protein

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Information about protein
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Published on February 24, 2014

Author: drmustansar

Source: authorstream.com

PROTEINS: PROTEINS Proteins are of primary importance to the life of the cell: Proteins are of primary importance to the life of the cell by dry weight proteins are the major components of an actively growing cell Proteins are constructed of monomers, called: : Proteins are constructed of monomers, called: amino acids How do we get the amino acids needed to build proteins?: How do we get the amino acids needed to build proteins? EATING Protein-Rich Foods Proteins ingested are digested by enzymes called……………………: Proteins ingested are digested by enzymes called…………………… proteases PowerPoint Presentation: Non-essential amino acids: can be synthesised by the body (e.g. cysteine ) Essential amino acids : must be taken in with the diet the body cannot make them (e.g. methionine ) Structure of an amino acid molecule: Structure of an amino acid molecule PowerPoint Presentation: What is an ‘amino acid’? An organic molecule possessing both carboxyl and amino groups R = Side group/chain [varies] Sometimes books give this [amino acid in solution]:: Sometimes books give this [ amino acid in solution ]: PowerPoint Presentation: The α carbon atom is: the first carbon that attaches to a functional group asymmetrical PowerPoint Presentation: Amino acids exist in two isomeric forms: D-amino acids ( dextro , “right”) L-amino acids ( laevo , “left”)—this form is found in organisms PowerPoint Presentation: How many different amino acids: e xist: over 170 are known are commonly found in proteins: 20 PowerPoint Presentation: Amino acids can be grouped based on side chains PowerPoint Presentation: The various side groups of amino acids Table 3.2 (Part 1) NONPOLAR Leucine Amino acids are nonpolar. PowerPoint Presentation: The various side groups of amino acids Table 3.2 (Part 1) s implest amino acid POLAR UNCHARGED Glycine: PowerPoint Presentation: The various side groups of amino acids Table 3.2 (Part 1) POLAR CHARGED Glutamic acid Amino acids are polar. PowerPoint Presentation: Table 3.2 (Part 1) The R-groups also have functional groups: Arginine [polar, positively charged] e.g. amino group Glutamic acid: e.g. carboxyl PowerPoint Presentation: The various side groups of amino acids Table 3.2 (Part 1) AROMATIC [NONPOLAR] Phenylalanine PowerPoint Presentation: Let’s mention three amino acids of special interest: Proline Methionine Cysteine PowerPoint Presentation: Table 3.2 (Part 4) Proline : causes kinks in chains PowerPoint Presentation: Table 3.2 (Part 3) Methionine : is often the first amino acid in a polypeptide contains sulfur PowerPoint Presentation: Table 3.2 (Part 4) Cysteine : contains sulfur can form disulfide bridges Sulfhydrl group PowerPoint Presentation: A Disulfide Bridge PowerPoint Presentation: When hair is permed – disulfide bridges in keratin are broken and reformed Disulfide bridges in straight hair Disulfide bridges broken & reformed PowerPoint Presentation: Same happens when hair is straightened PowerPoint Presentation: Why do amino acids differ in their chemical and physical properties (size, water solubility, electrical charge)? Because of their different R groups PowerPoint Presentation: The side groups of amino acids determine folding of polypeptide Table 3.2 (Part 1) PowerPoint Presentation: Side chains of amino acids : show a wide variety of chemical properties are important to determine the: 3D structure function of the protein PowerPoint Presentation: hydrophilic amino acids hydrophobic amino acids Where do you expect these types of amino acids to be placed in the ion channel spanning the plasma membrane? PowerPoint Presentation: Ions (black) can only pass through the pore of the ion channel because this is the only part with hydrophili c amino acids lining the pore  ( green = area of ion channel with hydrophilic water-loving amino acids ).    The rest of the ion channel mostly consists of hydrophobic amino acids (purple).    