Cell Biology

• Human tissues are made of cells.
• Most cells are of the order of 10^-3 cm in diameter. Some cell like nerve cell can stretch to 1 m!!
• There are about 4 x 10¹³ cells in an average adult.
• There are two kinds of cells:
  • Somatic Cells (Body cells).
  • Germ Cells (Reproductive Cells).
• Every Cell has a nucleus and the surrounding cytoplasm. There are several components performing different functions (Refer Lamarsh).

• One of the important constituent of the cell is chromatin. Its role shall be discussed later.
• Cells multiply by cell division. The division of somatic cell is called Mitosis.
• Every cell follows a cycle. There are four stages in this cycle. These are denoted by M-G1-S-G2. G1 and G2 refer to time gaps between the Mitosis and Synthesis of DNA phases.
• The chromatin is normally a tangled bunch strands of DNA (De-oxyribose Nucleic Acid) molecules and some nuclear proteins.
• During Mitosis, the chromatin untangles itself and becomes distinct set of bundles called Chromosomes.
• In humans there are 46 chromosomes in somatic cells and 23 chromosomes in germ cells.
• During Mitosis, each chromosome replicates itself.
• Certain segments of  DNA molecules in chromosomes  provide coding that control the synthesis of proteins. These are called genes.
• Changes brought about in genetic codes can result in inheritable changes.