cell signaling - imp

8/2/2019 Cell Signaling - Imp

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Cell signaling Cell signaling can best be defined as the process of

cells communicating with each other and within the

cell. The three stages of cell signaling are reception,

transduction, and response. Some different ways

cells receive signals are through G-proteins, ligands,

tyrosine-kinase, and steroids and hormones. All of

these involve the phospholipid bilayer and its

.

These communication mechanisms depend heavily

on extracellular signal molecules, which are

produced by the cells to signal to their neighbors or

to cells further away.

The signal molecules are mainly proteins.

These proteins include cell-surface receptor proteins,

which bind the signal molecule, plus a variety of

intracellular signaling proteins that distribute thesignal to appropriate parts of the cell.


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Stages of cell signaling

The three stages of cell signaling.

1. Signal reception - changes the receptor molecule in some way. Molecules that

activate receptors can be classified as hormones, neurotransmitters, cytokines, and

growth factors, but all of these are called receptor ligands.

2. Signal transduction - moves signal to inside of cell, and converts it to a form the cell

can actually respond to

a. this is the si nal transduction athwa

b. molecules in the pathway are often called relay molecules

3. Cellular response - Specific cellular response may be almost anything imaginable

a. movement of cytoskeleton

b. activation of specific genes in nucleus

c. anabolic or catabolic rearrangement of molecules etc.


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Secreted Molecules Mediate Three Forms of

Signaling: Paracrine, Synaptic, and Endocrine Paracrine Signaling: Signal molecules released to local cells. It depends on

signals that are released into the extracellular space and act locally on

neighboring cells. Cells can communicate with cells in the immediateenvironment. It is especially important in the local immune response.

Growth factor and clotting factors are paracrine signalling agents.

Synaptic Signaling: Signal molecules released to close neighboring cell. It is

performed by neurons that transmit signals electrically along their axonsand release neurotransmitters at synapses, which are often located far

away from the body.

Endocrine Signaling: Signal molecules released into circulatory system and

signaling is done at a distance. It occurs through the presence of hormones.Hormones are biologically active substances which are secreted into the

bloodstream. It depends on endocrine cells which secrete hormones into

the bloodstream that are then distributed widely throughout the body.


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There Are Three Known Classes of Cell-Surface Receptor Proteins: Ion-

Channel-linked, G-Protein-linked, and Enzyme-linked


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Ion channel linked receptor

Ion channel receptors

1. ligand gated ion channel

2. part of receptor acts as a gate when ligand binds to it


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Ion channel linked receptor


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G - Protein linked receptor

G proteins function as molecular switches. When they bind guanosine triphosphate (GTP), they

are 'on', and, when they bind guanosine diphosphate (GDP), they are 'off'. G proteins regulate

metabolic enzymes, ion channels, transporters, and other parts of the cell machinery,

controlling transcription, motility, contractility, and secretion, which in turn regulate systemic

functions such as embryonic development, learning and memory, and homeostasis. Humanvision and smell require these receptors.


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Enzyme linked receptor

cell signaling - imp

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