hydrophilic amino acids hydrophobic amino acids WHY? PowerPoint Presentation: ORDER of the side chains of amino acids in a protein : determines how it folds into a three dimensional configuration From amino acids to proteins: From amino acids to proteins two amino acids dipeptide three amino acids tripeptide more than 50 amino acids polypeptide 6 000-1000 000 protein PowerPoint Presentation: All proteins can be hydrolysed into amino acids   Some: need time & a particular medium A ll proteins are broken when: heated in 6M HCl at 115  C for several hours Let’s discover how two amino acids link together: Let’s discover how two amino acids link together Amino acids are joined together by a condensation reaction: H 2 N H H C C O OH Carboxyl group N H CH 3 C C O OH H 2 N H H C O C N C C H H CH 3 OH O Peptide bond Amino group H H H 2 O + Amino acids are joined together by a condensation reaction A peptide bond is a covalent C-N bond formed by condensation between the -NH 2 of one amino acid and -COOH of another PowerPoint Presentation: H H H H H H H O O O H H O H H O N C C N N C C C C H CH 3 CH 2 OH N-terminus N C C CH 2 C O OH CH 2 N C C CH CH 3 H 3 C CH 2 OH H H O N C C H H O N C C H H O N C C CH 2 SH OH C-terminus Many amino acids joined together = Polypeptide chain PowerPoint Presentation: Note R groups alternate in the Polypeptide chain Show the position of a peptide bond PowerPoint Presentation: C-N atoms of the peptide bonds: lie in the same plane to form the backbone Side chains of the individual amino acids: are arranged transversal to each other across the backbone – this confers stability to the molecule PowerPoint Presentation: A protein molecule: contains 100’s and 1000’s of amino acids joined together by peptide links into one or more chains 3 chains in collagen (in mouse tail) PowerPoint Presentation: Polypeptide chains can be folded in various ways PowerPoint Presentation: Proteins are unbranched , not like carbohydrates Branched molecule Unbranched molecule Protein Many different types of proteins exist. How can this be?: Many different types of proteins exist. How can this be? MILLIONS of Antibodies exist A LARGE NUMBER OF ENYZMES PowerPoint Presentation: Because any of 20 different amino acids might appear at any position E.g. a protein containing 100 amino acids could form any of 20 100 different amino acid sequences this is 10 130 , i.e. 1 followed by 130 zeros Number and Sequence of amino acids determine the protein: Number and Sequence of amino acids determine the protein 6 amino acids 5 amino acids 7 amino acids 6 amino acids but in a different sequence Test for Protein: Biuret Test: Test for Protein: Biuret Test Protein present Test for Protein: Biuret Test: Test for Protein: Biuret Test Cheese is rich in protein. Add an equal amount of NaOH to the solution followed by 1-2 drops of CuSO 4 solution pestle mortar PowerPoint Presentation: Purple / Lilac: Positive test When a protein reacts with copper(II) sulfate (blue), the positive test is the formation of a violet colored complex. PowerPoint Presentation: What dictates the function of each protein? The exact sequence of amino acids. Proteins have many functions: enzymes hormones structural proteins PowerPoint Presentation: Where is the information stored in a cell that determines the sequence of amino acids? DNA PowerPoint Presentation: MUTATION Scrambled sequences of amino acids are useless: in some cases, just one wrong amino acid can cause a protein to function incorrectly What is the cause of ‘scrambled sequences of amino acids’? PowerPoint Presentation: a genetic disorder n o enzyme is present to process phenylalanine Is the amino acid sequence really important? Let’s illustrate by an example: PKU (phenylketonuria) p henylalanine builds up – causes mental retardation PowerPoint Presentation: A person with PKU must avoid foods that are high in protein, such as milk, cheese, nuts or meats PowerPoint Presentation: Enzyme has about 452 amino acids One amino acid is present instead of another PowerPoint Presentation: PKU: no cure Testing at birth PowerPoint Presentation: Glycine is one of the 20 amino acids that occur in proteins. Proteins, in turn are useful organic components of cells. Proteins