BCH 282 Dr.Saba Abdi

Building Blocks of Protein

Amino Acids 20 common amino acids in food, each with a different side chain More than half amino acids are non-essential (body can synthesize them) Nine amino acids are essential ( body cannot make or makes in insufficient quantities). Must be supplied by diet. Conditionally essential amino acids are nonessential amino acids that some time become essential. Eg. Tyr (NE) synthesized by Phe (E). If diet low in Phe then Tyr becomes conditionally essential.

Essential amino acids Leucine Isoleucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine Non-essential amino acids Alanine Arginine Asparagine Aspartic acid Cysteine Glutamic acid Glutamine Glycine Histidine (essential in children) Proline Serine Tyrosine (The 11 amino acids that we can produce)

Amino Acids: structural & functional roles cell membrane • connective tissue(collagen & elastin) • inert protein(hair & nails) • Enzymes • Hormones(insulin) • Fluid balance(aquaporins) • blood proteins(albumin & haemoglobin) • skeletal & smooth muscle • antibodies • energy source • Acid- base regulator • Transporters

How Proteins are used in the body

Protein Metabolism

Protein Turnover and amino acid pool AA’s and proteins are continually synthesised & catabolised in the body this is called protein turnover. The AA’s released during protein break down form an AA pool. • daily turnover @3 – 4 g/kg body weight/day • dietary intake @ ¼ - ½ this amount

Quality of proteins The quality of a dietary protein is a measure of its ability to provide the essential amino acids required for tissue maintenance. The Protein Digestibility-Corrected Amino Acid Scoring (PDCAAS) is the standard by which to evaluate protein quality. PDCAAS is based on the profile of essential amino acids and the digestibility of the protein. The highest possible score is 1.00. This amino acid score provides a method to balance intakes of poorer-quality proteins by vegetarians and others who consume limited quantities of high-quality dietary proteins.

Sources of protein

Proteins from animal sources Proteins from animal sources (meat, poultry, milk, and fish) have a high quality because they contain all the essential amino acids in proportions similar to those required for synthesis of human tissue proteins [Note: Gelatin prepared from animal collagen is an exception; it has a low biologic value as a result of deficiencies in several essential amino acids.]

Proteins from plant sources Proteins from wheat, corn, rice, and beans have a lower quality (except soy protein) than do animal proteins. However, proteins from different plant sources may be combined in such a way that the result is equivalent in nutritional value to animal protein. Plant Proteins are less digestible. [Note: Animal proteins can also complement the biologic value of plant proteins.]

Mutual supplementation yeilds Complementary proteins

Complementary proteins IsoLeu Lys Met Trp Legumes x X Cereals x x Combined

Measure of Protein Quality Biological Value (BV)of Protein – based on NITROGEN RETENTION – higher the protein quality= more Nitrogen retained= more protein synthesis than catabolism BV of EGG protein = 100%, all absorbed protein retained

Nitrogen balance Nitrogen balance occurs when the amount of nitrogen consumed equals that of the nitrogen excreted in the urine, sweat, and feces. Most healthy adults are normally in nitrogen balance.

Nitrogen Balance Positive nitrogen balance: This occurs when nitrogen intake exceeds nitrogen excretion. It is observed during situations in which tissue growth occurs, for example, in childhood, pregnancy, or during recovery from an emaciating illness. Negative nitrogen balance: This occurs when nitrogen loss is greater than nitrogen intake. It is associated with inadequate dietary protein, lack of an essential amino acid, or during physiologic stresses, such as trauma, burns, illness, or surgery.

Requirement for protein in humans 1 gram protein supplies 17kJ The RDA for protein is computed for proteins of mixed biologic value at 0.8 g/kg of body weight for adults, or about 56 g of protein for a 70-kg individual. Women who are pregnant or lactating require up to 30 g/day in addition to their basal requirements. To support growth, children should consume 2 g/kg/day. sedentary individuals: balanced diet: 10-15% of Etotal from protein Athletes: balanced diet: 12-17% of Etotal from protein

Consumption of excess protein Protein consumed in excess of the RDA is deaminated, and the resulting carbon skeletons are metabolized to provide energy or acetyl coenzyme A for fatty acid synthesis. When excess protein is eliminated from the body as urinary nitrogen, it is often accompanied by increased urinary calcium, increasing the risk of nephrolithiasis and osteoporosis

The protein-sparing effect of carbohydrate When the intake of carbohydrates is low, amino acids are deaminated to provide carbon skeletons for the synthesis of glucose that is needed as a fuel by the central nervous system. If carbohydrate intake is less than 130 g/day, substantial amounts of protein are metabolized to provide precursors for gluconeogenesis. Therefore, carbohydrate is considered to be “protein-sparing,” because it allows amino acids to be used for repair and maintenance of tissue protein rather than for gluconeogenesis.

Protein from food - Food with high Protein content( g/100g):- Beef & lamb 28 Cheese 26 Chicken 25 Fish 18 Eggs 12 Beans 7 Peas 5 Milk 3.3

Food Protein g/100g MEDIUM CONTENT Cornflakes 8.6 Bread (white) 7.8 Spaghetti 4.2 Sweetcorn 4.1 Rice 2.2 Cauliflower 1.6 Potatoes 1.6 Cabbage 1.3

Food Protein g/100g LOW CONTENT Apples 0.3 Honey 0.5 Butter & margarine <0.4 Wine 0.1 Soft drink 0

Protein-energy malnutrition(PEM) People are deprived of protein, energy or both result in PEM. Forms of PEM are kwashiorkor and marasmus. In developed contries PEM is seen most frequently in hospital patients with chronic illness, or in individuals who suffer from major trauma, severe infection, or the effects of major surgery. In developing countries, an inadequate intake of protein and/or energy may be observed.

Kwashiorkor: Kwashiorkor occurs when protein deprivation is relatively greater than the reduction in total calories. Significant protein deprivation is associated with severe loss of visceral protein. Frequently seen in children after weaning at about one year of age, (diet predominantly of carbohydrates). Symptoms: stunted growth, edema, skin lesions, depigmented hair, anorexia, enlarged fatty liver, and decreased plasma albumin concentration. Edema results from the lack of adequate plasma proteins to maintain the distribution of water between blood and tissues

Marasmus Marasmus occurs when calorie deprivation is relatively greater than the reduction in protein. Marasmus usually occurs in children younger than one year of age when the mother's breast milk is supplemented with thin watery gruels of native cereals, which are usually deficient in protein and calories. Symptoms: arrested growth, extreme muscle wasting (emaciation), weakness, and anemia. Victims of marasmus do not show the edema or changes in plasma proteins observed in kwashiorkor

Health effects of Protein-problem of excess Heart Disease-food rich in animal protein are rich in saturated fats.The amino acid homocysteine may be a risk factor for heart disease. But arginine may be protective. Cancer-colon, breast , kidney , pancreas & prostrate. Adult bone loss (osteoporosis)- Calcium excreation rises as protein intake increases. Weight control-protein rich food are often fat rich foods. Kidney diseases-protein rich diet increases the work of kidney