F234: Module 2: Amino acids, proteins and peptides Flashcards
I) What is the general formula for an Amino acid?
RCH(NH2)COOH
It has both an amine and carboxylic acid group.
I) Why do Amino acids exhibit optical isomerism and what is the only structure where they don’t?
They exhibit optical isomerism because the central (chiral) carbon has 4 different groups bonded to it. This means that if you reflected the structure of the amino acid in a mirror, you would get a non-superimposable image (optical isomer) of the amino acid.
The only case where this isn’t true is if the ‘R’ group is another Hydrogen in which case the central carbon has 2 hydrogens bonded to it and therefore can’t exhibit optical isomerism.
I) Whats the name given to molecules that and act as both an acid and a base?
Amphoteric
I) What do most amino acids look like?
White crystalline solids.
I) What happens to an amino acid at low pH values?
In low pH values, the NH2 group is likely to be protonated forming an NH3+ ion.
Alternatively, using the zwitterion as a starting point, the COO- is likely to accept a proton forming a COOH group.
I) Define the term isoelectric point and state what happens to an amino acid at its isoelectric point?
How does this affect the melting and boiling points of an amino acid?
The isoelectric point of an amino acid is the point at which the average overall charge of an amino acid is zero.
At the isoelectric point, the amino acid forms a zwitterion with NH3+ and COO- groups.
The positive and negative charges on individual zwitterions mean that zwitterions become attracted to each other, forming ionic bonds which raises their melting points.
I) What happens to an amino acid at high pH values?
In high pH values the COOH is likely to loose a proton forming a COO- ion.
Alternatively, using the zwitterion as a starting point, the proton on the NH3+ ion is likely to be removed forming an NH2 group.
I) What happens to the isoelectric point when the ‘R’ group is basic (there are 2 amino groups)?
The isoelectric point is raised to a higher pH value.
I) What happens to the isoelectric point when the ‘R’ group is acidic (there are 2 carboxylic acid groups)?
The isoelectric point is moved to a lower pH value.
I) What are proteins in terms of amino acids?
Proteins are chains of amino acids linked by peptide bonds.
I) What is a peptide bond?
The CONH link
I) Why are proteins considered condensation polymers?
Because proteins are formed from amino acids by the loss of water as the peptide bonds are formed.
The OH from the COOH group and an H from the NH2 group combine to form water.
I) What is a dipeptide and why might they be used in an exam question (I had to get this in….sorry)?
A molecule composed of 2 amino acids.
Dipeptides are interesting because they can combine in different ways to form compounds with different structures.
I) How would you get individual amino acids back from a polypeptide?
By Hydrolysis which involves the addition of water to break the peptide bonds.
I) Describe the process of hydrolysis to split up a polypeptide into its constituent amino acids.
A polypeptide is refluxed with water and concentrated HCl for a few hours. It is hydrolysed and is split up into its constituent amino acids. This is known as acid hydrolysis.
