Attention:This article was written a couple of years ago and might not reflect the latest alters in the AP® program. We are gradually updating these posts and will eliminate this disclaimer as soon as this article is updated. Thank you for her patience!

What is a Nucleotide?

Deoxyribonucleic acid, fondly recognized as DNA, is a molecule in the form of a double helix, i m sorry is responsible because that storing hereditary information in the cells of all living organisms. Most civilization know or should know this. Yet what is DNA make of exactly?


Image Source: Wikimedia Commons

Figure 1: The double-helix of the DNA

DNA, and also other nucleic acids such as RNA, are comprised of nucleotides. Nucleotides room the building blocks of DNA and RNA. The structure ofDNA’s have the right to be visualized or believed of favor a ladder. If we continue with this analogy, every “step or rung” that this ladder is consisted of of a cable of nucleotides, in a very details and managed order. Each nucleotide, in turn, is consisted of of a nitrogenous base, a pentose sugar, and a phosphate. InFigure 2, the nitrogenous basic is enclosed in the red square top top the right, while the phosphate is enclosed in the blue square on the left. The remainder the the molecule forms the pentose sugar. This details molecule is adenine; we will uncover out much more about this later.

You are watching: What are the three parts that make up a nucleotide

Image Source: Wikimedia Commons

Figure 2: The chemistry assembly that the three components of the nucleotide, the phosphate (blue box), nitrogenous basic (red box) and also the pentose sugar. This specific nucleotide is adenine

The assembly of nucleotides (1) differentiates them from nucleosides, which do not contain a phosphate team (in the blue box); (2) enables the nucleotide to affix to other nucleotides as soon as the nitrogenous base forms a hydrogen link with another nucleotide’s nitrogenous base; and (3) permits the phosphate to kind a phosphodiester shortcut with another nucleotide’s pentose sugar. This results in a complex double-stranded “string or ladder”, as viewed in figure1.This is the basis of the form of DNA.

The Nitrogenous Base

The native “nucleotide” was an initial coined by P.A. Levene, who observed the DNA contained four comparable building blocks, in about equal amounts. These structure blocks room what we now know as the nitrogenous bases found in DNA and also RNA.

A nitrogenous basic is a molecule containing nitrogen, through the chemical properties the a base as result of a pair of electrons on the nitrogen atom. These nitrogenous bases space Adenine (A), Cytosine (C) and also Guanine (G) i beg your pardon are found in both RNA and also DNA and also then Thymine (T) which is only found in DNA and Uracil (U), i beg your pardon takes the ar of Thymine in RNA.

Nitrogenous bases have the right to be more classified as pyrimidines or purines. Cytosine, uracil and also thymine space all pyrimidines. The is, your molecular structure comprises a nitrogenous base in the form of a six-member solitary ring. Guanine and adenine, on the various other hand, room purines. These contain a nitrogenous base in the type of a nine-member twin ring. In short, pyrimidines have actually only one ring while purines have two (figure 3).

Now the you get the basic idea that purines matches pyrimidines let’s speak biochemistry. A purine is a heterocyclic aromatic organic compound that comprises of a pyrimidine ring that is join to one imidazole ring. The following logical question, the course, becomes“what climate is a pyrimidine, biochemically speaking”? Well, pyrimidines space a course of nitrogenous link that have only one heterocyclic ring.


Image Source: Wikimedia Commons

Figure 3: Chemical structure of purines (A, G) and also pyrimidines (C, T/U)

Nitrogenous bases form base pairs with each other in DNA: Adenine always pairs v thymine; guanine is always bonded come cytosine. If you to be paying attention, you’ll an alert that this method that a pyrimidine is constantly bonded come a purine. The bond formed is a hydrogen bond, and also is responsible for the rungs developed in the DNA “ladder”.This design is very important for the perfect building and construction of the DNA molecule. Otherwise, there would certainly be bumps and crevices top top the molecule. This wouldn’t perform at all because the an extremely careful packaging, unwinding, and winding that the DNA would be a mess through some more complicated to preserve than others.

This pairing is, therefore, critical for genetic function, and also is the structure for DNA replication and also gene expression. The order in which base pairs appear determines the to work of her physiology. In protein synthesis, because that example, the password is review in triplicates where three bases password for a certain amino acid. Deletions and also insertions of nucleotides in this case can cause a finish frame shift disrupting the synthesis of the protein in question. Substitutions can also be problem although much less so, as they may readjust the identity of an amino mountain in the protein code.

The Phosphate Group

The phosphate group (PO4) is what differentiates a nucleotide native a nucleoside. This addition changes the nucleoside indigenous a base to one acid. This phosphate groups are important, together they form phosphodiester bonds with the pentose sugars to create the political parties of the DNA “ladder”. This is critical, together the hydrogen bond which join the nitrogenous bases space not an extremely strong. This sides the the ladder room hydrophilic (attracted come water), enabling the DNA molecule to bond v water.

What are Nucleoside Diphosphates and Triphosphates?

