1. Monomers: Nucleic acids are polymers made up of individual monomers called nucleotides. Each nucleotide consists of:
* A nitrogenous base: Adenine (A), guanine (G), cytosine (C), thymine (T) in DNA, or uracil (U) in RNA.
* A five-carbon sugar: Deoxyribose in DNA or ribose in RNA.
* A phosphate group: This group carries a negative charge.
2. Connecting the Monomers: The bond between nucleotides is formed through a dehydration reaction. This means a water molecule is removed to create the bond.
* The phosphate group of one nucleotide attaches to the hydroxyl group (OH) on the 3' carbon of the sugar of the next nucleotide.
* This creates a phosphodiester bond, which is a strong covalent bond.
3. The Backbone: This process repeats, creating a long chain of nucleotides linked together. The sugar-phosphate backbone forms the structural framework of the nucleic acid.
4. Directionality: The phosphodiester bonds give nucleic acid chains a directionality:
* One end of the chain has a free 5' phosphate group (the 5' end).
* The other end has a free 3' hydroxyl group (the 3' end).
* Nucleic acids are synthesized in the 5' to 3' direction.
5. Double Helix (DNA): In DNA, two strands of nucleotides associate through complementary base pairing (A with T, G with C) via hydrogen bonds. These strands run in opposite directions (antiparallel) and twist around each other to form the famous double helix structure.
In summary, nucleotides join together to form nucleic acids through the formation of phosphodiester bonds between the phosphate group of one nucleotide and the hydroxyl group on the sugar of the next nucleotide. This process creates a sugar-phosphate backbone with a specific 5' to 3' directionality.
