Biochemistry Flashcards
7 cards from real PCAT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Biochemistry flashcards as text
Which coenzyme is required for the transamination reactions that transfer amino groups from amino acids to alpha-keto acids?
Answer: Pyridoxal phosphate (PLP)
Pyridoxal phosphate (PLP), derived from vitamin B6, is the essential coenzyme for all aminotransferase (transaminase) reactions, shuttling amino groups via a Schiff base intermediate.
What is the net ATP yield from complete aerobic oxidation of one glucose molecule (using the malate-aspartate shuttle)?
Answer: 30-32 ATP
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.
Which of the following is a characteristic of allosteric enzymes?
Answer: They show sigmoidal (S-shaped) velocity vs. substrate concentration curves
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.
Ceramide is the backbone of which class of sphingolipids?
Answer: Sphingomyelins and glycosphingolipids
Ceramide (sphingosine + fatty acid) is the hydrophobic core of all sphingolipids; addition of phosphocholine gives sphingomyelin, while addition of sugars gives glycosphingolipids (cerebrosides, gangliosides).
During translation, which site on the ribosome holds the tRNA carrying the growing polypeptide chain?
Answer: P (peptidyl) site
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.
Which enzyme deficiency is responsible for Phenylketonuria (PKU)?
Answer: Phenylalanine hydroxylase
PKU results from a deficiency in phenylalanine hydroxylase (PAH), which normally converts phenylalanine to tyrosine, causing toxic accumulation of phenylalanine and its metabolites.
Which process is described as the movement of acetyl groups from the mitochondria to the cytoplasm for fatty acid synthesis?
Answer: The citrate shuttle
Acetyl-CoA cannot cross the inner mitochondrial membrane directly; it condenses with oxaloacetate to form citrate, which is exported and then cleaved by ATP-citrate lyase in the cytoplasm to release acetyl-CoA for fatty acid synthesis.