degeneration. deterioration; change from a higher to a lower form, especially change of tissue to a lower or less functionally active form. When there is chemical change of the tissue itself it is true degeneration; when the change consists in the deposit of abnormal matter in the tissues, it is infiltration.apetoretinal degeneration degeneration of the pigmented layer of the retina. transneuronal degeneration atrophy of certain neurons after interruption of afferent axons or death of other neurons to which they send their efferent output.
There are four different DNA nucleotides, each defined by a specific nitrogenous base: adenine (often abbreviated A in science writing), thymine (abbreviated T), guanine (abbreviated G), and cytosine (abbreviated C) (Figure 2).
DNA. DNA (or deoxyribonucleic acid) is the molecule that carries the genetic information in all cellular forms of life and some viruses. It belongs to a class of molecules called the nucleic acids, which are polynucleotides-that is, long chains of nucleotides.Each nucleotide consists of three components:1  a nitrogenous base: cytosine (C), guanine (G), adenine (A) or thymine (T). 2  a five-carbon sugar molecule (deoxyribose in the case of DNA).t belongs to a class of molecules called the nucleic acids, which are polynucleotides-that is, long chains of nucleotides. Each nucleotide consists of three components: 1  a nitrogenous base: cytosine (C), guanine (G), adenine (A) or thymine (T). 2  a five-carbon sugar molecule (deoxyribose in the case of DNA).