Question

Which of the following is true of the differences between DNA and RNA? A. DNA contains a five-carbon sugar, while RNA contains a six-carbon sugar. B. DNA contains phosphate groups, while RNA does not. C. RNA contains the purine base adenine in place of the purine base guanine contained in DNA. D. RNA contains a different fivecarbon sugar than DNA.

Short answer

D. RNA contains a different five-carbon sugar than DNA.

Step-by-step solution

Understand the composition of DNA

DNA, or deoxyribonucleic acid, is composed of a five-carbon sugar called deoxyribose, a phosphate group, and four nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G).

Understand the composition of RNA

RNA, or ribonucleic acid, is similar to DNA, but instead of the sugar deoxyribose, it contains a different five-carbon sugar called ribose. RNA also contains adenine, cytosine, and guanine, but instead of thymine, it contains uracil (U).

Evaluate the provided options

Examine each option and determine its validity based on the compositions of DNA and RNA described in Steps 1 and 2. A is incorrect because RNA does not contain a six-carbon sugar, it contains ribose, which is a five-carbon sugar. B is incorrect because both DNA and RNA contain phosphate groups. C is incorrect because both RNA and DNA contain the purine base adenine, and guanine is not replaced in RNA. D is correct because RNA contains ribose, whereas DNA contains deoxyribose, and both are five-carbon sugars but are different from each other.

Key concepts

Nucleic Acids

Nucleic acids are complex organic substances that are the fundamental building blocks of living organisms. They are responsible for storing, transmitting, and expressing genetic information. There are two main types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

Both DNA and RNA are made up of monomers called nucleotides, which consist of a phosphate group, a five-carbon sugar, and a nitrogenous base. In DNA, this sugar is deoxyribose, which lacks one oxygen atom that is found in the ribose sugar of RNA. This small but vital difference is part of what distinguishes DNA from RNA at a chemical level.

The sequence of these nucleotides in the DNA and RNA strands encodes the information necessary for the synthesis of proteins, which are critical for the structure and function of cells. Although DNA and RNA have similar structures, they have distinct roles in cells: DNA is the keeper of genetic codes, while RNA translates that code into proteins in a process called protein synthesis.

Ribonucleic Acid

Ribonucleic acid, or RNA, is important for using the genetic information in DNA to synthesize proteins during gene expression. Unlike DNA’s stable, double-helix structure, RNA is typically single-stranded and can take on various shapes that are crucial to its functions within the cell.

RNA plays many roles but is chiefly involved in the synthesis of proteins. Messenger RNA (mRNA) is the template for protein synthesis, transfer RNA (tRNA) brings the appropriate amino acids to the ribosome during protein assembly, and ribosomal RNA (rRNA) is a key component of ribosomes, the site where proteins are produced.

Differences in sugar molecules and one of the nitrogenous bases between DNA and RNA affect not only their structures but also their resistance to enzymes and their functionality. The presence of uracil in place of thymine in RNA allows for the formation of temporary hydrogen bonds during transcription and translation, processes essential for protein production.

Five-Carbon Sugars

The five-carbon sugars play a pivotal role in the structure and function of DNA and RNA. These sugars are pentose sugars, and they differ by just one atom. In DNA, the sugar is deoxyribose, which has a hydrogen atom attached to its second carbon (2') instead of a hydroxyl group (OH). In contrast, RNA contains ribose, where the 2' carbon has a hydroxyl group.

This might seem like a minor difference, but it greatly influences the physical and chemical properties of the nucleic acids. For instance, the absence of an oxygen atom in deoxyribose makes DNA more chemically stable than RNA, which is more reactive due to the extra oxygen atom in ribose. This stability is necessary for DNA’s role in long-term storage of genetic information. RNA's relative instability and reactivity suit its roles in protein synthesis and regulation, where molecules often need to be quickly synthesized and degraded.

Understanding the impact of the five-carbon sugars is crucial for comprehending the differences between DNA and RNA and their respective roles in cellular biology. While both sugars have a five-carbon ring structure, the presence or absence of an oxygen atom drastically alters the behavior and lifespan of the nucleic acid they compose.