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Proteins Learning objectiveLearning objective To be able to describe the primary, secondary, tertiary and quarternary structure of proteinsTo be able.

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Presentation on theme: "Proteins Learning objectiveLearning objective To be able to describe the primary, secondary, tertiary and quarternary structure of proteinsTo be able."— Presentation transcript:

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2 Proteins Learning objectiveLearning objective To be able to describe the primary, secondary, tertiary and quarternary structure of proteinsTo be able to describe the primary, secondary, tertiary and quarternary structure of proteins

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4 In a protein the polypeptide chain may be hundreds of amino acids long.In a protein the polypeptide chain may be hundreds of amino acids long. Amino acid polymerisation to form polypeptides is part of protein synthesis.Amino acid polymerisation to form polypeptides is part of protein synthesis. It takes place in ribosomes, and is special because it requires an RNA template.It takes place in ribosomes, and is special because it requires an RNA template. The sequence of amino acids in a polypeptide chain is determined by the sequence of the genetic code in DNA.The sequence of amino acids in a polypeptide chain is determined by the sequence of the genetic code in DNA.

5 Protein Structure Polypeptides are just a string of amino acids,Polypeptides are just a string of amino acids, They fold up to form the complex and well-defined three-dimensional structure of working proteins.They fold up to form the complex and well-defined three-dimensional structure of working proteins. To help to understand protein structure, it is broken down into four levels:To help to understand protein structure, it is broken down into four levels:

6 Primary Structure This is just the sequence of amino acids in the polypeptide chain, so is not really a structure at all.This is just the sequence of amino acids in the polypeptide chain, so is not really a structure at all. However, the primary structure does determine the rest of the protein structure.However, the primary structure does determine the rest of the protein structure. Finding the primary structure of a protein is called protein sequencing, and the first protein to be sequenced was the protein hormone insulin, by the Cambridge biochemist Fredrick Sanger, for which work he got the Nobel prize in 1958.Finding the primary structure of a protein is called protein sequencing, and the first protein to be sequenced was the protein hormone insulin, by the Cambridge biochemist Fredrick Sanger, for which work he got the Nobel prize in 1958.

7 Secondary Structure Interactions between the R groups of the amino acids in the chain cause the chain to twist and fold into a three dimensional shapeInteractions between the R groups of the amino acids in the chain cause the chain to twist and fold into a three dimensional shape Lengths of the chain may first coil into α-helices or β-pleated sheets.Lengths of the chain may first coil into α-helices or β-pleated sheets. These are known as the secondary structures.These are known as the secondary structures.

8 α-helices Within the helix, hydrogen bonds form between the C=O of the carboxylic acid group and the NH of the amine group of the different amino acids.Within the helix, hydrogen bonds form between the C=O of the carboxylic acid group and the NH of the amine group of the different amino acids.

9 β-sheets Several chains may link together with hydrogen bonds holding the parallel chains together.Several chains may link together with hydrogen bonds holding the parallel chains together.

10 Tertiary structure The polypeptide chain often folds and bends to produce a three dimensional shapeThe polypeptide chain often folds and bends to produce a three dimensional shape The tertiary structure is held together by bonds between the R groups of the amino acids in the protein, and so depends on what the sequence of amino acids is. There are three kinds of bonds involved:The tertiary structure is held together by bonds between the R groups of the amino acids in the protein, and so depends on what the sequence of amino acids is. There are three kinds of bonds involved: –hydrogen bonds, which are weak. –ionic bonds between R-groups with positive or negative charges, which are quite strong. –sulphur bridges - covalent S-S bonds between two cysteine amino acids, which are strong.

11 The secondary structure is due to backbone interactions and is thus largely independent of primary sequence.The secondary structure is due to backbone interactions and is thus largely independent of primary sequence. The tertiary structure is due to side chain interactions and thus depends on the amino acid sequenceThe tertiary structure is due to side chain interactions and thus depends on the amino acid sequence

12 Quaternary Structure This structure is found in proteins containing more than one polypeptide chain, and simply means how the different polypeptide chains are arranged together.This structure is found in proteins containing more than one polypeptide chain, and simply means how the different polypeptide chains are arranged together. The individual polypeptide chains are usually globular, but can arrange themselves into a variety of quaternary shapes.The individual polypeptide chains are usually globular, but can arrange themselves into a variety of quaternary shapes.

