PCAT Biochemistry 5

Question 1

Which coenzyme is required for the transamination reactions that transfer amino groups from amino acids to alpha-keto acids?

Accepted Answer

Pyridoxal phosphate (PLP)

Answer

Pyridoxal phosphate (PLP), derived from vitamin B6, is the essential coenzyme for all aminotransferase (transaminase) reactions, shuttling amino groups via a Schiff base intermediate.

Question 2

What is the net ATP yield from complete aerobic oxidation of one glucose molecule (using the malate-aspartate shuttle)?

Accepted Answer

30-32 ATP

Answer

Modern estimates calculate approximately 30-32 ATP net from aerobic glucose oxidation, accounting for the actual P/O ratios of NADH (~2.5 ATP) and FADH2 (~1.5 ATP) rather than the older theoretical values.

Question 3

Which of the following is a characteristic of allosteric enzymes?

Accepted Answer

They show sigmoidal (S-shaped) velocity vs. substrate concentration curves

Answer

Allosteric enzymes display sigmoidal kinetics (positive cooperativity) rather than hyperbolic Michaelis-Menten kinetics, because binding of substrate at one subunit increases affinity at other subunits.

Question 4

Ceramide is the backbone of which class of sphingolipids?

Accepted Answer

Sphingomyelins and glycosphingolipids

Answer

Ceramide (sphingosine + fatty acid) is the hydrophobic core of all sphingolipids; addition of phosphocholine gives sphingomyelin, while addition of sugars gives glycosphingolipids (cerebrosides, gangliosides).

Question 5

During translation, which site on the ribosome holds the tRNA carrying the growing polypeptide chain?

Accepted Answer

P (peptidyl) site

Answer

The P (peptidyl) site holds the tRNA attached to the growing polypeptide chain; the incoming aminoacyl-tRNA enters the A site, and the uncharged tRNA exits through the E site.

PCAT - Pharmacy College Admission Test Practice Test

PCAT - Pharmacy College Admission Test Practice Test

PCAT Biochemistry 5