Question

Identify each of the following as a nucleoside or nucleotide: a. deoxythymidine b. guanosine c. deoxyadenosine-5'-monophosphate d. uridine- \(5^{\prime}\) -monophosphate

Short answer

a. nucleoside, b. nucleoside, c. nucleotide, d. nucleotide

Step-by-step solution

Identify if the molecule is a nucleoside or a nucleotide

A nucleoside consists of a nitrogenous base attached to a sugar molecule, while a nucleotide consists of a nitrogenous base, a sugar molecule, and one or more phosphate groups.

Analyze the first molecule: deoxythymidine

Deoxythymidine has 'deoxy' indicating it contains deoxyribose sugar and 'thymidine' indicating it's thymine as a base attached to the deoxyribose sugar. Since there is no phosphate group mentioned, it is a nucleoside.

Analyze the second molecule: guanosine

Guanosine has 'guanosine' indicating it's guanine as a base attached to a sugar molecule (ribose), with no phosphate mentioned. Therefore, it is a nucleoside.

Analyze the third molecule: deoxyadenosine-5'-monophosphate

Deoxyadenosine indicates 'adenine' as a base attached to deoxyribose sugar, and '5'-monophosphate' indicates the presence of one phosphate group attached to the 5' position. Therefore, it is a nucleotide.

Analyze the fourth molecule: uridine- 5'-monophosphate

Uridine indicates 'uracil' as a base attached to ribose sugar, and '5'-monophosphate' indicates the presence of one phosphate group attached to the 5' position. Therefore, it is a nucleotide.

Key concepts

Nucleosides

Nucleosides are a fundamental unit in molecular biology. They consist of two parts: a nitrogenous base and a sugar molecule. The sugar can either be a ribose or a deoxyribose. This structure distinguishes nucleosides from other molecules involved in genetic material.

A key point to remember is that nucleosides do not include any phosphate groups. They are the building blocks that, when combined with phosphate groups, form nucleotides. Examples of nucleosides include deoxythymidine and guanosine, which are mentioned in the exercise.

Nucleotides

Nucleotides are crucial molecules for life, forming the basic structural unit of nucleic acids like DNA and RNA. A nucleotide is composed of three parts:

- A nitrogenous base
- A sugar molecule (either ribose or deoxyribose)
- One or more phosphate groups

Nucleotides are more complex than nucleosides because they include the additional phosphate group(s). For instance, deoxyadenosine-5’-monophosphate and uridine-5’-monophosphate are nucleotides. These molecules play significant roles in cellular processes, including energy transfer and cell signaling.

Nitrogenous Bases

Nitrogenous bases are aromatic molecules that contain nitrogen atoms. They are an essential component of both nucleosides and nucleotides. There are two types of nitrogenous bases: purines and pyrimidines.

Purines, which include adenine and guanine, have a two-ring structure. Pyrimidines, such as thymine, cytosine, and uracil, have a single-ring structure. These bases pair specifically in DNA and RNA (adenine with thymine or uracil, and cytosine with guanine), allowing the molecules to store and transmit genetic information.

Phosphate Groups

Phosphate groups are vital for the functionality of nucleotides. They consist of a phosphorus atom bonded to four oxygen atoms. One or more phosphate groups can be attached to the 5' carbon of a sugar in a nucleotide.

The presence of phosphate groups distinguishes nucleotides from nucleosides. Phosphate groups play a critical role in the formation of the sugar-phosphate backbone of nucleic acids. Additionally, they are important in energy transfer within cells, particularly in molecules like ATP (adenosine triphosphate).

Deoxyribose Sugar

Deoxyribose sugar is a type of sugar molecule found in DNA. It is a five-carbon sugar that lacks an oxygen atom at the 2' carbon position, which is why it is called 'deoxy'. This minor structural difference compared to ribose sugar profoundly affects the stability and compactness of DNA.

Deoxyribose sugar forms part of the backbone of DNA when it connects with phosphate groups. It binds to nitrogenous bases to form nucleosides, which can be further phosphorylated to become nucleotides. Examples include deoxyadenosine and deoxythymidine.

Ribose Sugar

Ribose sugar is a pivotal component in RNA. Unlike deoxyribose, ribose has one more oxygen atom bonded to the 2' carbon. This structural variation makes RNA more reactive and less stable compared to DNA.

Ribose sugar is key in forming the nucleosides and nucleotides in RNA. For example, guanosine and uridine are nucleosides that include ribose. When these nucleosides link to phosphate groups, they form nucleotides like uridine-5'-monophosphate, crucial for RNA functions in protein synthesis and regulation.