proteins

proteins

1. what they are?

   • Are found in every cell in the body
   • involved in most of the body’s functions
   • Large molecules
     • Made up of chains of amino acids
   • The sequence of amino acids is determined by DNA

2. Structure

   • Made up of chains of amino acids
     • classified by
       • by number of amino acids in a chain
         • Dipeptides: 2 amino acids
         • Peptides: fewer than 50 amino acids
           • Peptide Bonds Link Amino Acids form when
             • when the acid group (COOH) of one amino acid joins with the amine group (NH2) of a second amino acid
               • Formed through condensation
               • Broken through hydrolysis
         • Tripeptides: 3 amino acids
         • Proteins: more than 50 amino acids
         • Polypeptides: more than 10 amino acids
     • Amino acids are composed of carbon, hydrogen, oxygen, and nitrogen
       • Limited supply of amino acids exist in the amino acid pool
         • The amino acid pool acts as a reservoir for protein synthesis
       • Surplus amino acids are
         • Used for glucose or energy
         • Stored as fat
         • Nitrogen is converted to urea and excreted in urine
     • Amino acids Are the building blocks of proteins
       • Contain a carboxylic acid group and an amino group on the alpha carbon.
         • Are ionized in solution
           • Types of Amino Acids
             • Nonpolar with hydrocarbon side chains
             • Polar with polar or ionic side chains
             • Acidic with acidic side chains
             • Basic with –NH2 side chains.
             • Amino Acid Metabolism
               • Liver metabolizes amino acids, depending on bodily needs
                 • Most amino acids are sent into the blood to be picked up and used by the cells
             • Amino Acid Absorption
               • Amino acids are absorbed in the small intestine
                 • Amino acids are transported to the liver from the intestines via
                   • In the liver, amino acids are
                     • Used to synthesize new proteins
                     • Released to the bloodstream and transported to cells throughout the body
                     • Converted to energy, glucose, or fat
     • When the amino acid pool reaches capacity
       • capacity the amino acids are broken down to their component parts for other uses
         • First deamination must occur
         • Carbon-containing remnants are
           • Converted to glucose, if they are glucogenic amino acids, through gluconeogensis
           • Converted to fatty acids and stored as triglycerides in adipose tissue
   • Four levels of structure
     • Primary structure
       • The particular sequence of amino acids
       • The backbone of a peptide chain or protein
       • The nonapeptides oxytocin and vasopressin have
         • similar primary structures
         • Differ only in the amino acids at positions 3 and 8
       • Insulin Was the first protein to have its primary structure
       • Primary structure is unchanged by denaturing
     • Secondary Structure
       • Has An alpha helix
       • indicate the three-dimensional spatial arrangements of the polypeptide chains.
     • Tertiary Structure
       • Gives a specific three dimensional shape to the polypeptide chain
       • Involves interactions and cross links between different parts of the peptide chain
       • Is stabilized by
         • Hydrophobic and hydrophilic interactions. Salt bridges
         • Hydrogen bonds
         • Disulfide bonds
       • The interactions of the R groups give a protein its specific three-dimensional tertiary structure
     • Quaternary Structure
       • Is the combination of two or more tertiary units
       • Is stabilized by the same interactions found in tertiary structures

3. Alteration of the protein’s shape and thus functions through the use of

   • Heat
   • Acids
   • Mechanical agitation
   • Salts
   • Bases

4. Functions

   • Provide structural and mechanical support
     • Maintain body tissues
       • Functions as enzymes and hormones
         • Help maintain acid base balance
           • Transport nutrients
             • Assist the immune system
               • Serve as a source of energy when necessary

5. Protein Quality

   • Complete proteins
     • Contain all nine essential amino acids
     • Usually animal source are complete proteins
     • Are considered higher quality
   • Incomplete proteins
     • Low in one or more essential amino acid
     • Usually plant sources are incomplete

6. digestion

   • Proteins are broken down to amino acids with the help of
     • Gastric juices
     • Enzymes in the stomach and small intestine
     • Enzymes from the pancreas and small intestine lining

7. Sources of protein

   • Exogenous
     • Animal products such as meat, poultry, fish, and dairy products
     • - plant products such as grains, grain products, legumes, and vegetables
   • Endogenous
     • digestive enzymes and glycoproteins, which generate about 17 g of protein each day
     • Desquamated mucoasal cells, which generate about 50 g of protein per day

8. Protein hydrolysis

   • Splits the peptide bonds to give smaller peptides and amino acids
   • Occurs in the digestion of proteins
   • Occurs in cells when amino acids are needed to synthesize new proteins

9. classification

   • Essential
     • must be consumed in the diet
   • Nonessential
     • can be synthesized in the body
   • Conditionally essential
     • cannot be synthesized due to illness or lack of necessary precursors