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 is a very large molecule, made up of smaller units called nucleotides that are strung together in a row, making a DNA molecule thousands of times longer than it is wide. Each nucleotide has three parts: a sugar molecule, a phosphate molecule, and a structure called a nitrogenous base.The nitrogenous base is the part of the nucleotide that carries genetic information, so the words nucleotide and base are often used interchangeably.The bases found in DNA come in four varieties: adenine, cytosine, guanine, and thymineoften abbreviated as A, C, G, and T, the letters of the genetic alphabet.ach nucleotide has three parts: a sugar molecule, a phosphate molecule, and a structure called a nitrogenous base. The nitrogenous base is the part of the nucleotide that carries genetic information, so the words nucleotide and base are often used interchangeably.