Biochemistry - Pentose Phosphate Pathway & Urea Cycle - MCAT Practice Questions

What is the starting material for the Pentose Phosphate Pathway (PPP)?

A. Glucose
B. Fructose 6-phosphate
C. Glucose 6-phosphate
D. Pyruvate

What are the two main products of the Pentose Phosphate Pathway?

A. NADPH and pentose sugars
B. NADH and ATP
C. FADH₂ and glucose
D. CO₂ and water

NADPH produced by the PPP is primarily used for which of the following processes?

A. ATP synthesis only
B. Protein synthesis only
C. Glycogen synthesis only
D. Fatty acid synthesis, steroid synthesis, and antioxidant defense

What type of sugar is ribose 5-phosphate?

A. Hexose sugar (6-carbon sugar)
B. Pentose sugar (5-carbon sugar)
C. Tetrose sugar (4-carbon sugar)
D. Triose sugar (3-carbon sugar)

Ribose 5-phosphate is essential for the synthesis of which biomolecules?

A. Fatty acids and steroids
B. Proteins and amino acids
C. Nucleotides (DNA, RNA) and coenzymes
D. Carbohydrates and lipids

What is the primary function of the Urea Cycle?

A. Convert toxic ammonia to less toxic urea
B. Synthesize amino acids from glucose
C. Break down fatty acids for energy
D. Produce ATP from ADP

Where does the Urea Cycle take place?

A. Only in the cytosol
B. Cytosol and mitochondrial matrix of the liver
C. Only in the mitochondrial matrix
D. Endoplasmic reticulum

Ammonia that enters the Urea Cycle is primarily a byproduct of which metabolic process?

A. Fatty acid metabolism
B. Carbohydrate metabolism
C. Amino acid metabolism
D. Nucleotide metabolism

The Urea Cycle is metabolically connected to the citric acid cycle through which two compounds?

A. Acetyl-CoA and pyruvate
B. Citrate and isocitrate
C. Succinate and malate
D. Oxaloacetate and fumarate

How does the PPP convert NADP⁺ to NADPH for use in anabolic pathways?

A. By directly phosphorylating NADP⁺
B. Through oxidation-reduction reactions during glucose 6-phosphate metabolism
C. By transferring electrons from ATP
D. Through hydrolysis of glucose