Foods and Nutrition 1021 Lecture Notes - Lecture 6: Toxic Heavy Metal, Peptide Bond, Quinoa
11 Jun 2018
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Chapter 6 Notes
"Proteios"- means of prime importance
• Prime material of life
Proteins
• C, H, O, N
• Strands of amino acids
Amino Acids (AA)
• 20 different kinds known
• Building blocks of protein
• Amine group (N-containing)
• Acid group
• Side chain (creates a unique chemical structure, differentiates one AA from another, makes
AA differ in size/shape/electrical charge)
• Join together via peptide bonds to form in the body
Peptide bond: chemical bond formed between the amine group end of one AA and the acid
group end of the next
• Each AA carries an electrical charge that attracts or repels various ends of each AA resulting
in different shapes and sizes
• Shape of AA enables them to perform different tasks (enzymes act as catalysts, globular
hemoglobin carries O2 & Fe, collage makes up tendons and ligaments)
EAA- cannot be synthesized at all or are present in insufficient amounts to meet physiologic
needs; must be supplied by the diet
Nine Essential AA:
1. Histidine
2. Isoleucine
3. Leucine
4. Lysine
5. Methionine
6. Phenylalanine
7. Threonine
8. Tryptophan
9. Valine
Dispensable AA- alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine,
glycine, proline, serine, tyrosine
Conditionally Essential AA- normally non-essential AA, but must be supplied by the diet when
the body cannot meet its needs; e.g., tyrosine from phenylketonuria (PK)
• Used to build body protein
• Altered to make another compound (niacin)
• Stripped of N, burned as fuel
• Converted to glucose or fat
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• Are wasted when: total energy is lacking, protein is overabundant, AA is oversupplied in
supplement form, quality of dietary protein is low (too few EAA)
• Body recycles and conserves AA by breaking protein molecules and reusing AA, discarding
N atom as waste
• Quinoa, soy, hemp hearts, chia seeds contain all of the essential amino acids
• Recycling conserves body AA for emergency energy needs
• Priority system in dismantling tissue proteins- uses the most dispensable ones first (small
proteins in blood & muscles) ; guards structural proteins of heart & vital organs
• The body will dismantle it's self on a priority basis (muscle tissue used in order to gain
muscle tissue if not enough carbohydrates)
• Body designed to handle whole proteins best (highly concentrated single AA may unbalance
absorption process)
• Use of AA as dietary supplements- high risk of toxicity, largely untested, impurities
(pregnant women, infants, elderly, smokers, etc)
Denaturation of proteins
• Irreversible change in protein's shape due to heat/acids/bases/alcohol/salts of heavy metals
(Hg, silver)
• Useful in cooking
• In heavy metal poisoning the person should drink milk so that the poison acts on the milk
proteins instead of the linings of the GIT & then can be expelled by vomiting.
Digestion
• Mouth- no digestion; simply breaking down food into small pieces by chewing
• Stomach- HCL denatures protein, enzyme pepsin breaks apart AA strands into polypeptides
& some single AA, for protection the stomach will secrete mucous
Note: no food can make the stomach acid more acidic as it is at a pH of 1.5 already
• The small intestine- Alkaline (basic) pancreatic juices neutralize the acidic solution that
comes from the stomach as it enters the small intestine and the liquids pH is raised to 7
(neutral)
Proteases from pancreas & intestine split peptide strands into tri- and dipeptides & AA
Peptidases on surface & within cells of the small intestine split tri- and dipeptides further into
AA
Intestinal cells move AA to blood stream, transported to liver for use and distribution to body
cells
Note: sometimes larger protein molecules sneak through into the blood stream which may lead
to an allergic reaction as these are seen as foreign to the body in the bloodstream
Protein Synthesis
• Body pool of AA- component AA of both food proteins & body proteins form a pool of raw
materials for building protein molecules
• Protein synthesis- involves DNA, (messenger) mRNA, ribosomes, (transport) RNA
DNA- serves as the template to make the mRNA
MRNA- has the instructions to make the needed proteins
Ribosomes- protein- making machinery of the cell
TRNA- collects AA from the body pool/cell fluid & brings them to the mRNA
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
proteios- means of prime importance: prime material of life. Proteins: c, h, o, n, strands of amino acids. Amino acids (aa: 20 different kinds known, building blocks of protein, amine group (n-containing, acid group, side chain (creates a unique chemical structure, differentiates one aa from another, makes. Join together via peptide bonds to form in the body. Eaa- cannot be synthesized at all or are present in insufficient amounts to meet physiologic needs; must be supplied by the diet. Nine essential aa: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine. Dispensable aa- alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine. Irreversible change in protein"s shape due to heat/acids/bases/alcohol/salts of heavy metals (hg, silver: useful in cooking. In heavy metal poisoning the person should drink milk so that the poison acts on the milk proteins instead of the linings of the git & then can be expelled by vomiting.
