Answer: C. Lysine

Explanation: Piperidine alkaloids are derived from lysine through a series of enzymatic reactions that convert the amino acid into the heterocyclic piperidine structure.

Answer: C. kidney

Explanation: The kidney is the principal site for the synthesis and secretion of renin. This enzyme initiates the renin-angiotensin system, playing a crucial role in blood pressure regulation.

Answer: C. Fibroblasts

Explanation: Fibroblasts are considered non-professional antigen-presenting cells because they can present antigens under certain conditions but are not as effective as professional APCs like dendritic cells, macrophages, and B cells.

Answer: C. Thrombin

Explanation: Thrombin is generated from its inactive precursor, prothrombin, making it a zymogen. Zymogens are inactive enzyme precursors that require activation for function.

Answer: D. p53

Explanation: p53 is a tumor suppressor protein that plays a critical role in triggering apoptosis in response to DNA damage or cellular stress, ensuring that damaged cells do not proliferate.

Answer: D. stereospecificity

Explanation: Fumarase shows stereospecificity by catalyzing the hydration of fumaric acid (trans-isomer) but not maleic acid (cis-isomer), due to the specific orientation required in its active site.

Answer: A. Sucrose

Explanation: Sucrose is a non-reducing sugar because its anomeric carbons are involved in the glycosidic bond, preventing it from acting as a reducing agent, unlike mannose, lactose, and fructose.

Answer: B. B

Explanation: In the structure of cholesterol, the only double bond is found in ring B. This unsaturation contributes to its fluidity and interaction with membrane lipids.

Answer: B. Arachidonic acid

Explanation: Series 1 eicosanoids are derived from DGLA, not arachidonic acid (series 2).

Answer: C. Ser-His-Asp

Explanation: Serine proteases share a catalytic triad of Serine, Histidine, and Aspartate. This arrangement is critical for their mechanism of hydrolyzing peptide bonds in proteins.

Answer: C. Ubiquitin

Explanation: Proteins destined for degradation in eukaryotic cells are tagged with ubiquitin, a small protein that directs them to the proteasome for controlled degradation, maintaining cellular protein quality.

Answer: A. Papillomavirus

Explanation: Human papillomavirus (HPV) is the primary viral agent involved in cervical cancer. Persistent infection with high-risk HPV types can lead to malignant transformation of cervical cells.

Answer: A. Plasmodium vivax

Explanation: Individuals lacking the Duffy antigen are naturally resistant to Plasmodium vivax infection because the parasite relies on this antigen for entry into red blood cells.

Answer: B. Glutamate

Explanation: Vitamin K catalyzes the carboxylation of glutamate residues in clotting factors, which is critical for their calcium-binding ability and subsequent activation in the coagulation cascade.

Answer: C. Calcitriol

Explanation: Calcitriol is the active form of vitamin D. It is produced from cholecalciferol through hydroxylation in the liver and kidney, and it regulates calcium and phosphate metabolism.

Answer: B. Helix-turn-helix

Explanation: Nuclear receptors use zinc finger motifs. Correct answer is D.

Answer: B. CCR5

Explanation: Individuals unable to produce a complete CCR5 protein on their cell surfaces resist HIV infection. The CCR5 receptor is crucial for HIV entry into T cells, and its absence confers natural resistance.

Answer: B. (A + G) / (T +

Explanation: According to Chargaff’s rules, the ratio of (A+G) to (T+C) is equal to 1 in double-stranded DNA. This reflects the complementary base pairing that maintains a consistent nucleotide ratio.

Answer: B. Ebola

Explanation: Ebola is a (-)ssRNA filovirus that has been in the news due to outbreaks causing severe hemorrhagic fever. It is highly contagious and often fatal, necessitating urgent public health responses.

Answer: D. All of the above

Explanation: Mitochondria contain their own DNA, ribosomes, and various enzymes. Together, these components allow mitochondria to synthesize proteins and generate energy through oxidative phosphorylation.