Introduction to Proteins

Proteins

Type of proteins

• Enzymes, biological catalysts that control biochemical reactions.
  


• structural proteins, for example collagen that make up tendons.
  


• signal proteins, carry a message around the body, for example insulin.
  


• storage proteins, protein store that form the white of egg.


• defensive proteins, for example, antibodies that fight infections.


• Transport proteins, for example haemoglobin, the carrier of oxygen in blood.

Proteins are polymers formed of amino acids, there are thousands of proteins bu only 20 differents amino acids.

Amino Acids

The amino acids have an amino group(-NH2) and a carboxyl group(-COOH). The amino group is attached by a covalent bond to the central carbon atom called the alpha carbon. In the amino acids the R varies for each different amino acid. The R groups are non-polar and hydrophobic but others are polar and hidrophilic.

Amino Acids as buffers

Amino acids are amphoteric, they have both acidic and basic properties when they dissociate in water. The acidic properties are derived from the carboxyl group, which can donate a proton and being negatively charged in an alkiline solution. The basic properties are derived from the amino group, which can take a proton to be positively charged in an acidic solution. Ions with both, negative and positive charges are called zwitterions. The ability to donate and receive protons allow amino acids to behave as buffers. A buffer solution tends to resist changes in ph. Buffer systems play an essential role in the human body, keeping the ph of blood in tolerable levels.

Peptide bonds

Two amino acids can combine to form a dipeptide by a condensation reaction , this bond is called peptide bond. Further amino acids can combine with the dipeptide to form a polypeptide chain. Proteins consist of one or more polypeptide chains.