Signaling Enzymes Introduction Flashcards
Chapter 3
What are the basic examples of signaling enzymes?
kinases, phosphatases, and G proteins (GAPs and GEFs)
What do signaling proteins do?
they convert conformational changes into catalytic activity changes
Signaling proteins often act as ____.
switches
How do enzymes speed up a reaction?
By reducing the free-energy barrier
Which enzyme is on the top arrow and which is on the bottom arrow?
Top: kinase “writer”
Bottom: phosphatase “eraser”
one adds phosphate and one takes it away
What are the different mechanisms where an enzyme can lower the activation energy?
a) binding and orienting reactive groups
b) providing acid & bases; achieves activation of an attacking nucleophile group
c) providing binding site; binding energy can reduce the FEB (ex. hydrolysis)
d) altering mechanism to form reaction intermediate with less of a FEB
What can enzymes not alter in a reaction?
deltaG
What do enzymes do to reach equilibrium?
they accelerate the approach to equilibrium
What three amino acids occur with phosphorylation?
tyrosine (unfavorable) & serine/threonin (neutral)
A kinase reaction is ____.
irreversible
Describe this form of catalysis
Enzyme orients two substrate molecules to be able to react with one another.
Describe this form of catalysis
Binding of the substrate rearranges electrons to allow for partial positive and negative charges to favor a reaction
Describe this form of catalysis
Enzyme strains the substrate to forcing it towards a transition state which favors a reaction.
The relative abundance of each species is determined by their ____.
Relative free energy
Which of these is the most stable?
A, A’, or A”
A
What does this represent?
ligand binding; reduces free energy of A’
What does this represent?
phosphorylation; reduces free energy of A”
What does this depict?
active-site conformation; different forms which the enzymes can take on due to allosteric binding
What kind of conformational change does this depict?
disorder/order transitions (secondary structure)
What kind of conformational change does this depict?
tetiary structure transitions
What kind of conformational change does this depict?
quaternary structure transitions
