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myoglobin
myoglobin
109
Biochemistry
Undergraduate 3
02/12/2016
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Term
___________, with its single heme prosthetic group, exhibits a hyperbolic O2-binding curve.
 Definition
myoglobin
Term
___________ can adopt the deoxy (T) or oxy (R) conformation, which differ in O2-binding affinity.
 Definition
Hemoglobin
Term
The _________ effect and ________ alter hemoglobin's O2-binding affinity.
 Definition
Bohr BPG
Term
____________ can change hemoglobin's O2-binding properties and cause disease.
 Definition
Mutations
Term
__________, the first protein whose structure was determined by X-ray crystallography, is a small protein with relatively simple oxygen-binding behavior.
 Definition
myoglobin
Term
___________, a tetramer of myoglobin-like polypeptides, is a more complicated protein that functions as a sophisticated system for delivering oxygen to tissues throughout the body.
 Definition
Hemoglobin
Term
Hemoglobin is a monomeric Oxygen-binding protein.
true
false
 Definition
false.
myoglobin is monomeric oxygen-binding protein.
Term
_____________ is a small intracellular protein in vertebrate muscle.
 Definition
myoglobin
Term
Myoglobin's X-ray structure, determined by John Kendrew in 1959, revealed that most of myoglobin's 153 residues are members of _______ alpha helices (traditionally labeled A through H) that are arranged to form a ____________ protein with approximate dimensions of 44x44x25 A.
 Definition
eight globular
Term
Structure of sperm whale myoglobin. This 153-residue monomeric protein
consists of eight  helices, labeled A through H, that are connected by short ____________ links (the last half of what was originally thought to be the EF corner has been shown to form a short helix that is designated the F' helix).
 Definition
polypeptide
Term
The _________ group is shown in red.
 Definition
heme
Term
The heme group. The central _______ atom is shown liganded to the ______ N atoms of the _________ ring, whose pyrrole group are labeled A-D.
 Definition
Fe(II) four porphyrin
Term
The heme is a ____________ system, so all the Fe-N bonds are _________.
 Definition
conjugated equivalent
Term
The Fe(II) is also liganded to a ____ side chain and, when it is present, to ____.
 Definition
His O2
Term
Refering to the heme group; the six ligands are arranged at the corners of an ___________ centered on the Fe ion (octahedral geometry).
 Definition
octahedron
Term
Myoglobin contains a heme ________ group.
 Definition
prosthetic
Term
Myoglobin, other members of the globin family of proteins, and a variety of other proteins such as cytochrome c all contain a single ______ group.
 Definition
heme
Term
The _________ is tightly wedged in a hydrophobic pocket between the E and F helices in myoglobin.
 Definition
heme
Term
The heterocyclic ring system of heme is a ___________ derivative containing four ________ groups linked by methane bridges.
 Definition
porphyrin pyrrole
Term
Porphyrins vary in the substituents attached to rings _______.
 Definition
A-D
Term
The Fe(II) atom at the center of heme is __________ by four porphyrin N atoms and one Nfrom a His side chain.
 Definition
cordinated
Term
His F8 is the _______ residue of the F helix.
 Definition
eighth
Term
A molecule of __________ can act as a sixth ligand to the iron atom.
 Definition
oxygen (O2)
Term
His ____ hydrogen bonds to the O2.
 Definition
E7
Term
Two hydrophobic side chains on the O2-binding side of the heme, ________ and ________, help hold the hem in place.
 Definition
Val E11 Phe CD1
Term
This side chains (Val E11 and Phe CD1) presumably swing aside as the protein __________, allowing O2 to enter and exit.
 Definition
breathes
Term
When exposed to oxygen, the Fe(II) atom of isolated heme is irreversibly oxidized to ________, a form that cannot bind O2.
 Definition
Fe(III)
Term
___________ alters the electronic state of the Fe(II)-heme complex, as indicated by its color change from dark purple to brillian scarlet.
 Definition
Oxygenation
Term
The color of hemoglobin in venous blood is _____________.
 Definition
dark purple
Term
The color of hemoglobin in arterial blood is _______________.
 Definition
brilliant scarlet
Term
Under some conditions, the Fe(II) of myoglobin or hemoglobin becomes oxidized to Fe(III) to form ____________ or ______________, respectively.
