Proteins Functions of Protein Building Body Constituents n
Proteins
Functions of Protein: Building Body Constituents n n All cells contain protein Many are primarily protein All body cells break down Protein is needed for continual repair and rebuilding
Functions of Protein: Maintaining Fluid Balance n n Fluid flows from capillary bed into extracellular space (spaces between cells) to nourish those cells Protein stays in the blood vessels (too large to move through vessel walls) Protein in the capillaries attracts fluid back into the blood If there is inadequate protein, extremities swell as fluid leaves bloodstream
Functions of Protein: Acid -Base Balance n n Proteins help regulate acid-base balance in the blood p. H measures acidity or alkalinity (base) – – – p. H of 7 = neutral p. H<7 = acid p. H>7 = alkaline or base Proteins pump ions in and out of cells to regulate p. H Proteins serve as buffers – compounds that maintain acidity within a narrow range
Functions of Protein: Hormones n n The body’s messenger system Regulate body functions including metabolic rate (thyroid hormone) and blood glucose (insulin and glucacon)
Functions of Protein: Enzymes Speed chemical reactions n Genetic errors may result in lack of a key enzyme n – Example: galactosemia, PKU
Functions of Proteins: Immune Function n White blood cells n Antibodies
Functions of Protein: Can be Converted to Glucose Maintain blood sugar for brain and red blood cells n Brain uses 19% of the body’s energy at rest n Amino acids can be converted to glucose (gluconeogenesis) n
Functions of Protein: Energy Provides little energy to the body except in prolonged exercise n Only carbon backbone used n Deamination n – Liver removes amine group – Nitrogen converted to urea and excreted by the kidneys n Inefficient and expensive energy source
Protein Structure Carbohydrates and lipids: contain carbon, hydrogen, oxygen n Proteins: contain carbon, hydrogen, oxygen and nitrogen n Building blocks of proteins are amino acids n
Amino Acid R NH 2 O C C OH H R group Acid group Amine group
Features Common to all Amino Acids Central carbon n Amino or amine group n Acid group n
Amino Acids Differentiated by Side group (“R” group) n 20 different side chains n 20 different amino acids n
Amino Acids n Nine “essential” amino acids – The body cannot make in sufficient quantities – Must consume in diet n Eleven “non-essential” amino acids – Body can produce from other amino acids
Essential AA Nonessential AA Histidine Alanine Isoleucine Arginine Leucine Asparagine Lysine Aspartic Acid Methionine Cysteine Phenylalanine Glutamic acid Threonine Glutamine Tryptophan Glycine Valine Proline Serine Tyrosine
Protein Turnover Protein undergo breakdown and synthesis n Responds to change n Amino acid can be recycled n
Proteins Very large molecules n 1000’s of amino acids joined together with peptide bonds n Myglobin →
Protein Shape Determined by amino acid sequence n Different amino acids joined → different shapes n Different shapes → different functions n
Protein Synthesis DNA contains coded instructions n Copies of codes are transferred to the cytoplasm (via m. RNA) n Amino acids added one at a time with aid of t. RNA n
Protein Synthesis
Protein Organization H H O N C OH CH SH SH CH 2 CH H N H H 2 O C OH H H N O CH 3 H 2 O n n Dipeptide Tripeptide Oligopeptide CH C N C CH Peptide bond n O CH 3 H O OH
Denaturation Changes in protein shape n n Non-functioning protein Not biologically active Denaturing agents n n n Acid Alkaline substances (bases) Heat Agitation Enzymes
Denaturation of Proteins Heat/acid/alkaline/enzymes Results in alteration of the protein’s three dimensional structure
Protein Deficiency: Protein. Energy Malnutrition Kwashiorkor: the disease that the first child gets when the new child comes n Older child is converted from breast milk to protein-deficient diet n Moderate energy deficit with severe protein deficit n Often overlaid with infections n
Symptoms of Kwashiorkor n Apathy, listlessness, withdrawal – Protein lacking for brain development – Lack energy for interaction n Failure to grow, poor weight gain – Protein unavailable for building tissue n Change in hair color – Melanin (a protein) gives hair color, not made
Symptoms of Kwashiorkor (cont) n Fatty infiltration in the liver – Lipoproteins are not made, fats accumulate, liver enlarges, abdomen protrudes n Massive edema in the abdomen and legs – Protein unavailable to maintain fluid balance n Some subcutaneous fat tissue
