Amino Acids
Chemistry: Cambridge International A Level, topic 3.7.5
Amino Acids
There are about 20 naturally-occurring amino acids in animal cells.
Amino acids
- Amino acids have the general formula RCH(NH2)COOH.
- Amino acids contain an acidic group (carboxylic acid) and a basic group (amine) in the same molecule.
- The -NH2 group is on the carbon next to the -COOH group and so they are known as α-amino acids.
Acid and base behaviour
- The -COOH group is acidic and can react with bases by donating a proton (H+).
- The -NH2 group is basic and can react with acids by accepting a proton (H+).
- Amino acids are amphoteric because they contain both acidic and basic groups in the same molecule.
Side chain
- An amino acid contains an -R group which is a side chain.
- This is different for different amino acids.
- E.g. Alanine has an -R group of -CH3.
Amino Acids as an Acid and Base
Amino acids have the ability to behave as an acid or a base.
Acidic and basic groups
- In an amino acid:
- The amine acts as a basic group.
- The carboxylic acid acts as an acidic group.
Zwitterions 1
- There is internal movement of an H+ from the carboxylic acid group and onto the amine group to create a zwitterion.
- The resulting zwitterion has both negative -COO- and positive -NH3+ groups.
Zwitterions 2
- Zwitterions exist in solids and in solution
- A zwitterion has no overall charge but parts of the molecule are positively and negatively charged.
Test yourself on Amino Acids
All amino acids have the same two functional groups. So what is different about the different types of α-amino acids?
What is a zwitterion?
In a zwitterion, which part of the molecule is negatively charged?