Lecture 17 - Biological Molecules I Flashcards
all amino acids except _______ are chiral
glycine
an oligopeptide contains:
3-10 amino acids
quaternary structure:
spatial arrangement of subunits
primary structure refers to:
the sequence of individual amino acids in a chain
the secondary structure of a protein refers to:
the regions of ordered structure adopted by the chain (e.g: a-helix & b-sheet)
quaternary structure refers to:
the association of several subunits to a closely packed system
protein structures is maintained by (3):
(1) electrostatic attractions
(2) hydrogen bonds
(3) van de walls interactions
in neutral solution amino acids exist in:
their zwitterionic form
the pKa of a protonated amino acid is:
around 9
the state of protonation of the amino acid groups can be altered by:
altering the pH of the solution
what does pKaH refer to?
pKaH refers to the pKa of the conjugate acid
why is there double bond character in an amide (peptide) bond?
there is double bond character due to the resonance and free rotation is not possible
why is the trans form favoured in the peptide bond?
the trans form is favoured due to steric hinderance
cleavage of the peptide bond:
chemically the slide bond is difficult to cleave, it can however be achieved by heating a base (NaOH) but the conditions are harsh
why are amide bonds hard to make and how to get around it?
amide bonds are hard to make due to the amines and carboxylic acids having their acid base properties
in order to get them to react the carboxylic acid usually has to be activates (i.e: converted into an acid chloride or an activated ester)
