13.9 Amino Acids

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Amino acids and proteins 

  • amino acids have one amino group (NH2) and one acid group (COOH)
  • they have an R group e.g. CH3
  • another adjacent hydrogen on a carbon

Amino acids are an example of bi-functional compound - compounds with two functional groups which interact with each other.

  • the proton donating -COOH and proton accepting -NH2 react with one another, forming a zwitterions.
  • a zwitterion = particles containing both negatively charged and positively charged groups.

An aqueous solution of an amino acid consists mainly of zwitterions, with very few molecules containing the un-ionised groups. Amino acids and very soluble in water because they are effectively ionic!

UNLESS there is an extra -COOH or -NH2 group in the molecule then the solution is neutral in aqueous solution.

  • amino acids can act as a buffer solution.
  • a buffer solution can withstand the addition of small amounts of acid or alkali.
  • the zwitterions neutralise the effect of addition.

Making peptides and proteins

When two…


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