Amino Acids, Proteins and DNA
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Structure of amino acids?
amine = -NH2 carboxyl = -COOH organic side chain (R) (exception: glycine, which has H as an R group) hydrogen
Which amino acid does not rotate plane polarised light and why?
glycine, as it is not a chiral molecule
Properties of amino acids
Amphoteric: -can act as an acid or a base Chiral: -have a central carbon atom with 4 different groups around it
What is a zwitterion? What happens to it at a low/high pH?
-molecule with both positive and negative ions -only exist at the amino acid’s isoelectric point -isoelectric point = pH at which overall charge is 0 = dependent on the R group -both the carboxyl and amino groups are ionised When the pH is higher than the isoelectric point -COO- is likely to accept a H+ When the pH is lower than the isoelectric point -NH3+ is likely to lose a H+
Method to separate and identify amino acids? Why does it work?
Thin Layer Chromatography (TLC) -works due to different solubilities -stationary phase of silica or alumina is mounted on a glass/metal plate -pencil base line is drawn -drops of amino acid mixtures added -place the plate in a solvent, with the base line above the solvent level (why?) -leave until solvent has moved up to near the top of the plate -remove, mark the solvent front and allow to dry -chromatogram has been produced -amino acids can be identified by their position on the chromatogram
Why are amino acids not visible? What can be used to see them?
colourless compounds iodine/ninhydrin solution -place chromatogram in a sealed jar with a few iodine crystals -iodine vapour sticks to chemicals on the plate -dyes them purple -iodine vapour = locating agent fluorescent dyes and UV light -place plate under UV light -spots will be fluorescent -draw around spots to mark where they are
Rf values are fixed for amino acids except when…
temperature, solvent or makeup of the TLC plate changes
What are proteins?
-condensation polymer of amino acid monomers -joined together by peptide link -dipeptide = 2 amino acid monomers
Cisplatin action
First ligand substitution reaction. One of the chloride ligands on cisplatin is substituted for water molecules. • Second ligand substitution reaction. The newly-substituted water molecules is, in turn, replaced by one of the guanine nitrogen atoms Dative covalent bonds are formed between the lone pair on one nitrogen atom on a guanine base and the central platinum ion at the centre of cisplatin.
Cisplatin limitations
unable to differentiate between the DNA of cancerous cells and those of healthy cells. Hence the cisplatin drug attacks healthy cells side effects such as kidney and nerve damage, and hair loss.