$$\text{Xylulose-5-phosphate} + \text{Ribose-5-phosphate} \rightarrow \text{Glyceraldehyde-3-phosphate} + \text{Sedoheptulose-7-phosphate}$$

C-1 (from \text{glucose-6-phosphate})

$$\text{Sedoheptulose-7-phosphate} + \text{Glyceraldehyde-3-phosphate} \rightarrow \text{Erythrose-4-phosphate} + \text{Fructose-6-phosphate}$$

Question 1

Transketolases transfer parts of sugar molecules to other sugar molecules. The transferred segment is composed of how many carbons?

Accepted Answer

2 carbons

Question 2

Transaldolases transfer parts of sugar molecules to other sugar molecules. The transferred segment is composed of how many carbons?

Accepted Answer

3 carbons

Question 3

Which of the following statements about the Pentose Phosphate Pathway is correct?

Accepted Answer

It is a major source of NADPH for biosynthetic reactions

Question 4

Which of the following is a substrate in the Pentose Phosphate Pathway?

Accepted Answer

ribulose-5-phosphate

Question 5

Which of the following acts as a product in the Pentose Phosphate Pathway?

Accepted Answer

ribose-5-phosphate

Question 6

During the oxidative phase of the Pentose Phosphate Pathway, which molecule is directly responsible for the production of NADPH?

Accepted Answer

glucose-6-phosphate

Question 7

If a cell requires more ribose-5-phosphate than NADPH, which phase of the Pentose Phosphate Pathway will be most active?

Accepted Answer

Oxidative phase

Question 8

Which enzyme catalyzes the conversion of glucose-6-phosphate to 6-phosphogluconolactone in the Pentose Phosphate Pathway?

Accepted Answer

Glucose-6-phosphate dehydrogenase

Question 9

A deficiency in glucose-6-phosphate dehydrogenase can lead to which clinical condition due to impaired NADPH production?

Accepted Answer

Hemolytic anemia

Question 10

Which of the following reactions in the Pentose Phosphate Pathway involves the transfer of a two-carbon unit?

Accepted Answer

$$	ext{Xylulose-5-phosphate} + 	ext{Ribose-5-phosphate} ightarrow 	ext{Glyceraldehyde-3-phosphate} + 	ext{Sedoheptulose-7-phosphate}$$

Question 11

Which carbon atom from glucose is lost as CO$$_2$$ during the oxidative phase of the Pentose Phosphate Pathway?

Accepted Answer

C-1 (from 	ext{glucose-6-phosphate})

Question 12

Which of the following is NOT a function of the Pentose Phosphate Pathway?

Accepted Answer

Generation of ATP

Question 13

Which molecule is a direct precursor for nucleotide synthesis produced by the Pentose Phosphate Pathway?

Accepted Answer

Ribose-5-phosphate

Question 14

Which enzyme in the Pentose Phosphate Pathway is regulated by the cellular ratio of NADP$$^+/$$NADPH?

Accepted Answer

Glucose-6-phosphate dehydrogenase

Question 15

A patient with a deficiency in transketolase activity would have difficulty converting which of the following?

Accepted Answer

Ribose-5-phosphate to fructose-6-phosphate

Question 16

Which of the following best describes the overall purpose of the Pentose Phosphate Pathway in red blood cells?

Accepted Answer

To produce NADPH for antioxidant defense

Question 17

Which of the following is a key difference between the oxidative and non-oxidative phases of the Pentose Phosphate Pathway?

Accepted Answer

The oxidative phase produces NADPH, while the non-oxidative phase does not.

Question 18

Which of the following reactions is catalyzed by transaldolase in the Pentose Phosphate Pathway?

Accepted Answer

$$	ext{Sedoheptulose-7-phosphate} + 	ext{Glyceraldehyde-3-phosphate} ightarrow 	ext{Erythrose-4-phosphate} + 	ext{Fructose-6-phosphate}$$

Question 19

Which of the following is a consequence of impaired NADPH production in the Pentose Phosphate Pathway?

Accepted Answer

Increased susceptibility to oxidative stress

Question 20

Which of the following best describes the carbon rearrangement catalyzed by transketolase?

Accepted Answer

Transfer of a two-carbon unit from xylulose-5-phosphate to ribose-5-phosphate

Pentose Phosphate Pathway: Practice Questions and Key Concepts

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