Download PDF Essentials of Medical Biochemistry With Clinical Cases by N . V. Bhagavan

Sinopsis

The unifying principle of biology is that all living organisms from the smallest and least complex (bacteria) to the largest (whales) and most complex (humans) are composed of cells. The precise location of cells in the multicellular organisms and the location of intracellular organelles within cells are vital in the normal development and function. In the simplest forms of life, such as the bacteria, cellular organization and biochemical functions are relatively uncomplicated and are primarily devoted to growth and reproduction. As a consequence, bacteria have evolved to survive and thrive in the widest range of environments imaginable – soil, rivers and oceans, hot springs, and frozen land, as well as in most areas of the human body. The only regions of the body that are normally sterile are: the respiratory tract below the vocal chords; the sinus and middle ear; the liver and gall bladder; the urinary tract above the urethra; bones; joints; muscles and blood; the linings around the lungs; and cerebrospinal fluid.

All bacteria belong to the super kingdom called prokaryotes . Yeasts, molds, and protozoa are also singlecelled organisms, but their cellular structures and functions are more complex than those of bacteria. These organisms belong to the other super kingdom called eukaryotes , along with all higher plants and all multicellular animals. A prokaryote cell has no true nucleus or specialized organelles in the cytoplasm. Bacteria reproduce asexually by cell division (fission). Because mitochondria (discussed later) have many properties in common with bacteria, it suggests that bacteria-like organisms were assimilated into eukaryotic

cells early in their evolution. All eukaryotic cells have a well-defined nucleus surrounded by a nuclear membrane and cytoplasm containing organelles that perform specialized functions. All eukaryotic somatic cells reproduce by the complex mechanisms of mitosis and cytokinesis. Germinal cells (sperm and ova) are formed by a slightly different mechanism called meiosis. Although the size and complexity of eukaryotic organisms differ enormously (amoeba, fly, worm, crab, bird, dog, dolphin, chimpanzee, human being), the basic organization and chemistry of their individual cells are quite similar. Sequencing of the nuclear DNA of many different organisms has shown remarkable conservation of key genes and proteins among widely dissimilar organisms. In some cases a protein produced by a human gene will function just as well when the human gene is swapped for the comparable gene in yeast.

Click here to download