COMSAE PHASE 1 FORM 113
FOUNDATIONAL BIOMEDICAL
SCIENCES PRACTICE
EXAMINATION QUESTIONS WITH
CORRECT ANSWERS PLUS
RATIONALES 2026/2027 EDITION
WITH INSTANT PDF DOWNLOAD
1. A researcher is studying a cell that contains abundant rough
endoplasmic reticulum and prominent Golgi apparatus. Which
cellular function is most characteristic of this cell?
A. ATP production
B. Steroid synthesis
C. Protein secretion
D. Glycogen storage
Correct Answer: C. Protein secretion
Rationale: Cells specialized for protein secretion require
extensive rough endoplasmic reticulum for synthesis of secreted
proteins and a well-developed Golgi apparatus for modification,
sorting, and packaging. Mitochondria primarily produce ATP,
smooth endoplasmic reticulum is associated with steroid
synthesis, and glycogen storage occurs predominantly in liver and
skeletal muscle cells.
,2. Which mechanism is primarily responsible for maintaining the
resting membrane potential of most neurons?
A. Calcium influx through voltage-gated channels
B. Potassium leak through membrane channels
C. Sodium influx through ligand-gated channels
D. Chloride secretion through active transport
Correct Answer: B. Potassium leak through membrane
channels
Rationale: The resting membrane potential is strongly influenced
by the high permeability of the neuronal membrane to potassium
through potassium leak channels. Potassium tends to diffuse out
of the cell, leaving the intracellular environment relatively
negative. The sodium-potassium ATPase maintains the ion
gradients that support this potential.
3. A mutation prevents a lysosomal enzyme from being properly
targeted to lysosomes. Which cellular structure normally adds
the targeting signal required for lysosomal enzyme trafficking?
A. Nucleus
B. Golgi apparatus
C. Smooth endoplasmic reticulum
D. Peroxisome
Correct Answer: B. Golgi apparatus
Rationale: Lysosomal enzymes are synthesized in the rough
endoplasmic reticulum and receive mannose-6-phosphate
tagging in the Golgi apparatus. This modification allows them to
be recognized and transported to lysosomes. Defective targeting
can result in accumulation of undegraded material within cells.
,4. Which phase of the cell cycle is characterized by DNA
replication?
A. G1 phase
B. S phase
C. G2 phase
D. M phase
Correct Answer: B. S phase
Rationale: The S phase, or synthesis phase, is the portion of the
cell cycle during which DNA replication occurs. G1 is primarily
associated with cellular growth, G2 prepares the cell for mitosis,
and M phase includes mitosis and cytokinesis.
5. A patient has a mutation affecting DNA repair after exposure to
ultraviolet radiation. Which type of DNA damage is most directly
associated with ultraviolet radiation?
A. Pyrimidine dimers
B. Double-stranded RNA breaks
C. Ribosomal translocations
D. Abnormal peptide bonds
Correct Answer: A. Pyrimidine dimers
Rationale: Ultraviolet radiation can cause covalent bonds
between adjacent pyrimidine bases, particularly thymine
residues, forming pyrimidine dimers. These lesions distort DNA
structure and can interfere with replication and transcription if not
repaired.
, 6. Which enzyme is responsible for unwinding the DNA double
helix during DNA replication?
A. DNA ligase
B. DNA polymerase
C. Helicase
D. Primase
Correct Answer: C. Helicase
Rationale: Helicase separates the two DNA strands by disrupting
hydrogen bonds between complementary bases. DNA
polymerase synthesizes the new DNA strand, primase creates
RNA primers, and DNA ligase joins DNA fragments.
7. During translation, which molecule carries an amino acid to the
ribosome according to the sequence specified by messenger
RNA?
A. rRNA
B. tRNA
C. DNA
D. snRNA
Correct Answer: B. tRNA
Rationale: Transfer RNA carries specific amino acids to the
ribosome. Each tRNA contains an anticodon that pairs with a
complementary codon on messenger RNA, allowing amino acids
to be incorporated into the growing polypeptide chain.
8. A mutation changes a codon from coding for an amino acid to a
stop codon. What type of mutation has occurred?
