Topic 4 Flashcards
function of protein determined by…
primary structure
myoglobin is a ….
monomer, no quaternary structure
Hemoglobin is a …..
oligomer, has quaternary
function of hemoglobin
binds O2 in the lungs and then releases in tissues
function myoglobin
binds O2 in muscle cells as ligand
local reserve of O2 during intense exercise
function of proteins depends on….
binds ligands reversibly
Kd is ____ if _____ is greater
smaller, affinity
the greater the affinity , the concentration is
higher
Structure of myoglobin
monomer, single polypeptide, hydrophobic pocket between helix E and F
Structure of Heme
- prosthetic group
- circular and planar
- large aromatic
- polar surface exposed, hydrophobic core
Porphyrin ring
Fe 2+ ion surrounded gy 4
Porphyrin ring
Fe 2+ ion surrounded by 4 N and 2 other bonds
5th coordination
His binds to Heme
6th coordination
attracts O2 by H-bonds
proximal histidine (F8)
binds heme in heme pocket, prevents oxidation of iron atom, 5th coordination
distal histidine (E7)
increases O2 binding affinity, lowers affinity for other molecules, increased specificity for O2, 6th coordination
O2 binding to myoglobin is a ____ plot and the reaction is ____
hyperbolic, reversible
Hemoglobin is a ____ (quaternary structure)
heterotetramer (2a and 2b)
3 polypeptides with 8 a-helices
alpha globin, beta globin, myoglobin
when proteins are homologous
they have the same ancestor, similar structure, similar function
how many O2 bind to Hb
4
how many O2 bind to Mb
1
Conservative substitutions
minor effects on structure and function
critical substitutions
change structure and function
Hyperbolic curve
constant affinity (Mb)
Sigmoidal curve
cooperative binding affinity (Hb)
Cooperatvie binding affinity
affinity changes as more ligand bind
Mb vs Hb
similar functions, Mb within tissue,Hb lungs and tissue
Tense state
low O2 affinity, deoxy Hb, large central cavity, His between Thr and Pro
Relaxed state
high O2 affinity, oxygen Hb, smaller central cavity, His between 2 Thr
Effector
alter affinity at other binding sites upon binding
Homoallosteric
binding of same compound effects itself
Heteroallosteric
binding of different compound affects itself
Activator , +
increase binding affinity
Inhibitor , -
decrease binding affinity
O2 is a ____ activator of Hb
homoallosteric
BPG is a ___
heteroallosteric inhibitor
H+
heteroallosteric inhibitor
Bohr Effect
changes pH to diminish H2O binding
metabolism generates H+ > lowers pH > Side chains protonate > BPG binding enhances
Increased BPG =
decreased O2 binding
BPG binds in (state)
T-state
high pH =
high BPG, low O2
why is this important
pH of lungs is low so O2 binding high, pH of tissue is high so O2 released
Sickle cell anemia
Glu replaced with Val, critical sub
Fetal Hb
higher O2 affinity
4 His in central cavity
BPG binding
