Amino acids proteins and DNA

Question 1

Amino acid

Answer 1

• contain 1 amine group and 1 carboxylic acid group
• are amphoteric (they act as an acid and a base)
• are chiral molecules, so are optically active
• they are named as if they are a carboxylic acid with an amino group

Question 2

Zwitterion

Answer 2

• Amino acids can form crystalline solids with higher melting points than expected because the -OH group donates its H+ to the -NH3, forming a neutrally charged ion that allows for ionic bonding that raises the melting point
• isoelectric point = the pH at which the zwitterion is 0, this is unique to every amino acid
• if the pH is below the isoelectric point charge is positive as there are more H+’s
• if the pH is above it the charge is negative because there aren’t enough H+’s

Question 3

chromatography

Answer 3

• separate and identify amino acids with thin layer chromatography
• ninhydrin is used to give amino acids a purple colour
• put spot of amino acid on TLC plate and stand the plate in an appropriate solvent
• the unique Rf value of an amino acid is distance travelled up plate by spot/distance travelled by solvent up the plate

Question 4

Proteins

Answer 4

• condensation polymers of amino acids, sometimes called peptides
• primary protein = single straight chain polymer
• secondary structure = peptide links form hydrogen bonds so the chain spirals or pleats, bonding into itself
• tertiary structure = ionic bonds, disulfide bonds and Van der Waals forces further coil the chain
• disulfide bonds are covalent bonds between the Sulfur atoms in residues of Cysteine

Question 5

Enzymes

Answer 5

• they are biological catalysts made of proteins, with active sites that fit only certain substrates so they only catalyse one specific reaction in the body each
• enzyme inhibitors are designed to fit in these active sites as well, so they block the reaction from happening
• enzymes can be broken under strong pH’s or temperatures
• only 1 enantiomers in an optical pair will fit in the active site so not some enantiomers are not effective while their pair is
• inhibitor drugs are very difficult to find as they have to be absolutely perfect, so computer programs are used

Question 6

DNA

Answer 6

• made up of nucleotides, which have a phosphate ion, 2-deoxyribose (as the sugar), and a base
• covalent bonds between sugar and phosphate form the backbone of DNA, with bases attached to the sugars
• bases can be adenine, guanine, thymine or cytosine
• adenine and thymine bond together with 2 sites
• guanine and cytosine bond together in 3 sites
• O, NH2 and NH groups act as the bonding sites to other bases
• each base has an NH group that bonds to the deoxyribose

Question 7

Cisplatin

Answer 7

• is used as a cancer treatment to stop DNA replicating
• platinum complex ion with 2 chloride ligands and 2 ammonia ligands, making it a cis/trans isomer
• cisplatin is in the Z-isomer pattern, and it stops DNA replicating by forming a co-ordinate bond with a nitrogen atom on guanine, and then another one on a different base to stop the DNA unwinding
• can bind to non-cancerous DNA, which stops hair/blood cells replicating
• transplatin does nothing and is useless