(Biological and Biochemical) Flashcards

Which process allows a single gene to produce multiple protein isoforms from the same pre-mRNA?

Answer: Alternative splicing

Alternative splicing allows different combinations of exons to be included or excluded, producing multiple distinct mRNA and protein isoforms from a single gene.

A patient lacks C3 complement protein. Which immune function is most directly impaired?

Answer: Opsonization and phagocytosis

C3b, derived from C3 cleavage, is a major opsonin that coats pathogens and enhances phagocytosis; C3 deficiency severely impairs this innate defense.

Which neurotransmitter is primarily responsible for the 'fight-or-flight' response at the adrenal medulla?

Answer: Acetylcholine

The adrenal medulla is innervated by preganglionic sympathetic fibers that release acetylcholine, which stimulates chromaffin cells to secrete epinephrine and norepinephrine.

Which event occurs during the S phase of the cell cycle?

Answer: DNA replication

During the S (synthesis) phase of interphase, the entire genome is replicated so that each chromosome consists of two identical sister chromatids.

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

Answer: Serine

Serine proteases (e.g., trypsin, chymotrypsin) use a catalytic triad of Ser-His-Asp, but serine is the nucleophile that attacks the peptide bond.

What is the net ATP yield from complete oxidation of one molecule of glucose via aerobic respiration (standard estimate)?

Answer: 30-32 ATP

The modern accepted estimate is 30-32 ATP per glucose under physiological conditions, accounting for the P/O ratios of ~2.5 for NADH and ~1.5 for FADH2.

Which DNA repair mechanism corrects thymine dimers caused by UV radiation?

Answer: Nucleotide excision repair

Nucleotide excision repair (NER) removes bulky lesions like UV-induced thymine dimers by excising a ~12-24 nucleotide oligonucleotide containing the lesion.