Distance Signaling & Signal Transduction

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Department
Biology
Course
BIOLOGY 151
Professor
Mark Huyler
Semester
Fall

Description
“Distance Signaling” & “Signal Transduction”  Distance signaling is accomplished by the synthesis. And release of hormones  Two broad categories of hormones: o Steroid based (fat/lipid soluble/vitamin D) o Protein based (water soluble)  This signal must penetrate or somehow be transferred across the cell membrane  Cell membranes are made up of a lipid bilayer  Lipid bilayers are made up of two major components… o Phospholipids (phosphate groups/glycerol) o Proteins  Lipids are nonpolar  Phosphate groups - (two or three) negative charges/very polar  Glycoproteins – identification of friend vs. foe  This all occurs in an aqueous solution (polar)  Fatty acids – no charge/nonpolar  Protein can be strictly outside the cell, inside the cell or can be located through the cell  How does a signal get across the membrane to deliver its message to the cellular “machinery”?  Lipid soluble (able to move through the cell) 1. Arrival of signal at lipid bilayer 2. Signal reception – receptor in cytosol binds hormone 3. Direct signal response at the nucleus  Lipid-insoluble (on the outside of the cell) 1. Signal reception – receptor protein in membrane comes us to bilayer/intracellular signal and is transduced 2. Signal transduction – signal comes from central nervous system 3. Signal amplification 4. Signal response in nucleus  Why do most peptide hormones require the process of signal transduction? o They may be very large molecules o They may be very hydrophilic o They may be very polar o They may be very hydrophobic  G Proteins 1. Signal received 2.G protein binds GTP and splits (from GDP  GTP) 3.Activated G proteins bind to enzymes which produces second messenger/substrate activates enzyme forming a second messenger Second messengers: cAMP cGMP IP3 DAG Ca+2 How do enzyme linked receptors work? 1. Signal received 2. Signal receptor complex is phosphorylated 3. Ras exchanges GDP for a GTP 4. Intracellular protein is activated 5. Phosphorylation cascade/results Phosphate group comes from ATP/having a phosphate group means that the protein is now activated. Cell Differentiation:  Cell gets signal  Receptor receives signal  Receptor activates protein kinases  Kinases activate transcription factors  Transcription factors mark genes for expression Enzymes involved in signal transduction transfer a phosphate group from ATP to one or more sites on particular proteins and are… a) ATPases b) Hydrolases c) Protein kinases d) ADP reverse synthases If hormonal signals are distributed via the blood why aren’t all tissues affected? - Receptors are only expressed on some specific target tissues… What about “down regulation” of cellular processes? - Signal (hormone increases/decrease) - Receptor (inactivated or endocytosed) - Kinases inactivated (phosphatases) - Proteolysis (ubiquitin dependent) o Occurs in cytoplasm. Takes a kinase and completely eliminates it *Kinases are involved in the transfer of a phosphate group from ATP. For every kinase there is a phosphatase which removes the phosphate group, inactivating it. The self renewal signaling pathway in a particular stem cell type has an additional kinase, TK3 that targets TK1 as well as TFa. How would the presence of TK3 change the behavior of the pathway? a) it would become a temporary circuit, ev
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