Special AAs Flashcards
1
Q
Cysteine
A
- has SH group, which can become oxidized with another cysteine SH group to form dimer, cystine (only in oxidizing env - so not in cell; ex: extracell. proteins or domains)
- forms disulfide bonds
- many extracellular proteins stabilized by disulfide bonds (ex: albumin - blood protein that transports); adds stability and rigidity
- the one exception to the rule that proteins are linear
2
Q
Proline
A
- side chain and alpha amino N form rigid, five membered ring (imino acid) - very bulky, steric hindrance
- contributes to fibrous structure of collagen and often interrupts alpha helices in globular proteins
- NH2 (instead of NH3) loses its H when incorporated into chain, so no H for H bonding
- only AA that can form cis configuration (~15%) so can stabilize a turn
- not in helices and sheets, but in loops and coils, so often on surface even though hydrophobic
3
Q
Glycine
A
- only achiral AA, so optically inactive (side chain is H)
(all other AAs are chiral and have two forms D and L; all AAs in proteins are L but D AAs are in some antibiotics and plant and bacterial cell walls)
4
Q
Histidine
A
- basic and largely uncharged at pH 7 but can be pos or neg charged when incorporated into a protein
- pka can come very close to phys pH so used to regulate enzyme activity or protein-protein reactions; use more for regulation than in protein structure
5
Q
AAs that are sites for phosphorylation
A
Ser, Thr, Tyr
6
Q
AAs that are sites for glycosylation
A
Ser, Thr, Asn
7
Q
AAs that can be in both interior and surface of proteins
A
Trp and Phe (bc of aromatic rings which give it polar character for surface, but also bulky for interior)
8
Q
Glutamic Acid
A
plays role in metabolism as Nitrogen donor (can donate from two sources)
major component of cytoplasm
