Hemoglobin Flashcards
1
Q
A
Switch from weak to strong binding state explains the sigmoidal curve
2
Q
B6
A
Glycine, Allows approach of B and E helices
2
Q
What is Hemoglobin Constant Spring?
A
(α-globin chain that
is abnormally long)
3
Q
what defines beta thal major
A
homozygous for defect. no beta chain made.
4
Q
Alpha 1
Arg141
Residue
(NH3+)
A
Alpha 2
Val1
N-terminus
(NH3+)
4
Q
Alpha 1
Lys40
Residue
(NH3+)
A
Beta 1
His146
C-terminus
(COO-)
4
Q
Alpha 2
Asp 126
Residue
(-O-)
A
Alpha 1
Arg141
Residue
(NH3+)
5
Q
Mb is used in some tissues, notably
____, as a storage reserve of O2 and for
________
A
muscle; intracellular transport
7
Q
Alpha 1
Tyr140
Residue
(-OH)
A
Alpha 1
Val93
Carboxyl
(=O)
8
Q
A
9
Q
What are the reasons why CO is toxic?
A
Acts as a competitive inhibitor - it ties
up oxygen binding sites and thereby
blocks respiration.
CO is bound with much greater affinity
to myoglobin and hemoglobin than is O2, and the
binding is not readily reversible - CO converts Hb to a high affinity
state for O2 that does not release O2 at low
pO2
9
Q
What is the concerted model? (MWF?)
A
the shift from T to R is a concerted one, so that mixed molecules wiht some subunits in the weak-binding state and some in the strong-binding state are specifically excluded.
10
Q
True or False:
The tertiary structure of each subunit of Hb is very similar to the tertiary structure of Mb
A
True
11
Q
What is the mutation for St. Lukes?
Cause? Mechanism?
A
Pro (α chain) (G2) to Arg
• This change produces a Hb variant known as St
Lukes.
• The loss of Pro results in a change of the
geometry of the subunit and therefore alters
subunit interactions due to continuation of the
helix. This results in Hb dissociation into subunits.
13
Q
In the lung, deoxy-hemoglobin exchanges its
load of _____ and ________ with
_____.
A
In the lung, deoxy-hemoglobin exchanges its
load of protons and carbon dioxide with
oxygen.
14
Q
What is the equation for theta (aka fractional saturation)?
A
14
Q
True or false: the heme pocket cannot bind other small molecules besides O2
A
False. CO2 is one of them.
16
Q
Beta 2
His146
C-terminus
(COO-)
A
Alpha 1
Lys40
Residue
(NH3+)
17
Q
How does the gamma chain differ from the beta chain in hb?
A
serine instead of His143
18
Q
What is the pO2 in the air (mmHg). Why are tissues and cells not exposed to this directly?
What does Hb transport do?
A
• O2 is a very strong oxidizing agent.
• In the air its pO2 is approximately 120-150
mmHg.
• If tissues and cells are exposed directly to
this high pO2, many cellular substances
may get oxidized and damaged.
• Hb transport reduces the pO2 to about 30-
40 mmHg.
19
Q
Beta 2
His146
Residue
(+)
A
Beta 2
Asp94
Residue
(COO-)
19
Q
What is the mutation for HbE?
A
β26 Glu to Lys
19
Q
What is the symbol for HbH?
A
(β4)
20
Q
How does CO toxicity differ between Mb and Hb
A
Only acts as a competitive inhibitor for Mb because it does not bind cooperatively
21
C2
Proline, terminates the helix
21
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the ___ of that gas in
equilibrium with that liquid.
What does this imply?
What is this statement known as?
Partial pressure
Thus [O2] is proportional to the partial
pressure of O2
Henry's Law
21
What is the sequential model?
cooperativity arises because the presence of some subunits carrying oxygen favors the strong binding state in adjacent subutnits whose sites are not yet filled. Thus, as oxygenation progresses almost all binding sites acquire affinity.
22
The heme group is buried within a _______ pocket in the protein
hydrophobic
23
What is Hb H disease?
a mildly to moderately severe hemolytic
anemia
24
Fractional Saturation (θ) is defined as:
The ratio of the protein's occupied binding sites to the total protein's unoccupied and occupied binding sites.
25
What are the properties of a preferred oxygen carrier?
* It binds O2 at high pO2
* It does not oxidize cellular compoents
* It gives O2 on demand
25
Which model (KNF or MWC) exactly explains the allosteric behavior of proteins including Hb?
Neither. Most such models retain the MWC concept of a concerted switch in conformation, but involve more than two states for the entire molecule.
Hb follows neither completely, but follows a novel path containing features of both. allosteric proteins; however, exist that appear to follow the MWC model almost exactly.
26
Beta 1
Tyr145
Residue
(-OH)
Beta 1
Val98
Carboxyl
(=O)
27
The residue of ________ interacts with Asp of the same β2 by
charge-charge interaction and with Lys 40 of the
α1 through charge-charge interactions
β2 (His146)
29
Alpha 2
Arg141
C-terminus
(COO-)
Alpha 1
Lys127
Residue
(NH3+)
30
O2 binds \_\_\_\_\_to the Fe+2 without
causing oxidation of the iron to Fe+3.
Reversibly
31
Beta 1
Asp94
Residue
(COO-)
Beta 1
His146
Residue
(+)
32
Alpha 1
Val1
N-terminus
(NH3+)
Alpha 2
Arg141
Residue
(NH3+)
32
What is the mutation for O Arab, Egypt?
## Footnote
What does it cause? By what mechanism?
β121 Glu (GH4) to Lys
• Enhanced sickling
• The reason for this enhanced sickling is
that switching from Glu (negative charge)
to Lys (positive charge) causes chargecharge
interactions with β6 Glu.
