Biology Finals Study Guide 1201 Cell Signaling What are first messengers Direct contact short distance signaling Extracellular molecule that elicits a cellular response when it binds to a receptor protein E g hormones neurotransmitters What are two examples of second messengers Non protein water soluble molecules or ions cAMP and Ca 2 cAMP o synthesized from ATP o activates an enzyme called protein kinase Ca 2 o Muscle contractions What is signal amplification and how does it benefit the cell Signal amplification is amplifying the cells response to a signal by phosphorylating the cascades of enzymes and cAMP molecules Amplify faint signal o A few first messenger molecules o Many second messengers o Each step in the cascade recruits more molecules Elicits a coordinated response What is the role of phosphorylation cascades in signal amplification Phosphorylation cascades activated kinase activates a different kinase etc At each step more enzymes are recruited Where are the receptors involved in cell signaling located On the cells surface or inside of the cell Plasma membrane o Integral membrane proteins Intracellular receptor o E g steroid hormone receptors Signal amplification in the breakdown of glycogen Epinephrine adrenaline activates a GPCR in liver cells e g Fig 11 10 11 16 45 7 and 45 9 Calcium activates a phosphorylation cascade in skeletal muscle after the Protein Kinase A step in Fig 11 16 activating the enzyme phosphorylase kinase As a result of signal amplification a small number of epinephrine molecules binding to receptors on the surface of a liver cell or muscle cell can lead to the release of hundreds of millions of glucose molecules from glycogen The relationship of adenylyl cyclase and cAMP Adenylyl cyclase catalyzes the formation of many cAMP molecules from ATP How is adenylyl cyclase activity regulated 1 Epinephrine outside the cell binds the receptors on the surface of the cell causing the activation of adenylyl cyclase which in turn can catalyze many molecules of cAMP The enzyme is modulated positively and negatively by different G proteins Intracellular cAMP levels go up or down o Depends on the summation of all the positive and negative signals on the What reactions do protein kinases and phosphatases catalyze Protein kinases phosphorylation rxns o Covalent transfer of PO3 4 group from ATP to specific amino acids of cell target protein o Acts as an on or off switch for the target protein Phosphatases remove phosphate group What is the role of cAMP dependent Protein Kinase Protein Kinase A in cell signaling Catalyzes phosphorylatin rxns What are the subunits of Protein Kinase A and what do they do 2 regualtory subunits 2catalytic subunits What is the subunit composition of the active enzyme In the cytoplasm cAMP binds to the R subunit R2C2 dissociates into an R dimer and 2 C monomers C monomers catalyze phosphorylation rxns Of the inactive enzyme R2C2 switch proteins either on or off activated by occupied activated receptor Gproteins GDP is bound to the alpha subunit of the inactive G protein heterotrimer Active on a GTPBy Activation of G proteins Inactive off a GDPBy o An activated receptor interacts with the g protein o GTP replaces GDB on the alpha subunit o The protein dissociated into alpha GTP and a By beta gamma dimer o The g protein is now on Then interacts with their target enzymes or ion channels o Turned off when an intrinsic GTPase activity of the alpha subunit hydrolyzes GTP to GDP Alpha GDP and beta gamma dimer reassociate membrane receptor is activated by an intracellular signal G protein transfers extracellular signal into the intracellular compartment by interactive with a target Target enzyme produces and intracellular second messenger What is G protein cycle Be sure you know all of the steps in the cycle and can reproduce it from memory 2 What are examples of the types of G proteins Gs stimulatory G protein o Stimulates adenylyl cyclase Gi inhibitory G protein o Inhibits adenylyl cyclase Golf olfactory protein Gt transducin the G protein involved in vision What are the subunits of G proteins Alpha Beta gamma Inhibitory and stimulatory signals and receptors What would happen if the G protein cycle is disrupted by mutations see Potential Targets for Disease on Moodle loss of function mutations prevent formation of stable mRNA or protein gain of function mutations e g activation of receptor in the absence of agonist first messenger See the G protein cycle sheet and the work sheet on Moodle figures 11 5 11 6 11 7 11 9 11 10 11 11 11 12 11 15 and 11 16 Regulatory system that maintains homeostasis through hormones Consists of hormones and the glands endocrine glands ductless glands which Hormones What is homeostasis Steady state physiological condition constancy of the interior environment of an organism What are examples of homeostasis E g constant pH body temp ion concentration What is meant by antagonistic Hormones that work against each other What is feedback regulation Fig 45 17 End product of a pathway inhibits an enzyme in that pathway What is the endocrine system secrete them How are hormones transported to their targets Endocrine glands secrete hormones into the blood stream Chem classification of hormones fig 45 5 What makes a cell a target for a particular hormone Have receptors for specific first messengers Differet cell types will have a different profile of receptors The regulation of blood glucose concentrations do FIG 45 13 Insulin Glucagon o Lowers bl Glucose levels What are the three hormones directly involved What do these three hormones 3 o Raises bl Glucose levels Osteocalcin o Makes beta cells in pancreas produce extra insulin What chemical class do these hormones belong to Peptide hormones Where are these hormones produced Unsulin and glucagon pancreas Osteocalcin skeleton bone cells Know the two types of diabetes discussed in lecture Type I and Type II What are the underlying causes o Type I autoimmune destruction of cells releasing insulin Inability to produce insulin o Type II onset related to obesity and heredity Failure of the signal transduction system to elicit a response to insulin or inadequate insulin production What are the hormones involved in blood calcium regulation Where are these hormones produced Fig 45 20 Calcitonin produced in the thyroid gland o Stimulates calcium deposition in bones Parathyroid Hormone PTH produced in the parathyroid hormone o Stimulates calcium release from bones What is osteoporosis
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