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Homework for next week Green q 1,2,3 p29 Do evaluation points from Biuret Practical Revise test on all work next week Bring evidence you have revised please
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3.1.2 Protein structure The relationship between primary, secondary, tertiary and quaternary structure to function in proteins
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Revise Structure of amino acid Formation of a peptide bond
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C amino group carboxylic acid group R group is different in different amino acids) Amino Acid Structure text p.26
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Peptide bonds and dipeptides
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Peptides
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Polypeptides When more amino acids are added to a dipeptide, a polypeptide chain is formed. A protein consists of one or more polypeptide chains folded into a highly specific 3D shape. There are up to four levels of structure in a protein: primary, secondary, tertiary and quaternary. Each of these play an important role in the overall structure and function of the protein.
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Protein structure Text p.26
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The structure of proteins
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Protein structure cont.. Secondary structure Hydrogen Bonds occur between the NH and C=O of the peptide bond, between different amino acids in the chain 1 hydrogen bond is weak The chain coils up into a helix shape (called ALPHA HELIX) (Beta pleated sheet is a different shape of secondary structure – again held by H bonds) Protein may have none, just alpha helix, just beta pleated sheet or both forms of secondary structure Alpha helixBeta pleated sheet
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Tertiary structure Further folding to give a complex 3d shape known as tertiary structure Shape is called GLOBULAR Depends on the a.a. sequence 3 types of bonds holding tertiary structure in place: 1 disulphide bonds – strong (between S in adjacent ‘R’ groups) 2 ionic between carboxyl and amino groups not involved in peptide bonds. Weaker than covalent, broken by extremes of pH 3 hydrogen bonds -numerous, weak animation
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Sulphur-containing amino acid Active site The tertiary structure of an enzyme
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Quaternary structure 2 or more polypeptide chains joined together Same types of bond hold it as tertiary structure (all 3) There can be non- protein (prosthetic) groups e.g. haem group containing iron E.g. haemoglobin Haemoglobin Molecule
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Globular protein 3˚ Metabolic eg. Enzymes, hormones
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Fibrous protein eg. Keratin (hair), collagen (tendons).
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Levels of protein structure LevelDescriptionBondsBetween groups Primary 1 o Sequence of amino acids PeptideAmino and carboxylic acid Secondary 2 o Alpha helix Beta sheet Hydrogen bondsC=O and N-H Tertiary 3 o Folding Globular shape Disulphide (Ionic) (Hydrogen) Amino acids with sulphur in Quaternary 4 o More than 1 polypeptide joined together As tertiary
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Protein structure
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3.1.2 Protein structure The relationship between primary, secondary, tertiary and quaternary structure to function in proteins A student model
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Use a highlighter to show what is ON YOUR SYLLABUS (get it out!)
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