Notes on Protein

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Proteins are made from long chains of amino acids

  • The monomers of proteins are amino acids
  • A dipetide is formed when two amino acids join together
  • A polypeptide if formed when more than two amino acids join together
  • Proteins are made up of one of more polypeptides.

AMINO ACID GROUPS.

  • Carboxyl group (-COOH)
  • Amino group (-NH2) attached to a Carbon atom
  • Variable group ( R) which is the difference between different amino acids
  • Also a hydrogen.

 POLYPEPTIDES ARE FORMED IN CONDESATION REACATIONS. A MOLECULE OF WATER IS RELEASED DURING THE REACTION. PEPTIDE BONDS ARE FORMED.

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Protein Primary Structure,Secondary Structure and

Primary structure

 The Sequence of amino acids in the polypeptide chain

Secondary Structure

Hydrogen bonds form between amino acids in the chain.

This makes it coil in to an alpha helix or fold in to a beta pleated sheet.

Tertiary Structure

Coiled or folden chains of amino acids are then coiled and folded further.

More bonds form between different parts of the polypeptide chain.

Proteins made from a SINGLE polypeptide chain, the tertiary structure is their final 3D shape

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Protein Quaternary Structure.

  • Some proteins are made of several different polypeptide chains held together by bonds
  • The quaternary structure is the way the polypeptide chains assemble together
  • for proteins ( eg. haemoglobin,insulin and collegen) made from more than one polypeptide chain, this is their final 3D shape

A proteins shape determines its function.

For example haemoglobin is a compact, soluble protein. Making it easier for transport

This makes it great for carrying oxygen around the body

Collagen has 3 polypeptide chains tightly coiled together which makes it strong

A great supportive tissue in animals.

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Proteins have a variety of Functions

1) Enzymes

  • Roughly sphrerical in shape ( due to tight folding of polypeptide chains
  • Soluble and have roles in metabolism ( eg. enzymes break down large food molecules)
  • Other enzymes help synthesise ( make) large molecules

2) Antibodies

  • Involved in the immune response
  • made of 2 light( short) polypeptide chains and two heavy polypeptidechains bonded together
  • they have variable regions, and amino acide sequences in these regions vary greatly.

3) Transport proteins

  • Present in cell membranes
  • they contain hydrophobic and hydrophilic amino acids, they cause the protein to fold up and form a channel. They transport molecules and ions across membranes.

4)Structural Proteins: physically strong and consist of long polypeptide chains lying parrallel with crosslinks between them. E.g keratin ( hair and nails) and collagen ( connective tissue)

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Biuret Test for Proteins

Two stages to this test

  • The test solution needs to be alkaline, so first you add a few drops of sodium hydroxide solution.
  • Then you add some copper (II) sulfate solution.
  • If protein is present a purple layer forms.
  •   If there is no protein, the solution will stay blue
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Biuret Test for Proteins

Two stages to this test

  • The test solution needs to be alkaline, so first you add a few drops of sodium hydroxide solution.
  • Then you add some copper (II) sulfate solution.
  • If protein is present a purple layer forms.
  •   If there is no protein, the solution will stay blue
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