13 Globular and fibrous proteins Proteins can be divided into two distinct groupsProteins can be divided into two distinct groups

14 Globular proteins The polypeptide chain is folded into a compact spherical shapeThe polypeptide chain is folded into a compact spherical shape These proteins are soluble due to hydrophilic side chains that project from the outside of the moleculesThese proteins are soluble due to hydrophilic side chains that project from the outside of the molecules Globular proteins are therefore important in metabolic reactionsGlobular proteins are therefore important in metabolic reactions

15 Globular proteins Enzymes – 3D shape gives the ability to form enzyme – substrate complexes and catalyse reactionsEnzymes – 3D shape gives the ability to form enzyme – substrate complexes and catalyse reactions Transport proteins – 3D shape allows them to bind with other molecules eg: proteins in cell membranes or haemoglobin in red blood cells.Transport proteins – 3D shape allows them to bind with other molecules eg: proteins in cell membranes or haemoglobin in red blood cells. Antibodies – precise shape binds to microorganismsAntibodies – precise shape binds to microorganisms

16 Fibrous proteins These do not fold into a ball shapeThese do not fold into a ball shape They remain in long chains, often with several polypeptide chains cross linked together for additional strengthThey remain in long chains, often with several polypeptide chains cross linked together for additional strength They are insolubleThey are insoluble

17 Fibrous proteins Keratin – in hair and skinKeratin – in hair and skin Collagen – in the skin, tendons, cartilage and blood vessel wallsCollagen – in the skin, tendons, cartilage and blood vessel walls

18 Types of proteins Fibrous proteins –e.g. collagen –Insoluble –structural Globular proteins –e.g.enzymes –Soluble –3D shape

19 Tertiary structure Bonding between R-groups gives rise to a 3D shapeBonding between R-groups gives rise to a 3D shape H-bonds =O HN-H-bonds =O HN- Ionic bonds –NH 3 -COO-Ionic bonds –NH 3 -COO- Disulphide bridgeDisulphide bridge --CH 2 S-SCH CH 2 S-SCH 2 - affected by temp & pH affected by pH affected by reducing agents

20 Examples of Quaternary Structures Haemoglobin, the oxygen-carrying protein in red blood cells, consists of four globular subunits arranged in a tetrahedral (pyramid) structure.Haemoglobin, the oxygen-carrying protein in red blood cells, consists of four globular subunits arranged in a tetrahedral (pyramid) structure. Each subunit contains one iron atom and can bind one molecule of oxygen.Each subunit contains one iron atom and can bind one molecule of oxygen.

21 Examples of Quaternary Structures Immunoglobulins, the proteins that make antibodies, comprise four polypeptide chains arranged in a Y-shape.Immunoglobulins, the proteins that make antibodies, comprise four polypeptide chains arranged in a Y-shape. The chains are held together by sulphur bridges. This shape allows antibodies to link antigens together, causing them to clump.The chains are held together by sulphur bridges. This shape allows antibodies to link antigens together, causing them to clump.

22 Examples of Quaternary Structures Actin, one of the proteins found in muscles, consists of many globular subunits arranged in a double helix to form long filaments.Actin, one of the proteins found in muscles, consists of many globular subunits arranged in a double helix to form long filaments.

23 Just to be awkward… A few proteins have both structures: the muscle protein myosin has a long fibrous tail and a globular head, which acts as an enzymeA few proteins have both structures: the muscle protein myosin has a long fibrous tail and a globular head, which acts as an enzyme

24 This diagram shows a molecule of the enzyme dihydrofolate reductase, which comprises a single polypeptide chain. It has been drawn to highlight the different secondary structures.This diagram shows a molecule of the enzyme dihydrofolate reductase, which comprises a single polypeptide chain. It has been drawn to highlight the different secondary structures. Can you identify which is which?Can you identify which is which? 1.β sheet 2.α – helix 3.α – helix 1 2 3

25 Questions 1.Name the elements found in proteins. 2.What are the monomers of proteins? 3.Draw the structure of an amino acid (label the groups). 4.What is the name for the bond between two amino acids? 5.What bonds are found in the secondary structure of proteins? 6.What is the test for protein? 7.List 6 functions of proteins. 8.What is hydrolysis? 9.What is denaturation? 10.What kind of protein is an enzyme? 11.What is the function of a fibrous protein?

26 Answers 1.Name the elements found in proteins. CHONSCHONS 2.What are the monomers of proteins? Amino acidsAmino acids 3.Draw the structure of an amino acid (label the groups). carboxylic acid group amine group C C R OO N H H H H The group that determines what amino acid is

27 4.What is the name for the bond between two amino acids? PeptidePeptide 5.What bonds are found in the secondary structure of proteins? Hydrogen bondsHydrogen bonds 6.What is the test for protein? Biuret test gives purple with proteinBiuret test gives purple with protein 7.List 6 functions of proteins. Enzymes, structural, carriers, pumps, hormones, antibodiesEnzymes, structural, carriers, pumps, hormones, antibodies 8.What is hydrolysis? Breakdown of a substance by adding waterBreakdown of a substance by adding water 9.What is denaturation? Altering the shape of a proteinAltering the shape of a protein 10.What kind of protein is an enzyme? GlobularGlobular 11.What is the function of a fibrous protein? StructuralStructural


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