DNA and RNA – Nucleotides, sugars, and bases

DNA and RNA: Roles

• DNA (deoxyribonucleic acid) stores genetic information—the instructions an organism needs to grow and develop from a fertilised egg to an adult.

• RNA (ribonucleic acid) transfers genetic information from DNA to ribosomes; ribosomes read RNA to make polypeptides (proteins) via translation; ribosomes are themselves made from RNA and proteins.

Nucleotides: Structure

• A nucleotide is a biological molecule consisting of:

  • a pentose sugar (that’s a sugar with 5 carbon atoms),

  • a phosphate group,

  • a nitrogen-containing organic base.

• Nucleotides are the monomers that make up DNA and RNA.

The Sugar in DNA: Deoxyribose

• The pentose sugar in a DNA nucleotide is called deoxyribose.

• Each DNA nucleotide has the same sugar and a phosphate group; the base on each nucleotide can vary.

• There are four possible bases: A, T, C, G.

The Sugar in RNA: Ribose

• RNA contains nucleotides with a ribose sugar (not deoxyribose).

• Like DNA, an RNA nucleotide also has a phosphate group and one of four different bases.

• In RNA though, uracil (U) replaces thymine as a base.

• The four bases in RNA are: A, U, C, G.