Biochemistry Flashcards

Which protein secondary structure is stabilized by hydrogen bonds between residues distant in primary sequence?

Answer: Beta sheet

Beta sheets form hydrogen bonds between backbone atoms of strands that are far apart in the primary sequence, while alpha helices bond residues close together (i and i+4).

During the fed state, glucokinase activity in hepatocytes increases because:

Answer: It is released from a nuclear inhibitor protein

Glucokinase is sequestered in the nucleus by a regulatory protein at low glucose; when glucose rises, it dissociates and enters the cytoplasm to phosphorylate glucose.

Ceramide is the backbone molecule for which class of lipids?

Answer: Sphingolipids

Ceramide consists of sphingosine plus a fatty acid and is the core structure of all sphingolipids, including sphingomyelin and glycosphingolipids.

Which amino acid residue is most commonly found at the catalytic site of serine proteases?

Answer: Histidine-Aspartate-Serine triad

The catalytic triad of serine proteases consists of His, Asp, and Ser working together to activate the serine nucleophile.

In the pentose phosphate pathway, transketolase requires which cofactor?

Answer: Thiamine pyrophosphate (TPP)

Transketolase, which transfers two-carbon units in the non-oxidative phase of the pentose phosphate pathway, requires thiamine pyrophosphate (TPP) as a cofactor.

A mutation that converts a UAG stop codon to a sense codon is called a:

Answer: Suppressor mutation

A suppressor mutation (typically in a tRNA gene) can read through a stop codon, allowing translation to continue past the original termination point.

Which metabolic pathway is uniquely active in the absorptive state to convert excess glucose to fatty acids?

Answer: De novo lipogenesis

De novo lipogenesis converts excess acetyl-CoA (from glucose catabolism) into fatty acids during the absorptive state when insulin is high.