Amino acids and proteins Flashcards
What groups do amino acids have?
An Amino group which is basic and Carboxyl group which is acidic. This means amino acids are amphoteric.
Are amino acids chiral and why?
Amino acids (except glycine) are all chiral as they have 4 different groups around a central carbon atom. They rotate plane polarised light.
What are zwitterions and when are amino acids zwitterions?
A zwitterion is a molecule that has both positive and negative ions. They only exist at the amino acid’s isoelectric point.
If pH is lower than the isoelectric point what happens to the amino acid?
The amino group has a positive charge (-NH3(+)).
How can amino acids be separated and identified?
Amino acids can be separated and identified by thin-layer chromatography as they have different solubilities.
How can you identify amino acids on a chromatogram?
Amino acids can be located on a chromatogram using developing agents such as ninhydrin or ultraviolet light and identified by their Rf values.
How are Rf values used to identify amino acids on a chromatogram?
Rf value = distance travelled by spot / distance travelled by solvent
Then compare to a library of Rf values (the number of spots says how many amino acids there are).
In what conditions is a protein broken down into its constitutent amino acids?
The protein can be broken down through hydrolysis although requires severe conditions. 6moldm^-3 HCl, 383K and reflux for 24 hours.
What causes the secondary structure of polypeptides?
The hydrogen bonds between amine group H (delta positive) and carboxyl group O (delta negative). They twist to form alpha helices and beta-pleated sheets.
Which bonds hold the specific 3D shape of tertiary proteins?
Disulphide bonds (cysteine contains -SH that lose hydrogens to form S-S bonds. Also hydrogen bonding.
What can change the shape of proteins?
Temperature and pH.
