Overview of Protein Structure
Applied Science: BTEC Level 3 National Extended Diploma, topic 3.3.1
Polypeptides
Amino acids are the monomers that join together to form polymers called polypeptides (proteins).
Structure of proteins
- Proteins are made up of amino acids.
- Dipeptides are formed from the condensation of two amino acids.
- Polypeptides are formed by the condensation of many amino acids.
Structure of amino acids
- Each amino acid has a central carbon atom (alpha carbon).
- There are four atoms or groups of atoms bonded to the central carbon atom:
- NH2 (an amino group).
- COOH (a carboxyl group).
- H (a hydrogen atom).
- R (a side group).
R groups
- The R group is different in each amino acid.
- The R group determines how the amino acid interacts and bonds with other amino acids in the polypeptide.
Essential amino acids
- There are 20 different types of amino acids that are common in all organisms.
- 10 of these are essential amino acids in humans because the human body cannot produce them and they are obtained from the diet.
Glycine
- Glycine is an example of an amino acid.
- Glycine has a hydrogen atom in its R group.
- Glycine is the only amino acid that does NOT have a carbon atom in its R group.
Peptide Bond
Each amino acid is attached to another amino acid as a result of a condensation reaction. These reactions cause peptide bonds to form.
Polypeptides
- Polypeptides are made from chains of amino acids.
- There are amino acids at each end of the polypeptide chain.
- These amino acids from the two end terminals:
- The N-terminal (amino terminal).
- The C-terminal (carboxyl terminal).
The peptide bond
- When two amino acids react together, a bond forms between the carboxyl group of one amino acid and the amino group of a second amino acid.
- One water molecule is released as a by-product.
- The bond formed between two amino acids is a covalent bond called a peptide bond.
Test yourself on Overview of Protein Structure
What monomers are bonded together to form polypeptides?
What are the four groups surrounding the central carbon atom in an amino acid?
How many different amino acids are there?
Dipeptides are formed by what reaction?
Which statements are true about the polypeptide chain?