The major function of oligodendrocytes and Schwann cells is the formation of myelin. Myelin acts as an insulator of axonal segments and is a prerequisite for the high velocity of nerve conduction, of up to 200 m/second.The association of glial cells with axons is also found in invertebrates.chwann cells are the cellular counterparts to oligodendrocytes in the peripheral nervous system. Similarly to oligodendrocytes they form the myelin sheath. In contrast to the oligodendrocyte each Schwann cell is associated with only one axonal segment.
DNA molecules are made of two twisting, paired strands. Each strand is made of four chemical units, called nucleotide bases. The bases are adenine (A), thymine (T), guanine (G) and cytosine (C). Bases on opposite strands pair specifically; an A always pairs with a T, and a C always with a G. The human genome contains approximately 3 billion of these base pairs, which reside in the 23 pairs of chromosomes within the nucleus of all our cells. Each chromosome contains hundreds to thousands of genes, which carry the instructions for making proteins.
DNA structure. DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). The order of these bases is what determines DNA's instructions, or genetic code.