plural: thymidine monophosphates
A nucleotide is an organic compound made up of three subunits: a nucleobase, a five-carbon sugar, and a phosphate group. The sugar component may either be ribose or deoxyribose. The ribose is the sugar component of the nucleotides that make up RNA. The deoxyribose is the sugar component of DNA. Nucleotides are the monomeric units of nucleic acids. Each phosphate group connects the sugar rings of two adjacent nucleotide monomers. The phosphate groups and the sugar moieties form the backbone of a nucleic acid. The directionality of the chain runs from 5'-end to 3'-end. In DNA, the orientation of the two strands is in opposite directions. This is to allow complementary base pairing between nucleobase constituents. A nucleotide is, thus, a nucleoside with a phosphate group. Depending on the number of phosphate groups attached to the sugar moiety, it may be called nucleoside monophosphate (if with only one phosphate group), nucleoside diphosphate (with two phosphate groups), or nucleoside triphosphate (when with three phosphate groups). Depending on the pentose sugar component, a nucleoside may be a ribonucleoside or a deoxyribonucleoside. A ribonucleoside is a nucleoside with a ribose sugar component. (Depending on the nucleobase component, the ribonucleoside may be adenosine, guanosine, cytidine, uridine, or 5-methyluridine). A deoxyribonucleoside is a nucleoside with a deoxyribose sugar. Depending on the nucleobase component, a deoxyribonucleoside may be deoxyadenosine, deoxyguanosine, deoxycytidine, thymidine, or deoxyuridine. Also, depending on the nucleobase component, the nucleosides may be grouped into either the "double-ringed" purine or the "single-ringed" pyrimidine.
Deoxythymidine monophosphate (dTMP) is a nucleoside phosphate in being comprised of a deoxyribonucleoside and one phosphate group. This means that it has a deoxyribose as its sugar constituent with one phosphate group attached. Its nucleoside contains a pyrimidine base, i.e. a thymine attached to the deoxyribose sugar. It has only one phosphate group attached to the nucleoside. Its conjugate base form is deoxythymidylate or simply, thymidylate.
Unlike the other fundamental nucleotides, dTMP is often referred to as thymidine monophosphate (abbreviated as TMP) and the prefix deoxy- is dropped since it is a nucleotide component of DNA and not of RNA. RNA does not have thymine but instead is replaced by another pyrimdine, uracil. DNA, in turn, does not have uracil. Rather, it has thymine in place of the uracil. Thus, the term deoxy- is often dropped since dTMP is implicitly comprised of a deoxyribose sugar. Nevertheless, the abbreviated form dTMP is more widely used than TMP. Both thymine and uracil complementary pairs with adenine.
Thymine, cytosine, and uracil are pyrimidine nucleobases. Thymine has two keto groups at positions 2 and 4, and a methyl group at position 5 in its heterocyclic aromatic ring. Thymine complementary base pairs with adenine by two hydrogen bonds. However, unlike cytosine that is present in both DNA and RNA, thymine is present only in the DNA molecule because uracil takes its place in RNA.
Uracil is similar to thymine in terms of structure except for the methyl group at position 5 in the heterocyclic aromatic ring present in thymine. One of the possible explanations why DNA has thymine instead of uracil is associated with the conversion of cytosine into uracil by spontaneous deamination. Cytosine can turn into uracil when it loses its amine group. This deamination of cytosine is a common occurrence. Nevertheless, the error is corrected through an inherent DNA repair systems. If not repaired though, it could lead to a point mutation. Had uracil been present in the DNA, the repair systems might not be able to distinguish the original uracil from the cytosine-turned-uracil and therefore may fail to discern which uracil to correct. The presence of methyl group in thymine (which is absent in uracil) helps avert this from happening, thereby, preserving the integrity and stability of the genetic code.
Cytosine can be differed from thymine and uracil by having a keto group at position 2 and an amine group at position 4 in its heterocyclic aromatic ring. It has a chemical formula of C4H5N3O. Cytosine complementary pairs with guanine in both DNA and RNA as opposed to thymine and uracil that pairs up with adenine in DNA and RNA, respectively.
Common biological reactions
Biosynthesis of thymine for dTMP
Thymine, similar to other pyrimidines, is formed from a series of steps, beginning with the formation of carbamoyl phosphate. Carbamoyl phosphate forms from a reaction involving bicarbonate, glutamine, ATP, and water molecule. This process is catalyzed by the enzyme carbamoyl phosphate synthetase. The carbamoyl phosphate is then converted into carbamoyl aspartate through the catalytic activity of aspartate transcarbamylase. Carbamoyl aspartate is next converted into dihydroorotate, which is then oxidized to produce orotate. 5-phospho-α-D-ribosyl 1-pyrophosphate (PRPP), a ribose phosphate, reacts to orotate to form orotidine-5-monophosphate (OMP). OMP is decarboxylated by the enzyme OMP decarboxylase to yield uridine monophosphate (UMP). Eventually, uridine diphosphate (UDP) and uridine triphosphate (UTP) are produced down the biosynthetic pathway by kinases and dephosphorylation of ATPs. In order to synthesize thymidine, uridine is reduced first to deoxyuridine (by the enzyme ribonucleotide reductase). After which, it is methylated by the enzyme thymidylate synthase to form thymidine.
dTMP is one of the monomer nucleotides in DNA, particularly when it is phosphorylated with two more phosphate groups, thus becoming dTTP (deoxythymidine triphosphate). dTTP complementary base pairs with deoxyadenosine triphosphate (dATP).
- thymidylic acid
- deoxythymidine monophosphate (dTMP)
- deoxythymidylic acid
- thymidine 5'-monophosphate
- thymine nucleotide
- Charma, K. & Somani, D. (2015). Pyrimidine Biosynthesis. Retrieved from Slideshare.net website: [Link]
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