Amino Acids (Zhao L1) Flashcards
What gives each amino acid its unique properties?
The side chain.
Amino acids are ______ at physiologic pH.
dipolar
NH3+
COO-
What is the bond between two adjacent amino acids in a polypeptide?
peptide bond
between the O on the N-terminal aa and the N on the C-terminal aa
What 5 major classes of aa’s are there?
- Nonpolar - aliphatic
- Polar - uncharged
- Negatively charged (acidic)
- Positively charged (basic)
- Aromatic
Which aa. can form disulfide bridges within a polypeptide?
Cysteine
-CH2-SH
What are the aromatic amino acids?
Phenylalanine
Tyrosine
Tryptophan
What are the negatively charged amino acids?
Aspartate
Glutamate
What are the positively charged amino acids?
Lysine
Arginine
Histidine
What are the polar uncharged amino acids?
Serine Threonine Cysteine Asparganine Glutamine
What are the nonpolar amino acids?
Glycine Proline Alanine Valine Leucine Isoleucine Methionine
What aa. modification is vitamin K essential for?
gamma-carboxylation of glutamate —> carboxyglutamate
What aa. modification is Scurvy related to?
Hydroxyproline
What tissue type is hydroxyproline found in?
Collagen
promotes collagen stability
allows “sharp twisting” in the collagen helix
What vitamin is required for hydroxylation of proline?
Vitamin C
Lack of vitamin C can lead to…
lack of hydroxyproline necessary for collagen
—> scurvy
In what common physiological response pathway is carboxyglutamate found?
The clotting cascade
What vitamin is required to induce the gamma-carboxylation of clotting factors (at their glutamate residues)?
Vitamin K
What is the pI of a protein?
The pH where the protein will have no net charge.
Where is Histidine often found and why?
pKa of His is 6.5
very close to physiological pH
can switch from neutral to + charged easily under phys. pH
Is often found in the active sites of enzymes
When pH<pKa which form of the aa dominates?
The protonated form.
Think about what low pH means…high [H+]
Think of pKa as the aa’s tolerance level for resisting protonation.
Henderson-Hasselbach eqn
pKa = pH + log[Acid]/[Base]
pH = -log[H+] pKa = -log( [Base] / [Acid][H+] )
standard prod/react business
Name three aa’s that are typically glycosylated (cell surface proteins) and what type of glycosylation linkage each has.
- Ser: O-linked
- Thr: O-linked
- Asn: N-linked
Give an example of the clinical relevance of glycosylation of cell surface proteins.
CDG: Congenital disorder of glycosylation
abnormal N-linked glycosylation pathway (Asparagine)
Giant range of symptoms and severity
Give an example of a protein that has a lot of post-translational acetylation and methylation.
Histones.
What does vorinostat do?
Inhibits histone deacetylases (HDAC)
Used in cancer treatments
Where can you generally phosphorylate / dephosphorylate amino acids post-translation?
Which aa’s receive this post-transl. modification?
On -OH groups
Ser -CH2-OH
Thr -CH(OH)-CH3
Tyr -C-(Ph)-OH
What does Ubiquination of a protein signal?
Marks the protein to be sent to the proteosome to be degraded.
What does Velcade do?
Inhibits ubiquintination and the proteosome.
Used to treat Multiple Myeloma
