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 subunit that is polymerized (connected into a long chain) to make nucleic acids (DNA and RNA). Nucleotides consist of three smaller components: a ribose sugar, a nitrogenous base, and phosphate group(s). Generic nucleotide structure. The connection that forms between nucleotides is between the sugar of the first nucleotide and the phosphate group of the second. 2  Each connection between nucleotides is a covalent bond, so the nucleic acids have a covalently attached sugar-phosphate backbone.