You know that a nucleotide is differentiated from a nucleoside by one phosphate group. Accordingly, a nucleotide can additionally be a nucleoside monophosphate(figure 4). If much more phosphates bond come the nucleotide (nucleoside monophosphate) the can come to be a nucleoside diphosphate (if 2 phosphates bond), or a nucleoside tree phosphate (if three phosphates bond), such as adenosine triphosphate (ATP). ATP is a an essential component the respiration and also photosynthesis, amongst other processes.


Image Source: Wikimedia Commons

Figure 4: The molecular structure of nucleoside mono-, di- and also triphosphate

A polynucleotide is a chain of more than 20 nucleotides join by a phosphodiester bond.

The Pentose Sugar

The pentose street is a 5-carbon monosaccharide with the formula (CH2O)5. These type two groups: aldopentoses and also ketopentoses. The pentose sugars found in nucleotides space aldopentoses. Deoxyribose and ribose are two of this sugars.

These sugars differ in DNA and RNA. The sugar in DNA is deoxyribonucleic acid, which contains deoxyribose. The street in RNA is ribonucleic acid, which consists of ribose. The structure difference in between these street is the ribonucleic acid includes a hydroxyl (-OH) group, conversely, deoxyribonucleic acid consists of only a hydrogen atom in the location of this hydroxyl group. Nucleotides i beg your pardon contain deoxyribonucleic acid are recognized as deoxyribonucleotides. Those comprise ribonucleic mountain are recognized as ribonucleotides. Thus, the street molecule determines even if it is a nucleotide forms part of a DNA molecule or a RNA molecule. Listed below is a perform of the names given to the sugars uncovered in RNA and DNA.

AAdenosineAdenylic acidDeoxyadenosineDeoxyadenylic acid
CCytidineCytidylic acidDeoxycytidineDeoxycytidylic acid
GGuanosineGuanylic acidDeoxyguanosineDeoxyguanylic acid
UUridineUridylic acid
TDeoxythymidineDeoxythymidylic acid

Putting it every Together

To recap, we have actually covered what a nucleotide is, what the three components of a nucleotide are, we have actually covered the specifics of nitrogenous bases, pentose sugars, and also phosphates, and we have debated how nucleotides different in DNA and RNA.

The phosphate is connected to the pentose sugar; the pentose street is associated to the nitrogenous basic pair (A, C, G or T), which in DNA is linked to its base pair partner. Something choose this:


Image Source: Wikimedia Commons

Figure 5: Nucleotide bonding in the DNA molecule with hydrogen and phosphate bonds.

The chemical structure of the phosphate, pentose sugar, and nitrogenous bases that adenine, thymine, cytosine and also guanine space shown over (figure 5).

During DNA synthesis, a hydrogen bond join A (adenine) to T (thymine), and C (cytosine) to G (guanine) (figure 5). In RNA, uracil would replace thymine.

A DNA strand is developed when the nitrogenous bases space joined through hydrogen bonds, and the phosphates the one team are join to the pentose sugars of the next group with a phosphodiester link (figure 5).

The double helix form is the result of the hydrogen bonds in between the nitrogen bases, which form the “rungs” of the ladder while the phosphate and pentose street (forming phosphodiester bonds) type the upright components of the ladder.

To conclude, nucleotides are necessary as they form the structure blocks of main point acids, such as DNA and also RNA. Nucleotides are made up of 3 parts. The an initial is a distinct nitrogenous base, which is adenine, cytosine, guanine or thymine. In RNA, thymine is changed by uracil. This nitrogenous bases space either purines or pyrimidines. Basic pairs are created when adenine forms a hydrogen bond with thymine, or cytosine forms a hydrogen bond with guanine. The second component of a nucleotide is the phosphate, which differentiates the nucleotide molecule native a nucleoside molecule. This phosphate is crucial in the formation of phosphodiester bonds, which connect several nucleotides in a straight fashion. The third component of a nucleotide is the pentose (5 carbon) sugar. The pentose sugars uncovered in nucleotides are aldopentoses: ribose in RNA and also deoxyribose in DNA. These sugars determine whether the nucleotide will type part of a DNA or a RNA molecule, and form part that the phosphodiester binding which attach several nucleotides. The mix of hydrogen bonds in between nitrogenous bases and phosphodiester bonds in between phosphates and sugars is what provides DNA its double helix shape.

Let’s put everything into practice. Shot this Cellular and also Molecular Biology exercise question:


Looking for more Cellular and also Molecular Biology practice?

Check out our other write-ups on Cellular and Molecular Biology.

You can likewise find thousands of exercise questions top top allows you customize your learning experience to target practice where you require the many help. We’ll give you daunting practice concerns to aid you attain mastery in Cellular and Molecular Biology.

See more: Ti 84 Convert Decimal To Fraction, How To Put In Fractions On A Ti

Start practicing here.

Are you a teacher or administrator interested in boosting Cellular and also Molecular Biology student outcomes?