Proteins

• proteins are made from long chains of amino acids
• proteins are polymers
• amino acids are monomers in proteins
• a dipeptide is formed when 2 amino acids join together
• polypeptide is when more than 2 amino acids join together
• proteins are made from 1 or more polypeptides
• amino acids are joined together by peptide bonds to form dipeptides and polypeptides
• a molecule of water is released during the reaction of amino acids which is a condensation reaction. the reverse is hydrolysis
• all amino acids have the same general structure - carboxyl group (-COOH) And an amino group (-NH2) attached to a carbon atom. difference between the groups is the variable group (R)

  
• proteins 4 structural levels:

  1. primary
  2. secondary
  3. tertiary
  4. quaternary
• • PRIMARY STRUCTURE - this is the sequence of amino acids in the polypeptide chain.
  • different proteins have different sequences of amino acids in there primary structure.
  • a change in one amino acid can change the structure of the whole protein

  
• • SECONDARY STRUCTURE - The poly peptide chain doesn't remain flat and straight
  • H bonds form between nearby amino acids in the chain
  • makes it automatically coil into an alpha, helix or fold into a beta pleated sheet

  
• TERTIARY STRUCTURE - the coiled or folded chain of amino acids is often coiled and folded further.

  • more bonds form between different parts of a polypeptide chain.
  • for proteins made from a single polypeptide chain tertiary forms their final 3D structure.

  
• QUATERNARY STRUCTURE - some proteins are made of several different polypeptide chains held by bonds

  • quaternary is the way the polypeptide chains are assembled together.
  • e.g. haemoglobin is made from 4 polypeptide chains bonded together.
  • for proteins made from more than one polypeptide chain the quaternary structure is the proteins final 3D Structure.

  
• primary structure - held together by the peptide bonds between amino acids
• secondary structure - held together by hydrogen bonds
• tertiary - ionic bonds

  • disulfide bonds- when 2 amino acids of cysteine come close together the sulphur atom in one cysteine bonds to the sulphur in the other cysteine
  • hydrophobic and hydrophilic reactions
  • hydrogen bonds
• quaternary structure - all bonds as it depends on the tertiary structure of the individual polypeptide chains being bonded toether.
• in a globular protein, hydrophilic R groups on the amino acids tend to be pushed to the outside of the molecule. caused by the hydrophobic and hydrophilic interactions in the proteins tertiary structure

  makes them soluble so are easily transported in fluids
• HAEMOGLOBIN - globular protein that carries O2 around the body in red blood cells

  • conjugated protein - protein with a non-protein group attached called a prosthetic group
  • each of the 4 polypeptide chains in haemoglobin has a prosthetic group called haem
  • a haem group contains iron which O2 binds too
• INSULIN - A hormone secreted by the pancreas. helps regulate blood glucose level.

  consists of 2 polypeptide chains held by disulfide bonds
• AMYLAZE- enzyme that catalyses the break down of starch in the digestive system. made of a single chain of amino acids.

  • secondary structure contains both a-helix and b-pleated sheet sections.
• fibrous proteins are insoluble and strong and are quite unreactive
• 3 fibrous proteins:

  1. collagen
  2. keratin
  3. elastin
• collagen - found in animal connective tissues, such as bone, skin and muscle.

  • very strong
  • minerals can bind to the protein to increase its rigidity e.g. in bone.
• keratin - found in many of the external structures of animals, skin, hair

  • can be flexible, hard or tough
• Elastin- found in elastic connective tissue : skin, large blood vessels, ligaments

  • elastic so tissues can return to their original shape after stretched
• what are the monomers of proteins

  amino acids
• what is a polypeptide

  a chain of more than 2 amino acids joined together
• main 5 elements found in proteins

  carbon, oxygen, hydrogen, nitrogen, sulfur
• name of the bind that forms between amino acids

  peptide
• the reaction that links amino acids together

  condensation
• the reaction that breaks amino acids apart

  hydrolysis
• how is the secondary structure formed

  H bonds form between the -NH and -CO groups of the amino acids in the chain. makes it coil into A-helix or Beta pleated sheet
• how is a disulphide bond formed

  when 2 molecules of the amino acid cysteine come together, sulfur atom in one cysteine bonds to sulfur in the other
• what is the quaternary structure of a protein

  the wat 2 or more polypeptide chains of a protein are assembled together
• how does globular structure of haemoglobin make it suited to its function

  it means that the hydrophilic side chains are on the outside of the molecule and the hydrophobic side chains face inward. Makes haemoglobin soluble in water, makes it good for transporting oxygen in blood
• what is a conjugated protein

  protein with a non protein group attached
• 2 properties of a globular protein that are different to those of a fibrous protein

  they are soluble and reactive
• what is the function of collagen


  forms connective tissue in animals