Kwashiorkor Treatment Cure infections, parasites n Adequate protein, energy, vitamins, minerals n Successful if in time n
Fig. 6. 10
Marasmus Starving to death n Often younger infants n Insufficient protein, energy, nutrients n “skin and bones” appearance n Little or no subcutaneous fat n Reduced brain growth n
Marasmus Little or no breast-feeding n Formula overdiluted, unsanitary water n Can occur in adults as well as infants and children n
Marasmus: Treatment Large amounts of energy and protein n Permanent retardation common n – Poor brain growth in the first year of life
Effect of High Protein Diet Generally low in n Dietary fiber n Some vitamins n Some minerals n Phytochemicals Generally high in n Saturated fat
Is a High-Protein Diet Harmful? n n n Low in plant foods (fiber), vitamins, phytochemicals Intake of animal protein increases risk for heart disease (high in saturated fat) Excessive intake of red meat is linked with colon cancer Burden on the kidney Increase calcium loss National Academy of Sciences recommend no more than 2 x RDA for protein
Protein in Foods
Plant Protein Provide protein, minerals, and dietary fiber n Contain no cholesterol n Limited saturated fats n Allow a few weeks for the GI tract to adjust to the higher fiber n Availability of Beano® n
Protein Digestion: Cooking food can be a first step in protein digestion n Cooking denatures and softens proteins and softens tough connective tissue in meat n Cooking makes protein-rich foods easier to chew, swallow, digest n Also makes protein-rich foods safer to eat n
Digestion of Protein in the Stomach n n n Proteins are denatured by cooking and acid in the stomach Gastrin stimulates the release of acid and pepsin Pepsin is activated and breaks down proteins into peptones (shorter chains of amino acids)
Digestion of Protein in the Small Intestine Proteins stimulate the release of CCK n Pancreas release the protein splitting enzymes: trypsin, chymotrypsin, and carboxypeptidase into the duodenum n The enzymes will break peptones into smaller peptides and amino acids n Peptides and amino acids are ready for absorption n
Protein Absorption Active absorption n Whole proteins are broken down at the microvilli surface and within the absorptive cells n Whole proteins are eventually broken down to amino acids n Many different amino acid transport mechanisms n Amino acids are sent to the liver via portal circulation n
Amino Acid Metabolism Amino acids are used to synthesize new body proteins n If not used to synthesize new proteins n – Deamination: liver removes amino group – Nitrogen is converted to urea – Kidneys flush nitrogen from the body
RDA for Protein (adults) n n Promotes equilibrium 0. 8 gm of protein / kg of healthy body weight 154 lb. = 70 kg 2. 2 kg/lb. 70 kg x 0. 8 g protein = 56 g protein kg healthy body wt
RDA for Protein Increased by ~10 -15 gm /day for pregnancy n Endurance athletes may need 1. 5 - 2 gm/kg healthy weight n About 8 -10% of total kcals n Most of us eat more than the RDA for protein n Excess protein cannot be stored as protein n New DRI for protein coming n
Fig. 6. 9
Individual Amino Acid Supplement may cause imbalances and toxicities n Body is designed to handle whole proteins n Supplement can overwhelm the absorptive mechanism n Excess of one AA can hamper absorption of other AAs n
Dietary Protein n High-quality – complete n Low-quality – incomplete All-or-none principle in protein synthesis n Limiting amino acid n Complementary protein n
Limiting Amino Acid C is the limiting amino acid in this example CCCCC AAAA RRRRRR CAR CAR CAR R A A A
Complementary Protein Food 1 Food 2 CC AAAA RRR CAR CCCC AA RRR CAR CAR CAR
Complementary Protein Beans (legumes) Grains Nuts/seeds Vegetables
Soy protein is similar to animal protein (used in school lunches) n High in linoleic acid and some linolenic acid n Calcium source and bone health n Isoflavones n Heart disease n Cancer n
Vegetarian Diets n Why become a vegetarian? – Ethical reasons – Health reasons n As a group, vegetarians are thinner and healthier than meat eaters – Religious reasons
Types of Vegetarians Vegans: eat only plant foods n Fruitarians: eat only the seed-bearing parts of plants n Lactovegetarians: use dairy products n Lactoovovegetarians: use dairy products and eggs n
The Vegetarian Diet Pyramid
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