Biology: Signal Transduction and Protein Kinases Essay

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Ligand- signaling molecule like calcium
Receptor protein- molecule to which the receptor binds
Signal transduction- the interaction of ligand and receptor proteins initiates this process, which converts the information in the signal into a cellular response. Events within the cell that occur in response to a signal, different cell types can respond differently to the same signal. An example is epinephrine. 4 mechanisms for cell communications are:
1. Direct contact- Molecules on the plasma membrane of one cell can be recognized by receptors on the plasma membrane of an adjacent cell. Many of the important interactions between cells in early development occur by means of direct contact between surfaces. Cells also signal through gap junctions.
2. Paracrine signaling- signals with short lived local effects. Plays an important role in early development, coordinating the activities of clusters of neighboring cells. The immune response in vertebrates also involves paracrine signaling between immune cells. Signals released from a cell have an effect on neighboring cells. Signal molecules released by cells can diffuse through extracellular fluid to other cells.
3. Endocrine signaling- are longer-lived signal molecules, which may affect cells very distant from the releasing cells are called hormones, and this type of intracellular communication is known as endocrine signaling. Both animals and plants use this signaling mechanism extensively. Hormones released from a cell travel through circulatory system to affect other cells throughout the body. A released signal molecule that remains in the extracellular fluid may enter the organism’s circulatory system and travel widely throughout the body.
4. Synaptic signaling- In animals, the cells of the nervous system provide rapid communication with distant cells. Nerve cells release the signal (neurotransmitter) which binds to receptors on nearby cells. Association of neuron and target cells is a chemical synapse. Where paracrine signals move through the fluid between cells, neuro-transmitters cross the synaptic gap and persist only briefly.
Terms associated with phosphorylation are:
1. Protein kinases- enzyme that adds phosphate groups from ATP to proteins. these phosphate groups can be added to the three amino acids that have an OH as part of their R group, namely serine, threonine, and tyrosine. We categorize protein kinases as either serine-threonine or tyrosine kinases based on the amino acids they modify. Most cytoplasmic protein kinases fall into serine-threonine kinase class.
2. Phosphatases- an enzyme that removes a phosphate from a protein. Reverses the action of kinases. A protein activated by kinases will be deactivated by a phosphatase, and a protein deactivated by kinases will be activated by a phosphatase.
2 receptor types as defined by location are:
1. Intracellular receptor- has no extracellular signal-binding site. Receives signals from lipid-soluble or non-charged, nonpolar small molecules. Located within the cell. Example receptor for NO, steroid hormone, vitamin D and thyroid hormone.
2. Cell surface receptors or membrane receptor- located on the plasma membrane to bind a ligand outside the cell. Transmembrane protein in contact with both cytoplasm and the extracellular environment. Example neurons, phosphorylation of protein kinases, peptide hormones, and rod cells in the eyes.
Chapter 9, Figure 9.5 is a description of how intracellular steroid receptors regulate gene transcription. Know all of the steps of this process, as well as the three functional domains of the hormone receptor are Hormone-binding domain, DNA-binding domain, and Domain that interacts with coactivators to affect level of gene transcription. 3 subclasses of membrane receptors are:
1. Chemically gated ion channels- channel-linked receptors that open to let a specific ion pass in response to a ligand.
2. Enzymatic receptors- receptor is an enzyme that is activated by the ligand
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