Problem 77 - General Chemistry: Principles and Modern Applications

Question

Of the following, the one that is not a constituent of a nucleic acid chain is (a) purine base; (b) phosphate group; (c) glycerol; (d) pentose sugar; (e) pyrimidine base.

Step-by-Step Solution

Answer

The constituent that is not part of a nucleic acid chain is (c) glycerol.

Step 1: Identify the components of a nucleic acid

A nucleic acid is composed of a phosphate group, a sugar (either ribose in the case of RNA or deoxyribose in the case of DNA) and a nitrogenous base.

Step 2: Match the components with given options

Let's try and match these to the given options.\n 1. A phosphate group: this is a component of a nucleic acid. \n 2. A purine base: this is a type of nitrogenous base and part of a nucleic acid. \n 3. A pyrimidine base: this is another type of nitrogenous base and part of a nucleic acid. \n 4. A pentose sugar: this is also part of a nucleic acid, with different molecules being part of DNA (deoxyribose) or RNA (ribose).

Step 3: Identify the option not found in nucleic acids

With the remaining option of glycerol, it can be identified that it is not part of a nucleic acid. Glycerol is a component of lipids (fats, oils, waxes, etc.), not nucleic acids.

Key Concepts

Nucleic Acid Components

Nucleic acids are essential biological macromolecules present in all living cells. They play a vital role in storing and transmitting genetic information. The primary components of nucleic acids are:

• Phosphate group
• Pentose sugar
• Nitrogenous bases

These components combine to form the basic building blocks of nucleic acids, known as nucleotides. Each nucleotide is composed of one phosphate group, one pentose sugar, and one nitrogenous base.
This structure forms the backbone of nucleic acid chains, such as DNA and RNA.

The sequence of nucleotides in DNA and RNA determines the genetic information carried by an organism. Understanding these components and their arrangement is key to grasping how genetic data is stored and utilized within living entities.

Nitrogenous Bases

Nitrogenous bases are organic molecules that serve as the "letters" of the genetic language. They come in two families: purines and pyrimidines.

• Purines include adenine (A) and guanine (G).
• Pyrimidines include cytosine (C), thymine (T), and uracil (U).

In DNA, the nitrogenous bases are adenine, guanine, cytosine, and thymine.
In RNA, thymine is replaced by uracil.

These bases pair specifically with each other through hydrogen bonds:

• A pairs with T (or U in RNA)
• C pairs with G

This specificity is known as complementary base pairing. It is essential for the replication and transcription processes of genetic information. Changes in the sequence of these bases can lead to mutations, making the structure of these bases crucial to understand and study.

Phosphate Group

The phosphate group is a critical component of nucleotides, forming part of the backbone of DNA and RNA. It consists of a phosphorus atom bonded to four oxygen atoms, of which at least one is bonded to the pentose sugar.
Phosphate groups play a dual role in nucleic acids:

• They provide the negative charge that allows nucleic acids to interact with proteins and other molecules.
• They form phosphodiester bonds between the 3' carbon of one sugar molecule and the 5' carbon of another, creating a chain.

This phosphodiester linkage is strong and resistant to enzymatic attack, giving nucleic acids their stability and preventing structural breakdown.
Without phosphate groups, the structure of DNA and RNA would not have the necessary stability or flexibility required for proper cellular function and replication.

Pentose Sugar

The pentose sugar is one of the key components of nucleic acids, distinguishing DNA from RNA.
Two critical types of pentose sugars are:

• Deoxyribose, found in DNA.
• Ribose, found in RNA.

The main difference between these sugars is that deoxyribose lacks one oxygen atom compared to ribose.
This small structural variation greatly influences the characteristics and functions of DNA and RNA.

Pentose sugars connect to the phosphate group at one end and to a nitrogenous base at the other, forming part of the nucleotide's backbone.
This allows DNA and RNA to form long chains, carrying genetic information vital for all processes in living organisms. The sugars' arrangement provides a structural platform that supports the double helix formation in DNA and the single-stranded form common in RNA.