Protein Structure

• Primary structure refers to the sequence of bonded amino acids in a polypeptide chain
• The primary structure of each protein is coded for by DNA
• A mutation in the DNA can change the primary structure of a protein. This can vastly change the overall shape of the protein and cause it to lose its function
• Secondary structure refers to the shape of specific sections of each polypeptide chain
• Hydrogen bonding between polar amino acids allows for overlapping and coiling to occur in the "folding" of the protein into its 3D shape
• All proteins must be "folded" in order to work. The polarity/nonpolarity of the "R" groups of the protein's amino acids determine how the protein will fold
• Two common types of secondary structure are the alpha helix and the beta pleated sheet
• Tertiary structure refers to the overall shape of each individual polypeptide chain
• Disulfide bridges help stabilize the protein's folded structure
• Disulfide bonds form when cysteines (a type of amino acid) are near each other in a polypeptide chain
• Tertiary structures are partially determined by ionic interactions between certain R groups and by hydrophobic interactions between certain R groups and water
• Quaternary structures is when two or more polypeptides are woven together to form a protein
• Hemoglobin has four polypeptides woven together
• Denaturation usually disrupts the secondary and tertiary levels of protein structure by affecting either the hydrogen bonds or disulfide bonds which stabilize the structure