Regulation fo Pathways

Assignments Module 8

The questions posed below are to be answered through the "Quiz" link at the end of this module. Your responses are Due by 11:55 pm (EST) on 24 April. You may use the threaded discussions to discuss with your classmates as you like prior to answering. The quiz itself is not timed; you may take as long as you like. Only your first answer to each question is accepted as your response. You may find it helpful to formulate your responses in an external editor then copy and paste your responses to the "quiz".

1. The half-life of many hormones in the blood is relatively short. For the peptide hormones like insulin and glucagon it is on the order of 30 minutes. Meaning 30 minutes after being secreted by the pancreas, about half of it has been lost.
   1. What is the purpose of the relatively short life time of circulating hormones
   2. In view of this short life time, how could one of these hormones be kept at constant levels under normal conditions
   3. In what ways can an organism make rapid changes in circulating concentrations of a peptide hormone.
2. Metabolic Differences in Liver and Skeletal muscles are important, especially during the "flight or fight" situation. Here the hormone, epinephrine, is released into the blood. It has much the same response as glucagon..... promoting the breakdown of glycogen. This happens in BOTH liver and muscle. The product of glycogen breakdown in the liver is glucose, just like with glucagon. In skeletal muscle on the other hand the product is pyruvate (through glycogen breakdown and then glycolysis)
   1. what is the advantage to the organism during a "flight or fight" condition to have these to having the different breakdown results in liver and skeletal muscle?
   2. Muscle cells do NOT express a protein that we have discussed. The lack of this protein (it's not a metabolic one... not one listed in modules 6 or 7) is responsible for the different pathways in these tissues. Which one and why?