Question

Nucleic acids are the polymers of (A) Nucleosides (B) Nucleotides (C) Bases (D) Sugars

Short answer

Nucleic acids are polymers composed of monomer units called nucleotides. Therefore, the correct answer is (B) Nucleotides.

Step-by-step solution

Understand the structure of nucleic acids

Nucleic acids, such as DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), are long chains of molecules called nucleotides.

Definition of key terms

- Nucleosides: A nucleoside consists of a nitrogenous base (adenine, guanine, cytosine, or thymine in DNA; and adenine, guanine, cytosine, or uracil in RNA) bonded to a sugar molecule (deoxyribose in DNA and ribose in RNA). - Nucleotides: A nucleotide is made of a nucleoside attached to one or more phosphate groups. - Bases: Nitrogenous bases are the parts of nucleic acids that participate in hydrogen bonding between complementary bases. These are adenine, guanine, cytosine, thymine (in DNA), and uracil (in RNA). - Sugars: The sugar molecules in nucleic acids are either deoxyribose (in DNA) or ribose (in RNA). They link to the nitrogenous base to form a nucleoside.

Identify the building block of nucleic acids

Nucleotide is the correct building block (monomer) that forms nucleic acids (polymers). So, the correct answer is: (B) Nucleotides

Key concepts

Nucleotides

Nucleotides are the foundational building blocks of nucleic acids, such as DNA and RNA. Think of them as the individual links in a long chain that forms the complex structures of our genetic material. Each nucleotide consists of three main components:

• A nitrogenous base: This could be adenine (A), guanine (G), cytosine (C), or thymine (T) in DNA; and in RNA, thymine (T) is substituted by uracil (U).
• A sugar: Specifically, deoxyribose in DNA and ribose in RNA, which helps differentiate these types of nucleic acids.
• One or more phosphate groups: These provide the energy necessary for nucleic acids to perform essential biological functions.

The phosphate groups not only energize the molecules but also enable nucleotides to link together into long strands through phosphodiester bonds, establishing the sugar-phosphate backbone vital for DNA's double-helix structure. This backbone is crucial in storing genetic information, leading to life's complexity.

Nucleosides

Nucleosides look quite similar to nucleotides but have one key difference: they do not have the phosphate group. A nucleoside is simply a combination of a nitrogenous base and a sugar molecule. These can be thought of as the backbone elements without the means to join together into longer chains.

• Nitrogenous base: Like in nucleotides, these are adenine, guanine, cytosine, and thymine in DNA; with uracil replacing thymine in RNA.
• Sugar: The sugar is either ribose (in RNA) or deoxyribose (in DNA), linking to the nitrogenous base.

Nucleosides play a crucial role as intermediates in the synthesis of nucleotides. Because they lack phosphate groups, nucleosides alone cannot form nucleic acids directly. However, once phosphate groups are added, they convert into nucleotides, becoming ready to construct the nucleic acid chains that are critical to biological processes.

Nitrogenous Bases

Nitrogenous bases are essential components of both nucleotides and nucleosides, acting as the pillars for nucleic acids' functionality and coding abilities. There are five key nitrogenous bases: adenine, guanine, cytosine, thymine (in DNA), and uracil (in RNA). These bases fall into two categories:

• Pyrimidines: Cytosine, thymine, and uracil are characterized by a single-ring structure.
• Purines: Adenine and guanine, noted for their two-ring structure.

In nucleic acids, these bases engage in specific base pairing through hydrogen bonds. In DNA, adenine pairs with thymine, and guanine pairs with cytosine, ensuring complementary strands. In RNA, adenine pairs with uracil instead. These specific pairings are critical for the accurate replication of genetic material during cell division and the transcription processes necessary for protein synthesis.