Eleanor Finch
Nucleotides are the building blocks of nucleic acids such as RNA and DNA. Each nucleotide is made up of three subunits: a nitrogenous base, a pentose sugar, and a phosphate group. The nitrogenous base is a molecule containing nitrogen, with the chemical properties of a base due to a pair of electrons on the nitrogen atom. The pentose sugar is a 5-carbon monosaccharide, and the phosphate group is what differentiates a nucleotide from a nucleoside.
| Characteristics | Values |
|---|---|
| Number of subunits | 3 |
| First subunit | Five-carbon sugar molecule (ribose or deoxyribose) |
| Second subunit | Nucleobase (nitrogenous base) |
| Third subunit | Phosphate group (one to three phosphates) |
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What You'll Learn
The role of nucleotides in nucleic acids
Nucleotides are the building blocks of nucleic acids, which are the macromolecules that carry the genetic information of a cell. The two main types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is the genetic material found in all living organisms, while RNA is primarily involved in protein synthesis.
Nucleotides are composed of three subunits: a nucleobase (or nitrogenous base), a five-carbon sugar (ribose or deoxyribose), and a phosphate group consisting of one to three phosphates. In DNA, the four nucleobases are guanine, adenine, cytosine, and thymine, while in RNA, uracil is used in place of thymine. These nucleobases form hydrogen bonds with each other, allowing the nucleotides to connect and create a complex double-stranded structure, such as the well-known double helix structure of DNA.
The phosphate groups in nucleotides play a crucial role in differentiating them from nucleosides, which lack a phosphate group. These phosphate groups also form phosphodiester bonds with the pentose sugars, creating the sides of the DNA "ladder." The order in which these base pairs appear is essential for genetic function and is the foundation for DNA replication and gene expression.
In addition to their role in constructing nucleic acid polymers, individual nucleotides also have important functions in cellular energy storage and provision, cellular signaling, and as enzymatic cofactors. They provide chemical energy in the form of nucleoside triphosphates such as adenosine triphosphate (ATP), which is crucial for processes like respiration and photosynthesis. Nucleotides also serve as a source of phosphate groups used to modulate protein activity and are involved in cell signaling pathways.
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The nitrogenous base
Nitrogenous bases are a key component of nucleotides, which are the building blocks of genetic information like DNA and RNA. Nitrogenous bases come in two forms, purines and pyrimidines. Purines are nitrogenous bases that have two rings fused together, while pyrimidines are nitrogenous bases that only have one ring. The purines include the nitrogenous bases adenine and guanine. Adenine is represented by the symbol A in DNA and RNA, and has the chemical formula C5H5N5. Guanine is represented by the symbol G in DNA and RNA, and has the chemical formula C5H5N5O.
The pyrimidine bases include thymine, cytosine, and uracil. Thymine is only found in DNA and is represented by the symbol T. Its chemical formula is C5H6N2O2. Cytosine is found in both DNA and RNA and is represented by the symbol C. Its chemical formula is C4H5N3O. Uracil is a pyrimidine base that is used in RNA in place of thymine and is represented by the letter U.
The specific order of bases in DNA is what transmits genetic information. Nitrogenous bases connect in groups of two, called complementary pairs, using hydrogen bonds. This pairing allows for the safe transfer of information through DNA replication and transcription, which is the process that makes RNA. For example, adenine forms a base pair with thymine with two hydrogen bonds, while guanine pairs with cytosine with three hydrogen bonds.
Changes to the nitrogenous base sequences can have disastrous consequences for both the cell and the organism. These changes, known as mutations, are the cause of numerous genetic diseases, including cancer.
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The pentose sugar
Nucleotides are the building blocks of nucleic acids such as DNA and RNA. Each nucleotide is made up of three subunits: a nitrogenous base, a pentose sugar, and a phosphate group.
Individual phosphate molecules connect the sugar-ring molecules in two adjacent nucleotide monomers, forming a long chain of nucleic acid. The phosphate groups also form phosphodiester bonds with the pentose sugars, creating the sides of the DNA "ladder". This structure is essential, as the hydrogen bonds that join the nitrogenous bases are relatively weak.
