Biology Lecture 15 - Exam 3
Biology Lecture 15 - Exam 3 BIO 121 A
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This 2 page Class Notes was uploaded by Devin Mart on Friday March 25, 2016. The Class Notes belongs to BIO 121 A at Missouri State University taught by Dr. Durham in Spring 2016. Since its upload, it has received 8 views. For similar materials see General Biology in Biology at Missouri State University.
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Date Created: 03/25/16
Mart 1 Lecture 15: Cell Communication ● Cellular communication is essential for both multi and unicellular organisms. ○ Biologists have discovered some universal mechanisms of cellular regulation, involving the same small set of cellsignaling mechanisms. ■ Signals: chemical, electromagnetic, and mechanical. ○ Signaltransduction pathway is the process by which a signal on a cell’s surface is converted into a specific cellular response. ○ Paracrine signaling is a form of cell to cell communication in which a cell produces a signal to induce changes in nearby cells, altering the behavior or differentiation of those cells. ○ Synaptic signaling only occurs between cells with thsynapse. ○ Hormones are a regulatory substance produced in an organism and transported in tissue fluids such as blood or sap to stimulate specific cells or tissues into action. ■ Cells communicate by direct contac. ● The three stages of cell signaling are reception, transduction, and response. ○ Reception is the process of a chemical signal binding to a cellular protein, typically at the cell’s surface. ○ In transduction, binding leads to a change in the receptor that triggers a series of changes along a signal transduction pathway. ○ In response, the transduced signal triggers a specific cellular activity. ○ A signal molecules (ligand) binds specifically to a receptor protein causing the protein to change shape activation. ■ Most signal receptors are plasma membrane proteins which are often watersoluble. ○ Three major types of receptors: Gproteinlinked receptors tyrosinekinase receptors, and ionchannel receptors. ○ The G protein cts as an onoff switch. ■ When a GDP is bound it is inactive, whereas when a GTP is bound it is active. ○ Tyrosinekinase receptors are used to regulate and coordinate many activities and trigger several signal pathways at once. ■ Tyrosine kinase transfers phosphate group from ATP to tyrosine on a substrate. ○ Ligandgated ion channels are protein pores that open or close in response to a chemical signal. ■ This is a very important aspect in the nervous system. ● Multistep pathways greatly amplify the signal with a large cellular response. ○ Pathways relay signals from receptors to cellular responses. Mart 2 ○ Protein phosphorylation is a posttranslational modification of proteins in which an amino acid residue is phosphorylated by a protein kinase by the addition of a covalently bound phosphate group. ■ Protein kinases regulate protein activity, phosphorylation cascade, inactive to active form, and phosphatases. ● Many signaling pathways involve small, non protein, watersoluble molecules or ions, calledecond messengers. ○ cAMP (adenylate cyclase) converts ATP to cAMP, activates protein kinase. ○ Calcium r egulates many functions of the cell. ● In response to a signal, a cell may regulate activities in the cytoplasm or transcription in the nucleus. ○ Signaling pathways are used to amplify response to signal and contribute to specificity of a response. ○ Various types of cells may receive same signal but produce very different responses. ○ Different kinds of cells have different collections of proteins. ○ Scaffolding proteins physically links signal pathways, and enhances speed and accuracy of signal transfer between cells. ○ Inherited disorder, WiskottAldrich syndrome (WAS), is due to the absence of a single relay protein. ○ Activated signals must be inactivated by appropriate enzymes to prepare the cell for a fresh signal.