3Amino acids Amino acids are the Lego Bricks of protein structure. Just like these bricks they have a direction with two different types of connection which fit together.Each has an N terminus and a C terminus.As a result all proteins have the same property and the N terminus is always called the beginning of the protein.
4Amino acid structure H R C C O O H N H 2 Alpha carbon (chiral if R is not –H)HSIDE CHAINRCCOOHCARBOXYLIC ACIDNH2PRIMARY AMINEIF ALL FOUR SITES ARE OCCUPIED BY DIFFERENT GROUPS THEN THE MOLECULE IS ASYMMETRIC
28Cysteine has a thiol/sulphydryl group. Like -OH but H is lost easily. can bond to other cysteines by a disulphide bond.binds to metals in proteins.H+Disulphide bondZn2+-:(anche Hg2+; Cu2+; Fe2+ ecc.)
29Metionine has a thioether group. binds to metals in proteins. Zn2+ H : 3HCCOO-CH2CH2SCH3HZn2+:SCHCHCCOOH22CHNH32(anche Cu2+; Fe2+ ecc.)
30Histidine is heteroaromatic. acts as a base - accepts a H+ at neutral pH; is thus positively charged.can bind metals instead.H+Zn2+:
31Tyrosine Phenol ring is a weak acid (pKa = 10) (can bind metals) H+ N 3HCCOO-CH2HHH+HHOHH-:OCHCCOOH2NH2
32Glycine has two hydrogens attached to the alpha carbon. has no D and L form.is found in flexible regions of the protein since its side chain is small.is a neurotransmitter.
33Proline ring joins alpha carbon to nitrogen two ways. no amide formed in proteins = imino groupforms very rigid bend in protein chainsa