C30 amino acids, proteins + DNA

• an amino acid is a compound with an amine group and a carboxylic acid group attached to a central carbon atom
• there are 20 naturally occuring amino acids
• the amine group is always on the second carbon so they are named 2-amino acids
• the central carbon atom in an amino acid is chiral as it has 4 different groups attached to it
• amino acids can display optical isomerism, but in reality almost all exist as the negative enantiomer
• in an amino acid, the carboxylic acid group tends to act as an acid by losing a proton, and the amine group tends to act as a base by accepting a proton
• amino acids exist as zwitterions, which means they have a permanent positive charge and a permanent negative charge, yet are neutral overall
• because amino acids are ionic, they have high melting points and dissolve in water but not well in non-polar solvents
• in an amino acid in strongly acidic conditions, the lone pair of the amine group accepts a proton to form the positive ion NH3(+), this is known as it becoming protonated
• in an amino acid in strongly alkaline conditions, the hydroxide group loses a proton to form the negative ion O(-), this is known as it becoming deprotonated
• the amine group of one amino acid can react with the carboxylic acid group of another amino acid, forming an amide linkage also known as a peptide link
• a peptide link is -CONH-
• amino acids can be joined together to form polypeptides
• two amino acids make up a dipeptide
• amino acids can form polymers as they each have both of the groups necessary to form a peptide link, so many can join together in a chain
• polypeptides are condensation polymers because a water molecule is eliminated for every peptide bond that is formed
• the primary structure of a protein is the sequence of amino acids in its chain
• the secondary structure of a protein is an alpha-helix or beta-pleated sheet, held together by hydrogen bonds
• the tertiary structure of a protein is the chain folding into a 3D structure, held together by a mixture of hydrogen bonds, ionic attractions and disulfide bridges
• disulfide bridges are sulfur-sulfur bonds which keep the protein stable by losing 2 hydrogen atoms
• when a polypeptide is boiled in concentrated HCl for 24 hours, it breaks down into a mixture of all of the amino acids that it was made up of, as all the peptide linkages are hydrolysed by the acid
• amino acids can be separated and identified by thin-layer chromatography
• the developing agent to use for amino acids in thin-layer chromatography is ninhydrin
• enzymes are protein-based catalysts found in living organisms
• each enzyme has an active site which is formed from the tertiary structure of the polypeptide, this is a specific shape, complementary to a specific molecule, called the substrate
• the substrate binds to the enzyme, this forms an enzyme-substrate complex
• enzymes are stereospecific, this means is a molecule displays stereoisomersim, they will only bind to and break down one of the pair of enantiomers
• enzymes can be inhibited if another molecule blocks their active site by binding to it, preventing any substrate molecules from binding and being broken down
• enzymes are denatured if the temperature or pH is too extreme, causing their active site to change shape and no long function
• DNA is deoxyribonucleic acid
• DNA is a condensation polymer made up of nucleotide monomers, formed from a sugar, a phosphate and a base
• the four possible bases in DNA are adenine, cytosine, guanine, and thymine
• the sugar in DNA is 2-deoxyribose
• DNA nucleotides are held together by phosphodiester bonds between the sugar of one nucleotide and the phosphate group of another nucleotide
• two DNA nucleotides can join together when an -OH group of a phosphate on one nucleotide reacts with an -OH group of a sugar on another nucleotide, eliminating a water molecule
• the phosphodiester bonds in DNA form a sugar-phosphate backbone
• DNA exists as two strands held together by hydrogen bonding
• adenine and thymine bond with each other forming 2 hydrogen bonds

  cytosine and guanine bond with each other forming 3 hydrogen bonds
• the two DNA strands wind around each other, forming a double helix
• cisplatin is an anti-cancer drug