Proteins The Building Blocks of our Body PDST

Proteins The Building Blocks of our Body © PDST Home Economics

Elemental Composition Proteins are made up of atoms of: Carbon C Hydrogen H Oxygen O Nitrogen N and sometimes Phosphorus (P), Sulphur (S) and Iron (Fe) Nitrogen is needed for growth. Proteins are the only nutrients that contain the element nitrogen. These elements are bonded together in small molecules called amino acids. Amino acids are bonded together into long chains called proteins

Basic Structure of proteins – Amino Acids Proteins are made up of chains of small molecules called amino acids. There are 20 different amino acids but each has the same basic structure. C = carbon atom H= Hydrogen atom NH 2 = Amino group (basic) COOH = Carboxyl group (acidic) R = Variable group, changes for every amino For example in the amino acid Glycine the R group = H (one Hydrogen Atom)

Essential Amino Acids There are over 20 different amino acids. 8 are Essential Amino Acids that cannot be made by the body and must be eaten. There are 2 extra essential amino acids for children. The rest are Non-Essential Amino Acids these can be made by the body

Essential and Nonessential Amino Acids

Essential Amino acids cannot be made by the body and must be obtained from food Vincent’s Lovely Valine Lysine Mother Methionine Took Trytophan Him Histidine (children) Threonine To Leucine London Isoleucine In a Pram Arginine (children) Phenylalnine 8 essential for adults and 10 for children

Peptide Bonds or Links Amino acids join together into long chains called proteins. Just like the 26 letters of the alphabet can form thousands of words by linking in different ways; the 20 amino acids can form many different proteins The bond that links one amino acid to another is called a peptide link or bond Each time 2 amino acids link together a water molecule is taken away and so the linking process is called Condensation. The reverse of condensation is called Hydrolysis, water molecules are added to protein chains and split the amino acids apart, this happens during protein digestion.

Peptide Bonds or Links The Amino group (NH 2) of one amino acid links with the Carboxyl group (COOH) of another amino acid. The Amino group (NH 2) looses one H, the Carboxyl group (COOH) looses an OH group. The H and OH bond together to form a water molecule (H 2 O) The remaining CO and NH bond together to form a peptide link. Two amino acids joined is called a Dipeptide Many amino acids joined in a chain is called a Polypeptide

Amino Acids Bonding to form protein

Protein structure - Primary Order and number of amino acids in a protein chain for example the protein insulin has over 50 amino acids in its chain arranged in a definite order.

Protein structure - Secondary Involves the folding of the protein chain into a spiral or zig-zag shape This structure is caused by crosslinks that form between different chains or within the one chain. There are different types of cross-links (a) Disulfide links which happen when 2 Sulphur atoms bond. (b) Hydrogen bonds where a Hydrogen atom in one chain bonds with an Oxygen atom in another chain.

Protein structure - Tertiary This refers to the 3 dimensional folding of the chain. This structure can be globular or fibrous. The shapes give certain properties to the protein Globular : In these the protein chain is rolled up like a ball of wool. This structure makes the protein soluble. This type of protein is found in body cells, myoglobin in meat, albumin in egg, haemoglobin in blood. Fibrous: In these the protein chain takes on a straight, coiled or zig-zag shape. These shapes make the protein insoluble and stretchy or tough. Gluten in wheat and elastin in meat have a coiled structure. Collagen in meat has a zig-zag structure.

Sources of protein Animal protein Cheese Chicken Meat Fish Eggs Milk Plant protein Soya beans TVP Nuts Lentils Peas Beans Cereal

PROTEIN CLASSIFICATION SIMPLE CONJUGATED DERIVED These proteins are formed due to a chemical or enzyme action on a protein : i. e: Rennin acts on caesinogen and makes caesin PROTEIN + NON-PROTEIN Protein + Lipid = Lipoprotein (lecithin) Protein + Phosphate = Phosphoprotein (caesin) Protein + nucleic acid = Nucleoprotein (DNA) Protein + Colour Pigment = Chromoprotein (Haemoglobin) ANIMAL Classified according to shape FIBROUS Collagen PLANT Classified according to solubility GLOBULAR albumin GLUTENINS : Soluble in acids & alkali Glutenin in wheat PROLAMINES: Soluble in alcohol gliadin in wheat

Properties of protein – effects of heat on protein Effect of heat Examples Coagulation: protein sets and then hardens Hard boiling eggs Colour change Myoglobin in meat - red to brown Bread crust Maillards reaction (dry heat) Tenderising (moist heat) Becomes indigestible Collagen in meat changes to gelatine and fibres fall apart Overcooked meat or cheese becomes tough and hard to digest

