Question

An RNA nucleotide differs from a DNA molecule in that RNA has a. ribose sugar. b. phosphate molecule. c. uracil base. d. Both a and c are correct.

Short answer

The correct answer is (d) Both a and c are correct, as RNA nucleotides have a ribose sugar and a uracil base, unlike DNA molecules.

Step-by-step solution

Identify the sugars found in RNA and DNA

In this step, we should identify the sugars found in the nucleotides of both RNA and DNA molecules. RNA contains ribose sugar, while DNA consists of deoxyribose sugar. So, option (a) ribose sugar is a correct answer.

Identify the bases present in RNA and DNA nucleotides

Now, we need to recognize the bases used in both RNA and DNA. Both RNA and DNA have adenine (A), guanine (G), and cytosine (C). However, RNA contains uracil (U) instead of thymine (T) found in DNA. Therefore, option (c) uracil base is also a correct answer.

Conclusion

Since both ribose sugar (option a) and uracil base (option c) are correct differences between RNA and DNA, the best answer is option (d) Both a and c are correct.

Key concepts

Nucleotides

At the heart of both RNA and DNA lies a structure called a nucleotide. Nucleotides act as the basic building blocks of these vital molecules. Imagine them as individual links on a charm bracelet, with each link representing a nucleotide. A nucleotide is composed of three parts: a sugar molecule, a phosphate group, and a nitrogenous base.

In DNA, the nucleotides come together to form a double helix structure, creating a sturdy and stable blueprint for genetic information. RNA's nucleotides, on the other hand, typically create single-stranded formations, which are more versatile for different tasks in the cell, such as conveying genetic messages or catalyzing biochemical reactions. The specific sequence of nucleotides encodes genetic instructions that are essential for cellular functions and the growth and development of organisms.

Ribose Sugar

The 'backbone' of RNA and DNA is partly made up from sugar molecules, but not just any sugar – each has its own distinctive type. DNA contains deoxyribose sugar, which is ribose sugar with one oxygen atom less, hence the prefix 'deoxy-'. This subtle difference significantly affects the molecule's stability and structure.

RNA's ribose sugar has a hydroxyl group (-OH) attached at the 2' position of the sugar ring, which isn't present in DNA's deoxyribose. This makes RNA more reactive and less stable than DNA, but it also allows RNA to take on a variety of shapes and functions that DNA cannot, facilitating RNA's roles in the cell, from genetic messengers to catalysts and regulators.

Uracil Base

In the alphabet of genetics, nitrogenous bases serve as the letters. While both RNA and DNA use the bases adenine, cytosine, and guanine, they diverge when it comes to the fourth base. RNA uses uracil in place of thymine, which pairs with adenine.

Uracil is a small-sized pyrimidine base, visually similar to thymine but without the methyl group at the 5' position that thymine has. This change from thymine to uracil in RNA influences the overall shape and function of the molecule. Uracil base's presence is critical for RNA's involvement in protein synthesis and gene expression, as it pairs up with adenine during the process of transcribing DNA into RNA.

Genetic Material

When we refer to genetic material, we're talking about the molecules that carry the biological instructions from generation to generation – DNA and RNA. DNA is well-known for its role in storing and transmitting genetic information, ensuring stability and continuity. It sits mostly in the cell nucleus and governs the long-term storage of genetic data.

RNA, however, is more of a multitasker, directly involved in the synthesis of proteins based on the instructions from DNA. Not only does it act as a messenger, but it can also be an enzyme or part of the cellular structure. Its diverse forms include messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA), each performing unique and crucial roles in the cell. This versatility of RNA complements the more archival role of DNA, thus sustaining the dynamic processes of life.