Biomolecules — Proteins

Amino Acids:

The basic building blocks of proteins are amino acids. Amino acids are the monomers which form polypeptide and proteins.

Properties of Proteins:

• sensitive to pH and heat
• shape determines function
• enzymes are special group of proteins
• contain H, N, C and S
• made up of amino acids

There are about 20 essential amino acids found in proteins, and they differ in their R group. 

Amino acids join together to form a polypeptide through the process called condensation.

Two amino acids are joined by a peptide bond to form a dipeptide via condensation. Water is formed as a by product. 

The reaction is between an amino group and a carboxyl group. 

Continued condensation leads to the addition of more amino acids and thus resulting in a polypeptide chain.

 

Structure of proteins:

1. Primary structure --> specific linear order which amino acids join to form a polypeptide chain
2. Secondary structure --> regular folding of segments by hydrogen bonds (α-helix and β-pleated sheet)
3. Tertiary structure --> (only for globular proteins) overall shape of polypeptide resulting from interactions* between the R group 
4. Quaternary structure --> association of 2 or more polypeptide chains 

*Bonds that form tertiary structures:

• hydrogen bonds
• ionic bonds
• disulfide bonds
• hydrophobic interaction

Classification of proteins (based on structure):

• Globular --> compact and spherical structure which is soluble
• Fibrous --> long polypeptide chains twisted around each other, forming long fibres that provide tensile strength, insoluble