Question

RNA contains (a) ribose sugar and thymine (b) ribose sugar and uracil (c) deoxyribose sugar and uracil (d) deoxyribose sugar and thymine

Short answer

(b) ribose sugar and uracil

Step-by-step solution

Understanding RNA Composition

RNA, or ribonucleic acid, is a molecule essential for various biological roles in coding, decoding, regulation, and expression of genes. It differs from DNA mainly in two respects: the sugar in its nucleotides and one of the nitrogenous bases it contains.

Identifying the Sugar in RNA

RNA contains ribose sugar in its backbone. Ribose is a five-carbon sugar with an additional hydroxyl group compared to deoxyribose, which helps distinguish RNA from DNA biochemically and functionally.

Identifying the Nitrogenous Base Unique to RNA

While DNA contains the nitrogenous bases adenine, thymine, cytosine, and guanine, RNA replaces thymine with uracil. Therefore, RNA contains adenine, uracil, cytosine, and guanine as its nitrogenous bases.

Conclusion Based on the Observations

Knowing that RNA contains ribose sugar and uracil as its distinct components, we conclude that the correct components of RNA from the given options are ribose sugar and uracil.

Key concepts

Ribose Sugar

Ribose sugar is a fundamental component of RNA (ribonucleic acid) and plays a crucial role in distinguishing RNA from DNA. It is a five-carbon sugar which is integral to RNA's structure:

• Ribose sugar has a chemical formula of C\(_5\)H\(_{10}\)O\(_5\).
• One of the most important features of ribose is the presence of an additional hydroxyl (OH) group compared to deoxyribose, which is found in DNA.
• This extra OH group is situated on the 2' carbon of the ribose.

This additional hydroxyl group not only gives RNA its characteristic flexibility and reactivity but also contributes to its unique functions in the cell. The presence of ribose sugar instead of deoxyribose allows RNA to engage in various biochemical roles such as coding, decoding, and gene regulation. This difference in sugar structure means that RNA is more chemically reactive than DNA, making ribose a critical component in its architectural and functional differences.

Uracil

Uracil is a nitrogenous base specific to RNA, which pairs with adenine during the formation of the RNA strand. Understanding uracil's role in RNA is key to appreciating its molecular structure:

• Uracil is one of the four primary bases in RNA – the others being adenine, cytosine, and guanine.
• Unlike DNA, which uses thymine, RNA utilizes uracil.
• Uracil pairs with adenine during transcription, a process influenced by hydrogen bonding.

The use of uracil instead of thymine allows RNA to perform its roles with greater efficiency in certain cellular processes. Uracil's simple structure enhances the inherent versatility of RNA molecules, helping them to fold into complex 3D shapes necessary for functions such as enzyme-like activities and interactions with proteins. Moreover, uracil’s presence makes RNA more susceptible to hydrolysis, contributing to its transient nature and rapid turnover in the cell.

Nucleotide Composition

The nucleotide composition of RNA is essential to its function and includes a sequence of nucleotides composed of a ribose sugar, phosphate group, and a nitrogenous base. These bases are adenine, uracil, cytosine, and guanine, differing slightly from DNA's base composition:

• Each RNA nucleotide consists of the ribose sugar, to which a phosphate group and a nitrogenous base are attached.
• The replacement of thymine with uracil is a distinguishing feature of RNA when comparing its nucleotide composition to DNA.
• These four bases pair complementary during synthesis: adenine with uracil and cytosine with guanine.

RNA nucleotides link together using the ribose sugars and phosphate backbone, forming single-stranded molecules crucial for protein synthesis and gene expression regulation. This single-stranded nature allows RNA to fold into various structures so that it can participate in a wide range of cellular processes. Understanding RNA nucleotide composition not only highlights its structural uniqueness but also underscores its dynamic role in cell biology.