Quiz 4 Flashcards
(37 cards)
Oxygen binding to myoglobin vs hemoglobin
myoglobin (monomer)
-mostly alpha helices
hemoglobin (tetramer)
-2 alpha subunits + 2 beta subunits (dimer of dimers)
What are the functions of the distal histidine vs the proximal histidine on hemoglobin
proximal - holds iron in place
distal - increases O2 bind
Draw out the histidine tautomers
find ss
Graph a binding curve
find ss
K_D = when half occupied/total
Dissociation constant
Kd = equilibrium constant for the breakdown of the receptor-ligand complex
Kd = [R][L]/[RL]
Low Kd = tight bind
Draw out the binding curve for why hemoglobin is best for O2 transportation in the body
find ss
- want medium transport protein binding in tissues = release (high Kd at high Po)
- want high transport protein binding in lungs = pick up + hold (low Kd at low Po)
Assumptions for law of mass action
- all receptors are equally accessible
- no partial binding
- binding does not alter receptor
- binding is reversible
Hill plot
- graph
- formula
find ss
1. x-intercept = log(Kd)
2. slope = hill coefficient
What info can we deduce from the slope of a hill plot?
slope > 1 = tell # ligans bound per protein
slope < 1 = tell nothing, negative cooperation
Cooperation and its two different affinity states. Draw them + the difference.
T = low affinity (open, more salt-bridges)
R = high affinity (closed, no salt-bridges)
Two main models of allosteric binding
allostery = uptake of one ligand by a receptor ultimately affects the next ligand
Sequential model (KNF)
-bind one at a time (low to high affinity)
Symmetry model (MWC)
-ligand binding shifts from one state to other, for all receptors, all at the same time
Difference between homotropic and heterotropic effectors
homotropic - bind to an active site
heterotropic - bind to a distant regulatory site
can be positive (Hb) or negative effectors (BPG)
How does BPG work as a negative effector?
2,3-bisphosphoglycerate
- bind to T state and crowds binding so no O2 bind
What is the Bohr effect?
allow more O2 to be released in low O2 areas to promote oxidative phosphorylation
Draw the enzyme energy before and after catalysis
find ss
velocity of a reaction (v) formula
v = k[S]^n
velocity = in Ms-1
k = rate constant
[S] = substrate concentration
n = order of reaction
reaction rate (k) formula
k = Ae^(-∆Gº(TS)/RT)
A - given
R - given
TS = transition state
Two ways to increase the rate of reaction
- increase T
- decrease ∆Gº (TS)
Weak binding drives enzymatic ______
catalysis
∆∆Gº(TS) > 0 =
∆∆Gº(TS) < 0 =
greater than 0 = u > c (E compliment TS)
less than 0 = u < c (E compliment S)
Four contributions to ∆Gº (TS)
- loss entropy
- increase weak interactions
- substrates desolvaded to free
- induced fit from S binding
Michaelis-Menton velocity
v = kcat[ES] or
v = Vmax[S]/Km + [S]
(Km = [S] at half Vmax)
(Vmax = Kcat[E]total)
Michaelis-Menton enzyme equation
find ss
Equation for enzyme efficiency
kcat/Km
