Answer: D. All of the above

Explanation: p53 functions as a transcription factor, acts as a tumor suppressor, and contains proline-rich domains, playing a multifaceted role in cell cycle regulation and apoptosis.

Answer: A. Glutamine

Explanation: Glutamine contains an amide group with nonbasic nitrogen in its side chain, unlike histidine or lysine which contain basic groups.

Answer: B. Tau

Explanation: Tau protein is closely associated with Alzheimer’s disease; its abnormal aggregation in the brain is a hallmark of the disease’s pathology.

Answer: C. IgG

Explanation: IgG is the predominant immunoglobulin in human serum, making up approximately 80% of the total immunoglobulin pool and playing a crucial role in systemic immunity.

Answer: A. Strep. pneumoniae

Explanation: Streptococcus pneumoniae is generally not able to survive inside phagocytes, unlike Mycobacterium tuberculosis, Yersinia, and Salmonella, which have developed mechanisms to resist intracellular killing.

Answer: D. Sucrose

Explanation: Sucrose is a non-reducing sugar because its anomeric carbons are involved in glycosidic linkage; thus, it does not give a positive Benedict's test or form osazone.

Answer: D. W

Explanation: Among the given options, tryptophan (W) is structurally and chemically distinct compared to the basic amino acids H, R, and K.

Answer: B. 0.02

Explanation: Only about 2% of the human genome consists of protein-coding sequences, with the remainder being non-coding DNA.

Answer: B. Gyrase requires ATP for its catalysis.

Explanation: Gyrase uniquely uses ATP to introduce negative supercoils into DNA; this energy dependence distinguishes it from other topoisomerases and is critical for bacterial DNA replication.

Answer: C. 61 codons

Explanation: Although there are 64 codons in the genetic code, three of them are stop signals; therefore, only 61 codons specify the 20 standard amino acids used in protein synthesis.

Answer: C. Enolase

Explanation: Fluoride inhibits enolase in the glycolytic pathway, thereby preventing glycolysis in blood samples and ensuring accurate glucose measurements.

Answer: D. All deactivating groups are electron-withdrawing groups.

Explanation: Not every deactivating group is purely electron-withdrawing; some may have additional effects, so the blanket statement is incorrect.

Answer: C. Type III

Explanation: The Arthus reaction is a local type III hypersensitivity reaction caused by immune complex deposition, leading to inflammation at the injection site.

Answer: B. Propionyl-CoA

Explanation: Odd-chain fatty acids undergo beta-oxidation yielding propionyl-CoA as the final product, which is then converted to succinyl-CoA and enters the TCA cycle.

Answer: B. Thromboxane A

Explanation: Thromboxane A₂ is a potent eicosanoid that activates platelets and causes vasoconstriction, playing a crucial role in hemostasis and thrombosis.

Answer: A. regenerating methionine from homocysteine using methyl-THF

Explanation: Vitamin B12 (cobalamin) is essential for the remethylation of homocysteine to methionine using methyl-tetrahydrofolate. This reaction is vital for maintaining adequate methylation reactions and amino acid metabolism.

Answer: D. diacylglycerol

Explanation: Diacylglycerol (DAG) remains in the plasma membrane where it activates protein kinase C, whereas other second messengers like cAMP, IP₃, and Ca²⁺ diffuse into the cytosol.

Answer: A. -GlcNAc β1,4 GlcNAc-

Explanation: Chitin is a natural polymer composed of N-acetylglucosamine (GlcNAc) units linked by β1,4 glycosidic bonds. It is a key component of fungal cell walls and exoskeletons of arthropods.

Answer: A. Isoleucine

Explanation: Isoleucine has two chiral centers, making it optically active in multiple configurations. The other amino acids listed either have one or are achiral.

Answer: C. Biotin

Explanation: Biotin is not part of the electron transport chain. Instead, nicotinamide (in NADH), ubiquinone, and riboflavin (in FADH2) are key components involved in cellular respiration.