Nucleotides

Monomers

• nucleotides are monomers and comes in 2 varieties:
  • deoxyribo nucleotide
  • ribo nucleotide

Macromolecules

• polynucleotide/nucleic acid are polymers/macromolecules made out of nucleotides and comes in 2 varieties:
  • deoxyribonucleic acid (DNA)
  • ribonucleic acid (RNA)

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Nucleotides

each nucleotide is made up of 3 parts:

• a nitrogenous base
• a five-carbon sugar
• at least one phosphate group

Nitrogenous Base

it’s called a base because the nitrogens can be protonated (pick up an extra H⁺ ion), which decreases the hydrogen ion concentration in a solution

there are 5 possible nitrogenous bases

Five-Carbon Sugar

In addition to having slightly different sets of bases, DNA and RNA nucleotides also have slightly different sugars. The five-carbon sugar in DNA is called deoxyribose, while in RNA, the sugar is ribose. These two are very similar in structure, with just one difference: the second carbon of ribose bears a hydroxyl group, while the equivalent carbon of deoxyribose has a hydrogen instead. The carbon atoms of a nucleotide’s sugar molecule are numbered as 1′, 2′, 3′, 4′, and 5′ (1′ is read as “one prime”), as shown in the figure above. In a nucleotide, the sugar occupies a central position, with the base attached to its 1′ carbon and the phosphate group (or groups) attached to its 5′ carbon.

Phosphate Group

Nucleotides may have a single phosphate functional group, or a chain of up to three phosphate groups, attached to the 5’ carbon of the sugar. Some chemistry sources use the term “nucleotide” only for the single-phosphate case, but in molecular biology, the broader definition is generally accepted

In a cell, a nucleotide about to be added to the end of a polynucleotide chain will bear a series of three phosphate groups. When the nucleotide joins the growing DNA or RNA chain, it loses two phosphate groups. So, in a chain of DNA or RNA, each nucleotide has just one phosphate group.