Proteins and Protein Rich Foods Lecture Notes PDF

Proteins and Protein rich foods 3 rd lecture Dr. Mohamed Elsaadany  Proteins Protein is a nitrogenous substance that occurs in the protoplasm of all animal and plant cells. Proteins can be broken down into smaller and smaller fragments until the amino acids are o...

Proteins and Protein rich foods 3 rd lecture Dr. Mohamed Elsaadany  Proteins Protein is a nitrogenous substance that occurs in the protoplasm of all animal and plant cells. Proteins can be broken down into smaller and smaller fragments until the amino acids are obtained. Proteins are the most structurally sophisticated molecules known, and all are polymers constructed from the same set of 20 amino acids. Polymers of amino acids are called polypeptides Proteins form key parts of the body’s main structural components—muscles and bones—and of blood, enzymes, cell membranes, and some hormones Chemically composed of carbon, hydrogen, oxygen and constant amount of nitrogen (16%) Many also contain sulfur, phosphorus and iron Amino acids are organic molecules possessing both carboxyl groups and amino Types of amino acids : Essential amino acids Nonessential amino acids Conditionally Essential amino acids 4 Dr. Mohamed Elsaadany 4  Types of Amino Acids Essential amino acids cannot be produced by your body, therefore it is essential to obtain them from your diet Nonessential amino acids are those that your body naturally produces and therefore not essential to acquire through dietary sources. Six of the eleven remaining nonessential amino acids are considered conditionally essential amino acids. Conditionally essential amino acids are amino acids that are produced by the body, yet in times of severe physical stress, growth, or trauma, may become depleted. At times your body requires additional stores of certain amino acids which can exceed the amount we naturally produce. 5 Dr. Mohamed Elsaadany 5  Biological value of protein Biological value : Is the term describes how well a particular protein food approximate the amount and combination of essential amino acids in the body. Types of protein: Complete proteins or higher quality proteins come from foods containing all of the essential amino acids in the quantity and correct ratio to maintain nitrogen balance and allow for tissue growth and repair. Sources are; Meat, fish, poultry, eggs, milk, cheese, and soy Incomplete proteins or lower quality proteins lack ore or more of the essential amino acid. Incomplete protein diets will eventually lead to protein malnutrition. Sources are ; Plants, including legumes, grains, and nuts 6 Dr. Mohamed Elsaadany 6  Complementary Proteins Combining two or more foods with incomplete proteins, to form complementary proteins, can provide adequate amounts of all the essential amino acids. Complementary proteins do not need to be eaten together, so long as the day's meals supply them all. 7 Dr. Mohamed Elsaadany 7  Nitrogen balance The nitrogen balance is a simple index of whether physiological protein requirements are being met. Urinary urea is taken as a rough indicator of protein degradation and loss from the body. Oral protein intake is quantified. Protein and urea are assumed to be rough indices of physiological nitrogen. 8 Dr. Mohamed Elsaadany 8  Classification of proteins Classification of protein is based on solubility and characteristic physical properties and partly on chemical composition.They are grouped into 1. Simple proteins: essentially pure proteins, when hydrolyzed, produce individual amino acids (e.g., egg albumin) 2. Conjugated: protein unit linked to another non-protein unit (e.g., casein, the protein component of milk with phosphorus esterified to it via the AA serine 3. Derived: modified proteins such as peptides, modified by heat, acidification, etc. 9 Dr. Mohamed Elsaadany 9  Classification of proteins 1. Simple proteins: are those which yield only amino acids upon hydrolysis. They include: a. Albumins: soluble in water , coagulated by heat b. Globulins : insoluble in water , soluble in dilute salt solution, coagulated by heat. c. Glutelins: insoluble in neutral solvents but soluble in dilute acids and alkalis , coagulated by heat. d. Prolamins: soluble in 70 to 80 % alcohol, insoluble in absolute alcohol, water and salt solution. e. Albuminoids: insoluble in all neutral solvents and in dilute acids and alkalis f. Histones and protamines: basic polypeptides , soluble in water , not coagulable by heat. They are found in nuclei of cells 10 Dr. Mohamed Elsaadany 10  Classification of proteins g. Elastin: present in walls of large blood vessels (such as aorta). It is very important in lungs, elastic ligaments, skin, cartilage, It is elastic fiber that can be stretched to several times as its normal length. h. Collagen protein of connective tissues found in bone, teeth, cartilage, tendons, skin and blood vessels. collagen is insoluble in all solvents and not digested. When collagen is heated with water or dil. HCl it will be converted into gelatin which is soluble , digestible and used as diet i. Keratein is protein found in hair, nails, enamel of teeth and outer layer of -helical polypeptide chain, rich in cysteine and hydrophobic (non polar) amino acids so it is water insoluble 11 Dr. Mohamed Elsaadany 11  Classification of proteins 2. Conjugated proteins : are combination of simple protein and some other non- protein substance , called prosthetic group, attach to the molecule. They include: a. Nucleoproteins ; protein + nucleic acid (DNA) are the principle constituents of the genes and (RNA) are necessary for the synthesis of proteins in cytoplasm (e.g., seed germs) b. Mucoproteins and Glycoproteins: protein + COH group (e.g., mucus) combination of protein and large quantities of complex polysaccharides such as that found in secretions from gastric mucous membranes 12 Dr. Mohamed Elsaadany 12  Classification of proteins c. Lipoproteins: compound of protein and triglycerides or phospholipids or cholesterol found in cell and organelle membrane d. Phospholipids : protein+ P-containing compound (e.g., casein). Phosphoric acid joined in ester linkage to protein found in casein of milk. e. Chromoproteins: compounds of proteins and a non-protein pigments found in flavoproteins , hemoglobin and cytochromes f. Metalloproteins : compounds of metals attached to protein found in ferritin, hemosiderin g. lecithoproteins: protein + lecithin (e.g., fibrinogen) 13 Dr. Mohamed Elsaadany 13  Classification of proteins Derived Proteins Derived proteins are degradation products obtained by the action of acids, alkalies, and enzymes on protein. These are classified into two types such as primary and secondary. Primary proteins are insoluble in water but soluble in acids and alkalis. Secondary proteins are soluble in water and coagulated by heat. 14 Dr. Mohamed Elsaadany 14 Protein functions 15 Dr. Mohamed Elsaadany 15  Sources of protein Lean meats and poultry. Eggs. fish and shellfish. trout. Nuts and seeds. peanuts. almonds. Lower fat dairy products. milk. Beans, peas and lentils. brown, green or red or other lentils. Fortified soy beverages, tofu, soybeans and other soy products Dr. Mohamed Elsaadany 16