2Elemental Composition Proteins are made up of atoms of:Carbon CHydrogen HOxygen ONitrogen Nand 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
3Basic 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 atomH= Hydrogen atomNH2 = Amino group (basic)COOH = Carboxyl group (acidic)R = Variable group, changes for every aminoFor example in the amino acid Glycine the R group = H (one Hydrogen Atom)
5Essential 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
78 essential for adults and 10 for children Essential Amino acids cannot be made by the body and must be obtained from foodVincent’sLovelyMotherTookHimToLondonInaPramValineLysineMethionineTrytophanHistidine (children)ThreonineLeucineIsoleucineArginine (children)Phenylalnine8 essential for adults and 10 for children
8Peptide Bonds or LinksAmino 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 proteinsThe bond that links one amino acid to another is called a peptide link or bondEach 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.
9Peptide Bonds or LinksThe Amino group (NH2) of one amino acid links with the Carboxyl group (COOH) of another amino acid.The Amino group (NH2) looses one H, the Carboxyl group (COOH) looses an OH group.The H and OH bond together to form a water molecule (H2O)The remaining CO and NH bond together to form a peptide link.Two amino acids joined is called a DipeptideMany amino acids joined in a chain is called a Polypeptide
11Protein 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.
12Protein structure - Secondary Involves the folding of the protein chain into a spiral or zig-zag shapeThis 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.Nother
13Protein 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 proteinGlobular : 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.
14Sources of protein Animal protein Plant protein Cheese Soya beans ChickenTVPMeatNutsFishLentilsEggsPeasMilkBeansCereal
15PROTEIN CLASSIFICATION SIMPLE CONJUGATED DERIVEDThese proteins are formed dueto a chemical or enzyme action on aprotein : i.e: Rennin acts oncaesinogen and makes caesinPROTEIN + NON-PROTEINProtein + Lipid = Lipoprotein (lecithin)Protein + Phosphate = Phosphoprotein (caesin)Protein + nucleic acid = Nucleoprotein (DNA)Protein + Colour Pigment = Chromoprotein (Haemoglobin)ANIMAL PLANTClassified Classified GLUTENINS : Soluble in acids & alkaliaccording according Glutenin in wheatto shape to solubilityPROLAMINES: Soluble in alcoholFIBROUS GLOBULAR gliadin in wheatCollagen albumin
16Properties of protein – effects of heat on protein Effect of heatExamplesCoagulation: protein sets and then hardensHard boiling eggsColour changeMyoglobin in meat - red to brownMaillards reaction (dry heat)Bread crustTenderising (moist heat)Collagen in meat changes to gelatine and fibres fall apartBecomes indigestibleOvercooked meat or cheese becomes tough and hard to digest
17Properties of Protein Denaturation Chemicals Denaturation is a change in the nature of the proteinThe protein chain unfolds, causing a change to the structureDenaturation is caused by a) heat, b) chemicals andc) agitationIt is often an irreversible processHeatMost proteins coagulate/set when heated.E.g. Egg white coagulates at 60˚C; egg yolk coagulates in the stomach at 68˚CChemicalsAcids, alkali, alcohol & enzymes cause changes to the protein structureE.g. Lemon juice added to milk causes the milk protein caesinogen to curdleE.g. Enzyme rennin coagulates milk protein caesinogen in the stomachAgitationThis is also known as mechanical actionIt involves whipping or whisking the proteinThis results in the protein chain unfolding & partial coagulation
18Properties of Protein Solubility Proteins are generally insoluble in waterThere are two exceptions – egg white in cold water & connective tissue, which is converted to gelatine in hot waterMaillard reactionMaillard reaction is also known as non-enzymic browning. It occurs when food is roasted, baked or grilledAmino Acid + Carbohydrates + Dry heat = Brown ColourExamples include roast potatoes, toastElasticityCertain proteins have an elastic property, e.g. Gluten, the protein found in flour, enables bread to rise during cookingFoam FormationWhen egg white is whisked, air bubbles are formed as the protein chains unravelWhisking also produces heat, which slightly sets the egg whiteThis foam will collapse after a while, unless it is subjected to heatThis property is used to make meringues
19Properties of Protein Gelatine Heat is applied Gel formation Collagen, when heated, forms gelatineGelatine can absorb large amounts of water and, when heated, forms a solOn cooling, this becomes solid & a gel is formedA gel is a semi-solid viscous solutionAll gels have a three-dimensional network whereby water becomes trapped. This property is used in making cheesecakes and soufflésGelatineHeat is appliedAs the proteinUncoils waterbecomes trappedSolPro gelWaterProtein Matrix – the mixture has set – it has become a gel
20Biological Functions of Protein Function typeFunctionResult of deficiencyStructural FunctionGrowth & repair of body cells muscles &skinRetarded growthDelayed healingPhysiologically active proteinMaking hormones, enzymes, antibodies, blood protein, nucleoproteinBody organs & systems malfunction. Easily infected.Nutritive ProteinProvides essential amino acids for the body.Excess protein used for energyLack of energy.Kwashiorkor, Marasmus
21DeaminationThis is the process by which excess protein is used for energy.Left over amino acids are brought to the liverThe NH2 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.
22Biological 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
23Biological Value of different proteins SourceFoodHBVLBVProteinAnimalEggs100%Ovalbumin, Livetin, VitelinMilk95%Casein, Lactalbumin, LactoglobulinMeat80-90%Collegen, Elastin, Myosin,FishActin, Myosin, CollegenGelatine0%PlantSoya Beans74%Rice67%OryzeninWheat53%GlutenMaize40%Zein
24Supplementary 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 foodExample; 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.
25RDA Protein & Energy value 1gram of protein per kilogram of body weight.Child 30-50g/dayTeenager 60-80g/dayAdults 50-75g/dayPregnant or lactating 70-85g/dayEnergy Value1g of protein gives 4kCal or 17 kJ energy
26Digestion of protein Part of System Physical Digestion Digestive Juice EnzymeSubstrateProductMouthChewedStomachChurnedGastricjuiceRenninPepsinCaseinogenProteinsCaseinPeptonesDuodenumPancreaticJuiceTrypsinProteinSmall IntestineIntestinal JuicePeptidaseAmino acids
27Absorption & Assimilation of Amino Acids 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
28Questions?? 1 What is the elemental composition of protein? 2 Draw the chemical structure of an amino acid3 Explain how a peptide link forms4 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 & deamination8 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.