Proteins

• Proteins


  The most abundant organic compounds found in any living organisms, responsible for as much as 15% of the body's dry weight
• A typical mammalian cell may contain as much as 10,000 different kinds of proteins having a diverse array of functions
• Proteins


  • Form the structural parts of cells and tissues such as the keratin in hairs, collagen in connective tissues, myosin and actin in muscle cells
  • Enzymes that accelerate chemical reactions
  • Antibodies responsible for the body's defense against infection
  • Hormones that regulate body functions
  • Growth factors that influence an organism's growth and development
  • Gene activators, membrane receptors, transporters, contractile elements, blood clots, toxins, etc.
  • Carry out virtually all the activities inside the cell
• Amino acids


  The basic building blocks of proteins
• There are 20 essential amino acids in living organisms that serve as building blocks in the formation of different proteins
• Amino acid


  Made up of amino group (NH2), a carboxyl group (COOH) and a hydrocarbon side chain referred to as the R group
• Types of amino acids

  • Essential
  • Nonessential
• Essential amino acids


  Not synthesized by the body but obtained from food
• Nonessential amino acids


  Naturally produced in the body
• Complete or high quality proteins


  Contain all essential amino acids in the ratio needed by the body, derived from animal sources such as meat, fish, poultry, and eggs
• Incomplete or low-quality proteins


  Deficient in one or more of the essential amino acids, obtained from plants such as legumes, rice, corn, wheat and vegetables
• Proteins have four levels of structure: primary, secondary, tertiary and quaternary

  
• Primary protein structure


  1. Combination of the carboxyl carbon of one amino acid and the amine group of another amino acid, forming a covalent bond called peptide bond

  2. Molecule formed when two amino acids are combined is called a dipeptide

  3. Chain of three or more amino acids is called polypeptide
• Secondary protein structure


  • Coiling of the protein chain into a α-helix structure, formation of β-sheets, or twisting into random structures
  • Results from interactions between R groups, H-bonding or formation of –S-S- bonds between chains
• Tertiary protein structure


  • Twisting, bending, and folding of the secondary structures that arise from the interaction among the side chains
  • Hydrogen bonding, acid base interactions between coils and the disulphide linkages stabilize these shapes
• Quaternary protein structure


  • Clustering of several individual peptides into a final specific shape
  • Held together by hydrogen bonding, salt bridges and disulphide bonds
• Functions of proteins


  • Build, maintain, and repair body tissues
  • Source of energy when intake is greater than required
  • Involved in the creation of hormones, help control body functions, regulate cell growth
  • Produce enzymes that increase the rate of chemical reactions
  • Transport small molecules through the organism (e.g. hemoglobin transporting oxygen)
  • Help rid of foreign protein and prevent infections, illnesses and diseases (antibodies)
  • Store other substances in the organism (e.g. iron stored in the liver with ferritin)
  • Mediate cell responses (e.g. rhodopsin in the eye for vision)
  • Make up muscle fiber and help in movement
  • Provide structural components like collagen in skin and bone