Chapter 7: Proteins
Chapter 7: Proteins HUMNNTR 2310 - 0010
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This 12 page Class Notes was uploaded by Victoria Gonzalez on Tuesday October 13, 2015. The Class Notes belongs to HUMNNTR 2310 - 0010 at Ohio State University taught by Irene Hatsu in Fall 2015. Since its upload, it has received 42 views. For similar materials see Fundamentals of Nutrition in Human Development at Ohio State University.
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Date Created: 10/13/15
Chapter 7 Proteins Victoria Gonzalez 1 Protein intro a Made up of amino acids b Accounts for about 17 of body weight c Important for building muscles connective tissue antibodies hormones and enzymes d North American diets are very rich in protein 2 Amino acids a Building blocks of proteinquot b The body needs 20 to function c Contain carbon hydrogen oxygen and nitrogen some suHurtoo Amino group contains nitrogen Acid group carboxyl Hydrogen atom R group side chain makes each amino acid unique determines structure and function i Changes with each amino acid 37 Hydrogen Amino Carlboxyl H H N C C H l quot0quot R Riglroup valiant h Essential amino acids 9 of them i lndispensible ii Body cannot make them because 1 Cells cannot make carbon skeleton 2 Cells cannot attach an amino group to the skeleton 3 Cells cannot complete synthesis fast enough iii Must be acquired from diet i Nonessential amino acids 11 of them i Dispensable ii Body cells make these j Conditionally essential amino acids i During infancy disease or trauma ii Phenylketonuria patients have a limited ability to metabolize the amino acid phenylalanine due to enzyme de ciency 1 Phenylalanine is used to make tyrosine 2 PKU patients cannot make suf cient tyrosine 3 Tyrosine is a conditionally essential amino acid because it must be obtained from diet in PKU patients iii Synthesis of non essential amino acids 1 Transamination the transfer of an amino group from one amino acid to another carbon skeleton this forms a new amino acid 2 Deamination when an amino group is lost but not transferred to another carbon skeleton a The carbon skeleton is then converted to glucose b The ammonia NH3 is converted to urea lost in urine 3 Protein synthesis a an Starts in the cell s nucleus i Genetic material 1 DNA and RNA nucleic acids 2 Nucleotide bases a DNA nucleotides Adenine Guanine Cytosine Thymine b RNA nucleotides Adenine Guanine Cytosine Uracil ii Codons a group of 3 nucleotides that serves as instructions on making proteins DNA unwinds and is transcribed to mRNA mRNA travels out of the nucleus to the cell s cytosol mRNA is translated at the cell s ribosomes i Ribosomes read mRNA codons ii Each codon attaches a tRNA unit iii tRNA units deliver amino acid to ribosomes ATP is used Polypeptide chain protein is formed 4 Peptide synthesis a Peptide bonds connect polypeptides b Dipeptides 2 amino acids tripeptides 3 amino acids oligopeptides 49 amino aids polypeptides 10 amino acids c Peptide bonds connect amino acids forming a chain i Most proteins are polypeptides 50 to 200 amino acids d Problems with peptide synthesis i DNA codes for the wrong amino acid 1 Result genetic disease 2 Ex sicklecell anemia a Valine amino acid replaces Glutamic acid b Change in hemoglobin structure 5 Protein organization a Primary structure sequence of amino acids peptide chain b Secondary structure peptide chain bends and folds through bonds c Tertiary structure forms the 3D shape of the protein i Determines the function d Quaternary structure 2 or more proteins interact with each other i EX hemoglobin 6 Protein denaturation a Changes in the protein s 3D structure b Results in a loss of function c Caused by heat acidity basicity or enzymes d Can be bene cial or harmful 7 Food protein quality a Refers to the digestibility of amino acids b Based on the composition of essential amino acids i High quality proteins 1 Complete protein 2 Contains all 9 essential amino acids in proper proportions 3 Animal protein a Best standard egg protein in the egg white b 90100 is digested and absorbed ii Low quality proteins 1 Incomplete protein 2 Low or lacking in one or more essential amino acids 3 Most plant proteins 4 Limiting amino acid the amino acid present in the smallest amount that limits protein synthesis 8 Vegetarian diets Vegan consumes no animal products Lactovegetarians consume dairy Lactoovovegetarians eat dairy and eggs Complementary proteins when 2 or more plant proteins are eaten together to compensate for de ciencies in essential amino acids of each protein i Need not to be consumed in the same meal just the same day ii Important for vegetarian diets iii Ex beans legumes grains nuts seeds vegetables e Plant proteins i Provide protein minerals ber ii Contain no cholesterol iii Low saturated fats iv May lower the risk of 1 Cardiovascular disease 2 Certain cancers 3 Obesity 4 Type 2 diabetes 006m i High quality plant source of protein ii Nutritional value 1 Protein content is very high 35 2 Good source of essential fatty acids 3 High ber 4 Phytochemicals phytosterols and iso avones iii Complete protein balanced set of all essential amino acids iv No need to supplement it with complementary foods v FDA approved health claim lowers blood cholesterol vi Ex legumes g Concerns with vegetarian diets i Possible nutrient de ciencies 1 Vitamin 812 2 Ribo avin B complex vitamin 3 Vitamin D 4 Calcium 5 Zinc ii Special concerns in children 1 Lack of iron 2 Excess ber which leads to low calorie diet h Vegetarians should drink soy milk to get all the same nutrients as dairy milk protein ribo avin vitamin Bl2 vitamin D calcium i Consuming complementary proteins and having variety