Protein Lecture 2 - Community 2025 PDF

protein All the tissues in our body such as muscle, blood, bone, skin and hair are made up of proteins. Many hormones and enzymes are either protein or protein derivatives. The nucleic acids in the cell nucleus occur in combination with proteins as nucleoproteins. Protein is thus essential...

protein All the tissues in our body such as muscle, blood, bone, skin and hair are made up of proteins. Many hormones and enzymes are either protein or protein derivatives. The nucleic acids in the cell nucleus occur in combination with proteins as nucleoproteins. Protein is thus essential to maintain cellular integrity and function and for health and reproduction.  COMPOSITION Proteins contain carbon, hydrogen, oxygen and nitrogen. They are distinguished from carbohydrates and fats by the presence of nitrogen. Protein is synthesized from basic units called amino acids. Protein molecules, which contain up to hundred amino acids are much larger than carbohydrates or lipid molecule. Chemically amino acids are composed of a carbon atom to which is attached a carboxyl (COOH) group, a hydrogen atom (H), an amino group (NH2) and an amino acid radical (R) as shown below.  ESSENTIAL AND NON-ESSENTIAL AMINO ACIDS An essential amino acid is one that cannot be synthesized by the body to meet the physiological needs and hence should be supplied by the diet. The essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine threonine, tryptophan and valine. Non-essential amino acids are those that the body can synthesize. They are alanine, arginine, aspargine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine and tyrosine. Proteins are functionally divided into complete, partially complete and incomplete proteins. A complete protein contains all essential amino acids in relatively the same amounts as human beings require to promote and maintain normal growth. (eg) Protein derived from animal foods. A partially complete protein contains sufficient amounts of amino acids to maintain life but fail to promote growth. (eg) Gliadin in wheat. Incomplete proteins are incapable of replacing or building new tissue and cannot support life or growth. (eg) Protein in Wheat germ. A good quality protein is digested and utilized well. Egg protein is a complete protein and is considered as a reference protein with the highest biological value. The quality of other proteins is determined based on their comparison with egg protein as in figure  The eight essential amino Wheat germ is an incomplete acids (EAA) must be present protein because it is deficient in a protein in specific in tryptophan (incomplete ratios. Egg protein has all circle). As a result of this eight in the correct deficiency only less of the proportions used most total protein can be used (as efficiently and completely represented by the inner by the body. dotted circle). The protein of animal foods like milk, meat, and fish generally compare well with egg in the essential amino acid composition and are categorized as good quality proteins. Plant proteins are of poor quality, since the essential amino acid composition is not well balanced. The resulting mixture of cereals and pulse will have an amino acid pattern better than either of the constituents. Thus a combination of cereal and pulse has a supplementary effect. All foods except refined sugar, oils and fats contain protein to varying degree. Animal foods like meat, fish, egg and plant foods like pulses oilseeds and nuts contain high amounts of proteins and are classified as rich sources of proteins.. Leafy vegetables, roots and tubers are poor sources of protein as they contain less than two percent proteins. The protein content of foods are listed in the table-18B. DIGESTION, ABSORPTION AND UTILIZATION OF PROTEINS / Proteins taken in the diet are digested to amino acids in the stomach and small intestine. Gastric juice contains enzymes pepsin which digests protein in acid medium. It hydrolyses proteins to polypeptides. Dietary Protein by Pepsin>>>>>> Polypeptides( large) In the small intestine, pancreatic and intestinal juices contain proteolytic enzymes. Pancreatic juice contains trypsin, chymotrypsin and elastase. They hydrolyse large protein molecule to smaller polypeptide. Then peptidase break down the peptides into free amino acids, which can then enter the bloodstream. Proteins are mainly absorbed in the form of amino acids. Amino acids are absorbed by active transport mechanism in the intestinal cells. Sometimes whole protein may be absorbed by the mechanism of pinocytosis. Absorbed amino acids pass into the portal blood and reach liver where they are converted to proteins. Other amino acids are transported through general circulation and are utilized for protein synthesis in the tissues  Amino Acids Are Recycled All cells in the body continually break down proteins and build new ones, a process referred to as protein turnover. Every day over 250 grams of protein in your body are dismantled and 250 grams of new protein are built. Amino acids are used not only to build proteins, but also to build other biological molecules containing nitrogen, such as DNA and RNA, and to some extent to produce energy. It is