Proteins

• Polypeptide is a linear hetero-polymer composed of amino acids linked together by peptide bonds.
• Protein is one or more polypeptides linked together either covalently or non-covalently.
• Protein subunit is an individual polypeptide that forms part of a protein.
• The 20 standard amino acids can mostly be put into three groups according to their side chains: polar, ionisable; polar, non-ionisable; non-polar.
• Amino acids found in proteins are α-L-amino acids, except glycine which has no stereoisomers.
• Prosthetic groups are non-amino acid components of proteins.
• Amino acids can also be classified as aliphatic or aromatic.
• Function of proteins depends on chemical structure and molecular conformation.
• Amino acids are the basic building blocks of proteins and are found in all species.
• α-amino acids (except proline) contain a primary amine group (–NH3) and a carboxylic acid (carboxyl–COOH) group attached to the central carbon atom adjacent to the carboxyl group.
• Amino acids in general contain at least one amine group and one carboxyl group.
• Dr Kris Jeremy can be contacted at B408 PSQ 26.
• Protein formation involves the formation of peptide bonds between amino acids, leading to the creation of dipeptides, tripeptides, and oligopeptides.
• An amine group attached to the α carbon is the most common.
• An amine group attached to the β carbon is rare.
• Polypeptides are linear heteropolymers composed of α amino acids linked by peptide bonds.
• Nucleic acid polymers are linear heteropolymers composed of nucleotides joined by phosphodiester links.
• The 'standard' amino acids are those found in proteins, all are α-amino acids, all except one are α-L-amino acids, and there are 20 different types (usually).
• D- and L-amino acids are distinguished by some enzymes.
• Aspartic acid and glutamic acid are negatively charged and unionised forms are present at physiological pH.
• Amino acids with acidic side chains have carboxyl groups that allow communication with amino acids via ionic interactions.
• Amino acids with polar, non-ionisable side chains are good at hydrogen bonding and are modifiable through phosphorylation or glycosylation.
• Conformation changes are important in thermophiles.
• The standard 20 amino acids have a 'R'group and are subdivided into properties of their side-chains.
• L-amino acids are rare in nature.
• The acid dissociation constant (Ka) determines whether an acid is classed as a strong acid or as a weak acid.
• Amino acids with alcoholic side chains have hydroxyl groups that allow communication with amino acids via ionic interactions.
• Methionine is an exception as its side chain is covalently linked to an amine group.
• Every acid has a (conjugate) base and every base has a (conjugate) acid.
• Amino acids with nonpolar side chains contain only carbon and hydrogen and are hydrophobic.
• Enantiomers are physically and chemically indistinguishable and are distinguished by different optical rotation of plane-polarized light.
• Amino acids with amide side chains have amide groups that are good at hydrogen bonding and can form disulphide bridges.
• Amino acids with basic side chains are ionised at typical cellular pH values and are positively charged.
• Amino acids with aromatic side chains are usually classified as non-polar.
• Amino acids with aliphatic side chains are hydrophobic and bulky.
• Amino acids with ionisable side chains have different properties depending on their side-chain: acidic - basic, small – large - bulky, aromatic - aliphatic, polar – non polar, hydrogen bonding.
• Proline is an imino acid with an imine group.
• Glycine is the simplest α amino acid with no stereoisomers.
• Dextrorotatory (D; Greek ‘dextro’ = right) and levorotatory (L; Greek ‘levo’ = left) are terms used to describe the rotation of plane-polarized light.
• Polysaccharides are linear or branched homo- or heteropolymers composed of monosaccharides joined by glycosidic links.