Final answer:
RNA bases are attached to ribose sugar at the 1' carbon position, and the growing RNA chain is formed by the addition of nucleotides at the 3' hydroxyl group, making the correct answer (c) 5.
Step-by-step explanation:
You asked about the addition of RNA bases to the ribose sugar in an RNA nucleotide. The RNA bases are added to the ribose sugar at the 1' carbon position. This is based on the numbering of the carbon atoms in the pentose sugar molecule, which are numbered as 1', 2', 3', 4', and 5'.
The nitrogenous base is always attached to the 1' carbon of the sugar, whether it is ribose in RNA or deoxyribose in DNA. For the backbone of the RNA strand to form, the 5' phosphate of an incoming RNA nucleotide attaches to the 3' hydroxyl group of the last nucleotide in the growing RNA chain, creating what is known as a phosphodiester linkage. Hence, the correct answer to your question is (c) 5.