A1: for growth, metablolism, regulation, evalution.etc.
Q2: how do cells communicate?
A2: cells send signals to other cells, bu a process of recceptor-transduction-response.
Q3: how often do cells do communication?
A3: Depends on different types of cells. skin cells do very often, but brain and nerve cells never do.
Five Facts:
1. external signals are converted to responses within the cell
2. reception: A signaling molecule binds to a receptor protein, causing it to chnge shape
3. transduction: cascades of molecular interactions relay signals from receptions to target molecules in the cell.
4. response: cell signaling leads to regulation of transcription ot cytoplasmic activities
5. apoptosis (programmed cell death) integrates multiple cell-signaling pathways
Figure:
cell communication between two yeast cells. Cells of the yeast Saccharomyces cerevisiae use chemical signaling to identify cells of opposite mating type and to initiate the mating process. First cells of mating type A release a-factor, which binds to receptors on nearby cells of mating type B. Meanwhile, B cells release b-factor, which binds to specific receptors on A cells. Both these "factors" are small proteins of about 20 amino acid in length. Binding of these factors to the receptors induces changes in the cells that lead to their fusion, or mating. The resulting A/B cell combines in its nucleus all the genes from both A and B cells, (diploid).
Summary:
In local signaling, animal cells may communicate by direct contract or by secreting local regulators, such as growth factor(paracrine signaling) or neurotransmitters(synaptic signaling). For signaling over long distances, both animals and plants use homones; animals also signals along nerve cells. Sutherland discovered how the hormone epinephrine acts on cells, by receptor-transduction-response.The signal is transmitted by successive shape changes in the receptor and relay molecules.
The binding between signaling molecule(ligand) and receptor is highly specific. There are three types of receptors in plasma membrane. 1. G protein-coupled receptor with help of a G protein, a protein that binds the energy-rich molecule GTP. Ligand binding activates the receptor, which then activetes a specific Gprotein, which activates yet another protein. 2. receptor tyrosine kinases react to the binding od singlaing molecules by forming dimers and then adding phosphate groups to tyrosines. 3. ion channel receptors have a gated-protein close or open for ions. intracellular receptors are cytoplasmic or nulcear proteins. singaling molecules that are small or hydrophobic and can readily cross the plasma membrane use these recptors. Many signal transduction pathways include phosphorylation cascades, in which a serise of protein kinase each add phosphate group to a next one in line, activating it. Phosphatase enzymes soon remove the phosphates. Second messengers, such as cyclic AMP(cAMP) and Ca2+, diffuse readily through the cytosol and thus help broadcast siganls quickly. many G proteins activate adenyly cyclase, which makes cAMP from ATP. cells use Ca2+ as a second messenger in both G-protein and tyrosine knase pathways. The tyrosine kinase pathways also involve two other second messengers, DAG and IP3 can trigger a subsequent increase in Ca2+ levels.some pathways regulate genes by protein turning specific genes on or off. Apoptosis is type of programmed cell death in which cell components are disposed of in an orderly fashionm without damage to neighboring cells.
Key Terms:
- adenylyl cyclase-An enzyme that converts ATP to cyclic AMP in response to a signal.
- amplification-The strengthening of stimulus energy during transduction.
- apoptosis-A program of controlled cell suicide, which is brought about by signals that trigger the activation of a cascade of suicide proteins in the cell destined to die.
- cyclic AMP (cAMP)-Cyclic adenosine monophosphate, a ring-shaped molecule made from ATP that is a common intracellular signaling molecule (second messenger) in eukaryotic cells. It is also a regulator of some bacterial operons.
- diacylglycerol (DAG)-A second messenger produced by the cleavage of a certain kind of phospholipid in the plasma membrane.
- growth factor-1) A protein that must be present in the extracellular environment (culture medium or animal body) for the growth and normal development of certain types of cells. (2) A local regulator that acts on nearby cells to stimulate cell proliferation and differentiation.
- inositol trisphosphate (IP3)-A second messenger that functions as an intermediate between certain nonsteroid hormones and a third messenger, a rise in cytoplasmic Ca2+ concentration.
- ligand-A molecule that binds specifically to another molecule, usually a larger one.
- protein kinase-An enzyme that transfers phosphate groups from ATP to a protein, thus phosphorylating the protein.
- epinephrine-A catecholamine that, when secreted as a hormone by the adrenal medulla, mediates “fight-or-flight” responses to short-term stresses; also released by some neurons as a neurotransmitter; also known as adrenaline.
Video:
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