Lecture 6A/ Chapter 6 Protein - Cape Breton Universityfaculty.cbu.ca/ebarre/lecture...
Transcript of Lecture 6A/ Chapter 6 Protein - Cape Breton Universityfaculty.cbu.ca/ebarre/lecture...
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Lecture 6A/ Chapter 6 Protein (pages 173 to 203)
Guest Lecturer for 2104Shannan Grant, MSc, RD, PhD Candidate
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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
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AminoAcidStructure(FIG6.1)
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ExamplesofAminoAcids(FIG6.2)
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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
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HowdoAminoAcidsFormProteins?
Figure 6.3. Formation of Dipeptide
Condensation
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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
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ProteinsintheHumanBody
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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)
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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
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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
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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
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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!
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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
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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
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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”
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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
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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.
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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
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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)
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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
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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?
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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).
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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
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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.
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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.
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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
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THANK YOU FOR YOUR ATTENTION!Questions, please.