Problem 80 - Chemistry The Central Science In Si Units

Question

Which statement best explains the chemical differences between DNA and RNA? (a) DNA has two different sugars in its sugar-phosphate backbone, but RNA only has one. (b) Thymine is one of the DNA bases, whereas RNA's corresponding base is thymine minus a methyl group. \((\mathbf{c})\) The RNA sugar-phosphate backbone contains fewer oxygen atoms than DNA's backbone. (d) DNA forms double helices but RNA cannot.

Step-by-Step Solution

Answer

Statement (b) is correct; RNA uses uracil, which is thymine minus a methyl group.

Step 1: Understanding the Basics

DNA and RNA are both nucleic acids that play crucial roles in genetics. DNA (deoxyribonucleic acid) stores genetic information, while RNA (ribonucleic acid) acts as a messenger and is involved in protein synthesis. They have different structures and chemical compositions.

Step 2: Differences in Sugar Composition

DNA contains the sugar deoxyribose, while RNA contains the sugar ribose. Deoxyribose lacks one oxygen atom compared to ribose, making RNA contain more oxygen atoms than DNA.

Step 3: Analyzing the Base Composition

DNA uses the base thymine (T), whereas RNA uses uracil (U) instead of thymine. Uracil is thymine minus a methyl group.

Step 4: Structural Formation

DNA typically forms a stable double helix structure. RNA, while it can form complex 3D shapes, is usually single-stranded and does not form a double helix in its standard state.

Step 5: Evaluating the Given Statements

Now, evaluate each statement in the exercise: (a) Incorrect - DNA and RNA each have one type of sugar in their backbones. (b) Correct - RNA has uracil, which is similar to thymine but without a methyl group. (c) Incorrect - RNA contains more oxygen atoms due to ribose. (d) Partially correct but doesn't explain chemical differences as RNA can sometimes form double-stranded regions.

Key Concepts

Nucleic Acids

Nucleic acids are essential biomolecules that are fundamental to life. They come in two main types: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). These molecules are the building blocks of genetic material and carry the instructions for the functioning, development, and reproduction of all living organisms. Both DNA and RNA are polymers made up of units called nucleotides.
Each nucleotide consists of three components:

• A phosphate group
• A sugar (deoxyribose in DNA and ribose in RNA)
• A nitrogenous base

DNA and RNA differ mainly in the type of sugar and the bases they contain. DNA is typically more stable due to its double-stranded structure, while RNA is more versatile and involved in various cellular processes.

Genetic Information

Genetic information is stored and expressed through the sequences of nucleotides in DNA and RNA. DNA holds the long-term storage of information necessary to build and maintain living organisms. It directs the synthesis of RNA, through a process called transcription, which is the first step of protein production. RNA then guides this information from the DNA in the nucleus to the cytoplasm where proteins are made, in a process known as translation.
Here’s a simplified flow of genetic information:

• DNA -> RNA: Transcription
• RNA -> Protein: Translation

By converting DNA into RNA, cells can express specific genes needed for the cell’s functions. Unlike DNA, which is typically found as double-stranded, RNA is single-stranded, allowing it to fit through nuclear pores to carry its message to the ribosomes.

Chemical Composition

DNA and RNA differ significantly in their chemical composition, affecting their structure and functions. The primary distinction lies in the sugar component of their nucleotides:

• DNA contains the sugar deoxyribose, which has one less oxygen atom than ribose.
• RNA contains the sugar ribose, which includes an additional oxygen atom.

This small change in sugar structure is crucial for the function and stability of these molecules. Additionally, the nitrogenous bases vary; DNA includes adenine (A), cytosine (C), guanine (G), and thymine (T), whereas RNA has uracil (U) in place of thymine. This means the chemical structures have slight variations but lead to vastly different cellular processes.

Sugar-Phosphate Backbone

The sugar-phosphate backbone is a fundamental structural feature of both DNA and RNA. It forms the framework of these nucleic acids, providing structural integrity and support to the sequences of nucleotides that store genetic information.
This backbone consists of:

• Alternating sugar and phosphate groups
• Sugar: deoxyribose in DNA and ribose in RNA
• Phosphodiester bonds linking the sugars and phosphates

In DNA, the sugar-phosphate backbone supports a paired, double-stranded helix, which protects the genetic code from damage. In contrast, the backbone in RNA is usually single-stranded, allowing it to fold into various structures necessary for its role in protein synthesis and other functions. The chemical difference due to the type of sugar (ribose vs. deoxyribose) distinguishes these molecules structurally and functionally.