proteins, while smooth
endoplasmic reticulum synthesizes lipids and steroids. It also
metabolizes carbohydrates and regulates calcium concentration, drug
detoxification, and attachment of receptors on cell membrane
proteins.
The surface of the rough endoplasmic reticulum is studded with the
protein manufacturing ribosome, which gives it a rough appearance.
Hence it is referred as a rough endoplasmic reticulum.
FUNCTIONS OF ER
1. Mainly responsible for the transportation of proteins and
other carbohydrates to another organelle, which includes
lysosomes, Golgi apparatus, plasma membrane, etc.
2. Provide the increased surface area for cellular reactions.
3. Help in the formation of nuclear membrane during cell
division.
4. Play a vital role in the formation of the skeletal
framework.
5. Play a vital role in the synthesis of proteins, lipids,
glycogen and other steroids like cholesterol,
progesterone, testosterone, etc.
Functions of RER
➢ Manufactures membranes and secretory proteins
➢ The ribosomes attached to the RER synthesize proteins
by the process of translation
➢ Produces antibodies in certain leukocytes (white blood
cells)
➢ Produces insulin In pancreatic cells
➢ Usually interconnected and the proteins and membranes
made by the rough ER move into the smooth ER to be
transferred to other locations
➢ Some proteins are sent to the Golgi apparatus by special
transport vesicles. After the proteins have been modified
in the Golgi, they are transported to their proper
destinations within the cell or exported from the cell
by exocytosis.
Functions of SER
➢ Has
a
wide
range
of
functions
including carbohydrate and lipid synthesis
(Lipids such as phospholipids and cholesterol are
necessary for the construction of cell membranes)
➢ Serves as a transitional area for vesicles that transport
ER products to various destinations
➢ Produces enzymes in liver cells that help to detoxify
certain compounds
➢ Assists in the contraction of muscle cells In muscles
➢ Synthesizes male and female hormonesin brain cells .
GOLGI COMPLEX
➢ Discovered in the year 1898 by an Italian biologist
Camillo Golgi
➢ A cellular organelle present in most of the cells of the
eukaryotic organisms.
➢ located in the cytoplasm next to the endoplasmic
reticulum and near the cell nucleus.
➢ Referred to as the manufacturing and the shipping
center of the cell
➢ Golgi is involved in the packaging of the protein
molecules before they are sent to their destination
➢ Help in processing and packaging the macromolecules
like proteins and lipids that are synthesized by the cell
and hence act as the ‘post office’ of the cell
Structure of Golgi Apparatus
Under the electron microscope, the Golgi apparatus
is seen to be composed of stacks of flattened
structures that contain numerous vesicles containing
secretory granules.
It is morphologically very similar in both plant and
animal cells. However, it is extremely pleomorphic:
in some cell types it appears compact and limited,
in others spread out and reticular (net-like).
Typically appears as a complex array
of interconnecting tubules, vesicles, and
cisternae.
✓ The Golgi apparatus is comprised of a series of five to
eight
cup-shaped,
membrane-covered
sacs
called cisternae that look something like a stack of
deflated balloons
✓ In some unicellular flagellates as many as 60 cisternae
may combine to make up the Golgi apparatus
✓ The number of Golgi bodies in a cell varies according to
its function
✓ Animal cells generally contain between ten and twenty
Golgi stacks per cell, which are linked into a single
complex by tubular connections between cisternae
Functions of Golgi Apparatus
1. Golgi vesicles are often, referred to as the “traffic police” of the
cell. They play a key role in sorting many of the cell’s proteins and
membrane constituents, and in directing them to their proper
destinations
2. In animals, the Golgi apparatus is involved in the packaging and
exocytosis of the following materials.
Zymogen
Mucus
Lactoprotein (casein)
Secretion of compounds (thyroglobulins) of thyroxine hormone by
thyroid cells;
Secretion of tropocollagen and collagen
Formation of melanin granules and other pigments
Formation of yolk and vitelline membrane of growing primary oocytes.
3. Involved in the formation of certain cellular
organelles such as plasma membrane, lysosomes,
acrosome of spermatozoa and cortical granules of a
variety of oocytes
4. Involved in the transport of lipid molecules around
the cell.
5. Plays an important role in the production of
proteoglycans. The proteoglycans are molecules that are
present in the extracellular matrix of the animal cells.
6. It is also a major site of synthesis of carbohydrates.
These carbohydrates include the synthesis of
glycosaminoglycans, Golgi attaches to these
polysaccharides which then attaches to a protein
produced in the endoplasmic reticulum to form
proteoglycans.
7. Involves in the sulfation process of certain
molecules.
8. The process of phosphorylation of molecules by the
Golgi requires the import of ATP into the lumen of the
Golgi.
9. In plants, Golgi apparatus is mainly involved in the
secretion of materials of primary and secondary cell
walls (e.g., formation and export of glycoproteins,
lipids, pectins and monomers for hemicellulose,
cellulose, lignin, etc.)