Proteins

• All have the same basic structure but differ in their side chain (R group).

• 4 groups amino acids are:

  • Non polar

  • Polar

  • Acidic

  • Basic

• Growth and maintenance

• biochemical reactions: enzymes, blood clotting, muscle contraction

• Messengers: hormones

• Structure: e.g. collagen

• Maintain pH

• Balance water

• Immunity

• Each protein has a specific 3-D conformation.

• 4 levels of protein structure are:

• Primary (1^o)

• Secondary (2^o)

• Tertiary (3^o)

• Quaternary (4^o)

• Unique sequence of amino acids joined by peptide bonds in a linear polypeptide chain

• The 20 common amino acids can be arranged in different ways (determined by genetic information)

• Eg: Glucagon consist of a sequence of 29 amino acids

• Once a linear chain of amino acids is formed, it spontaneously coils to form the alpha helix or folds to form the beta pleated sheet.

• Because of hydrogen bonds between the repeating constituents of the polypeptide backbone (not the amino acid side chains).

• Two forms:

  - alpha helix (coiled)

  - beta pleated sheet (folded)

• alpha helix - Keratin found in hair, nails, horn

• beta pleated sheet - Silk protein produced by many insects & spiders  

• A polypeptide may be further coiled into a globular shape which is maintained by bonds & interactions among side chains.

• The bonds and interactions that maintained the structure are:

  i. Disulfide bridges

  ii. Ionic bonds

  iii. Hydrogen bonds

  iv. Hydrophobic interactions

  v. Van der Waals interactions

• Consists of 2 or more polypeptide chains joined to form a single functional molecule.

• The bonds that formed between the polypeptide chains are :

  i) Disulfide bonds

  ii) Ionic bonds

  iii) Hydrogen bonds

  iv)  Hydrophobic

  v)  Van der Waals interactions

• Eg : haemoglobin and collagen

  a) Haemoglobin

   • Consists of 4 polypeptide chains

   • 2 α-chains

   • 2 β-chains

• b) Collagen

   • Consists of 3 polypeptide chains that  forms triple- stranded helical coils.

   • Fibrous protein

Denaturing a
Protein

Proteins have their shape changed under harsh conditions

Conditions that can
denature enzymes:

▪ High temperature
▪ concentration
▪ extreme pH