Peptides and proteins Flashcards
a peptide bond is
the bond formed by a condensation reaction between the carbonyl group of one amino acid and the amino group of another amino acid
when two amino acid molecules react together, an acid-base reaction occurs whereby:
the OH from the COOH group combines with a H atom from the NH2 group to form water while the two amino acids join together through an amide group (CO -NH). this bond is known as a peptide bond
the organic product formed is a dipeptide
when amino acids react together to form a dipeptide, there are always two (and sometimes more) possibilities for the reaction because
the OH could be lost from either molecule
the two possibilities for the reaction between glycine and alanine are:
alanine + glycine:
H2N-CH(CH3)-COOH + H2N-CH2-COOH → H2H-CH(CH3)-CO-NH-CH2-COOH + H2O
glycine + alanine:
H2N-CH2-COOH + H2N-CH(CH3)-COOH → H2N-CH2-CO-NH-CH(CH3)-COOH + H2O
proteins are extended and complex …………………. chains
polypeptide chains
proteins have very large
molar masses
the polypeptide chains in a protein can be broken down into their individual amino acids by
prolonged heating with concentrated hydrochloric acid which breaks the peptide bonds between the amino acids, although all the amino acids formed will have protonated NH3+ groups due to the acidic conditions
the equation for the hydrolysis of dipeptide formed with alanine and glycine (in that order) is:
H2H-CH(CH3)-CO-NH-CH2-COOH + H2O + 2H+ → H3N+-CH(CH3)-COOH + H3N+-CH2-COOH
we can use chromatography to identify the different amino acids in a mixture of amino acids by:
spotting the different amino acids onto chromatography paper and spraying the chromatogram with a developing agents because all amino acids are colourless, so helping to identify where each amino acid rises to (ninhydrin is such a developing agent, though it is toxic so used less widely nowadays).
then the Rf value can be calculated so the individual amino acid can be identified
