Which of the following statements is correct?

• Option A: RNA controls the synthesis of proteins.

  This statement is correct. One of the primary biological roles of RNA molecules (including mRNA, tRNA, and rRNA) is to direct and control the translation of genetic information into functional proteins within the ribosome.




• Option B: The sugar present in DNA is D-(-)-ribose.

  This statement is incorrect. The sugar backbone unit found in DNA is $$\text{D-2-deoxyribose}$$, while $$\text{D-ribose}$$ is the sugar component found exclusively in RNA.




• Option C: RNA has double stranded $$\alpha$$-helix structure.

  This statement is incorrect. RNA typically exists as a single-stranded molecule that can fold into complex tertiary shapes. It is DNA that typically forms the classic double-stranded helical structure.




• Option D: DNA mainly occurs in the cytoplasm of the cell.

  This statement is incorrect. In eukaryotic organisms, DNA is primarily localized and sequestered inside the nucleus of the cell (as well as small amounts in mitochondria and chloroplasts), not loose in the cytoplasm.

Conclusion:

Only statement A accurately describes the standard biological function and property of the nucleic acids.

Answer: Option A — RNA controls the synthesis of proteins.