2.3.a Describe the structure of an amino acid and the formation and breakage of a peptide bond. 

• Amino acids are compounds that have the following general structure:

This image shows the general structure of an amino acid. 

• Each carbon atom is bonded to an -NH2 group (amine), a -COOH group (carboxylic acid), and a hydrogen. 
• There are 20 amino acids, that differ from each other based on which R group is present:

This image shows the 20 amino acids and their structures! You do not need to memorise this! 

• Peptide bonds are the link formed between the two amino acids. 
• When two amino acids are aligned next to each other, one loses a hydroxyl (–OH) group from its -COOH group, and the other loses a hydrogen atom from its -NH2 group. 
• This leave a carbon to bond with the nitrogen.
• The formation of this bond occurs via condensation, in a reaction similar to triglyceride synthesis during glycosidic bond formation. 
• On the other hand, hydrolysis (i.e., addition of water) breaks peptide bonds and proteins break down into amino acids.

This image shows the formation and breakage of peptide bonds to form dipeptides, via condensation and hydrolysis. 

• Two amino acids linked together are called a “dipeptide”. 
• Many amino acids linked together are called a “polypeptide”. 
• Proteins are made up of one or many polypeptide chains. 

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Written by Aayushi | GCE CIE Biology Specialist @ TUTTEE

References:

Jones, M., & Parkin, M. (2018). Cambridge International AS and A Level Biology. Cambridge: Cambridge University Press.