Amino acids, peptides and proteins Flashcards
Amino acid
A class of organic compound with at least one amino group and one carboxyl group
Peptide
An organic compound formed from the linking of <= 50 amino acids
Peptides are written from their…
…N to C terminus.
Protein
Macromolecules consisting of one of more polypeptide chains linked via non-covalent or dithiane interactions
Functions of proteins
Enzymes
Transporters
Regulatory proteins
Conjugated proteins
Have additional groups that may or may not be covalently bound
e.g. glycoproteins, lipoproteins, nucleoproteins, metalloproteins
Secondary structure
Interactions between amino acids in the same polypeptide chain
Alpha-helix
H bond interactions between the carbonyl of one amino acid (i) and the amine of another amino acid (i+4)
Which amino acids disfavour alpha-helix formation?
Amino acids with bulky R groups e.g. V T I
Charged amino acids e.g. S D N
Glycine (flexible)
** Alpha-helices are broken by proline due to its locked structure **
Beta-sheet
H bonding of amino acids through space
Can be parallel or anti-parallel depending on the N–>C direction of the chains
Beta-turn
A number of short turns that cause beta-sheets to form through folding of peptide chains back on themselves
Usually involve 3 amino acids (i) and (i+3)
Tertiary structure
How all the polypeptide chains fold together to form the protein
Examples of tertiary structures
Coordination of metals
Disulfide bridges
Ionic interactions
Hydrophobic interactions e.g. Leucine zipper
Leucine zipper
= coiled-coil
The vdW interaction between a pair of amphipathic alpha-helices through their hydrophobic faces
Amphipathic
Having both hydrophilic and hydrophobic parts
