Biochemistry
6th Edition
ISBN: 9781305577206
Author: Reginald H. Garrett, Charles M. Grisham
Publisher: Cengage Learning
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Textbook Question
Chapter 27, Problem 20P
Figure 27.3 illustrates the response of R (ATP-regenerating) and U (ATP-utilizing) enzymes to energy charge.
a. Would hexokinase be an R enzyme or a U enzyme? Would glutamine: PRPP amidotransferase, the second enzyme in purine biosynthesis, be an R enzyme or a U enzyme?
b. If energy charge = 0.5: Is the activity of hexokinase high or low? Is ribose-5-P pyrophosphokinase activity high or low?
c. If energy charge = 0.95: Is the activity of hexokinase high or low? Is ribose-5-P pyrophosphokinase activity high or low?
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When ATP and xylose are added to hexokinase, the enzyme produces a small amount of xylose-5-phosphate along with a large amount of ADP. How does this observation support the induced fit model?
A sequence of amino acids found in a subunit of the ATP synthase enzyme in several species is shown below. Which amino acids are likely to be most important to the function of ATP synthase?
Which of the following statements about de novo purine synthesis is true?
(A) Purine nucleotides are formed by separately synthesizing the phosphorylated ribose and the purine ring and then joining them together.(B) GMP is formed first and is used as a precursor to form AMP.(C) The synthesis of AMP from inosinate is driven forward by ATP hydrolysis.
(D) GMP synthetase uses NADPH and glutamine to modify the inosinate ring to form GMP.(E) Replacement of the C-1 PPi on PRPP with an amine is required to construct the purine ring on the ribose sugar.
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