Molecular Biology

How Proteins are Broken down into Amino Acids



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Dietary protein intake is critical to the maintenance of the body.  Protein that people eat (such as meat and dairy products) gets digested and broken down into much smaller, simpler components, which are then re-assembled into one of many different things.  Without sufficient dietary protein intake, the body can’t manufacture the necessary levels of peptide hormones or structural proteins to sustain bodily functions

Protein breakdown (digestion) into amino acids begins with mastication (chewing the food).  After the food is ground down it passes through the esophagus and into the stomach.  There, mucus, hydrochloric acid and pepsinogen all mix with and chemically start to break down the complex proteins.  The hydrochloric acid and the pepsinogen combine to form a proteolytic enzyme (breaks down proteins) called pepsin.  The hydrochloric acid denatures the protein’s amino acid strands so that the pepsin can break the polypeptide bonds. The mechanical churning of the stomach facilitates the breakdown of the complex proteins.  This mixture gets passed into the small intestine in the form of peptone and proteose.

In the small intestine, intestinal proteases (proteolytic enzymes) and trypsin (a proteolytic enzyme that comes from the pancreas) further act to break the complex amino acids down into simpler versions.  Once they are completely broken down into single amino acids, they are then transported into the blood stream via the capillaries in the intestinal wall.

Amino acids within the body fall into one of two categories:  Essential amino acids and non-essential amino acids.  An essential amino acid is one that the body requires to meet physiological needs.  It cannot be produced by the body and has to be derived from dietary intake.  The essential amino acids are isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. non-essential amino acids are all produced by the body.  It is not that they aren’t important, but are so-named because the body produces them in sufficient quantities provided there is adequate dietary intake of proteins.

Protein consumption can affect one’s health in a number of ways.  Too little protein can cause protein energy malnutrition, which is the most widespread and common form of malnutrition in the world.  Too much dietary protein also comes with its hazards.  Excessive protein intake can induce severe strain on the kidneys and liver.  Animal proteins tend to be higher in saturated fats which can lead to cardiovascular issues.  Diets high in animal (but not vegetable) proteins cause increased excretion of calcium which can lead to osteoporosis.  People who consume high levels of dietary protein may be preventing adequate dietary intake of other essential nutrients.

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ARTICLE SOURCES AND CITATIONS
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  • InfoBoxCallToAction ActionArrowhttp://library.thinkquest.org/11226/main/c14txt.htm
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  • InfoBoxCallToAction ActionArrowhttp://www.texashste.com/documents/curriculum/nutrition/proteins_and_amino_acids.pdf