Properties of Protein 1. Denaturation is a change in the nature of the protein The protein chain unfolds, causing a change to the structure Denaturation is caused by a) heat, b) chemicals and c) agitation It is often an irreversible process A. Heat Most proteins coagulate/set when heated. E. g. Egg white coagulates at 60˚C; egg yolk coagulates in the stomach at 68˚C B. Chemicals Acids, alkali, alcohol & enzymes cause changes to the protein structure E. g. Lemon juice added to milk causes the milk protein caesinogen to curdle E. g. Enzyme rennin coagulates milk protein caesinogen in the stomach C. Agitation This is also known as mechanical action It involves whipping or whisking the protein This results in the protein chain unfolding & partial coagulation

Properties of Protein 2. Solubility Proteins are generally insoluble in water There are two exceptions – egg white in cold water & connective tissue, which is converted to gelatine in hot water 3. Maillard reaction is also known as non-enzymic browning. It occurs when food is roasted, baked or grilled Amino Acid + Carbohydrates + Dry heat = Brown Colour Examples include roast potatoes, toast 4. Elasticity Certain proteins have an elastic property, e. g. Gluten, the protein found in flour, enables bread to rise during cooking 5. Foam Formation When egg white is whisked, air bubbles are formed as the protein chains unravel Whisking also produces heat, which slightly sets the egg white This foam will collapse after a while, unless it is subjected to heat This property is used to make meringues

Properties of Protein 6. Gel formation Collagen, when heated, forms gelatine Gelatine can absorb large Heat is applied amounts of water and, when heated, forms a sol As the protein On cooling, this becomes solid Uncoils water & a gel is formed becomes trapped Sol A gel is a semi-solid viscous Pro gel solution All gels have a three. Water dimensional network whereby water becomes trapped. This property is used in making Protein Matrix – the mixture has set – it cheesecakes and soufflés has become a gel

Biological Functions of Protein Function type Structural Function Growth & repair of body cells muscles &skin Physiologically Making hormones, active protein enzymes, antibodies, blood protein, nucleoprotein Nutritive Protein Provides essential amino acids for the body. Excess protein used for energy Result of deficiency Retarded growth Delayed healing Body organs & systems malfunction. Easily infected. Lack of energy. Kwashiorkor, Marasmus

Deamination This is the process by which excess protein is used for energy. Left over amino acids are brought to the liver The NH 2 group is broken off, changed to ammonia, then to urea and then excreted. The rest of the molecule is converted to glucose and used for releasing energy.

Biological Value of Protein The Biological Value of a protein is a measure of the quality of the protein and is expressed as a %. It is decided by the number of essential amino acids a protein contains in proportion to how much of them the body needs. There are 2 types of protein foods: (a) High Biological value, contain all essential Amino Acids, complete proteins, animal sources. (b) Low Biological value, lack some essential amino acids, incomplete protein, plant sources

Biological Value of different proteins Source Animal Food HBV LBV Eggs 100% Ovalbumin, Livetin, Vitelin Milk 95% Casein, Lactalbumin, Lactoglobulin Meat 8090% Collegen, Elastin, Myosin, Fish Gelatine Plant Protein Actin, Myosin, Collegen 0% Gelatine Soya Beans 74% Rice 67% Oryzenin Wheat 53% Gluten Maize 40% Zein

Supplementary Value of Protein When low biological value foods, that lack essential amino acids, are eaten together they can provide all the essential amino acid. The essential amino acids missing in one food can be made up for by being present in the other food and visa versa. This complementary value of protein means that vegans can get all the essential amino acids without eating animal food Example; Bread is lacking Lysine but is high in Methionine. Beans are lacking Methionine but high in Lysine. By eating beans on toast both essential amino acids are included in the meal.

RDA Protein & Energy value RDA 1 gram of protein per kilogram of body weight. Child 30 -50 g/day Teenager 60 -80 g/day Adults 50 -75 g/day Pregnant or lactating 70 -85 g/day Energy Value 1 g of protein gives 4 k. Cal or 17 k. J energy

Digestion of protein Part of System Physical Digestion Mouth Chewed Stomach Churned Digestive Juice Gastric juice Enzyme Rennin Pepsin Duodenum Pancreatic Trypsin Juice Small Intestine Intestinal Juice Substrate Product Caseinogen Casein Proteins Peptones Protein Peptidase Peptones Amino acids

Absorption & Assimilation of Amino Acids are absorbed into blood capillaries in the villi of the small intestine. These capillaries connect into the portal vein which carries the amino acids to the Liver. From here the Amino Acids will be sent to (a) replace & repair body cells, (b) form new cells, antibodies, hormones, enzymes or (c) be deaminated

Questions? ? 1 What is the elemental composition of protein? 2 Draw the chemical structure of an amino acid 3 Explain how a peptide link forms 4 What are essential amino acids? 5 List the biological functions of protein. 6 What is meant by ‘biological value’ of protein? 7 Difference between denaturation & deamination 8 List (a) the energy value (b) the RDA of protein? 9 List 4 sources of (a) HBV and (b) LBV protein. 10 Describe the digestion of protein in humans.