Organic Chemistry
9th Edition
ISBN: 9781305080485
Author: John E. McMurry
Publisher: Cengage Learning
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Chapter 29.SE, Problem 23MP
One of the steps in the pentose phosphate pathway for glucose catabolism is the reaction of sedoheptulose 7-phosphate with glyceraldehydes 3-phosphate in the presence of a transaldolase to yield erythrose 4-phosphate and fructose 6-phosphate.
(a) The first part of the reaction is the formation of a protonated Schiff base of sedoheptulose 7-phosphate with a lysine residue in the enzyme followed by a retro-aldol cleavage to give an enamine plus erythrose 4-phosphate. Show the structure of the enamine and the mechanism by which it is formed.
(b) The second part of the reaction is a nucleophilic addition of the enamine to glyceraldehyde 3-phosphate followed by hydrolysis of the Schiff base to give fructose 6-phosphate. Show the mechanism.
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In the glycolytic pathway, a six-carbon sugar (fructose 1,6-bisphosphate) is cleaved to form two three-carbon sugars, which undergo further metabolism . In this pathway, an isomerization of glucose 6-phosphate tofructose 6-phosphate (shown below) occurs two steps before the cleavage reaction (the intervening step is phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate ). What does the isomerization step accomplish from a chemical perspective? (Hint: Consider what might happen if the C—C bond cleavage were to proceed without the preceding isomerization.)
Pyruvate carboxylase is thought to activate CO2 by ATP, through formation of carboxyphosphate as an intermediate. Propose a mechanism for the formation of this intermediate.
One step in glycolysis is the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate. The direct reaction of fructose-6-phosphate with inorganic phosphate
fructose-6-phosphate + Pi ⇌ fructose-1,6-bisphosphate + H₂O
is very unfavorable, with ∆G'°= 16.3 kJ/mol and K'eq = 1.39×10⁻³. However, in glycolysis the reaction is coupled to ATP hydrolysis:
fructose-6-phosphate + ATP ⇌ fructose-1,6-phosphate + ADP
and the reaction if favorable.
What is the equilibrium [fructose-1,6-bisphosphate]/[fructose-6-phosphate] ratio in the coupled reaction when [ATP] = [ADP]? For ATP hydrolysis ∆G'°= -30.5 kJ/mol at 25°C.
Chapter 29 Solutions
Organic Chemistry
Ch. 29.1 - Prob. 1PCh. 29.3 - Write the equations for the remaining passages of...Ch. 29.3 - Prob. 3PCh. 29.4 - Write a mechanism for the dehydration reaction of...Ch. 29.4 - Evidence for the role of acetate in fatty-acid...Ch. 29.4 - Does the reduction of acetoacetyl ACP in step 6...Ch. 29.5 - Prob. 7PCh. 29.5 - Look at the entire glycolysis pathway, and make a...Ch. 29.6 - Prob. 9PCh. 29.7 - Prob. 10P
Ch. 29.7 - Write mechanisms for step 2 of the citric acid...Ch. 29.7 - Prob. 12PCh. 29.8 - Prob. 13PCh. 29.9 - Write all the steps in the transamination reaction...Ch. 29.9 - What -keto acid is formed on transamination of...Ch. 29.9 - Prob. 16PCh. 29.SE - Prob. 17VCCh. 29.SE - Identify the following intermediate in the citric...Ch. 29.SE - The following compound is an intermediate in the...Ch. 29.SE - Prob. 20VCCh. 29.SE - In the pentose phosphate pathway for degrading...Ch. 29.SE - Prob. 22MPCh. 29.SE - One of the steps in the pentose phosphate pathway...Ch. 29.SE - One of the steps in the pentose phosphate pathway...Ch. 29.SE - Prob. 25MPCh. 29.SE - Prob. 26MPCh. 29.SE - Prob. 27MPCh. 29.SE - Prob. 28MPCh. 29.SE - Prob. 29MPCh. 29.SE - Prob. 30MPCh. 29.SE - Prob. 31MPCh. 29.SE - Prob. 32APCh. 29.SE - Prob. 33APCh. 29.SE - Prob. 34APCh. 29.SE - Prob. 35APCh. 29.SE - Prob. 36APCh. 29.SE - Prob. 37APCh. 29.SE - Prob. 38APCh. 29.SE - Prob. 39APCh. 29.SE - Prob. 40APCh. 29.SE - Prob. 41APCh. 29.SE - Prob. 42APCh. 29.SE - Prob. 43APCh. 29.SE - Prob. 44APCh. 29.SE - Prob. 45APCh. 29.SE - Prob. 46APCh. 29.SE - Prob. 47APCh. 29.SE - Prob. 48APCh. 29.SE - Prob. 49APCh. 29.SE - Prob. 50APCh. 29.SE - In glycerol metabolism, the oxidation of...Ch. 29.SE - Prob. 52APCh. 29.SE - Prob. 53APCh. 29.SE - Prob. 54APCh. 29.SE - In step 7 of fatty-acid biosynthesis (Figure...Ch. 29.SE - Prob. 56AP
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