General cytogenetics / J. Sybenga.

  • Sybenga, J. (Jacob), 1926-
Date:
1972
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: General cytogenetics / J. Sybenga. Source: Wellcome Collection.

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    Chapter 1 BACKGROUND 1.1. The material basis 1.1.1. Self-reproduction An essential characteristic of living material is its capacity for self-reproduction. In its absence, life, once originated, would not escape extinction: there are numerous internal and external pro¬ cesses that carry out an efficient break-down. This self-reproduc¬ tion must be extremely exact as the vital processes of even the simplest forms of hfe are so complicated that slight deviations from an estabhshed pattern, proven to be efficient, will almost certainly result in a reduction of fitness. All living material, from virus to complex multicellular organism contains a single basic substance that combines two essential functions; (1) exact replication (self-reproduction) and (2) strict regulation of the vital processes. The two functions are carried out in sequence, not simultaneously. This basic substance is usually DNA (deoxyribonucleic acid). In some cases (plant viruses for instance) it is the related substance RNA (ribonucleic acid). The exact replication of the basic regulating substance is the root of the self-reproduction of the species. 1.1.2. DNA, RNA DNA and RNA consist of long molecular chains of nucleotides, which are the mono-phosphate esters of nucleosides. Nucleosides contain a pentose sugar (deoxyribose in DNA and ribose in RNA) and one of four nitrogenous bases: adenine, guanine (both pu¬ rines), thymine (only in DNA and substituted by uracil in RNA)