FOUR MAJOR FUNCTIONAL GROUPS:
Physiological
Switching
Inhibition
Catalysis
Binding
Modification
Structural
How is amide bond formed
reduction
oxidation
hydrolysis
dehydration
addition
The acidity of the carboxylic acid is due to....
overall bonding
the charge of the carboxylate residue
stability of the carboxylate anion relative to the acid
charge distribution
when the charge of the carboxylate resides two equivalent electronegative oxygens the structure is called
resonance form
protonated form
assymetric form
chiral form
pKa values vary somewhat depending on
the environment in which the acid-base chemistry is taking place.
how homogenous is the solution
the temperature of the solution
the precise molecular structure
The corresponding carboxylate anion is more stable in the presence of the adjacent, positively charged, ammonium ion, therefore
the carboxylic acid group of glycine is more acidic than a simple carboxylic acid since
the simple carboxylic acid is more acidic than the carboxylic acid group of glycine
The effect of environment on pKa is particularly important in non-polar conditions such as..
the outer part of the protein
the interior of a protein
the acidic part of the protein
the basic part of the protein
What stereoisomers predominate in nature
L-amino acids
D-amino acids
Into which groups can amino acids be divided
suphur containing side chains
amino acids with hydrocarbon side chains
acyclic with basic N containing side chains
hydroxyl functional groups
hydrophobic side chain
nitrogen heterocycles and proline
amide side chains
hydrophilic side chains
carboxylic acid side chains
phosphorus containing side chains
Which amino acid imparts unusual structural flexibility
Glycine
Guanine
Proline
Serine
What amino acid has two chiral centres due to the both of its α and β- carbons being asymmetric, and therefore has four possible stereoisomers.
Cysteine
Valine
Isoleucine
Glutamine
Confer negative charge on proteins because their side chains are ionised at pH 7, under physiological conditions acidic side chains exist as the conjugate base
arginine
histidine
glutamate
aspartate
The most basic of the 20 amino acids.
Histidine
Lysine
Asparagine
Arginine
The pKa of this protein is around pH 7 and thus at physiological pH it can act as either an acid or a base. This makes it especially important in acid-base catalysis and it has an important role to play in many enzymes. It also forms complexes with zinc in proteins which has importance for both structure and mechanism.
Alanine
Methionine
Tryptophan
Fill in the blanks
Contains a non-polar methyl thioether group. This makes it one of the more hydrophobic amino acids
methionine
serine
threonine
cysteine
The hydroxymethyl group of this amino acid does not appreciably ionise at physiological pH. Essentially hydrophilic.
The side chain is somewhat hydrophobic, but also extremely reactive. It is polarisable and can lose its proton to bercome the thiolate anion. Can form disulphide bridges in proteins.
Has two chiral centres and thus can have four stereoisomers
The formation of disulphide bonds in proteins is an important teriarysecondaryquaternaryprimary( secondary, primary, teriary, quaternary ) structural feature. This helps to impart reactivityaciditystabilityinertness( stability, acidity, reactivity, inertness ) and conformational rigidity to some proteins
This amino acid is unique in that its three carbon side chain is bonded to both the α carbon and the α amino group. The heterocyclic pyrrolidine ring created restricts the geometry of polypeptides.
tyrosine
proline
aspertate
valine
This amino acid has a hydroxyl function associated with the phenol ring. Acid base chemistry is facilitated as the ring enhances the stability of the conjugate base. It can sometimes act as an acid.
tryptophan
phenyalanine
Phe, Tyr and TrpSer, Thr and CysLys, Arg, HisVal, Leu, Ile( Phe, Tyr and Trp, Ser, Thr and Cys, Val, Leu, Ile, Lys, Arg, His ) are all highly aromatic and can absorb UV light at 280nm. Proteins have an optical density at 280nm because of these side chains
drag the appropriate amino acid to the blank space
The more hydrophilichydrophobic( hydrophobic, hydrophilic ) amino acids have a tendency to be sequestered away from the solvent towards the inner partouter partcentre( centre, inner part, outer part ) of protein molecules. This provides one of the major driving forces for protein bindingfoldinginhibition( folding, binding, inhibition )
hydrophobicHydrophilic( Hydrophilic, hydrophobic ) residues tend to interact with the solvent more easily via hydrogencovalent( hydrogen, covalent ) bonding and thus can be on the insideoutside( outside, inside ) of proteins.
Under physiologicalcellular( physiological, cellular ) conditions this effectively restricts the peptideionic( peptide, ionic ) bond to one of two configurations: cis or trans To minimise steric crowding due to close proximity of bulky groups on th carbonyl carbon and the nitrogen the cistrans( trans, cis ) form is favoursed, except where HistidineProline( Proline, Histidine ) is involved.
Proline has an carboxylalkyl( alkyl, carboxyl ) chain rather than a oxygenhydrogen( hydrogen, oxygen ) atom as the thirdsecond( second, third ) substituent on nitrogen In amides containing proline the trabscis( cis, trabs ) form is not dramatically disadvantaged In proteins about 5%15%10%( 10%, 15%, 5% ) of all peptide bonds involving proline are cis.
THE SHAPE OF POLYPEPTIDES IS DEFINED BY SPINROTATIONMOMENTUMSIDE CHAIN( ROTATION, SPIN, SIDE CHAIN, MOMENTUM ) ABOUT THE C-N AND C-C BONDS
All atoms around the peptide bond lie in a cistransplanarprimary( planar, primary, cis, trans ) conformation. This rotation is described by the torsion angles φ Phi between C-NC-C( C-N, C-C ) and ψ Psi between C-N.C-C.( C-C., C-N. ) If all psi and phi angles are the same the peptide assumes a repeatedsaturated( repeated, saturated ) structure. For certain combinations of angles this can take the form of a coil structurehelical stucture (the alpha helix)( helical stucture (the alpha helix), coil structure ) or a beta-sheet structure. Clearly the peptide structure exhibits motitlityflexibility( flexibility, motitlity ) and this is important for the complex structurebinding( structure, binding ) of proteins.
What characteristic of atoms and groups of atoms limits the possible psi and phi torsion angles that the backbone of the polypeptide chain can adopt without causing protruding R groups to bump into each other.
The flexibility
The chemical properties
The physical size
The amount
The Ramachandran plot shows the allowed
binding of the protein
carboxyl and amino groups
secondary structure of the protein
psi and phi angles
Label the chemical structure
Amino acids with basic R groups
Aspargine
Phenylalanine