problem set 3 answers

# problem set 3 answers - Question 1 Carbon monoxide(CO is a...

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Question 1 Carbon monoxide (CO) is a potentially fatal poison. Amongst other things, CO exposure causes anoxemia, a reduced oxygen concentration in blood. CO binds avidly to hemoglobin (Hb), to form carboxyhemoglobin, COHb. For answering these questions, you can assume that if a sample of blood or Hb is described as containing (for example) 50% COHb, this means that 50% of the total available O 2 binding sites are occupied by CO. In this case, individual Hb molecules will be bound by, on average , two molecules of CO. This diagram shows oxygen-binding curves for Hb, in the presence of increasing proportions of COHb (I = 0% COHb, II = 10% COHb, III = 25% COHb, IV = 50% COHb, V = 75% COHb). Here, oxygen binding on the y-axis is expressed as the % of available O 2 binding sites in Hb that are bound by O 2 (so each curve is normalized to 100%). (a) What is the effect of CO on the oxygen binding properties of hemoglobin? On the basis of the shapes of these curves, how could you best describe the behavior of CO with regards to its effect on O 2 binding?

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Oxygen binding curves shift to the left and become less sigmoidal in the presence of CO. So, CO is causing oxygen to bind to Hb with higher affinity; the degree of cooperativity of oxygen binding is reduced in the presence of oxygen. Hence, CO is acting as an allosteric activator. Note though that CO is binding to the same site as oxygen, so CO binding reduces the overall oxygen binding capacity of Hb. This diagram shows the oxygen binding curve of hemoglobin in the absence and presence of 50% COHb (curves I and IV on the previous Figure), but now oxygen binding is expressed as the oxygen content of whole blood. (b) What are the two major differences between the oxygen binding curves in the presence and absence of COHb? The curve is shifted to the lest and is less sigmoidal, and the total oxygen content of blood is reduced by half.
(c) Can you suggest two reasons why CO restricts the delivery of O 2 to tissues? CO reduces the overall oxygen carrying capacity of blood. CO increases the affinity of oxygen binding, meaning that at the prevailing oxygen tension in muscle and other tissues, Hb gives up its oxygen less easily. (d) Is CO poisoning (to a level of 50% COHb) more or less severe than 50% anemia, in terms of the ability of blood to deliver O 2 to tissues? More severe, because oxygen binds to Hb more tightly in the presence of 50% HbCO. Question 2 Glyceraldehyde-3-phosphate dehydrogenase catalyzes the following reaction from glycolysis: Glyceraldehyde-3-phosphate + P i + NAD + 1,3-bisphosphoglycerate + NADH In a spectrophotometer, NADH absorbs light at 340 nm, NAD + does not. The

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## This note was uploaded on 02/08/2012 for the course CHEM 3361 taught by Professor Marsh during the Spring '11 term at University of Texas at Dallas, Richardson.

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problem set 3 answers - Question 1 Carbon monoxide(CO is a...

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