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Biochem Ch. 9
Biochem Ch. 9
39
Biochemistry
Undergraduate 3
01/06/2018

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Term
what hemoglobin does for the body
Definition
carries oxygen to tissues and contributes to the transport of CO2 and H ions back to the lungs
Term
is allostery limited to enzymes?
Definition
no; hemoglobin is an allosteric protein
Term
myoglobin
Definition
found in muscle, this protein facilitates the diffusion of O to cellular sites and provides reserve supply of O
Term
the kinetics of hemoglobin
Definition
sigmoidal curve
Term
the kinetics of myoglobin
Definition
hyperbolic curve (like that of a Michaelis-Menten enzyme)
Term
what determines the amount of O hemoglobin releases as it passes thru the tissues?
Definition
allosteric regulators at the tissues
Term
why does hemoglobin release more O than myoglobin would?
Definition
because of cooperativity between O binding sites in hemoglobin
Term
the 2 forms myoglobin can exist in
Definition
-deoxymyoglobin
-oxymyoglobin
Term
where O binds in hemoglobin and myoglobin
Definition
heme groups
Term
depiction of a heme group
Definition
[image]
Term
oxidation state of hemoglobin's Fe in normal conditions
Definition
ferrous (Fe+2)
Term
proximal histidine
Definition
the histidine residue that occupies the 5th coordination site of the Fe atom in hemoglobin; it's on one side of the plane of the heme group
Term
the part of the Fe atom in hemoglobin available for binding with O
Definition
the 6th coordination site; this is on the opposite side of the proximal histidine
Term
distal histidine
Definition
resides on the opposite side of the heme group from the proximal histidine
Term
what the distal histidine does for hemoglobin
Definition
-prevents oxidation of the heme to the ferric (Fe+3) ion -reduces the ability of CO to bind to the heme -H bonds with bound O to stabilize it
Term
depiction of deoxyhemoglobin and oxyhemoglobin
Definition
[image]

in deoxy form, the Fe is slightly outside the plane, but in the oxy form, the Fe is in the plane
Term
how O bound to hemoglobin is stabilized
Definition
by forming a H bond wit the distal histidine
Term
the structure of hemoglobin
Definition
quaternary
Term
the subunits of hemoglobin
Definition
-2 α subunits -2 β subunits functions as a pair of identical αβ dimers, together forming a tetramer α1β1 dimer and α2β2 dimer
Term
the αβ dimers of hemoglobin are linked by...
Definition
an extensive interface which includes, among other regions, the carboxyl terminus of each chain
Term
the interface between the αβ dimers of hemoglobin consists of...
Definition
among other regions, the carboxyl terminus of each chain
Term
the allosteric state deoxyhemoglobin corresponds to
Definition
T (tense) state
Term
the allosteric state oxyhemoglobin corresponds to
Definition
R (relaxed) state
Term
how O binding to hemoglobin affects the quaternary state of hemoglobin
Definition
binding of O on one subunit makes the α1β1 and α2β2 dimers rotate about 15 degrees with respect to each other converts from T to R state
Term
the molecule that regulates hemoglobin within red blood cells
Definition
2,3-biphosphoglycerate (2,3-BPG)

regulates hemoglobin's affinity for O such that sufficient amounts are supplied to aerobic tissues
Term
how 2,3-biphosphoglycerate (2,3-BPG) regulates hemoglobin's O affinity
Definition
goes in the center of the deoxyhemoglobin (T state) and binds to 3 positively charged groups on each β chain by way of ionic bonds, stabilizing the T state and reducing its affinity for O
Term
what must happen to 2,3-biphosphoglycerate (2,3-BPG) for hemoglobin to change from the T to the R state?
Definition
the bonds between hemoglobin and 2,3-biphosphoglycerate (2,3-BPG) must break ad the 2,3-biphosphoglycerate (2,3-BPG) must be expelled from the molecule
Term
depiction of 2,3-biphosphoglycerate (2,3-BPG) in deoxyhemoglobin (T state)
Definition
[image]
Term
the β chain groups 2,3-biphosphoglycerate (2,3-BPG) ionically bonds with
Definition
-His 2
-His 143
-Lys 82
Term
depiction of 2,3-biphosphoglycerate (2,3-BPG) and the β chain groups it ionically bonds with
Definition
[image]
Term
is 2,3-BPG the only allosteric regulator of hemoglobin?
Definition
no
Term
how tissues most in need of O, such as muscle, get the O they need
Definition
1: muscle releases CO2 2: CO2 diffuses into the red blood cell 3: this rxn occurs in the red blood cell: CO2 + H2O <--> H2CO3 <--> HCO3- + H+ this enhances the release of O fromn hemoglobin
Term
Bohr effect
Definition
the regulation of O binding by H+ and CO2
Term
other than regulatory molecules, what can affect hemoglobin's affinity for O?
Definition
-pH
-partial pressure
Term
effect of pH on hemoglobin's affinity for O
Definition
lower pH leads to lower affinity for O
Term
effect of partial pressure on hemoglobin's affinity for O
Definition
lower partial pressure leads to lower affinity for O
Term
the chemical basis of pH regulating hemoglobin's affinity for O (Bohr effect)
Definition
at low pH, the side chain of histidine gets protonated to form a salt bridge with the CO2- group on the aspartate, stabilizing the T state, favorin greater release of O at actively metabolizing tissues at high pH, histidine's side chain is not protonated and the salt bridge does not form, favoring O binding
Term
how CO2 reduces hemoglobin's affinity for O
Definition
CO2 binds with the terminal amino groups to form negatively charged carbamate groups, stabilizing the T state, favoring the release of O
Term
where the amino termini are in hemoglobin
Definition
at the interface between the αβ dimers
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