Download Lecture 6A/ Chapter 6 Protein

Lecture 6A/ Chapter 6
Protein
(pages 173 to 203)
Guest Lecturer for 2104
Shannan Grant, MSc, RD, PhD Candidate
The Chemist’s View of Proteins
• 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
Amino Acid Structure (FIG 6.1)
Examples of Amino Acids (FIG 6.2)
Getting to Know…Amino Acids
• 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
How do Amino Acids Form Proteins?
Condensation
Figure 6.3. Formation of Dipeptide
Protein Structure: Unraveling the Mystery
• Primary structure
Shape => Function
• 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
Proteins in the
Human Body
Protein Synthesis
• 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-vegetablediet-genetic-heartdisease-111012/
• “Highlight 6” (Pages 198 to 199 only; including definitions)
Protein Synthesis continued
• Transcription
Know Figure 6.7. Protein Synthesis
• 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
Roles of Proteins
• 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
Roles of Proteins – 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
Dietary Protein
• Protein Quality
Quality and Quantity
are both important!
• 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
Dietary Protein continued
• 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 Proteins
Figure. 6.15.
Vegetarian/vegan diets
can provide more than
enough protein
Protein Digestion and Absorption
• 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
Pepsin and HCl
Protein ----------------------------> Smaller polypeptides
Key definitions to know: Hydrolysis, denatures,
pro-enzyme, and digestive enzymes (Page 177).
Protein Digestion and Absorption
• Several pancreatic and intestinal proteases (Fig 6.6)
hydrolyze polypeptides passed from the stomach.
Intestinal “-ases”
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
Protein Quantity
• 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=0309085373
Health Canada; DRI for Protein: http://www.hc-sc.gc.ca/fn-an/nutrition/reference/index-eng.php
Fad Diets
• 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
Clinical Classification of PEM
• 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)
Dietary Protein and Human Health
• 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 literature
Foods and nutrient perspective
Dietary Protein and Human
Health Continued (Page 191-192)
• 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?
How much should you have?
• 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).
Are you getting enough?
•
•
•
•
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
Protein Supplements
• 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 Protein
A by-product of cheese production; the watery part of
the milk that separates from the curds.
Protein Supplements - 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; falsely
Promoted as supplements for exercising
muscles.
A Preview of Protein Metabolism
The 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.