Proteins

1. Proteins Iva Řehová

2. Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of all living organisms and participate in every process within cells.

3. The protein of the body tissues, particularly the muscle tissue, is the large reservoir of energy but is not used under normal circumstances. • The building blocks of human proteins are 20 amino acids that may be consumed from both plant and animal sources. • Of these 20 amino acids, 8 are considered to be essential because their carbon skeletons cannot be synthesized by human enzymes. • The remaining 12 that can be manufactured by the body are termed nonesential. This doesn't mean that they are unimportant, but simply that the body can synthesize them from ingested protein and nonprotein nutrients.

4. Classification of Amino Acids *These amino acids, along with taurine, may be considered conditionally essential in that their requirements are increased during periods of catabolic stress.

5. Amino acids are joined together by peptide bonds, • the joining of two amino acids produces a dipeptide (three a tripeptide) • configuration of up to as many as 11-100 amino acids is known as a polypeptide • more than 100 amino acids produces proteins The condensation of two amino acids to form a peptide bond:

6. Proteins differ chemically from carbohydrates and lipids in that they contain nitrogen in addition to other elements such a sulfur, phosphorus, and iron.

7. Protein is the basic structural material of all cells. • Biologically active proteins include enzymes, immunoglobulins, hormones, neurotransmitters, nutrient transport and storage compounds, and cell membrane receptors. • Many proteins are enzymes that catalyze biochemical reactions, and are vital to metabolism. • Biological value of a dietary protein is determined by the amountand proportion of essential amino acids it provides. • If any one of the essential amino acids is not available in sufficient amounts or is present in excessive amounts relative to other essential amino acids, protein synthesis will not be supported! • Egg protein has been found to have the highest known biological value of any protein in humans.

8. Protein from animal sources (meat, fish, dairy products, egg white) is considered high biological value protein or a "complete" protein because all essential amino acids are present in these proteins.

9. Plant sources of protein (grains, legumes, nuts, and seeds) generally do not contain sufficient amounts of one or more of the essential amino acids. • Plants that are entirely lacking in essential amino acids are considered incomplete proteins or sources of low biological value protein.

10. The recommended Dietary Allowance • The RDA of protein intake for adults is 0.8 g per kilogram of body mass. • For children, a higher intake of protein is recommended 2 to 4 g/kg of body mass. • Also, protein intake should be increased by 10 g a day for pregnant women and 20 g daily for nursing mother. • The protein requirements tends to decrease somewhat with age; • conversely, stress, disease, injury, and prolonged heat exposure increase the protein requirement

11. Vegetarian approach • Grains and legumes are excellent proteins sources, but neither provides the full complement of essential amino acids (AA). • Grains lack the essential AA lysine, while legumes contain lysine but lack of the sulfur-containing essential AA methionine for which grains are rich sources. • However, because large quantities of those foods must be eaten to obtain the requirement quantity of essential AA, most people eat some animal food.

12. Evidence from a few large cohort studies suggests that vegetarians have lower overall mortality ratios than the general population, but this is not the case when vegetarians are compared with similar non-vegetarian groups who follow a health-conscious lifestyle. • Vegetarianism has been associated with a reduction in several of the established risk factors for coronary heart disease (CHD), including more favourable blood lipid profile, lower body mass index and lower blood pressure.

13. There are hundreds if not thousands of ways to be vegetarian. There are four major types of lifestyles and eating habits that vegetarians may include in a diet:

14. Possible benefits of vegetarian eating:

15. Possible risks of vegetarian eating: The major source that may be lacking in this type of lifestyle is protein. Because of this, it is important to make sure that protein is eaten through grains, beans, tofu, nuts, eggs or peas. The second nutrient that is needed in a vegetarian diet is calcium. If you eat dairy, this will be easier to consume. However, if not, you can find calcium in darker greens. Vitamin D, Iron and Vitamin B12 are the other three nutrients that may be lacking in this diet.

16. Meat in the Diet • Meat makes an important contribution to intake of a number of nutrients, in particular micronutrients such as iron and zinc.  • Iron deficiency anaemia is one of the most common nutritional deficiencies in the westernized society, particularly in young children and women of childbearing age.  • When red meat is included in the diet, it should be lean, and poultry should be consumed without skin. Lower fat versions of traditional meat products such are better choices than the standard versions, which may be higher in fat.  • Meat products that include high fat ingredients, such as pastry, should not be consumed in excess. 

