quiz 3 Flashcards
describe myoglobin
a monomer
small and compact
where is myoglobin found? why?
muscle tissue for oxygen storage
what does myoglobin contain
8 alpha helices
prosthetic heme groups
what does myoglobin do
reversibly binds O2
describe hemoglobin
a porphyrin ring system in a hydrophobic pocket with an iron at the center for covalent bonds
how can the iron be formed
can be ferrous (Fe2+) or ferric (Fe3+)
what are the 6 coordination sites of ferrous iron
4 pyrrole N
1 proximal histidine
1 O2
1 histidine to O2
what function does histidine play
keeps heme coordinated in protein
keeps other hemes from binding
define binding affinity
ligand (L) binding to protein (P)
BA equations:
P+L=PL
Keq=PL/[P][L]
Ka= PL/[P][L]
dissociation: Kd=[P][L]/[PL]
what does an increased Ka cause?
stronger binding
what does an increased Kd cause?
weaker binding
what is the equation for fractional saturation
occupied binding sites/total binding sites
OR
[PL]/[PL]+[P]
describe a stronger binding
left curve
lower Kd
less [L] needed
describe a weaker binding
right curve
higher Kd
more [L] needed
define hyperbolic
one binding site
define KD
concentration of O2 when half of mb binds to O2
where is hemoglobin found
in red blood cells
define heterotetramer
4 subunits
define cooperative binding
binding of ligand to one site increases binding affinity for another ligand at another site
describe deoxygenated
heme is domed and nonpolar
describe oxygenated
heme is planar and polar
describe deoxyhemoglobin
no bound O2
heme ring is not planar
describe oxyhemoglobin
O2 is bound
heme ring is planar
relaxed (R) conformation
describe conformational switch
O2 binding pulls iron into plane of heme
histidine is pulled up with iron
entire F helix moves
define allostery
conformational switches underlie cooperatively
transmits change in one subunit across the interface of the next subunit
15° rotation
describe concerted heme bonding
protein found at T or R
binds to single subunit
stabilizes R state
more complex
describe sequential heme bonding
protein found at T and R
does not convert only to R state
alters affinity of adjacent subunits
shifts equilibrium to R state
describe positive effectors
increase Hb affinity for O2
shifts equilibrium to R state
describe negative effectors
decreases Hb affinity for O2
shift equilibrium to T state
