In this A-Level Biology Lesson "Amino acids structure, dipeptides and polypeptides" you’ll learn that Proteins are diverse macromolecules and that ALL proteins are polymers composed of smaller monomers known as amino acids. We’ll take a good look at the structure of a typical amino acid (remember you should be able to label this up under exam conditions, so make sure you’re super familiar with it). Once we’ve illustrated the general structure of an amino acid we’ll go though how amino acids join together via condensation reactions to form dipeptides. Here we can also emphasise that Proteins are polymers made up from Hydrogen, Oxygen and Carbon… and we’ll take a look at a couple of common amino acids (Glycine (GLY)) and Methionine (MET). (If you only remember 1 amino acid make it MET!). We’ll finish here with the key point that Polypeptides are many amino acids joined together by peptide bonds and summarise this lesson. 

When you’re happy you know all about amino acids, their structure and can easily describe (and illustrate) how amino acids join together to form dipeptides and therefore polypeptides you’ll be ready to download the knowledge check PDF and test your knowledge. When you’ve answered all the questions, compare your answers to the ones I’ve written - you’ll see exactly how you should write answers in a way that gains maximum marks in the exams.

A-Level Biology "Proteins: Amino Acids - Dipeptides and Polypeptides"

Proteins are extremely diverse, Whether the protein is an enzyme, transport protein, antibody… etc. All are polymers made up from Amino Acids.

Amino Acids join together via condensation reactions to form polypeptides.

You have to be able to recognise the structure of an amino acid, be able to label it and show how they join together to form dipeptides, [and therefore, tripeptides and polypeptides]. Can you draw and label the structure of a typical amino acid?

When amino acids join together via condensation reactions, the NH2 group from one amino acid joins with the COOH group of another. A H2O molecule is released and a Peptide bond linking the amino acids is formed.

Polypeptides range from a few amino acids to thousands in length.

A functional protein maybe just one of these polypeptides (which has folded and coiled – see next lesson), or could be more than one polypeptide associated together to form a functional protein, e.g. collagen and haemoglobin.