Biology Essay Example | Topics and Well Written Essays - 500 words - 9

Biology - Essay Example Each protein is formed in accordance with a set of instructions contained within the nucleic acid, which accounts for the cells genetic material. These set of instructions regulate which of the twenty amino acids are to be incorporated into the protein, and in what sequence. The final shape of the protein and its chemical properties is decided by the R groups of the amino acid subunits. There are four levels of protein structural organization: primary (1Â °), secondary (2Â °), tertiary (3Â °), and quaternary (4Â °). Primary structure is defined as the linear sequence of amino acids in a polypeptide chain. The secondary structure refers to certain spatial arrangement of the main peptide chain, examples of which are the alpha helix and the beta pleated sheet. Tertiary structure results from long-range contacts within the chain. The quaternary structure is the organization of protein subunits, or two or more independent polypeptide chains, as found in hemoglobin and certain enzymes. Proteins are broken down in the stomach into amino acids by enzymes known as proteases. These amino acids help build protein for the body organs, muscles, bones, blood, besides also acting as an important nutritional source of nitrogen. They also act as a storehouse of energy, containing around 4 kilocalories per gram. In addition to their function in growth and cell maintenance, proteins are also responsible for muscle contraction. Insulin, hormones and most digestive enzymes are all proteins. The antibodies in the immune system are well known proteins, and they are also the chief constituents of hemoglobin, which does the work of carrying oxygen to all parts of the body. The cell theory states that all organisms are made up of similar units of organization, called cells. This idea was conceived by Schleiden and Schwann in the year 1839 and has been one of the major milestones in the history of biology. The road