Problem 72 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

A nucleotide consists of : (a) phosphoric acid (b) nitrogen containing base (c) carbon sugar. (d) all of these

Step-by-Step Solution

Answer

(d) all of these

Step 1: Understand the Components of a Nucleotide

A nucleotide is a basic building block of nucleic acids like DNA and RNA. It consists of three main components: a phosphate group (phosphoric acid), a five-carbon sugar (either ribose or deoxyribose), and a nitrogenous base (which can be a purine or pyrimidine).

Step 2: Analyze the Given Options

Review each option provided to see if they match the components of a nucleotide. - (a) phosphoric acid: This corresponds to the phosphate group. - (b) nitrogen containing base: This corresponds to the nitrogenous base. - (c) carbon sugar: This corresponds to the five-carbon sugar. - (d) all of these: This option would include all the components necessary to form a nucleotide.

Step 3: Compare and Select the Correct Option

Since a nucleotide contains phosphoric acid, a nitrogen-containing base, and a five-carbon sugar, option (d) "all of these" is the correct choice. It accounts for all three essential components of a nucleotide.

Key Concepts

phosphate group

The phosphate group is one of the three essential parts of a nucleotide. It consists of a phosphorus atom bonded to four oxygen atoms. This group plays a significant role in forming the backbone of nucleic acids like DNA and RNA. By doing so, it connects one nucleotide to the next, creating a chain.

In addition to its structural function, the phosphate group also provides the nucleotide with a certain charge. This negative charge is crucial because it helps to stabilize the structures of DNA and RNA through interactions with water and metal ions in the body.

Understanding the role of the phosphate group helps us appreciate its importance in the overall shape and function of nucleic acids. It provides both stability and a means to link the nucleotide units together, playing a key role in the storage and transmission of genetic information.

nitrogenous base

A nitrogenous base is a molecule that contains nitrogen and is an integral part of nucleotides. These bases are the information-carrying section of the nucleic acids. There are two types of nitrogenous bases: purines and pyrimidines.

• Purines: These include adenine (A) and guanine (G), which have a double-ring structure.
• Pyrimidines: These include cytosine (C), thymine (T), which is found in DNA, and uracil (U), which is found in RNA, and these have a single-ring structure.

The sequence of these bases along the DNA or RNA strand encodes the genetic instructions for the development, functioning, and reproduction of all organisms.

One of the key characteristics of nitrogenous bases is their ability to form hydrogen bonds with complementary bases. This property is fundamental in the structure of double-stranded DNA, where adenine pairs with thymine and guanine pairs with cytosine.

five-carbon sugar

The five-carbon sugar in a nucleotide is specifically known as a pentose sugar. There are two main types of these sugars found in nucleic acids: ribose and deoxyribose.

• Ribose: This sugar is present in RNA. It has one more oxygen atom than deoxyribose.
• Deoxyribose: Found in DNA, it lacks one oxygen atom compared to ribose, hence the name 'deoxy'.

The sugar is crucial because it forms part of the nucleotide's backbone, linking the phosphate group and nitrogenous base. Its structure helps to determine the secondary and tertiary structures of DNA and RNA. The difference between ribose and deoxyribose also explains why DNA is more stable than RNA because the lack of an oxygen atom in deoxyribose makes DNA less reactive.

Understanding the role of five-carbon sugars in nucleotides helps highlight their function in providing structural support and ensuring the proper assembly and functioning of nucleic acids.