1. BCH 282
Dr.Saba Abdi

2. Building Blocks of Protein

3. 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.

4. 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)

5. 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

6. How Proteins are used in the body

8. Protein Metabolism

9. 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 – 4 g/kg body weight/day
• dietary ¼ - ½ this amount

10. 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.

11. Sources of protein

12. 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.]

13. 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.]

14. Mutual supplementation yeilds Complementary proteins

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

16. 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

17. 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.

18. 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.

19. 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

20. 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

21. 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.

22. Protein from food - Food with high Protein content( g/100g):-
Beef & lamb 28
Cheese
Chicken
Fish
Eggs
Beans
Peas
Milk

23. 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

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

25. 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.

26. 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

27. 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

28. 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