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Lecture 12

BI110 Lecture 12: Biology Note 12 (module 21)

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Wilfrid Laurier University
Matthew Smith

Sunday Nov 8 2:00-3:50 BA101 Signal Transduction (Module 21) Signal Transduction Pathways - Signals are transmitted from the receptor to a response in cell by a series of biochemical reactions, usually involving protein kinases  Kinases are enzymes that transfer a phosphate group from ATP to one or more sites on particular target proteins (phosphorylation of a target protein)  The added phosphate groups stimulate or inhibit activities of the target proteins - often , target proteins in singal transduction cascades are other kinases - Protein phsophatases  Responses can be reversed (or “turned off”) by removing phosphate groups from target proteins  ALWAYS active Phosphorylation cascade 1. Receptor (bound to the singal molecule – ligand) 2. When the receptor gets turned on it transducts by phosphorylation cascade 3. Then there is activation of inactivation of target molecules 4. Which then triggers the response Amplification 1. Signal enzyme activates 10 of the first molecules in pathway 2. Each of these activates 100 of the second enzyme in pathway, producing 1000 activations 3. Continued amplification of signal Phosphorylation - 1 amino acid of a protein (serine – can be phosphorylated) + ATP  phosphorylated serine +ADP - Phosphate group is added to molecule (here, serine). - Phosphate group usually donated by ATP - Some proteins have 1 phosphorylation site, some have many phosphoylation sites (but it is usually serines or tyrosines that are phosphorylated) Phosphorylation continued… - Phosphorylation frequently changes a protein’s conformation and surface charge - Phosphate groups affect electrostatic attraction and repulsion within a protein, changing its shape - Yellow indicates negatively charged section of protein (this is where it has been phosphrylated bc phosphate groups are negative) - Purple indicates positive charged section of protein - Changes in electrostatic interactions may also affect the proteins surface, potentially affecting how it interacts with other molecules - Phosphatases are important component of phosphorylation cascades (the phosphatases are always present and active - without phosphatases (deactivated), the cellular response could not be turned “off” aka the cell would always be responding even in the absence of the signal. Cyclic AMP (cAMP) - cAMP is an important second messenger; relays initial signaling event - cAMP synthesized from ATP: ATP  cAMP + PP
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