play various roles within a cell. On the otherhand , glycine , is the simplest amino acid, having hydrogen as the radical and could have formed much more easily than the other amino acids. Complex machinery is required to convert amino acids to functional proteins. PowerPoint Presentation: Structure of a Protein each protein has a characteristic three dimensional shape called its conformation four levels of organisation exist:- 1) Primary structure 2) Secondary structure 3) Tertiary structure 4) Quaternary structure PowerPoint Presentation: Structure of a Protein the number and sequence of amino acids held together by peptide bonds in a polypeptide chain : the number and sequence of amino acids held together by peptide bonds in a polypeptide chain the primary structure of each type of protein is unique Primary structure of a protein: Primary structure of insulin: 51 amino acids: Primary structure of insulin: 51 amino acids PowerPoint Presentation: Secondary structure: the way in which the polypeptide is arranged in space secondary structure of many different proteins may be the same bonds present: Peptide Hydrogen Hydrogen bonds between amino acids lead to the secondary structure of a protein:  Hydrogen bonds between amino acids lead to the secondary structure of a protein Two common secondary structures are the - helix and  -pleated sheet PowerPoint Presentation:  helix is in a right-handed coil PowerPoint Presentation:  helix is in a right-handed coil, maintained by H-bonds between: CO of one amino acid and NH group of the fifth amino acid radical groups jut out in all directions PowerPoint Presentation: helix: the most common form of secondary structure PowerPoint Presentation: Keratin: is entirely helical and thus fibrous hardness & stretchability of keratin varies with degree of disulfide bridges PowerPoint Presentation:  -pleated sheet occurs when two adjacent peptide chains bind to one another PowerPoint Presentation: 2)  -pleated sheet chains run parallel but in opposite directions PowerPoint Presentation:  -pleated sheet Side chains stick perpendicular to the plane of the chains assuming a zig-zag pattern PowerPoint Presentation: S ilk is an example of a  -pleated sheet Silk Protein Structure PowerPoint Presentation: Elastin in elastic connective tissue consists of many cross-linked polypeptides PowerPoint Presentation: It is common for a polypeptide to be partly: an - helix a  - beta pleated sheet :  - beta pleated sheet - helix PowerPoint Presentation: Tertiary structure: is when the polypeptide chain bends and folds extensively to form a precise compact is a complex, three-dimensional that determines the final configuration of the polypeptide PowerPoint Presentation: Tertiary structure is determined by interactions of R-groups : Disulfide bonds Aggregation of hydrophobic side chains Ionic bonds Hydrogen bonds Further folding of the polypeptide chain contributes to the tertiary structure of a protein:  Further folding of the polypeptide chain contributes to the tertiary structure of a protein Which amino acid forms disulfide bridges? Cysteine Hydrophobic Interactions are a major force in the folding of globular proteins: Hydrophobic Interactions are a major force in the folding of globular proteins PowerPoint Presentation: Myoglobin : 153 amino acids in a single polypeptide chain no disulfide bridges Haem molecule is unusual as it consists almost entirely of helices PowerPoint Presentation: Quaternary structure: the precise arrangement of the aggregation of polypeptide chains held together by hydrophobic interactions, H-bonds and ionic bonds occurs in many highly complex proteins a huge variety of quaternary structures Quaternary structure of various proteins: Quaternary structure of various proteins Antibodies comprise four chains arranged in a Y-shape. Quaternary structure of various proteins: Quaternary structure of various proteins Actin - hundreds of globular chains arranged in a long double helix Quaternary structure of various proteins: Quaternary structure of various proteins ATP synthase - 22 chains forming a rotating motor. The joining of more than one polypeptide chain leads