Biochemistry Flashcards

Which of the following best describes the role of ubiquitin in protein degradation?

Answer: Ubiquitin marks proteins for degradation by the 26S proteasome

Polyubiquitin chains attached to substrate proteins serve as a recognition signal for the 26S proteasome, which then unfolds and degrades the tagged protein.

Phenylketonuria (PKU) results from accumulation of phenylalanine due to deficiency of:

Answer: Phenylalanine hydroxylase

Phenylalanine hydroxylase converts phenylalanine to tyrosine; its deficiency causes phenylalanine accumulation and toxic metabolite formation, leading to intellectual disability.

The Bohr effect describes which phenomenon in hemoglobin physiology?

Answer: Decreased O₂ affinity at low pH

The Bohr effect states that increased H⁺ (lower pH) and CO₂ decrease hemoglobin's oxygen affinity, promoting O₂ release in metabolically active tissues.

Which step of fatty acid synthesis requires the direct input of CO₂ (as bicarbonate)?

Answer: Carboxylation of acetyl-CoA to malonyl-CoA

Acetyl-CoA carboxylase adds CO₂ to acetyl-CoA to form malonyl-CoA, the activated two-carbon donor for fatty acid chain elongation.

Which base is found in RNA but NOT in DNA?

Answer: Uracil

RNA contains uracil instead of thymine; uracil lacks the methyl group at position 5 that thymine possesses.

A patient with G6PD deficiency is at risk for hemolytic anemia because red blood cells cannot adequately:

Answer: Regenerate NADPH to maintain glutathione in reduced form

G6PD produces NADPH via the pentose phosphate pathway; without NADPH, glutathione cannot be reduced to protect RBCs from oxidative stress, causing hemolysis.

In DNA replication, which enzyme removes RNA primers and fills in the resulting gaps with DNA?

Answer: DNA polymerase I

In prokaryotes, DNA polymerase I has 5'→3' exonuclease activity to remove RNA primers and then fills in the gaps using its 5'→3' polymerase activity.