Proteins in the human body have a wide range of functions which include: Hormones (insulin, testosterone), Muscle Fibers (actin, muasin), Carrier Protein (Oxygen carrying hemoglobin), Structure/ Support (nails/ hair), Enzymes (biological catalyst), Membrane Transport (Na/ K pump), Cell-to-Cell Recognition, Antibodies.

Structure

Proteins are polymers made up of amino acid subunits bonded together by peptide bonds.

This occurs by a condensation reaction.

Primary Structure

  • Given by the sequence of amino acids in the polypeptide.
  • Controls all levels of further folding.

All proteins have an amino terminal end and a carboxyl terminal end.  These ends are significant to the sequencing of a polypeptide.  Insulin was the first protein to be sequenced.  Our DNA codes for the sequence of every protein our cells make.  A change in one amino acid residue can alter the final shape of the protein making it dysfunctional.  This is the root cause of genetic disorders (e.g. sickle cell anemia hemoglobin defect).

Secondary Structure

  • Second level of folding due to hydrogen bonding between main chain amino and carbonyl groups

α-helix:

  • springy/ flexible

β-sheet:

  • Hydrogen bonding
  • (e.g silk)
  • High tensile strength due to hydrogen bonding

Tertiary Structure

  • further folding and super coiling of the polypeptide
  • controlled by interactions (covalent, ionic, van der Waals) between the R-groups or side chains of the amino acids

Interacts with watery environment of the cytoplasm to drive folding process.

  • Gives protein a specific 3-dimensional shape and a specific function.  What would happen to the protein if these bonds were broken? Denaturation

Quaternary Structure

  • Two or more polypeptides interacting to form a functional protein
  • Metal ions may be part of the protein structure as in

Hemoglobin with Fe2+

  • Allows for very specific activity of the protein due to detailed globular shape and
    • collagen triple helix
  • Indivisible, tensile (strong), flexible
  • Responsible for skin elasticity
  • 4 heme groups allows it to bind 4 oxygen molecules
  • Successive oxygen binding is accelerated
  • 1st oxygen is hardest to bind

Allosteric Co-operativity

  • Property of quaternary structure
  • Activates activity of a protein through its initial bonding

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