How it works
An amino acid is the building block of a protein. The first drawing is the structure all of them share, the second is one real example, leucine, and the third shows two amino acids joined.
Read the full guide
Read each drawing from the central carbon
Every amino acid has a central carbon, called the alpha carbon, bonded to four things: a hydrogen atom, an amino group, a carboxyl group and a side chain, written R. Only the side chain differs from one amino acid to the next. In leucine it is a branched chain of four carbons. When two amino acids join, the carboxyl group of one bonds to the amino group of the other and a water molecule is given off. The new bond is a peptide bond. The free amino end of the chain is the N-terminus and the free carboxyl end is the C-terminus.
- For a draw-and-label sheet, press Print blank; the first drawing is the basic structure.
- Typing NH2 or COOH counts for the two groups.
Questions and answers
How do you draw and label the basic structure of an amino acid?
Draw a carbon atom in the middle with four bonds. Put an amino group on one side, a carboxyl group on the other, a hydrogen atom above and the letter R below for the side chain. Label the middle atom the alpha carbon.
How do you label the chemical structure of the amino acid leucine?
Find the central carbon first. The group with the nitrogen is the amino group and the group with two oxygens is the carboxyl group. Everything else hanging from the central carbon, a branched chain of four carbons, is the side chain of leucine.
What is the R group of an amino acid?
The side chain: the one part that differs between amino acids. Proteins are built from twenty amino acids, each with a side chain of its own, and R stands in for any of them.
How does a peptide bond form?
The carboxyl group of one amino acid reacts with the amino group of the next. A bond forms between the carbon and the nitrogen, and one molecule of water is released. Chemists call this a condensation reaction.