to the quaternary structure of proteins:  The joining of more than one polypeptide chain leads to the quaternary structure of proteins PowerPoint Presentation: Collagen is: a triple helix a fibrous protein cannot be stretched due to H-bonds connecting the chains PowerPoint Presentation: Collagen is f ound in: cartilage t endon cartilage t endons (attach muscles to bones) PowerPoint Presentation: Collagen is f ound in: cornea the underlayers of skin cornea of the eye PowerPoint Presentation: Haemoglobin : 574 amino acids 4 polypeptide chains  -chain  -chain  -chain  -chain PowerPoint Presentation: (one molecule of oxygen binds to one haem ) (a) Haemoglobin (b) Iron-containing haem group PowerPoint Presentation: haem is an iron-containing porphyrin , acting as prosthetic group of several pigments prosthetic group is a non-protein group which when firmly attached to a protein results in a functional complex (a conjugated protein) porphyrin is a macromolecule composed of four subunits PowerPoint Presentation: How is it possible for foetal haemoglobin to obtain oxygen from the maternal haemoglobin? PowerPoint Presentation: Foetal haemoglobin is structurally different from that of an adult : as it has gamma chains instead of beta What does this difference in structure result in? PowerPoint Presentation: Structural difference results in foetal haemoglobin being able to obtain oxygen from the placenta as it has a higher affinity for oxygen than the mother’s haemoglobin PowerPoint Presentation: Structure of foetal haemoglobin varies from that of maternal haemoglobin. PowerPoint Presentation: The final three-dimensional shape of a protein can be classified as: Fibrous T ough Insoluble in water Globular Soluble Keratin Silk Collagen Enzymes Antibodies PowerPoint Presentation: myosin A few proteins have both structures e.g. the muscle protein : long fibrous tail a globular head PowerPoint Presentation: Proteins have tertiary and quaternary structure. The tertiary and quaternary structures of proteins create a variety of molecules, each able to carry out a particular function. PowerPoint Presentation: Since proteins can twist and fold in many ways, forming a variety of active site shapes. Two Types of Protein: Two Types of Protein CONJUGATED : globular proteins + non-protein material ( prosthetic group ) SIMPLE : only amino acids e.g. albumins, histones PowerPoint Presentation: Name Prosthetic group Location Haemoglobin Haem Red blood cells Glycoprotein Carbohydrate Blood plasma Lipoprotein Lipid Cell membranes Denaturation & Renaturation: Denaturation & Renaturation PowerPoint Presentation: A protein spontaneously refolds into its original structure under suitable conditions The loss of the specific three-dimensional conformation (secondary structure) of a protein PowerPoint Presentation: Why is denaturation of proteins considered as harmful to an organism? The molecule unfolds and cannot perform its normal biological functions. Denaturation agents can be:: Denaturation agents can be: Heat ii) Strong acids & alkalis and high concentrations of salts   iii) Heavy metals (e.g. mercury)   iv) Organic solvents and detergents PowerPoint Presentation: i ) H eat weak h ydrogen bonds and non polar h ydrophobic interactions are disrupted Why? PowerPoint Presentation: Heat increases the kinetic energy Causes the molecules to vibrate so rapidly and violently that bonds break PowerPoint Presentation: protein coagulates PowerPoint Presentation: ii) Strong acids & alkalis + high concentrations of salts ionic bonds are disrupted the protein is coagulated PowerPoint Presentation: Coagulation of milk by adding salts PowerPoint Presentation: Breakage of peptide bonds may occur if the protein remains in the reagent for a long time PowerPoint Presentation: iii) Heavy metals cause the protein to precipitate out of the solution   Cations (+) form strong bonds with carboxylate anions (COOH - ) and often disrupt ionic bonds PowerPoint Presentation: disrupt hydrophobic interactions form bonds with non-polar groups this in turn disrupts intramolecular H-bonding iv) Organic solvents & detergents PowerPoint Presentation: Why does the solution become purple when beetroot discs are placed in detergent? 