 Definition
metmyoglobin methemoglobin
Term
These proteins are responsible for the brown color of old meat and dried blood?
_____________ and ______________
 Definition
metmyoglobin and methemoglobin
Term
In addition to O2, certain other small molecules such as ____, _____ and _____ can bind to heme groups in proteins.
 Definition
CO NO H2S
Term
Those compounds like CO, NO, and H2S bind with lower affinity than O2?
yes
no
 Definition
no.
These compunds bind with much higher affinity than O2, which accounts for their toxicity.
Term
_________ binds O2 to facilitate its diffusion.
 Definition
myoglobin
Term
Myoglobin major physiological role is to _________oxygen diffusion in _______.
 Definition
facilitate muscle
Term
The most rapidly respiring tissue under conditions of high exertion are __________.
 Definition
muscles
Term
The rate at which O2 can ___________ from the capillaries to the tissues is limited by its low _____________ in aqueous solution.
 Definition
diffuse solubility
Term
___________ increases the effective solubility of O2 in muscle cells, acting as a kind of molecular ___________ brigade to boost the O2 diffusion rate.
 Definition
Myoglobin bucket
Term
The ____________ function of myoglobin is probably significant only in aquatic mammals such as seals and whales, whose muscle myoglobin concentrations are around 10-fold greater than those in terrestrial mammals.
 Definition
oxygen-storage
Term
Vertebrates also express two recently discovered globins: ______________, which is present mainly in brain, retina, and endocrine tissues, and ________, which occurs in most tissues.
 Definition
neuroglobin cytoglobin
Term
___________ protects neurons (nerve cells) from damage under conditions of __________ (inadequate blood flow, such as in a stroke), most likely by preventing ___________________ (the damage caused by the oxygen radicals generated when blood flow is restored).
 Definition
Neuroglobin ischemia reperfusion-injury
Term
Myoglobin's Oxygen-binding curve is ____________.
 Definition
hyperbolic
Term
The reversible binding of O2 to myoglobin (Mb)is described by a simple equilibrium reaction:
 Definition
Mb + O2 <--> MbO2
Term
The dissociation constant, K, for the reaction Mb+O2<-->MbO2 is:
 Definition
K= [Mb][O2]/[MbO2]
Term
The O2 dissociation of myoglobin can be characterized by its _____________ _________, Yo2, which is defined as the fraction of O2-binding sites occupied by O2.
 Definition
fractional saturation
Term
Yo2 is:
 Definition
[MbO2]/[Mb]+[MbO2]
Term
Yo2 ranges from ______(when no O2 is bound to the myoglobin molecule) to ____ (when the binding sites of all the myoglobin molecules are occupied).
 Definition
Term
Since O2 is a gas, its concentration is conveniently expressed by its __________ ________, PO2 (also called the oxygen tension).
 Definition
partial pressure
Term
This equation describes a rectangular hyperbola and is identical in form to the equation that describes a hormone binding to its cell-surface receptor or a small molecular substrate binding to the active site of an enzyme.
 Definition
Yo2 = PO2/K+PO2
Term
Myoglobin is half-saturated with O2 (YO2=0.5) at an oxygen partial pressure (pO2) of _____ torr.
 Definition
2.8
Term
At low pO2, very little O2 binds to myoglobin.
true
false
 Definition
true
Term
As the pO2 decreases, more O2 binds to myoglobin.
true
false
 Definition
false.
As the pO2 increases, more O2 binds to myoglobin
Term
At very high pO2, virtually all the O2-binding sites are occupied and myoglobin is said to be _________ with O2.
 Definition
saturated
Term
The steepness of the hyperbola for a simple binding event, such as O2 binding to myglobin, increases as the value of K ______________.
 Definition
decreases
Term
The lower the value of K, the _______ is the binding.
 Definition
tighter
Term
K is equivalent to the concentration of ligand at which _____ of the binding sites are occupied.
 Definition
half
Term
When pO2 = K, myoglobin is ______________ with oxygen.
 Definition
half-saturated
Term
At what oxygen concentration will myoglobin be 75% saturated with oxygen?
