In biology, cell signaling or cell communication is the ability of a cell to receive, process, and transmit signals with its environment and with itself. ell signaling is a fundamental property of all cellular life in prokaryotes and eukaryotes . Signals that originate from outside a cell (or extracellular signals) can be physical agents like mechanical pressure, voltage, temperature, light, or chemical signals (e.g., small molecules, peptides, or gas).Signaling molecules can be synthesized from various biosynthetic pathways and released through passive or active transports, or even from cell damage. Receptors play a key role in cell signaling as they are able to detect chemical signals or physical stimuli. Receptors are generally proteins located on the cell surface or within the interior of the cell such as the cytoplasm, organelles, and nucleus.  Cell surface receptors usually bind with extracellular signals (or ligands), which causes a conformational change in the receptor that leads it to initiate enzymic activity, or to open or close ion channel activity. Some receptors do not contain enzymatic or channel-like domains but are instead linked to enzymes or transporters. Other receptors like nuclear receptors have a different mechanism such as changing their DNA binding proper properties and cellular localization to the nucleus.

1. Cell Communication
PRESENTED BY : JAGRUTI MARATHE
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2. Cell signaling
 In biology, cell signaling or cell communication is the ability of a cell to receive, process, and
transmit signals with its environment and with itself.
 ell signaling is a fundamental property of all cellular life in prokaryotes and eukaryotes .
 Signals that originate from outside a cell (or extracellular signals) can be physical agents like
mechanical pressure, voltage, temperature, light, or chemical signals (e.g., small molecules, peptides, or
gas).
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3. Classification of
cell signaling
Cell signaling can occur over short or long
distances, and as a result can be classified as :
autocrine,
juxtacrine,
intracrine,
paracrine, or endocrine.
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4. Signaling molecules
 Signaling molecules can be synthesized from various biosynthetic pathways and
released through passive or active transports, or even from cell damage.
 Receptors play a key role in cell signaling as they are able to detect chemical signals or
physical stimuli.
 Receptors are generally proteins located on the cell surface or within the interior of the
cell such as the cytoplasm, organelles, and nucleus.
 Cell surface receptors usually bind with extracellular signals (or ligands), which causes
a conformational change in the receptor that leads it to initiate enzymic activity, or to
open or close ion channel activity. Some receptors do not contain enzymatic or
channel-like domains but are instead linked to enzymes or transporters.
 Other receptors like nuclear receptors have a different mechanism such as changing
their DNA binding properties and cellular localization to the nucleus.
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5. Cell commutation is necessary:
Each cell is programmed to respond to specific extracellular signal molecules, and is the basis
of development, tissue repair, immunity, and homeostasis.
Errors in signaling interactions may cause diseases such as cancer, autoimmunity, and diabetes
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6. Different types of extracellular signaling
 Many cell signals are carried by molecules that are released by one cell and move to make contact with
another cell.
 Signaling molecules can belong to several chemical classes: lipids, phospholipids, amino
acids, monoamines, proteins, glycoproteins, or gases.
 Signaling molecules binding surface receptors are generally large
and hydrophilic (e.g. TRH, Vasopressin, Acetylcholine), while those entering the cell are generally small
and hydrophobic (e.g. glucocorticoids, thyroid hormones, cholecalciferol, retinoic acid), but important
exceptions to both are numerous, and the same molecule can act both via surface receptors or in an
intracrine manner to different effects.
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7. • In animal cells, specialized cells release these hormones and send them
through the circulatory system to other parts of the body.
• They then reach target cells, which can recognize and respond to the hormones
and produce a result.
• This is also known as endocrine signaling
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8. Exocytosis  EXOCYTOSIS IS THE PROCESS BY WHICH
A CELL TRANSPORTS MOLECULES SUCH
AS NEUROTRANSMITTERS AND PROTEINS
OUT OF THE CELL.
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9. • As an active transport mechanism, exocytosis requires the use of energy to transport
material.
• Exocytosis and its counterpart, endocytosis, the process that brings substances into
the cell, are used by all cells because most chemical substances important to them
are large polar molecules that cannot pass through the hydrophobic portion of
the cell membrane by passive transport.
• Exocytosis is the process by which a large amount of molecules are released; thus it
is a form of bulk transport. Exocytosis occurs via secretory portals at the cell plasma
membrane called porosomes.
