Question

1.  Show  4 metabolic reactions catalyzed by phosphatases and describe their role in metabolism and also describe the regulation of each of these enzymes.  You must include at least two different metabolic pathways.

2.  a. The statin drugs are prescribed for people with high cholesterol levels.  Describe their mechanism of action including a kinetic analysis.  

b. What are the differences/similarities between the various statin drugs and the natural substrate?  

c. Like the statins, many drugs act as inhibitors of metabolic pathways.  Choose another drug that inhibits a different pathway and discuss its mechanism of action and its effects.

3.   Within a few days after a fast begins, nitrogen excretion accelerates to a relatively high level.  After a few weeks, the rate of urea excretion falls to a lower level. The excretion of nitrogen then continues at a relatively constant rate until the body is depleted of triacylglycerol stores when the rate of urea and ammonia excretion again rises to a very high level.

a.  Describe the events that trigger and the purpose of the initial surge of nitrogen excretion? Include the hormones and metabolic pathways that are involved.  

b.  Why does the nitrogen excretion rate decrease after several weeks of starvation?

c.  Explain the increase in nitrogen excretion that occurs when lipid stores are depleted?

4.   In lab we studied the kinetics of the enzyme acid phosphatase. Acid phosphatases are found in many organisms, describe the role of acid an phosphatase, its location inside cells and the reaction it catalyzes.

b. Inorganic phosphate is an inhibitor of this enzyme.  How does it inhibit the enzyme?  How would it change the kinetics of this enzyme catalyzed reaction? Be specific.

c. Describe another inhibitor of acid phophatase?  What is its mechanism of action?

5.  We have seen many NAD⁺-linked dehydrogenases and fewer FAD linked dehydrogenases.  

a.  What is the difference(s) between the two types of dehydrogenases?

b. Discuss the importance of dehydrogenases in metabolism and the role and regulation of three different dehydrogenases in three different metabolic pathways.

Answer 1

Answer:                 This question i have to write pointswise,because it's easy to understand you....

3):a):

• Within a few days after a fast begins, nitrogen excretion accelerates to a higher than normal level due to a particular reason and that is nothing by protein catabolism which results in the production of nitrogen due to which urinary nitrogen losses increases.
• when an individual is on fasting condition, in order to maintain the body's glucose levels fatty acid oxidation takes place and there is a surge in ketone body generation because brain solely depends on either glucose or ketone bodies for energy.
• Thus, there is a close relationship between blood ketone bodies, glucose and fatty acids and urinary nitrogen losses during fasting.
• Fasting disturbs the energy supply, which is made up by the mobilization of the lipid reserves and by increasing the conversion of liberated fatty acids into ketone bodies which serves as substrates for energy production.
• Brain and kidneys depend on them for energy.
• But there is a problem, that is, the mobilization of fat tissue and the continuous production of ketone bodies from the fatty acids need a few days to stabilize.
• During this time, the body's energy needs are met by the available labile protein reserve and serves as a precursor of gluconeogenesis in order to prevent a drop in glucose.
• Thus, protein reserves of the muscles, liver are used up in these initial days to make up for the energy needs of our body.

b):

• As I have stated in my previous answer, that for stabilisation and mobilisation of the fatty acids for the production of ketone bodies requires a few days.
• So when they are available to produce ketone bodies protein reserves are again not used for energy production and the fat reserves are used for ketone bodies which acts as a source of energy for the body organs.
• thus the nitrogen excretion falls ater several weeks of fasting.

c):

• When the lipid stores have been depleted body's energy needs are fulfilled by the proteins again especially the skeletal muscle proteins.thus amino acids are released for maintaining glucose homeostasis especially alanine and glutamine.
• Alanine in the liver is converted to glucose and ammonia is released by the urea cycle.
• High demand for glutamine accounts for the purine synthesis. During the later stages of starvation glutamine is required for gluconeogenesis in kidneys.
• And thus, these events trigger the nitrogen excretion when the lipid stores have been depleted.

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