 Definition
Yo2 = pO2/p50+pO2

pO2= Yo2(p50+pO2)
pO2=Yo2p50 + Yo2pO2
pO2 - Yo2pO2 = Yo2p50
pO2 = Yo2p50/(1-Yo2)
pO2 = (0.75)(2.8torr)/(1-0.75)
=8.4 torr
Term
Over the physiological range of pO2 in the blood (____ torr in arterial blood and __ torr in venous blood), myoglobin is almost fully saturated with oxygen.
 Definition
100 30
Term
Myoglobin, is a single ___________ chain with one heme group and hence one oxygen-binding site, is useful model for tohter binding properties.
 Definition
polypeptide
Term
A hyperbolic binding curve occurs when ligands interact independently with their binding sites.
true
false
 Definition
true
Term
Hemoglobin is a tetramer with ____ conformations
 Definition
two
Term
two characteristics of the protein of hemoglobin:
___________
____________
 Definition
-gives blood its red color
-oxygen transport
Term
Mammalian hemoglobin, is an ______ tetramer (a dimer of _____protomer)
 Definition
alpha2beta2 alphabeta
Term
Oxygen binding alters the structure of the entire hemoglobin tetramer, so the structure of _____________ and _______________ are noticeably different.
 Definition
deoxyhemoglobin oxygemoglobin
Term
In both forms of hemoglobin, the alpha and beta subunits form extensive contacts: thoses at the alpha1-beta2 (and its alpha2-beta2 symmetry equivalent) involve _____ residues, and those at the alpha1-beta2 (and alpha2-beta1) interface involve ____ residues.
 Definition
35 19
Term
When oxygen binds to hemoglobin, the alpha1-beta2 (and alpha2-beta1) contacts shift, producing a change in __________ structure.
 Definition
quaternary
Term
Oxygen binds cooperatively to _______________.
 Definition
hemoglobin
Term
Hemoglobin has a p50 of ________ torr (i.e., hemoglobin is half-saturated with O2 at an oxygen partial pressure of _______ torr), which is nearly ____ times greater than the p50 of myoglobin.
 Definition
26 26 10
Term
O2 binding to hemoglobin is described by a ______________ (S-shaped) ________.
 Definition
sigmoidal curve
Term
having a sigmoidal curve (in hemoglobin), this permits the blood to deliver much more ________ to the tissues than if hemoglobin had a hyperbolic curve with the same p50.
 Definition
O2
Term
When oxygen binds to hemoglobin, the alpha1-beta2 (and alpha2-beta1) contacts shift, producing a change in __________ structure.
 Definition
quaternary
Term
Oxygenation rotates one alphabeta dimer ~15 degrees with respect to the other alphabeta dimer, which brings the beta subunits ______________ and narrows the solvent-filled central channel.
 Definition
closer together
Term
In any binding system, a sigmoidal curve is diagnostic of a _____________ interaction between binding sites.
 Definition
cooperative
Term
binding of a ligand to one site affects the binding of additional ligands to the other site.
true
false
 Definition
true
Term
What counts for the increasing slope of the middle portion of the sigmoidal curve in the "Oxygen binding curve of Hemoglobin"?
 Definition
An O2 molecule bound to one of hemoglobin's subunits increases the O2-binding affinity of its other subunits.
Term
The hill equation describes Hemoglobin's _____________ curve.
 Definition
O2-binding
Term
what is the Hill equation?
 Definition
Yo2= (pO2)^n/(p50)^n + (pO2)^n
Term
What does the Hill equation describes?
 Definition
it describes the degree of saturation of hemoglobin as a function of pO2.
Term
Calculate the fractional saturation of hemoglobin at pO2 = 50 torr and n=3.
 Definition
let p50=26 torr

using Hill equation:

= (50)^3/(26)^3+(50)^3 = 125,000/17,576 + 125,000 = 0.88
Term
The quantity __, the Hill constant, increases with the degree of cooperative of a reaction and therefore provides a convenient although simplistic characterization of the a ligand-binding reaction.
 Definition
n
Term
If n=1, describes a _________ as does for myglobin, and the O2-binding reaction is said to be _________________.
 Definition
hyperbola noncooperative
Term
If n>1, the reaction is described as being _______________ ___________, because O2 binding increases the affinity of hemoglobin for further O2 binding.
 Definition
positively cooperative
Term
If n<1, the reaction is said to be ____________ _____________, because O2 binding would then reduce the affinity of hemoglobin for subsequent O2 binding.
