Finals 3

• Protein digestion

  1. Chewing

  2. Stomach

  3. Small intestine

  4. Bloodstream
• You can increase the protein absorption through the consumption of certain foods
• Protein


  • It is one of the most important substances of our body
  • Muscles, hair, eyes, organs, and many hormones and enzymes are primarily made up of protein
  • Protein helps us to repair and maintain body tissues
• Not all proteins are created equal. There are things that we can do for our body to use it efficiently
• Protein


  A macromolecule made up of small molecules called amino acids
• Amino acids

  • 20 amino acids
  • 11 can be made by our body
  • 9 essential amino acids that we can only get from our diet or food
• Complete proteins or whole proteins


  High quality protein sources such as meat, fish, eggs, milk, or dairy products contains 9 amino acids
• Incomplete proteins


  Other sources of protein such as nuts, seeds, beans, contain some of the essential amino acids
• We can combine some of these proteins sources such as rice and beans to create a complete protein that contains all the 9 essential amino acids
• Protein digestion in the mouth

  1. Amylase

  2. Lipase
• Protein digestion in the stomach

  1. Hydrochloric Acid (HCl)

  2. Proteases
• Protein digestion in the small intestine

  1. Pancreas releases enzymes and bicarbonate buffer

  2. Trypsin

  3. Chymotrypsin

  4. Carboxypeptidase

  5. Aminopeptidase
• Protein absorption


  Happens in the small intestine where there are microvilli that increase absorption
• Once absorbed, the amino acids are released into the bloodstream which takes them into other parts of our body to help repair or maintain different parts of our body
• Protein digestion (denaturation and hydrolysis)


  1. Starts in the stomach

  2. Denatured by HCl

  3. Enzyme pepsin hydrolyzes about 10% peptide bonds
• Protein digestion (denaturation and hydrolysis) in the small intestine

  1. pH 7.0-8.0 helps neutralize acidified gastric content

  2. Trypsin, chymotrypsin and carboxypeptidase in pancreatic juice hydrolyze proteins to smaller peptides

  3. Aminopeptidase further hydrolyze the small peptides to amino acids
• Amino acids liberated are transported into blood stream via active transport process
• The passage of polypeptides and small proteins across the intestinal wall is uncommon in adults. In infants it allows the passage of proteins such as antibodies in colostral milk from a mother to a nursing infant to build up immunologic protection
• Enzymes are produced in inactive forms called zymogens that are activated at their site of action
• Amino acid pool


  The total supply of free amino acids available for use in the human body, derived from dietary protein, protein turnover, and biosynthesis of amino acids in the liver
• Nitrogen balance


  The state that results when the amount of nitrogen taken into the human body as protein equals the amount of nitrogen excreted from the body in waste materials
• Types of nitrogen imbalance

  • Negative nitrogen imbalance
  • Positive nitrogen imbalance
• Negative nitrogen imbalance


  Protein degradation exceeds protein synthesis, amount of N in urine exceeds nitrogen consumed, results in tissue wasting
• Positive nitrogen imbalance


  Rate of protein synthesis (anabolism) is more than protein degradation (catabolism), nitrogen intake is higher than nitrogen elimination, results in large amounts of tissue synthesis
• The greater the nitrogen balance, the faster the recovery
• Ways amino acids from the body's amino acid pool are used

  • Protein synthesis
  • Synthesis of non-protein nitrogen-containing compounds
  • Synthesis of non-essential amino acids
  • Production of energy
• Protein synthesis

  About 75% of amino acids go into synthesis of proteins needed for continuous replacement of old tissues and to build new tissues
• Synthesis of non-protein nitrogen-containing compounds

  Synthesis of purines and pyrimidines for nucleic acid synthesis, synthesis of heme for hemoglobin, neurotransmitters and hormones
• Synthesis of non-essential amino acids

  Essential amino acids can't be synthesized because of the lack of appropriate carbon chain, non-essential amino acids can be synthesized
• Production of energy

  Amino acids are degraded to provide energy, excess proteins can be converted into triglycerides and used as energy
• Amino acid degradation


  1. Amino nitrogen atom is removed and converted to ammonium ion, which is excreted as urea

  2. Remaining carbon skeleton is converted to pyruvate, acetyl CoA, or a citric acid cycle intermediate
• Liver is the principal site of amino acid metabolism, but other tissues like kidneys, muscles, and adipose tissues also contribute
• Amino acid degradation

  1. First step is the separation of amino group (N) from the carbon skeleton (C) - Transamination Reaction

  2. Carbon skeleton forms glucose or fats

  3. Nitrogen portion can be eliminated via Urea, biosynthesis of non-essential amino acids, or used in Non-Protein Nitrogen-containing compounds
• Transamination


  The -amine group of amino acid is exchanged with the -keto group of another compound, amino acid becomes ketoacids
• Oxidative deamination


  Amino acid loses its amino group or the -amine group, produces ammonia, responsible for the breakdown of excess protein in the liver
• Transamination

  Involves transfer of the amino group of an -amino acid to an alpha keto acid, major biochemical reaction responsible for the synthesis of the non-essential amino acids
• Transamination is an enzyme catalyzed reaction, there are at least 50 transaminase enzymes associated with transamination reactions
• Effect of transamination

  Collects the amino groups from a variety of amino acids into just two amino acids—glutamate (most cells) and alanine (muscle cells), net effect is the collection of the amino groups into glutamate
• Oxidative deamination

  Ammonium ion (NH4+) group is liberated from the glutamate amino acid formed from transamination, glutamate is converted into alpha-keto glutarate with the release of an ammonium ion
• The ammonium ion produced by oxidative deamination is a toxic substance, so it is quickly converted carbomoyl phosphate and then to urea via the urea cycle