- Nucleic acids are a class of biopolymers that play a fundamental role in the storage and transmission of genetic information in living organisms. There are two primary types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
- DNA, typically a double-stranded helix, holds the genetic code that defines an organism's characteristics, from physical traits to cellular functions. RNA, often single-stranded, acts as a versatile intermediary, conveying genetic instructions from DNA to protein synthesis machinery.
- Nucleic acids consist of nucleotides, each composed of a sugar (deoxyribose in DNA or ribose in RNA), a phosphate group, and one of four nitrogenous bases (adenine, thymine, cytosine, or guanine in DNA; uracil replaces thymine in RNA).
- This chemical structure allows nucleic acids to store, replicate, and transmit genetic information, enabling the continuity of life and the intricate processes within cells.
- A nucleotide, the building block of polynucleotide chains like DNA and RNA, comprises three components: a nitrogenous base (either purine or pyrimidine), a pentose sugar (ribose for RNA, deoxyribose for DNA), and a phosphate group.
- DNA contains the purines adenine (A) and guanine (G) and the pyrimidines cytosine (C) and thymine (T), while RNA replaces thymine with uracil (U).
- Nucleotides join through N-glycosidic linkage between the nitrogenous base and the 1' carbon of the pentose sugar, forming nucleosides like adenosine and deoxyadenosine.
- The addition of a phosphate group to the 5' carbon of a nucleoside via phosphodiester linkage creates a nucleotide (or deoxynucleotide in DNA).
- Two nucleotides link via a 3'-5' phosphodiester bond to form a dinucleotide. Further nucleotides can join in this manner to create a polynucleotide chain.
- The 5'-end of the chain has a free phosphate group, while the 3'-end has a free hydroxyl group.
- The backbone of the polynucleotide chain consists of alternating sugar and phosphate units, while the nitrogenous bases extend inward.
- In RNA, each nucleotide possesses an additional hydroxyl group at the 2'-position on the ribose sugar, and uracil replaces thymine.
- Friedrich Meischer identified DNA as an acidic substance in the nucleus in 1869, initially calling it 'Nuclein.'
- The elucidation of DNA's structure faced technical limitations until 1953 when James Watson and Francis Crick proposed the famous Double Helix model based on X-ray diffraction data from Maurice Wilkins and Rosalind Franklin.
- Base pairing between adenine-thymine and guanine-cytosine was a hallmark of Watson and Crick's model, influenced by Erwin Chargaff's observation of constant ratios between these base pairs.
- Complementary base pairing allows one strand's sequence to predict the other, facilitating DNA replication where each parental DNA strand acts as a template, producing identical daughter DNA molecules. This underpins the genetic significance of DNA's structure.