 Definition
negatively cooperative
Term
Hemoglobin's two conformations exhibit different _____________ for oxygen
 Definition
affinities
Term
The cooperativity of oxygen binding to hemoglobin arises from the effect of the _____________ state of one heme group on the __________ affinity of another.
 Definition
ligand-binding ligand-binding
Term
Information about the O2-binding status of a heme group is mechanically transmitted to the other heme group by _______ of the proteins.
 Definition
motion
Term
Oxygen binding to Hemoglobin triggers a conformational change from __ to ___.
 Definition
T R
Term
In the ________ _______________, hemoglobin has two stable conformational states, the __ state (the conformation of deoxyhemoglobin) and the __ state (the conformation of oxyhemoglobin).
 Definition
Perutz mechanism T R
Term
In the T state, the _____ in each of the four hemes is situated ~0.6 A out of the heme plane because of a pyramidal doming of the porphyrin group towared His F8 and because the _______ bonds are too long to allow the ___ to lie in the porphyrin plane.
 Definition
Fe(II) Fe--Nporphyrin Fe
Term
___________ changes the heme's electronic state, which shortens the Fe--Nporphyrin bonds by 0.1~ A and causes the porphyrin doming to subcide.
 Definition
O2 binding
Term
During the T-->R transition, the Fe(II) moves into the _______ of the heme plane.
 Definition
center
Term
During the T-->R, The Fe(II) drags the covalently linked His F8 along with it.
true
false
 Definition
true
Term
The Fe(II) drags the linked His F8. The F helix ____ and __________ by ~1 A across the hem plane (to avoid steric clash.
 Definition
tilts and translates
Term
The largest change produced by the T-->R transition is the result of movements of residues at the ____________ and __________interfaces, that is, at the interface between the two protomeric units of hemoglobin.
 Definition
alpha1-beta2 alpha2-beata1
Term
During T-->R transition in hemoglobin, an intermediate position would be severely strained because it would bring _________ and _________ too close together.
 Definition
His 97 Thr 41
Term
During T-->R transition in hemoglobin, the C-terminal residue of each subunit (Arg 141alpha and His 146beta) in T-state hemoglobin each participate in a network of intra- and intersubinit ion pairs that _________ the T state.
 Definition
stabilize
Term
The essential feature of hemoglobin's T-->R transition is that its subunits are so tightly coupled that large ______ structural changes within one subunit cannot occur without __________ structural changes in the entire tertrameric protein.
 Definition
tertiary quaternary
Term
Hemoglobin is limited to only two quaternary forms, T and R, because the
intersubunit contacts act as a binary switch that permits only two stable positions of the subunits relative to each other
true
false
 Definition
true
Term
The T state of hemoglobin has low O2 affinity, mostly because of the 0.1 A greater length of its ________ bond relative to that of the R state.
 Definition
Fe--O2
Term
Experimental evidence indicates that when at least one O2 has bound to each alphabeta dimer, the strain in the T-state hemoglobin molecule is sufficient to tear away the __________ ion pairs, thereby snapping the protein into the _______.
 Definition
C-terminal R-state
Term
The Bohr Effect enhances ___________ transport.
 Definition
oxygen
Term
In the T-state hemoglobin, the N-terminal amino group of the alpha subunits and the C-terminal His of the beta-subunits are __________ charged and participate in ion pairs.
 Definition
positively
Term
The formation of ion pairs increases the _______ values (makes them less acidic and therefore less likely to give up their proton).
 Definition
pK
Term
In R-state hemoglobin, these ion pairings are _______, and the pK's of the group decreases (making them more acidic and more likely to give up protons).
 Definition
absent
Term
Under physiological conditions, hemoglobin releases ~.6 protons for each O2 it binds. Conversely, _________the pH, that is, removing protons, stimulates hemoglobin to bind more O2. (Bohr effect phenomenon)
 Definition
increasing
Term
CO2 dissolves very slowly from the tissue,reaction;
CO2+H2O <--> H+ +HCO3^-
However, in the erythrocyte, the enzyme ____________ _____________ greatly accelerates this reaction.
 Definition
carbonic anhydrase
Term
In the absence of carbonic anhydrase, _________ of CO2 would form in the blood.
 Definition
bubbles
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