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19 Cards in this Set

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  • Back
What AA R-groups are optically active in the UV range?
- Phe (250 nm)
- Tyr (280 nm)
- Trp (290 nm)
- His
- Cys
What are the charged AA?
- Asp
- Glu
- Lys
- Arg
What AA exhibit a (-) charge at physiological pH?
- Asp
- Glu
- each contain carboxyl groups with pK of ~4
What AA exhibit a (+) charge at physiologic pH?
- Arg
- Lys
- His
What AA are important metal ion chelators?
- Asp
- Glu
- Since they carry (-) charges, they can bind to (+) charges metal ions such as Ca and Zn
What AA are commonly modified? What are the modifications?
- Arg: methylation
- Lys: methylation, acetylation (histones, chromatin organization), ubiquitination (protein degradation)
- Ser: PO4-alation (signal transduction, O-linked glycosylation in cell surface proteins

- Thr: PO4-alation (signal transduction, O-linked glycosylation in cell surface proteins
- Tyr: PO4 alated in signaling molecules
What are the polar AA? What important feature do they all share?
- Ser
- Thr
- His
- Gln
- Asn
- They can be H bond donors and acceptors
What AA commonly form salt bridges?
- Asp
- Glu
- Thr
- Ser
What AA are often used O-linked glycosylation in cell surface proteins?
- Ser
- Thr
What AA is important in N-linked glycosylation?
- ASN
- in the context of the following sequence: NXS/T
What is one of the strongest bases that can exist at neutral pH? Why?
- His
- pK ~6
- two nitrogen atoms, one can act as a H-bond donor and the other as an H-bond acceptor
Why is DTT (or B-ME) often used in protein purifications?
- DTT and BME will reduce the covalent link for disulfide bonds in cysteine
- Oxidation forms the disulfide bonds, reduction breaks them
Disulfide bonds are often found in what environment?
- in an oxidative environment (i.e. outside the cell)
- many cell surface receptors, antibodies, hormones contain disulfide bonds
What are the aromatic AA?
- Phe
- Tyr
- Trp
What AA are often PO4-alated?
- Tyr
- Ser
- Thr
What are the hydrophobic AA?
- Ala
- Val
- Leu
- Ile
- Met
What AA is not chiral?
- gly
What AA are often found in turns?
- gly
- Pro
What bond angle is constrained in proline?
- the Phi angle (Ca-N bond) since the proline sidechain is covalently bound to the peptidyl-N