critical to maintaining amino acid levels within this cellular pool by consuming high- quality proteins in the diet, or the amino acids needed for building new proteins will be obtained by increasing protein destruction from other tissues within the body, especially muscle. the body does not store protein as it does with carbohydrates (as glycogen in the muscles and liver) and lipids (as triglycerides in adipose tissue). REQUIREMENTS 1.0 g/kg/day as the safe level of intake in terms of dietary protein. During pregnancy and lactation additional allowances are recommended. Protein requirements for children vary depending on body weight and expected weight gain EFFECTS OF DEFICIENCY Deficiency of energy and protein commonly occur in developing countries. This is manifested as Marasmus and Kwashiorkor. Protein Energy Malnutrition (PEM) is a term used to describe clinical disorders resulting from varying degrees of protein and energy deficiency. Kwashiorkor is due to quantitative and qualitative deficiency of protein in diet in which energy intake is adequate. Marasmus is due to continued restriction of energy intake. PEM is prevalent in all parts of the World and in all ages. It is primarily a disease that occurs in young children who live in poverty. In India PEM is the most widespread form of malnutrition among pre-school children. The name Kwashiorkor comes from a language in Ghana and means, “rejected one.” The syndrome was named because it occurred most commonly in children who had recently been weaned from the breast, usually because another child had just been born. Subsequently the child was fed watery porridge made from low-protein grains, which accounts for the low protein intake. Marasmus is a Greek word, meaning “starvation. Marasmus occurrence increases prior to age 1, whereas kwashiorkor occurrence increases after 18 months. It can be distinguished from kwashiorkor in that kwashiorkor is protein deficiency with adequate energy intake whereas marasmus is inadequate energy intake in all forms, including protein. Clinical symptoms of Protein Energy Malnutrition 1) Failure to grow accompanied by thinning, weakening and wasting of muscles. 2) Behavioural changes ranging from the irritability of kwashiorkor to the apathy of marasmus. 3) Oedema which is the accumulation of fluid in the tissues making them soft and spongy. 4) Skin changes including changes in colour, lack of colour, peeling and ulceration. 5) Changes in hair which becomes dry and sparse and takes on a characteristic red color (Flags syndrome). 6) Loss of appetite, Vomitting, diarrhoea resulting in dehydration. 7) Enlargement of the liver. 8) Anaemia 9) Increased susceptibility to infection and fever.  Undernutrition-induced Alteration in Tissue mass & ftrnction Body composition: loss in muscle & fat MASS. Body water:, malnourished patient may have intravascular volume depletion together with the presence of whole body fluid overload $kinl;Scalp hair becomes thin & sparse & is easily pulled out, in contrast the eye lashes become long GIT: Malnutrition causes structural & functional deterioration of intestinal tract, pancreas & liver, mucosal epithelial cell proliferation rate decrease & intestinal mucosa becomes atrophic with flattened villi,. Heart: Chronic undernutrition affects cardiac mass & function, cardiac muscle mass decrease, bradycardia & decrease stroke volume can cause a marked decrease in cardiac output & low BP, Lungs: Respiratory muscle function is altered by undernutrition as evidenced by decrease in vital capacity, tidal volume & minute ventilation Kidneys ; renal mass & function are relatively Well preserved during malnutrition provided that adequate water is consumed to prevent a severe decrease in renal perfusion & acute renal failure. However when malnutrition is severe, there is decrease in kidney weight, GFR, ability to excrete acids, the ability to excrete NA & the ability to concentrate urine, mild proteinuria may also occur Immune System: severe malnutrition causes atrophy of all lymphoid tissue including thymus, tonsil & lymph nodes, cell mediated immunity is diminished more that antibody production, the abilitY to kill bacteria is diminished because of decrease complement & impaired neutrophil function, gastrointestinal IgA secretion is also decreased, malnourished patient are at increased risk for opportunistic infection & should be considered immunocompramized Endocrine svstem: Decrease plasma insulin concentration & glucose intolerance are common in severe malnutrition; GH is usually increased & is much greater in kwashiorkor type than the marasmic type of PCM, serum thyroxine level is low & the conversion of thyroxine to triiodothyronine is decreased with increase conversion to reverse triiodothyronine, plasma cortisol concentration is usually greater than normal.  High protein diet diets high in animal protein, specifically those in which the primary protein source is red meat, are linked to a higher risk for kidney stones, kidney disease, liver malfunction, colorectal cancer, and osteoporosis. However, diets that include lots of red meat are also high in saturated fat and cholesterol and sometimes linked to unhealthy lifestyles, thanks