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).
Nucleotides are the basic structural units of nucleic acids, which control the production of proteins in living organisms. The nucleotides are made up of a phosphate group, a pentose sugar, and a nitrogen base.This shows the basic structure of a nucleotide.This example has the sugar ribose, and is characteristic of RNA.he nucleotide could contain the sugar deoxyribose, characteristic of DNA. For DNA, the bases may be adenine, guanine, cytosine or thymine. For RNA the bases are adenine, guanine, cytosine and uracil.