1. A nitrogenous base: These come in two main types:
- Purines: Adenine (A) and Guanine (G)
- Pyrimidines: Cytosine (C), Thymine (T) (found in DNA), and Uracil (U) (found in RNA)
2. A five-carbon sugar:
- Deoxyribose: Found in DNA
- Ribose: Found in RNA
3. A phosphate group: This gives the molecule its acidic properties.
Subunit Assembly:
Nucleotides are linked together by phosphodiester bonds. The phosphate group of one nucleotide forms a bond with the hydroxyl group on the sugar of the next nucleotide. This creates a long, chain-like structure, known as a polynucleotide.
Structure of DNA and RNA:
* DNA: Two polynucleotide chains, each forming a helix, are held together by hydrogen bonds between the nitrogenous bases. Adenine always pairs with thymine (A-T), and guanine always pairs with cytosine (G-C). This pairing is known as complementary base pairing.
* RNA: RNA is typically single-stranded, although it can fold into complex three-dimensional structures. It uses the same bases as DNA, except that thymine is replaced by uracil (A-U).
Key Points:
* The sequence of nitrogenous bases in a nucleic acid determines its genetic information.
* The structure of nucleic acids allows for the storage and transmission of genetic information.
* The subunit structure of nucleic acids is crucial for their biological functions.
