chem Flashcards
(17 cards)
What is Phosphorylation?
Catalyzed by kinases. Transfers γ-phosphate from ATP → hydroxyl group on Ser/Thr/Tyr.
What is Challenge 1 of Phosphorylation?
Alcohol OH is a poor nucleophile → needs activation.
What is Challenge 2 of Phosphorylation?
Builds high charge in transition state → needs electrostatic stabilization.
What is Mechanism Step 1 of Phosphorylation?
Base (e.g., Asp) activates OH (→ O⁻).
What is Mechanism Step 2 of Phosphorylation?
O⁻ attacks ATP’s γ-phosphate.
What is Mechanism Step 3 of Phosphorylation?
Transition state stabilized by Mg²⁺ and Lys.
What is Mechanism Step 4 of Phosphorylation?
ADP leaves as a by-product.
What is the PPP Type of Phosphatase?
Uses 2 metals to activate OH⁻; His donates proton to leaving group.
What is the PPM Type of Phosphatase?
Uses 1 metal; Glu donates proton, Arg stabilizes charge.
What is the Asp-Based Type of Phosphatase?
Asp attacks phosphate forming phospho-aspartate intermediate, which is then hydrolyzed.
What is ADP-Ribosylation?
Transfers ADP-ribose from NAD⁺ to target protein. Clear, non-spontaneous, reversible signal.
What do PARP and PARG do?
PARP adds ADP-ribose units; PARG removes them.
How do pathogens use ADP-Ribosylation?
Bacterial toxins use NAD⁺ to modify proteins like actin, disrupting function.
What is Methylation?
Adds methyl groups to Lys/Arg or DNA. SAM (S-adenosylmethionine) is the methyl donor.
What is Mechanism Step 1 of Methylation?
Base activates Lys/Arg → neutral nucleophile.
What is Mechanism Step 2 of Methylation?
Nucleophile attacks CH₃ on SAM; positive S facilitates leaving.
What is Demethylation?
Flavin-based oxidative demethylation → generates formaldehyde. Energetically challenging.