The nitrogenous base forms a hydrogen bond with another nucleotide's nitrogenous base, allowing the nucleotide to connect to other nucleotides. In DNA, the four nucleobases are guanine, adenine, cytosine, and thymine. In RNA, uracil is used instead of thymine.
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Phosphate groups
A nucleotide is differentiated from a nucleoside by the presence of a phosphate group. This addition changes the nucleoside from a base to an acid. The phosphate group present in the nucleotide creates a covalent bond with the sugar molecule of the adjacent nucleotide to form a long chain of nucleotide monomers. The sugar-phosphate groups form the backbone in the single strand of DNA. The nucleotides protrude out from the backbone.
The phosphate group is attached to the 5’ carbon of a nucleotide and the 3’ carbon of the adjacent nucleotide. Phosphate groups are important as they form phosphodiester bonds with the pentose sugars to create the sides of the DNA "ladder". This is critical as the hydrogen bonds that join the nitrogenous bases are not very strong. The phosphate group is what allows the nucleotide to connect to other nucleotides. This occurs when the nitrogenous base forms a hydrogen bond with another nucleotide’s nitrogenous base.
The phosphate group is also involved in cellular signalling. Signalling cyclic nucleotides are formed by binding the phosphate group twice to the same sugar molecule, bridging the 5' and 3' hydroxyl groups of the sugar. Some signalling nucleotides differ from the standard single-phosphate group configuration, in having multiple phosphate groups attached to different positions on the sugar.
Phosphorus concentration in the blood is regulated by the kidneys. The kidneys maintain homeostasis between urinary phosphorus excretion and phosphorus absorption from the gastrointestinal tract.
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Nucleotide monomers
Nucleotides are the basic building blocks of nucleic acids such as RNA and DNA. Each nucleotide is made up of three subunits: a nitrogenous base, a pentose sugar, and a phosphate. The nitrogenous base is a molecule containing nitrogen, with the chemical properties of a base due to a pair of electrons on the nitrogen atom. The four nucleobases in DNA are guanine, adenine, cytosine, and thymine, while in RNA, uracil is used in place of thymine.
The pentose sugar molecule is a 5-carbon monosaccharide with the formula (CH2O)5. These sugars differ in DNA and RNA. The sugar in DNA is deoxyribose, a type of aldopentose, while the sugar in RNA is ribose. Individual phosphate molecules repetitively connect the sugar-ring molecules in two adjacent nucleotide monomers, thereby connecting the nucleotide monomers of a nucleic acid end-to-end into a long chain. This chain of more than 20 nucleotides joined by a phosphodiester bond is known as a polynucleotide.
The presence of a phosphate group is what differentiates a nucleotide from a nucleoside. Nucleotides can also be referred to as nucleoside monophosphates, nucleoside diphosphates, or nucleoside triphosphates, depending on the number of phosphates present. The phosphate groups are essential as they form phosphodiester bonds with the pentose sugars, creating the sides of the DNA "ladder." This structure is crucial for genetic function and is the foundation for DNA replication and gene expression.
Nucleotides play a central role in metabolism at a fundamental cellular level. They provide chemical energy in the form of nucleoside triphosphates such as adenosine triphosphate (ATP), which is crucial for various cellular functions, including amino acid, protein, and cell membrane synthesis, as well as cell division and cellular signalling.
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Frequently asked questions
A nucleotide is composed of three subunits: a nitrogenous base, a pentose sugar, and a phosphate.
A nitrogenous base is a molecule containing nitrogen, with the chemical properties of a base due to a pair of electrons on the nitrogen atom. The four nucleobases in DNA are guanine, adenine, cytosine, and thymine. In RNA, uracil is used instead of thymine.
A pentose sugar is a 5-carbon monosaccharide with the formula (CH2O)5. The pentose sugars found in nucleotides are aldopentoses, specifically, deoxyribose in DNA and ribose in RNA.
A phosphate group is what differentiates a nucleotide from a nucleoside. This group forms phosphodiester bonds with the pentose sugars to create the sides of the DNA "ladder".
A nucleoside is a molecule composed of a nitrogenous base and a pentose sugar. It does not contain a phosphate group.
