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Lecture 6A/ Chapter 6 Protein (pages 173 to 203)
Guest Lecturer for 2104Shannan Grant, MSc, RD, PhD Candidate
TheChemist’sViewofProteins• A protein is a compound composed of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) atoms.
• Proteins are like carbohydrates (CHO) and lipids.BUT
• Proteins also contain a N atom.
• Amino acids: the building blocks of proteins.• Amino group• Acid group• H atom• Distinctive side group
AminoAcidStructure(FIG6.1)
ExamplesofAminoAcids(FIG6.2)
GettingtoKnow…AminoAcids• Essential Amino Acids
• cannot make at all or cannot make enough • 9 essential amino acids exist • must be supplied by the diet (dietary) • NOTE: Table 6.1. (text) lists essential amino acids
• Non‐essential Amino Acids• can make as long as the following ingredients are present:
• Nitrogen (amino group) • Fragments from carbohydrate and fat (rest of the structure)
• Conditionally Essential Amino Acids• What do you think?
There are 20 amino acids
HowdoAminoAcidsFormProteins?
Figure 6.3. Formation of Dipeptide
Condensation
ProteinStructure:UnravelingtheMystery• Primary structure
• Sequence of amino acids or chemical bonds• Secondary structure
• Electrical attractions within the polypeptide• Shape The chain can twist into a helical shape• Shape give the protein strength
• Tertiary structure • A side group can be hydrophilic or hydrophobic• The resulting “tangles” provide stability
• Quaternary structure • Two or more polypeptides• Example (Figure 6.5. The Structure of Hemoglobin)
• 4 associated polypeptide chains
Shape => Function
ProteinsintheHumanBody
ProteinSynthesis• We are unique because our proteins are unique.
• Amino acids sequence determined by genes
• Diet plays a role• Adequate intake• Nutri‐genomics or Nutritional Genomics
• Are we what we eat? Can we modify our risk with lifestyle? http://www.ctv.ca/CTVNews/Health/20111012/fruit‐vegetable‐diet‐genetic‐heartdisease‐111012/
• “Highlight 6” (Pages 198 to 199 only; including definitions)
ProteinSynthesiscontinued• Transcription
• Deoxyribonucleic acid (DNA) => template to make Messenger Ribonucleic acid (mRNA)
• mRNA carries the code/”message” to ribosome• Ribosomes are “protein factories “; moves along mRNA
• Translation • mRNA specifies sequence of amino acids (“manager”)• Transfer (tRNA); amino acid specific
• Sequencing Errors Communication break‐down• Example: Sickle Cell Anemia; Valine replaced Glutamic Acid
Know Figure 6.7. Protein Synthesis
RolesofProteins• Structural (e.g. collagen)
• Building blocks for most body structures• Replacement of dead or damaged cells
• Enzymes (e.g. proteases, lipases) • Break down, build up, and transform substances • Catalysts for reactions
Figure 6.9. Enzyme Action
RolesofProteins– continued…• Hormones (e.g. insulin, parathyroid hormone, table 6.2.)
• Messenger molecules; transported in blood to target tissues• Regulators of fluid balance
• When inadequate; Edema• Acid‐base regulators
• Tight control of bloods acid‐base balance• Prevention on acidosis and alkalosis
• Transporters (e.g. glucose transporters, hemoglobin) • Active transport system (Fig. 6.10: An example of transport protein)
• Antibodies (e.g. immunoglobin)• Defend body against disease
• Gluconeogenesis• Insufficient dietary intake of energy and carbohydrate• Energy and glucose at the expense of lean body tissue
DietaryProtein• Protein Quality
• Two factors influence protein quality:1. Digestibility
• Source (Flesh foods, type of plant foods etc.)• Other foods eaten
2. Amino acid composition• 9 essential amino acids, N‐containing amino groups and energy• Limiting amino acid we cannot make partial proteins
• High Quality Protein (sometimes called “complete”)• A dietary protein containing all the essential amino acids that humans require. • Animal proteins (flesh foods), soy protein
Quality and Quantity are both important!
DietaryProteincontinued• Limiting Amino Acids
• An essential amino acid found in the shortest supply relative to the amounts needed for protein synthesis in the human body. Four amino acids are the most likely to be limiting: Lysine, Methionine (soy is lacking), Threonine, Tryptophan.
• Complementary ProteinsFigure. 6.15.
