# Nucleotide --- A **nucleotide** is the monomer of [[nucleic acid|nucleic acids]]. In humans they are: **adenine**, **guanine**, **cytosine**, **uracil** and **thymine**. DNA uses the nucleotides A, G, C and T, while RNA uses A, G, C and *U*. A **ribonucleotide** is a nucleotide whose sugar component is [[ribose and deoxyribose|ribose]], and is used in [[RNA]]. A **deoxynucleotide** is a nucleotide whose sugar component is a [[ribose and deoxyribose|deoxyribose]], and is used in [[DNA]]. In double-stranded nucleic acids, each base forms a [[complementary base pairing]] with a specific other base. Guanine and cytosine always pair together, and adenine always pairs with either thymine or uracil. ## Structure Nucleotides are made up of a phosphate group, a 5-carbon sugar and a nitrogenous base. ![[nucleotide.png]] The **phosphate group** of the nucleotide is a [[functional group#Biologically Important Functional Groups|phosphate]], and when it's free floating is a triphophsate. This is where the energy needed to link up comes from. The phosphate is bound to the 5' carbon of the sugar molecule. The **[[monosaccharide#Monosaccharide|sugar]] of a nucleotide** is either [[ribose and deoxyribose|a ribose or a deoxyribose]], depending on if it's an RNA or a DNA, respectively. Both are 5 carbon simple sugars, with distinctive pentagram shapes. The sugar is bound to the phosphate group on it's 5' carbon and to the nitrogenous base by it's 1' carbon. The **nitrogenous bases** are what make each otherwise identical nucleotide unique. In other words the only difference between an adenine and a guanine is the nitrogenous base. The nitrogenous base is bound to the 1' carbon of the sugar molecule. ## Dideoxynucleotides **Dideoxynucleotides** are basically fake deoxyribonucleotide because they lack a [[functional group#Biologically Important Functional Groups|hydroxyl]] on *both* the 2' *and* the 3'. This results in [[DNA polymerase]] being unable to further extend the chain once the dideoxynucleotide has been added. ## Other Functions Nucleotides fuel the cell and coordinate its metabolism. [[adenosine triphosphate]] is one of the ribonucleotides that make up [[RNA]] molecules. ___