Proteins

• Proteins constitute approximately 50-67% of cell dry mass.
• Proteins are organic compounds, containing C, H, O, and N (and often S).
• Proteins are condensation polymers, which are large, complex macromolecules.
• The monomer of proteins is an amino acid, which are the 20 most common.
• Amino acids form a polypeptide chain, which is the protein molecule.
• Salt links are stronger than H bonds but weaker than S-S bonds.
• Quaternary 3-D arrangement of two or more polypeptides or of polypeptide chain/s with non-protein component, i.e. prosthetic group (conjugated protein) is usually referred to as a quaternary structure.
• Formation between ionised amino and carboxyl parts occurs on some R-groups.
• Large numbers help maintain structure.
• A protein molecule may comprise multiple polypeptide chains.
• Amino acids have two functional groups, which confer different properties.
• The alpha or central carbon and the ever-present H atom are key elements in amino acids.
• Amino acids have four bonds per carbon, with only the R group varying.
• Amino acids are the monomers of proteins.
• Types of bonds found in proteins include peptide, hydrogen, ionic, disulphide (or disulfide), hydrophobic interactions, and van der Waals forces.
• Peptide bonds are covalent and can be broken by hydrolysis.
• Polypeptides can be catalysed by enzymes (proteases) or using dilute acid.
• Hydrogen bonds involve H, which is part of -OH or -NH group, becoming slightly electropositive and attracted to electronegative O or N atoms.
• KOH or NaOH with CuSO4…Cu2+ react with peptide linkages (C-N) to form a complex with a strong purple colour.
• Peptide bonds are formed by condensation reaction between two adjacent amino acids, where the -OH of carboxyl group of one, and -H of amino group of other combine.
• The biuret test can be performed using premixed reagent or separate chemicals.
• 129 amino acids make up the single polypeptide chain of Lysozyme, with the C and N terminus specified.
• Peptide bonds link the adjacent amino acids in the polypeptide chain of Lysozyme.
• The primary structure of a protein is the sequence of amino acids that comprises its simplest level of organization and determines all others.
• A polypeptide forms when 10 or more amino acids join together using peptide bonds, resulting in a dehydration synthesis.
• Amino acids are great pH buffers.
• A zwitterion can take up hydrogen ions from acid solutions and release hydrogen ions in alkaline conditions, thus resisting change in pH.
• Alanine and glycine combine to form alanylglycine.
• The amino group acquires a proton and becomes positively charged.
• The buffer effect of amphoteric compounds is very important as different chemical groups may occur.
• The carboxyl group ionises, freeing a proton and becoming negatively charged.
• An ion is a dipole or double ion, forming a zwitterion at neutral pH.
• Making a peptide with 9 amino acids involves forming 9 peptide bonds and forming 9 water molecules.
• Having any number and order of amino acids leads to an infinite number of different polypeptides with varying properties.
• Making a tripeptide involves forming two peptide bonds and forming two water molecules.
• Peptide bonds are broken by hydrolysis.
• Valine is an amphoteric compound that can act as an acid and a base when dissociating in water.
• The order of R groups determines the shape and properties of the resulting polypeptide.
• A zwitterion can move in an electric field and is overall electrically neutral.
• Formula for polypeptides: P = number of types of amino acids available, n = number of amino acid residues present in chain.