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Proteins Proteins Presentation Transcript

  • Proteins Building blocks, structure and function
  • Learning outcomes
    • The basic structure of an amino acid (structure of specific amino acids is not required).
    • The formation of polypeptides and proteins (as amino acid monomers linked by peptide bonds in condensation reactions)
    • The significance of the proteins primary structure in determining its 3-d structure and properties (globular and fibrous proteins and types of bond involved in 3-d structure)
  • Homework – learning objectives
    • Compare and contrast the structures and functions of globular and fibrous proteins. Use examples of different types of proteins to illustrate your answer.
    • Minimum 500 words
    • Reference your work. Include at least three different references, at least one must be a book or journal.
  • Proteins
    • Chemical nature
    • Contain the elements C, H, O, N ( S, P sometimes)
    • Monomer : Amino Acid
    • They all have the same basic structure
    • Apart from a variable group ‘R ’
    • JOBS of Proteins
    • Structural components
    • Membrane carriers
    • Enzymes
    • Hormones
    • Antibodies
    • Enzymes – amylase, sucrase, pectinase
    • Hormones – insulin, glucagon
    • Oxygen transporters - haemoglobin
    • Cell membrane transport – sodium channels
    • Cell surface receptors – beta receptors
    • Structural – hair, skin
    • Cytoskeleton – spindle fibres cell division
    • Antibodies - immunoglobulins
    • Pigments - melanin
    1000s different proteins different functions
  • All proteins are made from amino acids Acid or carboxyl group Amino Group
  • The simplest Amino Acid
  • Joining amino acids togehter
    • 2 amino acids molecules bond together
    • via a
    • condensation reaction
    • to form
    • a peptide bond
    • to make
    • a dipeptide
    • A Condensation Reaction
    © Pearson Education Ltd 2008 This document may have been altered from the original
    • The same condensation reaction occurs over and over again to join many amino acids together to make a polypeptide
  • Breaking a peptide bond - Hydrolysis
  • Proteins from amino acids – Protein Synthesis
    • Site of manufacture: Ribosome
    • Uses m-RNA to put amino acids in the right order
    • A specific polypeptide is made
    • PRIMARY Structure
    • The sequence of an amino acids linked together in a polypeptide chain
  • PRIMARY STRUCTURE sequence of amino acids in the polypeptide chain Held together by STRONG peptide bonds val lys phe gly arg cys val gly
  • Definition of secondary structure
    • A regular repeating pattern of shape in a polypeptide chain, for example an alpha- helix or beta pleated sheet
  • SECONDARY STRUCTURE Polypeptide chain folds forming α-HELIX or β-SHEET Structure held by HYDROGEN BONDS α-HELIX β-SHEET Hydrogen bonds Polypeptide Chain
  • β- SHEET α-HELIX
  • How is the shape maintained?
    • By hydrogen bonds between different amino acids in chain.
    • Although weak there are many of them
    • So great stability given
  • Tertiary Structure
    • The overall 3-D shape of a protein molecule.
  • What holds the shape in place?
    • ..Different types of bond and interaction.
    • Disulphide bridges
    • Ionic bonds
    • Hydrogen bonds
    • Hydophobic and hydrophillic interactions
  • What is the role of the tertiary structure?
    • Vital to the protein’s function
    • Many molecules must have a specific shape in order to do a job:
    • Examples –
    • hormones to fit into the receptor site on a membrane
    • an enzymes’s active site must have a complementary shape to its substrate
  • Types of Protein
    • The 3-D shape of proteins fall into two main categories
    • Globular – e.g. haemoglobin
    • compact and globe shaped
    • water soluble
    • Fibrous - e.g. collagen
    • regular repeating sequences, fibres, insoluble
    • P103 OCR text book has a good table
  • What happens when there is a change of a single amino acid in the sequence its primary structure? The places in which the different types of bonds can form are determined by the amino acid sequence. Change this and there is a change on the tertiary structure – its 3-D shape And therefore the proteins ability to carry out is function
  • Quaternary Structure
    • Where protein structure consists of more than one polypeptide chain – the overall 3-D structure of the molecule.
  • Haemoglobin
    • Job – to transport oxygen around body
    • Globular protein
    • Soluble in water
    • Wide range of amino acids in primary structure
    • Contains prosthetic group (a non-protein part) called haem
    • Much of moleclue would into an alpha-helix
  • Collagen
    • Job – provide mechanical strength arteries, bones tendons and cartilage
    • Fibrous protein
    • Insoluble
    • 35% of amino acids are glycine
    • No prosthetic group
  • Collagen