• Porosomes are permanent cup-shaped lipoprotein structures at the cell plasma
membrane, where secretory vesicles transiently dock and fuse to release intra-
vesicular contents from the cell.
• In exocytosis, membrane-bound secretory vesicles are carried to the cell membrane,
where they dock and fuse at porosomes and their contents (i.e., water-soluble
molecules) are secreted into the extracellular environment.
• This secretion is possible because the vesicle transiently fuses with the plasma
membrane.
• In the context of neurotransmission, neurotransmitters are typically released
from synaptic vesicles into the synaptic cleft via exocytosis; however,
neurotransmitters can also be released via reverse transport through membrane
transport proteins.
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10. Forms:
Autocrine Paracrine Endocrine
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11. Autocrine :
• Autocrine signaling is a form of cell signaling in which a cell secretes a hormone or chemical
messenger (called the autocrine agent) that binds to autocrine receptors on that same cell, leading to
changes in the cell.
• This can be contrasted with paracrine signaling, intracrine signaling, or classical endocrine signaling.
• An example of an autocrine agent is the cytokine interleukin-1 in monocytes. When interleukin-1 is
produced in response to external stimuli, it can bind to cell-surface receptors on the same cell that
produced it.
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12. Paracrine :
• Paracrine signaling is a form of cell signaling, a type of cellular communication in which a cell
produces a signal to induce changes in nearby cells, altering the behaviour of those cells.
• Signaling molecules known as paracrine factors diffuse over a relatively short distance (local action),
as opposed to cell signaling by endocrine factors, hormones which travel considerably longer distances
via the circulatory system; juxtacrine interactions; and autocrine signaling.
• Cells that produce paracrine factors secrete them into the immediate extracellular environment.
• Factors then travel to nearby cells in which the gradient of factor received determines the outcome.
• However, the exact distance that paracrine factors can travel is not certain.
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13. Paracrine :
• Although paracrine signaling elicits a diverse array of responses in the induced cells, most paracrine
factors utilize a relatively streamlined set of receptors and pathways.
• In fact, different organs in the body - even between different species - are known to utilize a similar sets
of paracrine factors in differential development.
• The highly conserved receptors and pathways can be organized into four major families based on
similar structures: fibroblast growth factor (FGF) family, Hedgehog family, Wnt family, and TGF-β
superfamily.
• Binding of a paracrine factor to its respective receptor initiates signal transduction cascades, eliciting
different responses.
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14. signal transduction pathways :
• Fibroblast growth factors (FGF) are a family of cell
signalling proteins produced by macrophages; they are
involved in a wide variety of processes, most notably as
crucial elements for normal development in animal cells.
• Any irregularities in their function lead to a range of
developmental defects.
• These growth factors typically act as systemic or locally
circulating molecules of extracellular origin that activate
cell surface receptors.
• A defining property of FGFs is that they bind
to heparin and to heparan sulfate.
• Thus, some are sequestered in the extracellular matrix of
tissues that contains heparan sulfate proteoglycans and
are released locally upon injury or tissue remodelling.
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15. Endocrine :
• Endocrine signals are called hormones.
• Hormones are produced by endocrine cells and they travel through the blood to reach all parts of the
body.
• Specificity of signaling can be controlled if only some cells can respond to a particular hormone.
• Endocrine signaling involves the release of hormones by internal glands of an organism directly into
the circulatory system, regulating distant target organs.
• In vertebrates, the hypothalamus is the neural control center for all endocrine systems. In humans, the
major endocrine glands are the thyroid gland and the adrenal glands.
• The study of the endocrine system and its disorders is known as endocrinology.
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16. Juxtacrine :
• Juxtacrine signaling is a type of cell–cell or cell–extracellular matrix signaling in multicellular organisms
that requires close contact.
• There are three types: A membrane ligand (protein, oligosaccharide, lipid) and a membrane protein of
two adjacent cells interact.
• A communicating junction links the intracellular compartments of two adjacent cells, allowing transit of
relatively small molecules.
• An extracellular matrix glycoprotein and a membrane protein interact.
• Additionally, in unicellular organisms such as bacteria, Juxtacrine signaling means interactions by
membrane contact.
• Juxtacrine signaling has been observed for some growth factors, cytokine and chemokine cellular
signals, playing an important role in the immune response. J
• Juxtacrine signalling via direct membrane contacts is also present between neuronal cell bodies and
motile processes of microglia both during development, and in the adult brain.
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17. drxjagrutimarathe@gmail.com
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