Amino Acids and Proteins

Amino Acids and Proteins

Amino Acids

  • Amino acids are the monomers that come together to form proteins. They are molecules containing an amine group (NH2), a carboxyl group (COOH), and a unique side chain, typically written as -R.

  • Amino acids can be categorised as polar or non-polar, representing their hydrophilic or hydrophobic properties.

  • The uniqueness of each amino acid is determined by its R group. The R group can be as simple as an H atom (like in glycine) or as complex as a six-membered carbon ring (like in phenylalanine).

  • Zwitterions are formed when internal acid-base reactions occur within amino acids. This gives them both positive and negative charges, which can influence their behaviour in solutions, such determining solubility or reactivity.

Peptide Bonds and Proteins

  • Amino acids link together via a condensation reaction, leading to formation of peptide bond. In this process, a molecule of water is released.

  • A single bond that combines two amino acids is called a dipeptide bond. A longer chain of amino acid is referred to as a polypeptide.

  • Proteins are essentially very large polypeptides. They fulfill a vast range of functions within living organisms, including structural function (i.e. collagen), transporting molecules (i.e. haemoglobin), as well as functioning as enzymes.

Protein Structures

  • Proteins can have four levels of structure: primary, secondary, tertiary, and quaternary structures.

  • The primary structure is the specific sequence of amino acids in the polypeptide chain. This determines the final 3D structure of the protein and essentially, its function.

  • The secondary structure refers to the specific shape that the polypeptide chain assumes as a result of hydrogen bonding. It is typically seen as an alpha helix or a beta pleated sheet.

  • The tertiary structure represents the three-dimensional arrangement of the protein, stabilised by different types of bonds and interactions, like ionic bonding, disulphide bridges, and Van der Waals forces.

  • The quaternary structure applies when a protein is made up of multiple polypeptide chains, such as haemoglobin. It describes the way these separate chains interact and arrange themselves.

  • Altering the protein’s environment can cause the protein to unravel and lose its shape, a process known as denaturation. This could result in the protein losing its functionality completely. Common factors causing denaturation include changes in pH levels, temperature or exposure to specific chemicals.