7.3.3 Amino acids

Amino acids carry both an amine group and a carboxylic acid group

1. Every amino acid molecule has two different functional groups.
   1. Amine group: the functional group ${-NH}_2$.
   2. Carboxylic acid group: the functional group $-COOH$.
2. Having both groups lets each amino acid link to other amino acid molecules.
3. Glycine is an amino acid with the formula $H_2{NCH}_{2}COOH$.

Amino acids join by condensation to make polypeptides

1. Condensation polymerisation joins many amino acids into a long chain.
2. The $-COOH$ group of one amino acid reacts with the ${-NH}_2$ group of another.
3. An $-OH$ from the carboxylic acid group and an $-H$ from the amine group combine to make $H_{2}O$.
4. The atoms left behind form a peptide link, $-CO-NH-$, between the two amino acids.
5. This joining repeats across many amino acids to build the chain.
6. A polypeptide is the long chain made when many amino acids join by peptide links.
7. For glycine, the repeating part of the chain is shown here.
   1. ${\left[-NH-{CH}_2-CO-\right]}_n$

Different amino acids join to make proteins

1. A polypeptide chain does not have to contain only one type of amino acid.
2. Different amino acids all carry the amine and carboxylic acid groups needed for condensation.
3. So different amino acids can join through peptide links in the same chain.
4. Combining different amino acids in one chain produces proteins.