Vegetarian/vegan diets can provide more than
enough protein
ProteinDigestionandAbsorption• Mouth and Salivary Gland
• Crushed and moistened in the mouth
• Stomach• Protein Hydrolysis (break‐down)
• Hydrochloric (HCl) acid uncoils the protein and converts pepsinogen into pepsin
Protein ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐> Smaller polypeptides
Key definitions to know: Hydrolysis, denatures, pro‐enzyme, and digestive enzymes (Page 177).
Pepsin and HCl
ProteinDigestionandAbsorption• Several pancreatic and intestinal proteases (Fig 6.6) hydrolyze polypeptides passed from the stomach.
Polypeptides ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐> Tri‐peptides Di‐peptides
• Enzymes on the surface of the small intestinal cells hydrolyze these peptides so that the intestinal cells can absorb the amino acids.
• When absorbed proteins are either: used for energy, synthesis (structure, facilitate, regulate) or transported to the liver.
See Fig. 6.6. Protein Digestion in the GI Tract
Intestinal “‐ases”
ProteinQuantity• How do we know if we are getting enough?
• Canadian Food Guide/ Dietary Reference Intakes• Acceptable Macronutrient Distribution Range (AMDR)
Ref: Institute of Medicine
IOM; DRI for Protein: http://www.nap.edu/openbook.php?isbn=0309085373Health Canada; DRI for Protein: http://www.hc‐sc.gc.ca/fn‐an/nutrition/reference/index‐eng.php
FadDiets• Manipulation of the macronutrient distribution
• Most high protein diets are in fact low carb diets and in turn low in fibre and B vitamins and high in cholesterol.
Examples: Atkins, The Zone Diet, Protein Power…
FAD: A phenomenon that becomes popular for a very short time.
Malnutrition• Malnutrition
• Exists in developing and non‐developing countries • No longer a malady of the starving
• Absorptive, hyper‐caloric diets
• Protein‐Energy Malnutrition (PEM)• Deprived of energy, protein or both• Acute PEM wasting• Chronic PEM Stunting
ClinicalClassificationofPEM• Marasmus
• Chronic PEM• Clinical presentation skin and bones• results from severe deprivation, or impaired absorption, of energy, protein, vitamins and minerals.
• Kwashiorkor• Acute PEM• Clinical presentation edema (swollen belly)• results from inadequate protein intake and infections
Treatment: rehydration and personalized nutritional intervention or medical nutrition therapy (MNT)
DietaryProteinandHumanHealth• Can one have too much of a good thing?Yes…?
• Heart disease, cancer, osteoporosis, overweight and obesity and kidney disease
OR• Have diets high in saturated and/or overall fat, low in fibre, low in antioxidants, high in salt have been implicated?
• Substituting vegetable protein and lean flesh products may improve clinical indicators of the above conditions.
Clinicians must learn how to critically appraise literatureFoods and nutrient perspective
DietaryProteinandHumanHealthContinued(Page191‐192)
• Overweight and Obese• Low carbohydrate diets
• Adequacy?• Satiety
• Osteoporosis• ↑ protein intake results in increased excretion of Ca• Ratio of protein to Ca may be important• Is animal protein more detrimental?
Howmuchshouldyouhave?• Dietary Reference Intakes (DRI)
• AMDR• Cautionary note
• RDA/ AI*• 0.80 g/kg body weight/ day
• Currently no Tolerable Upper Intake
• RDA = recommended dietary allowance, AI = Adequate intakes (see the end of the text for more information on DRIs).
• Know how to calculate recommended protein intakes (page 193).
Areyougettingenough?• Canadian Food Guide • Space on Your Plate• Food Labels• Registered Dietitian
• http://www.dietitians.ca/
• Canadian Nutrient File • http://webprod3.hc‐sc.gc.ca/cnf‐fce/index‐eng.jsp
ProteinSupplements• Protein powders
• Often used by athletes and “dieters” • Work builds muscle, not supplements• A balanced healthy diet is sufficient
• Energy needs will ↑ as activity/ demand ↑• Intake beyond needs will be stored
Example: Whey ProteinA by‐product of cheese production; the watery part of the milk that separates from the curds.
ProteinSupplements‐ continued• Amino acid supplements
• Single amino acids do not occur naturally in food• May be harmful
• Side effects may include: diarrhea, deficiency, toxicity
Example: Branched‐chain amino acids are leucine, isoleucine, and valine; falselyPromoted as supplements for exercisingmuscles.
APreviewofProteinMetabolismThe following concepts will be key to your understanding of protein metabolism in chapter 7:• Protein Turnover• Amino acid pool• Nitrogen balance/ imbalance• Deamination
• Keto acid
THANK YOU FOR YOUR ATTENTION!Questions, please.