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cell signals, cell signals - Coggle Diagram
cell signals
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Endocrine signalling.
- Signal to a far away cell
Paracrine signalling
- cells signals to a lose by cell.
Conceptual basis
- to make multicellular organism cells must communicate.
- this communication is mediated by extracellular signal molecules.
- Sophisticated mechanism control which signal molecules are released from specific cell type , at which time and concentration they are secreted, and how these signals are interpreted by the target cells.
- some signalling molecules act over long distances, some act only on immediate neighbour cells.
- most cells in higher organism are both emitters and receivers of signals.
Budding yeast cells responding to mating factor
- the cells are normally spherical.
- in response to mating factor secreted by neighbouring yeast cells,
- they put out protrusions towards the source of the factor in preparation for mating.
Basic terms
Transcription factor - A ligand binds to its receptor.
- allowing for the complex to move into the cell nucleus. , there, the complex acts as a transcription factor.
- Different ligands can activate/ inhibit transcription.
- signalling molecules (ligands)
- bind to (ligate)
- Specific receptors.
- Binding to a ligand to receptor outside the cells. - Receptor is integrated in the cell membrane.
- Intracellular signalling cascade gets activated. - these in return active effector proteins which change metabolism., gene expression, shape/movement of cell.
Basic terms intercellular signalling
- how one cell communicates with others cells within an organism.
- Direct physical contact.
- Nearby
- Distant tissue.
Intracellular signalling
- how signals from receptors are transmitted within a cell.
- how ligation of a receptor causes changes to cell behaviour.
Conceptual basis.
- Extracellular signal molecules (ligands) can bind to (ligate) either cell-surface receptors or intracellular receptors.
- most signal molecules are hydrophilic and are therefore unable to cross the plasma membrane directly: instead, they bind to cell surface receptors, which in turn generates one or more signals within the targeted cell.
- some small signal molecules, by contrast, diffuse across the plasma membrane and bind to receptors inside the target cell either in the cytosol or in the nucleus.
- many of the small signal molecules are hydrophobic and nearly insoluble in aqueous solution: they are therefore transported in the bloodstream. and other extracellular fluids after binding to carrier proteins, which the disassociate from before entering targeted cells.
Cell surface or intracellular receptor signalling -
- Hydrophilic signal activates
cell-surface receptor-> intracellular signalling cascade is activated.
- Hydrophobic signal detaches
from carrier protein, passes through cell membrane and activates receptors in the nucleus.
four forms of intercellular signalling Contact- dependent.
immune cells: Antigen presentation.
- Paracrine
- Budding yeast cells
Synaptic
- Nerve cells.
Endocrine
- Hormones.
Synaptic vs Endocrine Endocrine signalling
- Transport of signals through blood stream
Synaptic signalling
- Transports of signal vai axons in nerve cells.
Effects of cell signalling
- Survive
- Grow and survive
- Differentiate
- apoptosis ( controlled cell death)
cell signals
Receptor classes. Nuclear receptors
- Found with the cell nucleus.
Cell surface.
Ions channels coupled
- G- protein coupled receptors
- enzyme coupled receptors.
Nuclear receptor
- Binding of ligand to receptor causes a conformational change, coactivator
protein can now bind ->transcription
Example: Steroid hormones signalling
- Activation of primary response genes
induces primary response proteins.
The primary response proteins a) shut
off primary response genes and b) activate secondary response genes -> secondary
response proteins are made.
Three surface receptor classes ion-channel-linked receptors
converts chemical signals to electrical signals.
Example Gap junctions
G-protein-linked receptor
- Signal transduction involves the production of 2nd messengers.
Example chemokine receptors, adrenergic receptors.
Enzyme linked receptors
Protein kinase receptors
Example is insulin
Ion channel coupled receptors
- Reside within excitable tissues.
- Example neuromuscular junction--> nerve impulse leads to release of acetylcholine which in turn activates cation channels.
How is signalling information encoded - Signal acts as molecular switch to
change the conformation of a protein active/inactive.
- this work through the addition/removal of a phosphate group.
- P gets added to protein.
- GDP gets substituted by GTP
Not all amino acids can be phosphorylated:
- Serine ( unchanged)
- Threonine (unchanged)
- Tyrosine (hydrophobic).
- Phospho-serine
-phospho-threonine
- phospho-tyrosine
all negative and polar.
Effects of phosphorylation.
- change of charge results in conformation change (shape is different)
- phosphorylation is the attachment of a phosphate group to a molecule or an ion.
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