FOUNDATIONAL BIOMEDICAL
SCIENCES PRACTICE
EXAMINATION QUESTIONS WITH
CORRECT ANSWERS PLUS
RATIONALES 2026/2027 EDITION
WITH INSTANT PDF DOWNLOAD
1. A researcher is studying a cell that contains abundant rough
endoplasmic reticulum and prominent Golgi apparatus. Which
cellular function is most characteristic of this cell?
A. ATP production
B. Steroid synthesis
C. Protein secretion
D. Glycogen storage
Correct Answer: C. Protein secretion
Rationale: Cells specialized for protein secretion require
extensive rough endoplasmic reticulum for synthesis of secreted
proteins and a well-developed Golgi apparatus for modification,
sorting, and packaging. Mitochondria primarily produce ATP,
smooth endoplasmic reticulum is associated with steroid
synthesis, and glycogen storage occurs predominantly in liver and
skeletal muscle cells.
,2. Which mechanism is primarily responsible for maintaining the
resting membrane potential of most neurons?
A. Calcium influx through voltage-gated channels
B. Potassium leak through membrane channels
C. Sodium influx through ligand-gated channels
D. Chloride secretion through active transport
Correct Answer: B. Potassium leak through membrane
channels
Rationale: The resting membrane potential is strongly influenced
by the high permeability of the neuronal membrane to potassium
through potassium leak channels. Potassium tends to diffuse out
of the cell, leaving the intracellular environment relatively
negative. The sodium-potassium ATPase maintains the ion
gradients that support this potential.
3. A mutation prevents a lysosomal enzyme from being properly
targeted to lysosomes. Which cellular structure normally adds
the targeting signal required for lysosomal enzyme trafficking?
A. Nucleus
B. Golgi apparatus
C. Smooth endoplasmic reticulum
D. Peroxisome
Correct Answer: B. Golgi apparatus
Rationale: Lysosomal enzymes are synthesized in the rough
endoplasmic reticulum and receive mannose-6-phosphate
tagging in the Golgi apparatus. This modification allows them to
be recognized and transported to lysosomes. Defective targeting
can result in accumulation of undegraded material within cells.
,4. Which phase of the cell cycle is characterized by DNA
replication?
A. G1 phase
B. S phase
C. G2 phase
D. M phase
Correct Answer: B. S phase
Rationale: The S phase, or synthesis phase, is the portion of the
cell cycle during which DNA replication occurs. G1 is primarily
associated with cellular growth, G2 prepares the cell for mitosis,
and M phase includes mitosis and cytokinesis.
5. A patient has a mutation affecting DNA repair after exposure to
ultraviolet radiation. Which type of DNA damage is most directly
associated with ultraviolet radiation?
A. Pyrimidine dimers
B. Double-stranded RNA breaks
C. Ribosomal translocations
D. Abnormal peptide bonds
Correct Answer: A. Pyrimidine dimers
Rationale: Ultraviolet radiation can cause covalent bonds
between adjacent pyrimidine bases, particularly thymine
residues, forming pyrimidine dimers. These lesions distort DNA
structure and can interfere with replication and transcription if not
repaired.
, 6. Which enzyme is responsible for unwinding the DNA double
helix during DNA replication?
A. DNA ligase
B. DNA polymerase
C. Helicase
D. Primase
Correct Answer: C. Helicase
Rationale: Helicase separates the two DNA strands by disrupting
hydrogen bonds between complementary bases. DNA
polymerase synthesizes the new DNA strand, primase creates
RNA primers, and DNA ligase joins DNA fragments.
7. During translation, which molecule carries an amino acid to the
ribosome according to the sequence specified by messenger
RNA?
A. rRNA
B. tRNA
C. DNA
D. snRNA
Correct Answer: B. tRNA
Rationale: Transfer RNA carries specific amino acids to the
ribosome. Each tRNA contains an anticodon that pairs with a
complementary codon on messenger RNA, allowing amino acids
to be incorporated into the growing polypeptide chain.
8. A mutation changes a codon from coding for an amino acid to a
stop codon. What type of mutation has occurred?
