Chapter 30 (Amino Acids, Proteins and DNA) Flashcards
What is the R group for Glycine?
H
What is an alpha amino acid?
The NH2 and COOH groups are attached to the same C
Why are amino acids optically active (except glycine)?
They have a chiral carbon as there are four different groups on the central C so they rotate plane polarised light.
What is a zwitterion?
The dipolar form an amino acid takes in neutral conditions with [NH3]+ group and [COO]- group.
Why do amino acids have a high melting point?
Ionic interaction between zwitterions
What happens to an amino acid in a high pH?
COOH loses H and forms COO-
What happens to an amino acid in a low pH?
NH2 gains a H and forms NH3+
What are dipeptides?
Combination of two amino acids with one amide (peptide) link
How are amino acids split?
Heated with concentrated hydrochloric acid or concentrated strong alkali and then salt into 2 amino acids
How are amino acids separated?
Chromatography
Describe the method for thin layer chromatography?
1) Wearing gloves, draw a pencil line 1cm above bottom of TLC plate and mark spots for each sample, equally spaced along line.
2) Use a capillary tube to add a tiny drop of each solution to a different spot to allow the plate to air dry.
3) Add solvent to a chamber or large beaker with a lid so that is not more than 1 cm in depth.
4) Place the TLC plate in the chamber, make sure that the level of solvent is below the pencil line. Replace the lid to get a tight seal.
5) When the level of the solvent reaches about 1cm from the top of the plate, remove the plate and mark the solvent level with a pencil. Allow the plate to dry in the fume cupboard.
6) Spray paper with ninhydrin/shine UV light to see spots.
7) Calculate Rf values of the observed spots.
Why id the line drawn in pencil in TLC`?
Will not dissolve into solvent
Why is only a small drop of amine acid used in TLC?
Big drops could merge together
Why is the solvent below the pencil line in TLC?
If above then the samples from the plate will dissolves into the solvent.
Why is a lid put on the experiment in TLC?
Prevents evaporation of a toxic solvent.
Why is the plate dried in a fume cupboard in TLC?
The solvent fumes are toxic.
How do you increase the accuracy of the Rf value in TLC?
Allow the solvent to rise to near the top of the plate.
What is the equation for Rf value?
Distance moved by amino acid/distance moved by solvent
Describe the primary structure of proteins
Sequence of amino acids joined together by condensation reactions to form peptide links.
Describe the secondary structure of proteins
Hydrogen bonding between N-H and C=O groups of the peptide links along the polypeptide chains.
Describe the structure of a beta-pleated sheet protein
Parallel regions of proteins lined up with hydrogen bonds between them leading to a slat, sheet-like structure.
Describe the structure of an alpha-helix protein
Hydrogen bonds are formed every four amino acids, forcing the chain in a cylindrical formation. The structure is elastic and flexible e.g. keratin.
Describe the tertiary structure of proteins
The 3D shape of the protein held together by H hydrogen bonding, ionic interactions and disulphide bonds between the R-groups of the amino acids.
How are disulphide bonds broken?
Heat, reduction or a reaction with a base
What type of reaction is the digestion of proteins?
Hydrolysis
What is the function of enzymes?
Act as biological catalyst, providing an alternative reaction with a lower activation energy.
Describe the lock and key hypothesis
Substrates must have the right shape to fit into the active site.
What is the isoelectric point of an amino acid?
The pH at which it has no overall charge.
The point midway between the two pKa values of its two functional groups.
What is a fibrous protein?
Long chains of polypeptides found in bundles and insoluble in water.
What are globular proteins?
Polypeptide chains folded into roughly spherical shapes that are soluble in water.
What is a stereo specific active site?
An active site that binds one enantiomer of a racemate
How do some drugs act as enzyme inhibitors?
Block the active site to prevent the substrate from binding so no E-S complexes can form.
What are the key molecules in a DNA nucleotide?
Phosphate
Deoxyribose sugar
Nitrogenous base
How many hydrogen bonds are between each base pair?
AT = 2 CG = 3
How does cisplatin work?
1) The two chloride ions are displaced by water molecules.
2) The N lone pair on guanine form dative covalent bonds with Pt which is a ligand replacement reaction.
