Question

Sketch the structures of the sugars ribose and deoxyribose. Which molecule, DNA or RNA, contains each sugar?

Short answer

Ribose is a pentose sugar with the chemical formula \(\text{C}_5\text{H}_{10}\text{O}_5\), having four hydroxyl groups (\(-\text{OH}\)) on each carbon. Deoxyribose, also a pentose sugar with formula \(\text{C}_5\text{H}_{10}\text{O}_4\), has one less oxygen atom and a hydrogen atom instead of a hydroxyl group on the second carbon. Ribose sugar is present in RNA, while Deoxyribose sugar is present in DNA.

Step-by-step solution

1. Structure of Ribose sugar

Ribose sugar is a pentose sugar, meaning it has a 5-carbon backbone. Its chemical formula is \(\text{C}_5\text{H}_{10}\text{O}_5\). It has four hydroxyl groups (\(-\text{OH}\)) attached to each of the four carbons, and one carbon is part of an aldehyde group (\(\text{HCO}\)). The structure of this sugar is as follows: 

2. Structure of Deoxyribose sugar

Deoxyribose sugar is also a pentose sugar with a chemical formula \(\text{C}_5\text{H}_{10}\text{O}_4\). The name deoxyribose comes from the fact that it is a ribose sugar lacking one oxygen atom (hence, de-oxy). The structure of this sugar is similar to ribose sugar, but with one crucial difference: the second carbon has one hydrogen atom instead of a hydroxyl group (\(-\text{OH}\)). The structure of this sugar is as follows: 

3. Identify which molecule contains Ribose sugar

The sugar component of the nucleotides in RNA (ribonucleic acid) is ribose sugar. Each nucleotide in RNA has a ribose sugar, a phosphate group, and a nitrogenous base. So, Ribose sugar is present in RNA.

4. Identify which molecule contains Deoxyribose sugar

The sugar component of the nucleotides in DNA (deoxyribonucleic acid) is deoxyribose sugar. Each nucleotide in DNA has a deoxyribose sugar, a phosphate group, and a nitrogenous base. Therefore, Deoxyribose sugar is present in DNA. In conclusion, Ribose sugar is found in RNA, while Deoxyribose sugar is found in DNA.

Key concepts

Ribose

Ribose is a type of sugar that is vital in the structure of RNA. It is classified as a pentose sugar because it consists of a five-carbon backbone. This smaller structure is crucial in the biology of living organisms because it forms part of the backbone of RNA molecules. The chemical formula for ribose is \(\text{C}_5\text{H}_{10}\text{O}_5\).
Notably, ribose has four hydroxyl groups (\(-\text{OH}\)) attached to each of the four carbons, while the fifth carbon is linked to an aldehyde group (\(\text{HCO}\)).

• It is present in each nucleotide of RNA.
• It allows RNA to perform various biological functions, including transferring genetic information and catalyzing chemical reactions in cells.

Deoxyribose

Deoxyribose is a closely related sugar to ribose but with one minor yet significant adjustment in its structure. Like ribose, it is a pentose sugar, but the critical difference is it has one less oxygen atom, giving deoxyribose the chemical formula \(\text{C}_5\text{H}_{10}\text{O}_4\).
This absence of an oxygen atom at the second carbon is what leads to its name: "de-oxy," meaning "lacking oxygen."

• Deoxyribose forms the sugar component of nucleotides in DNA.
• This minor change contributes to the increased stability of DNA compared to RNA.

DNA

DNA, or deoxyribonucleic acid, is the genetic blueprint that is found in the cells of all living organisms. Its backbone is formed with deoxyribose sugars and phosphate groups, and it plays a critical role in storing and transferring genetic information. The structure of DNA consists of two long chains that twist into a double helix.

• Each nucleotide within DNA contains a deoxyribose sugar.
• The double helix structure gives DNA its stability, allowing for the long-term storage of genetic information.

This stability is a key reason why DNA is the primary medium for storing genetic information across generations.

RNA

RNA, or ribonucleic acid, is crucial in various biological roles including coding, decoding, regulation, and expression of genes. RNA is typically single-stranded and contains ribose sugars within each of its nucleotides.
The presence of ribose makes RNA less stable than DNA but allows it to be versatile and function in several roles, such as messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).

• RNA's ribose sugar allows it to fold into complex three-dimensional shapes.
• The flexibility and variety of RNA's forms enable it to perform multiple roles within the cell, alongside its main role of protein synthesis.

Pentose Sugars

Pentose sugars are a class of sugars that consist of five carbon atoms. They play a critical role in the formation of nucleic acids. Both ribose and deoxyribose fit into this category and are integral parts of RNA and DNA nucleotides, respectively.

• Pentose sugars are fundamental building blocks of nucleotides.
• Differences in their structure influence the functionality and stability of the nucleic acids.

Understanding pentose sugars helps explain the structural and functional differences between RNA and DNA, highlighting the significance of each sugar in genetic materials.