Protein Structure and Function

Protein Structure and Function

• Proteins are organic macromolecules composed of amino acids.
• Twenty different amino acids exist, each with a unique "R group" which determines its properties.
• Amino acids contain carbon, hydrogen, oxygen, and nitrogen.
• Amino acids share a similar backbone structure featuring a central carbon atom, hydrogen, carboxyl and amino groups.

Amino Acid Bonding and Polypeptides

• Amino acids bond together via dehydration synthesis.
• This reaction links the carboxyl group of one amino acid to the amino group of another, forming a covalent peptide bond.
• The resulting linear chain of amino acids is called a polypeptide.
• Polypeptides have directionality, with a free amino (N-terminus) end and a free carboxyl (C-terminus) end.
• The specific sequence of amino acids in a polypeptide defines the protein's primary structure.

Protein Secondary, Tertiary, and Quaternary Structures

• Secondary structure involves the polypeptide chain folding into patterns like alpha helices and beta sheets, stabilized by hydrogen bonds between the backbone.

• Tertiary structure describes the overall 3D shape of the polypeptide, determined by interactions between R groups.

• R group interactions (hydrophobic, hydrophilic, ionic) shape the protein's 3D structure.

• Hydrophobic R groups tend to cluster inside the protein, while hydrophilic and ionic groups interact with the surrounding water.

• Quaternary structure occurs when multiple polypeptide chains associate to form a functional protein.

• An example of a protein with quaternary structure is haemoglobin.

Protein Shape and Function

• A protein's unique 3D shape (tertiary structure) dictates its specific function.
• Proteins perform diverse roles in cells, including structural support, cellular communication, metabolism, defense, and transport.
• Proteins can be enzymes, hormones, receptors, or transport channels, depending on their shape.