prob_set4_solns - prob_set4_solns Page 1 of 4 Solutions to...

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Solutions to the remaining questions on Problem Set #3 3. Although thyroid hormone and epinephrine are both derived from the amino acid tyrosine, they operate by way of very different mechanisms, so the time course of their action would be expected to be much different. Epinephrine influences cellular metabolism through the action of cell-surface receptor molecules. These receptors influence cell function by way of second-messengers in the cytoplasm; the second messengers change activity levels of existing enzyme molecules, often by modifying their state of phosphorylation. Thus, epinephrine can modulate cellular function in seconds or minutes, and the effects persist as long as the hormone remains in the blood or as long as the level of second-messenger molecules persists. Thyroid hormone exerts its effects by modifying the transcription of genes thereby changing the expression of proteins. It binds to an intracellular (apparently intranuclear) receptor, and the hormone- receptor complex binds to DNA, modifying the transcription of particular genes. Thyroid hormone, therefore, requires longer than epinephrine does to produce its effect and the effect persists longer - until new gene products are degraded or repressed gene products are once again produced. 4. Several possible abnormalities in the target cells could account for adult-onset diabetes, including: a. Fewer insulin receptor proteins are synthesized, or receptors bind insulin less strongly, so less insulin binds to cells, making many cells less able to take up glucose efficiently. b. Insulin receptors might recognize insulin normally, but be modified causing bound glucose to be less efficiently transported into cells. c. Intracellular machinery that modulates the function of insulin receptors may become abnormal.
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prob_set4_solns - prob_set4_solns Page 1 of 4 Solutions to...

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