Epinephrine binds to several types of receptors called adrenergic receptors. Hea

Question

Epinephrine binds to several types of receptors called adrenergic receptors. Heart muscle cells contain ?i-adrenergic receptors, where as the smooth muscle cells of the gut contain many ?2-adrenergic receptors. Which of the following is most likely true concerning these two types of receptors? ?

A. ?i-adrenergic receptors activate Gs-proteins while ?2-adrenergic receptors activate Gi-proteins

B. ?i-adrenergic receptors activate Gi-protein while ?2-adrenergic receptors activate Gs-proteins

C.Both ?i-adrenergic receptors and ?2-adrenergic receptors activate Gi-proteins

D.Both ?i-adrenergic receptors and ?2-adrenergic receptors activate Gs-proteins

phate from ATP to select protein amino acid residues. The Passaggettfrusstigaom93-100) biological effects of cyclic AMP are mediated by changes in protein phosphoryla General hormones which circulate in the blood can be divided into 3 categories: 1) Steroid hormones, synthesized in In 1957, Earl Sutherland found tha ver homogenates ncul the smooth endoplasmic reticulum of endocrine glands and bated with either epinephrine or glucagon would stimulate the secreted from the cell via exocytosis, bind to proteins for trans activity of glycogen phosphorylase. an enzyme which govern port to their target tissue. They then diffuse through the target the conversion of giycogen to glucose-1-phosphate. However, cell membrane and normally bind to a large receptor protein in f the membranes present in the homogenate were removed by the cytosol, which in turn camies them into the nucleus where longer be still be acti activated by epinephrine or glucagon, but could they exert their effect directly at the transcriptional level. 2) Peptide hormones bind to membrane bound receptors and act vated by the addition of cyclic AMP via a second messenger system. 3) Tyrosine derivatives are further divided into thyroid hormones and the catecholamines, diffuse epinephrinc and norepinephrine. Thyroid 93. Cortisol most likely binds to a receptor protein hrough the cell membrane and bind to receptors in the nucleus. bound to the ce membrane They also act directly at the transcription level. The cate- cholamine ac membrane through a second n the cytosol at the ce C. on the nuclear membrane messenger system. just outside the cel 94. Phosphodiesterase breaks down cyclic AMP to AMP. Caffeine, a drug abundant in coffee, suppresses the activ ity of phosphodiesterase. According to the information in receptor he passage, which of the following would most likely be found in a blood sample of someone who has recently drunk large amounts of coffe adenyly cyclase A. high ADH levels stimulation B. ow insulin levels C. high glucose levels GTP G protein ATP CAMP D. ow glucose levels GDP activation 95. A certain mutant tumor cell line has normal epinephrine receptors and normal adenylyl cyclase; however. fails to Protein Kinase A increase c in the presence of epinephrine. The mos likely explanation for this is: The G -prot ein in the cel s either missing or mal functio The Gi-protein in the ce s either missing or mal various proteins functioning Figure 1 Epinephrine diffuses directly into the cell to act on protein kinase A One second messenger system, shown in Figure 1, works as D. The mutation resuits in a change in the structure of follows: The activated membrane bound hormone receptor acti protein kinasc A nside the cell, called a G-protein. Once vates a protein activated, the G-protein exchanges G for GTP, which causes Depending upon the a portion of the G-protein to dissociate type of G-protein, the dissociated portion may stimulate or inhibit adenylyl cyclase, another membrane bound protein. Inhibitory G-proteins are called Giproteins; stimulating G proteins are called G proteins. After activating adenyly dissociated portion of the G-protei cyclase, the mu hydrolyze GTP to GpP in order to become inactive and recom bine with ts other portion. Adenylyl cyclase converts ATP to cyclic AMP Cyclic AMP activates protein kinase A. Kinases are a family of enzymes that catalyze the transfer of y-phos 210 Copyright 2007 Examkra ckers GO ON TO THE NEXT PAGE.

Explanation / Answer

93 (b) in the cytosol ( as cortisol is a steroid hormone)

94 (c) high glucose levels (inhibition of phosphodiesterase causes cAMP activity to rise causing PKA levels to rise)

95 (a) Gi protein in the cell is either missing or non functional ( effect of adrenaline is through G protein, transmits signals from outside the cell across the membrane to the cells. Adrenaline binds to receptors, transmits signals to G protein which transmits to adenylyl cyclase -convert ATP to cAMP

96. (a) beta adregenic receptors activate Gs proteins whilealpha adregenic receptors activate Gi proteins

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