Amino Acids And Chirality Flashcards
Amino acids exist as…….. at a ph value called the…….
Zwitterion
Isoelectric point
State the general formula for an α-amino acid
RCH(NH2)COOH
Why do the isoelectric points differ for different amino acids?
Different R groups result in different isoelectric points
Explain the properties of an α-amino acid at a pH more acidic than the isoelectric point
At a pH more acidic than the isoelectric point, the amino acid acts as a base and accepts a proton from the acid, the N becomes positively charged
RCH(NH2)COOH + H+ –> RCH(NH3+)COOH
Explain the properties of an α-amino acid at a pH more alkaline than the isoelectric point
At a pH more alkaline than the isoelectric point, the amino acid behaves as an acid and donates a proton, the O becomes negatively charged
RCH(NH2)COOH + OH- –> RCH(NH2)COO- + H2O
What is a peptide bond?
O=C-NH
How are peptides formed?
When two amino acids join together a dipeptide is formed with the elimination of a water molecule. This is a condensation reaction
Define condensation reaction
Two small molecules react together to form a larger molecule with the elimination of a small molecule eg water
What is a protein?
Long polypeptides
Describe the acid hydrolysis of a polypeptide
Water and 6moldm^-3 HCl are added to the peptide and is heated under reflux
The N atoms become positively charged (NH3+ at the end)
Describe the alkaline hydrolysis of polypeptides
Aqueous NaOH is added to the peptide, and is heated to around 100C
Carboxylate salts are formed (COO-Na+)
Define optical isomers
Non-superimposable mirror images about an organic chiral centre
Name 2 types of stereoisomerism
Optical isomerism, E/Z isomerism
Define chiral carbon
A carbon atom attached to 4 different atoms or groups of atoms
