Summary AQA Chemistry A-Level - Amino acids, Proteins, DNA
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I completed chemistry A-Level in one year, teaching most of the course to myself, earning an A overall. I found it easiest like this as all the information from the textbook is streamlined and in one place. Comparing all past mark schemes I wrote the summaries using words and highlighting phrases y...
Amino acids, proteins, DNA
30.1 Introduction to amino acids: Thin layered chromatography-
1. Break the peptide/amide linkages between amino acids
Amino acids are the monomer of proteins, they have two to get the separate amino acids via hydrolysis.
functional groups-carboxylic acid group and amine. 2. A small spot of the mixture of amino acids is place on
A-amino acids is where the amine group is on the C the line 1cm up and the chromatography plate is put in
atom next to the COOH group. Therefore the tank
amino acids have acid and basic 3. A lid is placed on the tank, means its saturated and the
properties. solvent vapour moves up the plate.
• high melting points, due to ionic 4. Amino acids move based on its affinity for the solvent
bonding in a giant lattice structure. compared to the affinity to the mobile phase, depends on
• Dissolves well in polar solvents c the intermolecular forces between them.
• In strong acids the amine group will accept a H+ 5. Plate is removed when solvent almost reaches the top, the
ion, it becomes protonated. plate is sprayed with a developing agent to show the
• In a strong base the carboxylic acid group donates a amino acids.
H+ ion, it’s become deprotonated. 6. Calculate the Rf values:
Zwitterion: ions that have both a Rf = distance moved by amino acid
permanent positive charge and a permanent negative distance moved by the solvent
charge, although the overall molecule is neutral.
30.2 Peptides, polypeptides and proteins:
Primary structure: the sequence of amino acids joined
together in condensation reactions to form an amide
linkage -CONH- between the amine and carboxyl
group of different amino acids, to from dipeptides.
You can use 2D chromatography if amino acids have
Primary structure can be undone through hydrolysis similar Rf values, once normal chromatography has been
reactions, boiling the dipeptides with HCl to produce the done, rotate the plate 90° and repeat with a different solvent,
separate amino acids. gives more accurate results.
Secondary structure: the folding of proteins due to 30.3 Enzymes:
hydrogen bonding in the same peptide. Creating either
an alpha helix or beta-pleated sheet shape. Enzymes: proteins that speed up the rate of reaction by
finding an alternative pathway with a lower activation
energy two there’s more successful collisions.
I
Alpha helix Beta-pleated sheet The active site of an enzyme is stereospecific therefore
·
only fits a certain substrate / one of the enantiomers, if a
reaction is not catalysed by the reaction its because the
substrates tertiary structure is not complimentary to the
specific tertiary structure of the enzymes active site
• more flexible • more rigid therefore it won’t bond to it.
• Spherical shapes • Layered, straight chains Due to this idea drugs / inhibitors can slow their function
• H bonds stretch • H bonds occur between as they can have a similar tertiary structure to the
sheets substrate and bond to the active site instead, this can
cause poisoning of the enzyme.
Tertiary structure: the 3D shape of a protein that’s
specific to each protein depending on the bonding Enzymes can denature from temperature, pH or
present. poisoning breaking the bonds in the tertiary structure so
• hydrogen bonding between the carboxyl and the it can no longer catalyse a certain reaction as the
amine group enzyme-substrate complex will no longer form.
• Ionic attractions between side chains on the amino
acids
• Sulphur-sulphur bonds, two amino acids must
have sulphur groups
• Van der waals
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