17. If meat is eliminated from the diet, a small increase in oil-rich fish such as mackerel, salmon, sardines or trout, would compensate for any deficit in intake of long chain fatty acids and vitamins D and B12.  • Care should be taken, however, to ensure adequate intakes of iron and zinc.  Inclusion of legumes, nuts and fortified cereals will help contribute to intake of these minerals for those who choose to avoid animal products.

18. Meat, poultry and fish are rich sources of high biological value protein. Plant sources of protein (legumes, nuts, and seeds) contribute additional amounts of protein. Food Protein (grams) Food Protein(grams) DAIRY MEAT SUBSTITUES Skim milk, 1 cup 8.3 Whole milk, 1 cup 8.0 Tofu, 3 oz 6.9 Ice cream, 1 cup 5.0 Peanut butter, 2Tbl 8.1 Yogurt,low-fat,1cup10.7 Almonds, 1 oz 5.4 Cottage cheese,1cup28.0 Sesame seeds, 1 oz 7.5 American cheese,1oz7.0 Black beans, 1/2 cup 7.5 Egg, 1 large 6.3 Pinto beans, 1/2 cup 7.0 FISH, MEAT & POULTRY Garbanzo beans, 1/2 cup 7.3 Tuna, 3 oz drained 21.7 FRUITS Salmon, 3 oz ckd 16.8 Banana, 1 medium 1.2 Ground beef, 3 oz 25.7 Apple, large 0 Beef, 3 oz ckd 27.0 Orange, large 1.7 Pork chop, 3 oz ckd 24.5 VEGETABLES Ham, 1 oz 5.9 Corn, ckd, 1/2 cup 2.2 Chicken breast, 3 oz 18.9 Carrots, ckd, 1/2 cup 0.8 Chicken,dark meat,3oz 23.6 Green beans, ckd, 1/2 cup 1.0 Turkey breast, 3 oz 25.7 Green peas, ckd, 1/2 cup 4.1 Turkey,dark meat,3oz 24.3 Potatoes, white, 1/2 cup 1.2

19. Vegetarianism based on sound nutrition principles can be a healthful choice, but neither vegetarians nor omnivores have a monopoly on healthful eating. • Vegetarians are just as diverse in their health status as are nonvegetarians. Similar health benefits can be gained from both well-selected omnivorous and vegetarian diets.

20. Digestion and absorption • Through the process of digestion, animals break down ingested protein into free amino acidsthat can be used for protein synthesis. • The digestion of protein begins in the stomach by the action of the enzyme pepsin. • Pepsin is particularly effective in the highly acid stomach medium (hydrochloric acid) in breaking down the collagenous connective tissue fibers in meat. • The hydrochloric acid: • activates pepsin, • helps to keep stomach free from bacteria, • improves absorption of the mineral iron and calcium, • inactivates plant and animal hormones. • Stomach enzymes and acids attack the long, complex protein. They are degraded to smaler units called polypeptides and peptides. • The peptide fragments are dismantled in the small intestine by alkaline enzymes released from the pancreas. • The smaller protein fragments are then absorbed and transported to the liver for further assimilation.

21. When amino acids reach the liver, one of three things happens. They are: • converted to glucose, • converted to fats, or • released directly into bloodstream as plasma protein such as albumin, or as free amino acids to serve the anabolic requirements of various tissues.

22. Dietary protein consumed in excess of requirements is not stored, but is deaminated, or its storage as glycogen or fat, depending upon the specific amino acid and the energy balance at the time. The nitrogen waste generated is excreted in the urine as either urea or ammonia. • High protein intakes can increase urinary calcium excretion. • Other health effects of high protein intakes are less clear including the relationship of long-term high protein intakes to risk of renal disease or of diabetic nephropathy.

23. Summary • Experts recommend that protein intake make up only 10-20% of our daily calorie intake. • Proteins are made of smaller units called amino acids. • Animal proteins, found in such food as eggs, milk, meat, fish, and poultry, are considered complete proteins because they contain all of the essential amino acids our bodies need. • Plant proteins, found in vegetables, grains, and beans, lack one or more of the essential amino acids.