1. Proteins in cell membrane & tonoplast are denatured. 2. Phospholipid bilayer is damaged. PowerPoint Presentation: Why is the skin wiped with alcohol before an injection is given? Alcohol is used as a disinfectant. It denatures the protein of any bacteria present on the skin. PowerPoint Presentation: What change has a protein undergone if it has been denatured When a protein is denatured it loses its three dimensional shape in space. Its tertiary structure is destroyed and cannot fold properly. Hydrogen bonds, ionic bonds and hydrophobic interactions that are useful to determine the final shape of the molecule are destroyed . :  List TWO agents that may cause denaturation of a protein. (2) Extreme changes in pH Heat Heavy metals Organic solvents Detergents Buffering capacity of proteins : Buffering capacity of proteins PowerPoint Presentation: A buffer can donate or accept H + to stabilise the pH. PowerPoint Presentation: Why are buffers needed? To keep solution at a constant pH. PowerPoint Presentation: The need of buffers in organisms Reactions in cells change pH in blood. Proteins change shape if pH changes. PowerPoint Presentation: Name THREE buffers in organisms: Hydrogen carbonate Buffering capacity of amino acids : Buffering capacity of amino acids Zwitterion : a compound with both acidic and basic groups Isoelectric point is that pH at which a zwitterion carries no net electrostatic charge Buffering actions by phosphate and hydrogen carbonate: Buffering actions by phosphate and hydrogen carbonate Functions of Proteins: Functions of Proteins Functions of Proteins: Functions of Proteins Type Example Occurrence / function Structural Collagen Component of bone, tendons, cartilage cartilage Functions of Proteins: Functions of Proteins Type Example Occurrence / function Structural Keratin Skin , feathers, hair, nails, horns Functions of Proteins: Functions of Proteins Type Example Occurrence / function Structural Elastin Elastic connective tissue (ligaments ) Functions of Proteins: Functions of Proteins Type Example Occurrence / function Structural Fibrin Viral coat proteins Forms blood clots ‘ Wraps up ‘ nucleic acid of virus Functions of Proteins: Functions of Proteins Type Example Occurrence / function Enzymes Hydrolytic enzymes Proteases Cleave polysaccharides Break down proteins Hormones Insulin Regulate blood sugar level Functions of Proteins: Functions of Proteins Type Example Occurrence / function Transport Haemoglobin Myoglobin Carries O 2 and CO 2 in blood Stores O 2 in muscle Functions of Proteins: Functions of Proteins Type Example Occurrence / function Transport Serum albumin Cytochrome Transport in blood e.g. lipids Electron transport Lipoprotein Electron carriers Functions of Proteins: Functions of Proteins Type Example Occurrence / function Transport Membrane transporters e.g. glucose transporters Transport sugars into cells Functions of Proteins: Functions of Proteins Type Example Occurrence / function Protective Antibodies Mark foreign proteins for elimination Functions of Proteins: Functions of Proteins Type Example Occurrence / function Protective Fibrinogen Thrombin Precursor of fibrin in blood clotting Involved in clotting mechanism Functions of Proteins: Functions of Proteins Type Example Occurrence / function Motion Myosin Actin Contraction of muscle fibres Contraction of muscle fibres Functions of Proteins: Functions of Proteins Type Example Occurrence / function Storage Caesin Stores ions in milk Functions of Proteins: Functions of Proteins Type Example Occurrence / function Storage Ferretin Stores iron, especially in spleen PowerPoint Presentation: Type Example Occurrence / function Toxins Bacterial neurotoxins Prolonged muscle contraction Patient Suffering From Tetanus. Painting by Sir Charles Bell, 1809. Functions of Proteins: Functions of Proteins Type Example Occurrence / function Antifreeze Glycoproteins In arctic flea Functions of Proteins: Functions of Proteins Type Example Occurrence / function Receptors Rhodopsin Light receptor in retina THE END: THE END

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