is important 9 Protein sources a Dietary sources i Meat poultry sh milk milk products legumes and nuts ii Worldwide 35 of protein comes from animals iii United States most of protein comes from animals b Protein in the body i Protein turnover and recycling ii Body proteins are digested and reabsorbed iii Recycling provides more amino acids for daily body needs than dietary protein 10 Determining protein need using nitrogen balance a Positive nitrogen balance during growth pregnancy recovering from illness building muscles i Eating more protein does not cause more body protein formation one must be in a situation where building more protein is necessary b Nitrogen equilibrium healthy adult meeting protein and energy needs i Healthy adults need to eat enough protein to maintain an amino acid pool and replace losses through urine feces sweat skin hair and nails c Negative nitrogen balance inadequate intake of protein and energy people on bed rest 11 Protein requirements AMDR 1035 kcal for adults Adult RDA i 08 gramskg of healthy body weight 1 Allows for nitrogen equilibrium balance ii For women who are pregnant or lactating increase protein by 25 gramsday iii If someone is obese the desired body weight is used iv RDA represents about 10 of total kcals v RDA is based on a need for essential amino acids for synthesis of nonessential amino acids vi Recovery state 0820 gramkg of body weight c Protein for athletes i RDA is not different for only exercising Sport organizations recommend higher protein intake iii 1017 gramskilogram of body weight iv Needs can be met through diet supplements are not needed d Amino acid supplements i The body is designed to handle whole proteins from foods U9 Amino acid supplements may cause imbalances and toxicities Excess of one amino acid can decrease absorption of others Some amino acids especially toxic in high amounts 12 13 14 U9 79 Is a high protein diet harmful Food and nutrition board recommends the protein does not exceed 35 of energy Highprotein animal foods contain extra fat and cholesterol i Increase risk of heart disease ii Increase calcium loss iii Burdens kidney especially in kidney disease iv Increases uid needs If diet is low in plant foods then it is low in ber vitamins and phytochemicals Protein digestion Cooking denatures proteins and softens tissues Mouth mechanical breakdown Stomach i Hydrochloric acid denatures proteins ii Enzymes shorten protein peptide chains 1 Gastrin a Stimulates parietal cells to release HCI b Stimulates the release of pepsinogen from chief cells 2 Pepsinogen converted to pepsin by stomach acid 3 Pepsin breaks down long polypeptide chains into shorter chains Small intestine nal digestion of proteins to amino acids i Pancreatic enzymes shorten proteins to amino acids ii Cholecystokinin triggers the release of enzymes 1 Pancreas releases proteases a Releases trypsin chymotrypsin and carboxypeptidase into duodenum i Enzymes break peptides into smaller peptides and amino acids 1 Ready for absorption Protein absorption Proteins are broken down to amino acids Peptides are broken down i At microvilli surface and within absorptive cells Active absorption i Many different amino acid transport mechanisms exist ii Most are sodium transporters Amino acids are sent to the liver via portal vein 10 15 Protein functions a Primary function i Produces vital body structures 1 Collagen actin myosin 2 During periods of growth new proteins are synthesized a Supports tissue and structure growth ii Builds body components 1 Enzymes more than 2000 are known 2 Hormones like insulin 3 Neurotransmitters like norepinephrine 4 Immune function antibodies a Protein malnutrition anergy lack of an immune response to foreign compounds entering the body b Secondary functions i Fluid balance 1 Low protein in the blood causes edema swelling ii Maintain blood acidbase balance 1 Proteins can act as buffers by taking up or releasing hydrogen iii Transport nutrients 1 Lipids iron oxygen vitamin A iv Make energy 4 kcalgram from glucose and fat 1 Protein is a costly source of energy because the liver and kidneys are forced to work a lot 2 Gluconeogenesis when there is insuf cient carbohydrates the liver is forced to make glucose from amino acids in body tissues a Only for some amino acids 3 Starvation wastes muscle because liver must make glucose from amino acids 11 16 17 an Health concerns related to protein Protein de ciency accompanies de ciency of dietary energy and other nutrients Proteinenergy malnutrition PEM results from insuf cient amounts of energy and protein causes body wasting and an increase susceptibility to infection and disease i Debilitating diseases ii Poverty iii Kwashiorkor severe protein de ciency 1 Children are breastfed when another child is born the older child is no longer given milk given high carb diet instead 2 Edema occurs 3 Mild weight loss still getting some energy from carbs 4 Develops rapidly iv Marasmus severe energy and protein de ciency 1 Children are not breastfed given water or formula Severe weight loss Severe growth impairment Cognitive impairment Develops gradually the result of chronic PEM Occurs due to poverty diluted formula unsafe water 7 Treatment large amount of calories and protein Food protein allergies P P Fl lquot Certain food proteins allergens cause hypersensitivity reaction Antibodies trigger immune responses Most allergic reactions are mild some are severe Allergen must be avoided i Reading labels ii Crosscontamination There are six foods are responsible for 90 of food allergies i Peanuts ii Tree nuts iii Milk products iv Soy v Wheat vL Eggs vii Fish viii Shellfish 12
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