MCAT Biology 4

Question 1

Which of the following structures is responsible for ribosome biogenesis in eukaryotic cells?

Accepted Answer

Nucleolus

Answer

The nucleolus is the site within the nucleus where rRNA genes are transcribed and ribosomal subunits are assembled before being exported to the cytoplasm.

Question 2

A patient has a genetic defect causing dysfunction of cilia in airway epithelial cells. Which cellular process is most likely impaired?

Accepted Answer

Mucociliary clearance of debris

Answer

Ciliary movement in airway epithelium drives mucociliary clearance, propelling mucus and trapped particles toward the throat for removal.

Question 3

In Mendelian genetics, two heterozygous parents (Aa × Aa) produce offspring. What fraction of offspring would display the recessive phenotype?

Accepted Answer

1/4

Answer

A monohybrid cross of Aa × Aa yields a 3:1 phenotypic ratio (3 dominant: 1 recessive), so 1/4 of offspring display the recessive phenotype (aa).

Question 4

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

Accepted Answer

It tags proteins for recognition and degradation by the proteasome

Answer

Ubiquitin is covalently attached to lysine residues of target proteins, marking them for recognition by the 26S proteasome for degradation.

Question 5

A researcher crosses true-breeding red flowers with true-breeding white flowers and obtains all pink flowers in F1. This result is best explained by:

Accepted Answer

Incomplete dominance

Answer

Incomplete dominance produces a blended intermediate phenotype (pink) in heterozygotes because neither allele is fully dominant over the other.

MCAT - Medical College Admission Test Practice Test

MCAT - Medical College Admission Test Practice Test

MCAT Biology 4