proteins and amino acids

• carbohydrates, proteins, and lipids


  three main classes of the food we consume
• carbohydrates


  main energy source
• lipids


  the body's main energy reserve
• protein


  the body's source of energy for growth and cellular maintainance
• proteins

  make up the second largest portion of cells after water
• proteins


  are large polymeric compounds that cells synthesize from amino acids
• 4 kcal/g


  during oxidation, proteins yields energy in the amount of
• albumin


  Group of proteins characterized by heat coagulability and solubility in dilute salt solution
• biuret test


  reagent is light blue but turns violet in the presence of proteins
• xanthoproteic test

  respond to aromatic amino acids
• yellow to orange color


  positive result for xanthoproteic test
• millon's test


  gives positive result to proteins containing the phenolic amino acid tyrosine
• old rose


  positive reaction to millon test
• hopkins cole reaction

  specific for tryptophan, the only acid containing indole group
• violet ring


  positive result for hopkins cole
• red coloration


  positive result for pauly's test
• pauly's test


  detection of tyrosine or histidine
• lead acetate reaction

  detects amino acid containing a sulfur group
• black precipitate


  positive result for lead acetate reaction
• nitroprusside test


  test for cysteine
• reddish-purple color


  positive result for nitroprusside test
• sakaguchi reaction


  detection of protein with the amino acid containing the guanidinium group, arginine
• red-orange color


  positive result for sakaguchi reaction
• heller's ring test


  detect the presence of albumin by the formation of white ring
• denaturation


  the unfolding and rearrangement of the secondary and tertiary structures of protein without breaking peptide bonds
• reverse denaturation


  For mild condition, protein can be restored to its original conformation by carefully reversing the conditions that caused the denaturation
• heat, violent shaking, very high pressure, and ultraviolet radiation


  physical agents of denaturation
• extreme ph, high salt concentration, heavy metal ions, organic solvents, and surface active solvents


  chemical agents of denaturation
• heat

  gentle heating-reversible denaturation
• vigorous heating


  disrupts different types of bonds
• pH


  disrupt h-bonds and salt bridges resulting in irreversible denaturation
• concentrated mineral acids


  disrupt h-bonds and salt linkages
• alcohol


  coagulates all types of proteins except prolamines
• salts of heavy metals


  disrupts salt bridges and disulfide bonds
• alkaloidal reagents


  denature protein by disrupting salt bridges and h-bonds
• tannic acid


  present in tea, which forms crusts and reduce the amount of water loss from the area and also reduces exposure to air