Basic Mechanism In Cell Communication

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Local regulators

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The signaling cell secretes messenger molecules and travel on short distances.

eg. Growth factors, consists of compounds that stimulate nearby target cells to grow and divide. Many cells receive and respond to the molecules of growth factor produced by a nearby cell.- paracrine signaling.

Synaptic signaling in the nervous system.

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Hormonal signaling/ endocrine signaling

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specialized cells releace hormone molecules, which travel via the circulatory system to other parts of the body, wher they reach target cells that can recognize and respond to the hormones

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local signaling

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a)Paracrine signaling a secreting cell acts on nearby target cells by discharging molcules of a local regulator ( growth factor) into the extracellular fluid

b)Synaptic signaling A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell

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Long-distance signaling

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c)Endocrine(hormonal) signaling. Specialized endocrine cells secrete hormones into body fluids, often blood. Hormones reach virtually all body cells, but are bound only by some cells

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Reception

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The target cell's detection of a signaling molecule coming from outside the cell. A chemical signal is detected when the signaling molecule binds to a receptor protein located at the cell's surface or, in some cases, inside the cell.

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Transduction

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Series of steps that converts the signal to a form that can bring about a specific cellular response. Transduction usually requires a sequence of changes in a series of different molecules- a signal transduction pathway. The molecules in the pathway are often called relay molecules

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Response

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The response may be almost any imaginable cellular activity- catalysis by an enzyme, rearrangement of the cytoskeleton, or activation of specfic genes in the nucleus.

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Signaling molecule

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The signaling molecule behaves like a ligand ( a molecule that specifically binds to another molecule, often a larger one.

Ligand binding causes the receptor protein to undergo change in shape.

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Receptors in the plasma membrane

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Transmembrane receptor transmits information from the extracellular environment to the inside of the cell by changing shape when a specific ligand binds to it.

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G protein-coupled receptor in action

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G protein - A protein that binds the energy rich molecule GTP, which is similar to aTP.

- Epinephrine, many hormones and neurotransmitters use GPCR.

1) when the appropriate signaling molecule binds to the extracellular side of the receptor, the receptor is activated and changes shape. Its cytoplasmic side then binds and activates a G protein. The activated G protein carries a GTP molecule

2) The activated G protein leaves the receptoir, diffuses along ther membrane and then binds to an enzyme, altering the enzyme's shape and a cellular response. Binding of signaling molecules is reversible. The activating change in the GPCR, as well as the changes in the G protein and enzyme, are only temporary; These molecules soon become available for reuse.

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Ion channel receptor

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Ligand-gated ion channel is a membrane receptor that has a region that can act as a gate for ions when the receptor assumes a certain shape.

1) a ligand-gated ion channel receptor in which the gate remains closed until a ligan binds to the receptor.

2) When the ligand binfds to the receptor and the gate opens, specific ions can flow through the channel and rapidly change the concentration of that particular ion inside the cell. This change may directly affect the activity of the cell in some way.

3) When the ligand dissociates from the receptor, the gate closes and ions no longer enter the cell.

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Steroid hormone interacting with an intracellular receptor

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1) The steroid hormone testosterone passes through the plasma membrane.

2) Testosterone binds to a receptor protein in the cytoplasm, activating it.

3) The hormonereceptor complex enters the nucleus and binds to specific genes

4) The boudn protein acts as a transcription factor, stimulating the transcription of the gene into mRNA.

5) The mRNA is translated into a specfic protein.

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Protein kinase

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An enzyme that transfers phosphate groups from ATP to a protein.

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Protein phosphatase

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Enzymes that can rapidly remove phosphate groups from proteins, a process called dephosphorylation

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Phosphorylation cascade

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1) a relay moleculke activates protein kinase 1

2) Active protein kinase 1 activates protein kinase 2

3) Active protein kinase 2 phosphorylates a protein that brings ab0out the cell's response to the signal

4) Protein phosphatase catalyze the remocal of the phosphate groups from the proteins, making them inactive again

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cAMP

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The first messenger activates a G protein coupled receptor, hich activates a specific G protein. In turn, the G protein activates adenylyl cylase, which catalyzes the conversion of ATP to cAMP. The cAMP then acts as a second messenger and activates another protein, usualkly protein kinase A leading to a cellular response.