Cell organic matter: nucleic acids
Nucleic acids (from the Latin nucleus – “nucleus”) were first discovered in 1868 in the nuclei of leukocytes by the Swiss scientist F. Mischer. Later it was found that nucleic acids are contained in all cells (in the cytoplasm, nucleus and in all organelles of the cell).
Primary structure of nucleic acid molecules
Nucleic acids are the largest molecules produced by living organisms. They are biopolymers composed of monomers – nucleotides.
Each nucleotide consists of a nitrogenous base, a five-carbon sugar (pentose), and a phosphate group (a phosphoric acid residue).
Depending on the type of five-carbon sugar (pentose), there are two types of nucleic acids:
- deoxyribonucleic acids (abbreviated as DNA) – the DNA molecule contains a five-carbon sugar – deoxyribose.
- ribonucleic acids (abbreviated as RNA) – the RNA molecule contains a five-carbon sugar – ribose.
There are differences in the nitrogenous bases that make up the nucleotides of DNA and RNA.
DNA nucleotides: A – adenine, G – guanine, C – cytosine, T – thymine.
RNA nucleotides: A – adenine, G – guanine, C – cytosine, U – uracil.
Secondary structure of DNA and RNA molecules
Secondary structure is the form of nucleic acid molecules.
The spatial structure of the DNA molecule was modeled by American scientists James Watson and Francis Crick in 1953.
Deoxyribonucleic acid (DNA) – consists of two helically twisted chains, which are hydrogen bonded to each other along their entire length. This structure (peculiar only to DNA molecules) is called a double helix.
Ribonucleic acid (RNA) is a linear polymer consisting of a single chain of nucleotides.
The exception is viruses that have single-stranded DNA and double-stranded RNA.
More details about DNA and RNA will be discussed in the section “Storage and transmission of genetic information. Genetic code”.