STEM CELL BACKGROUND

STEM CELL BACKGROUND
To understand stem cells, one must consider that cells are the basic unit of living things. Cell theory, set forth in the I850s, holds that cells are the building blocks of every tissue and organ in both plants and animals. With only a few exceptions, each animal cell has a nucleus, cytoplasm, and cell membrane.
  The term mitosis is used to describe cell division. In this process, cells replicate exactly to make daughter cells that have a full complement of 46 chromosomes. The process of cell division proceeds as follows:Inside
the nucleus are encoded instructions for the synthesis of proteins, in the form of a helical, double-stranded molecule called deoxyribonucleic acid (DNA). One might describe DNA as a genetic instruction manual made of many chapters. DNA makes a template. called messenger ribonucleic acid (mRNA), to produce molecules. The process of copying a DNA sequence to RNA is called transcription. A transcriptional factor initiates or rcgulates the process. Each kind of cell is structured o perform a highly specialized function. Bone, muscle, heart, nerve, and skin cells make up part of the organism. and each of these cells is distinct and different.

   The genome is the organism’s full complement of genes, or DNA. With the exception of the red blood cells and a few types of cells in the bone marr ow. every cell has the entire genorne. It is amazing that a cell in the skin has the complete genome of about 30,000 genes, as well as a cell in the muscle.
    meiosis is the process by which germ cells in the ovaries and testes divide to produce gametes, the generic term for sperm and egg. In melosis the cells divide, and then divide again so that the sperm and egg have only half the original number, or 23 chromosomes. Meiosis occurs in phases. In phase one, chromosomes exchange genetic material so that they are not exact copies but may be mixed. In phase two, the cells contain two SetS of chromosomes. which divide again to form half the number of chromosomes. These are packaged into sperm or eggs with only 23 chromosomes. At the point of fertilization, nature’s arithmetic will
come out right, with 23 chromosomes from the mother and 23 from the father making 46 chromosomes—the number required to form a human being.