33
Alpha 1
Val93
Carboxyl
(=O)
Alpha 1
Tyr140
Residue
(-OH)
34
Alpha 1
Lys40
Residue
(NH3+)
Beta 2
His146
C-terminus
(COO-)
35
Alpha 1
Asp 126
Residue
(-O-)
Alpha 2
Arg141
Residue
(NH3+)
36
Beta 2
Asp94
Residue
(COO-)
Beta 2
His146
Residue
(+)
37
When subjected to a solution of 2 M urea, the
Hb molecule dissociates into:
What does this suggest?
α/β dimers
suggesting that the interactions between a and b
are stronger than
α/α or β/β interactions.
37
If only one α gene is defective, what is this known as?
a silent carrier of α thalassemia.
38
What defines a silent carrier of alpha thalassemia?
If only one α gene is defective
40
Alpha 1
Arg141
Residue
(NH3+)
Alpha 2
Asp 126
Residue
(-O-)
42
The
α subunits (may or may not be identical,
i.e. product of one or two different genes) are
each comprised of ___ amino acid residues; the
two β subunits are identical (product of the same
gene) each comprised of ___ amino acid
residues.
141; 146
42
Where does BPG bind? How does it bind?
BPG binds in the cavity between the β-
chains, making electrostatic interactions
with positively charged groups surrounding
this opening
42
What is a genetic indicator of Hb H disease?
If three α genes are defective
43
What is the role of 2,3 BPG
efficient O2 release
44
Beta 2
Val98
Carboxyl
(=O)
Beta 2
Tyr145
Residue
(-OH)
45
What is the mutation for M Iwate?
What does it cause? By what mechanism?
His, F8, α chain (α 87) to Tyr
• When histidine (proximal His, F8) of the α chain (α 87) is
replaced by tyrosine, it produces a variant of Hb referred
to as M Iwate.
• Replacement of His with Tyr results in ligating the ferrous
atom in the heme and the Fe+2 becomes susceptible to
oxidation to the ferric state (Fe+3)and no longer binds
oxygen, resulting in reduced oxygen binding affinity.
47
HC2
Tyrosine; hydrogen bond between the H and F Helices
48
What is the result of the equation given below for carbamate formation?
## Footnote
-NH3 + HCO3-
-NH- COO- + H+ + H2O
48
What is the mutation for Shepherd's Bush?
What does it cause? By what mechanism?
β Gly74 to Asp.
• This changes produces a variant known as
Shepherds Bush and characterized by increased
affinity for oxygen (smaller p50).
• This is explained by the fact that introducing a
negatively charged residue in this region reduces
the binding of 2,3-bisphosphoglycerate to Hb
resulting in higher affinity Hb.
49
what chromosomes are alpha and beta chain genes?
16, 11 respectively
50
In tissues, \_\_\_\_\_is unloaded to the cells
from oxy-Hb and the \_\_\_\_\_\_are picked up
by deoxy-Hb.
In tissues, oxygen is unloaded to the cells
from oxy-Hb and the protons are picked up
by deoxy-Hb.
52
Alpha 1
Arg141
C-terminus
(COO-)
Alpha 2
Lys127
Residue
(NH3+)
53
What is the mutation for HbS?
β6 Glu to Val
53
What is the mutation for Suresnes?
What does it cause? By what mechanism?
Arg 141 (α chain) (HC3) to His
• This change produces a Hb variant known
as Suresnes. This variant is characterized
by increased oxygen affinity (smaller p50)
favoring the R state.
• This is attributed to the elimination of the
interactions between Arg and Asp126 of α
chain in deoxyHb.
55
How do you calculate oxygen saturation in Hb?
57
The hydrophobic character of the heme binding
pocket is responsible for:
Protecting the heme from oxidation thus maintaining
the iron in the Fe+2 state.
58
What is the mutation for Bibba?
Cause? Mechanism?
Leu136 (α chain) (H19) to Pro
## Footnote
• Since introduction of proline into the helix
interrupts the helix, it results in dissociation of the
tetramer and results in high oxygen binding
affinity.
58
What are the three possible causes for Thalassemias?
One or more of the genes coding for the hemoglobin
chains are deleted.
• All genes may be present but one or more may have
undergone a nonsense mutation resulting in production
of a shortened polypeptide chain or a frameshift mutation
that results in a nonfunctional chain.
• All genes may be present but a mutation may have
occurred which blocked transcription or proper
processing of pre-mRNA so the protein is either not
produced or is non-functional.
59
How does HbF differ from HbA?
decreased affinity for BPG, less bound BPG therefore increase in O2 affinity at the same conc of BPG as mother.
60
What is the mutation for Hiroshima?
What does it cause? By what mechanism?
β His146 (HC3) to Asp
• This change results in Hb variant known as
Hiroshima.
• Since this residue is critical for the Bohr
effect and it plays a role in deoxy to Oxy Hb
switching, the changes to Asp results in
formation of Hb with high affinity for oxygen.
62
The affinity of Hb to O2 varies considerably with changing \_\_\_\_. The affinity of Hb to O2 also varies in response to changes in:
Oxygent concentration
[H+] (pH), and
CO2 concentrations and physiological levels of
bisphosphoglycerate
62
What happens If all four α genes are defective?
the result
is hydrops fetalis and death of the fetus at
or before birth (blue baby).
γ4 (hemoglobin Bart) β4 (hemoglobin H)
64
Beta 1
Val98
Carboxyl
(=O)
Beta 1
Tyr145
Residue
(-OH)
65
The tertiary structure of myoglobin is comprised
of
eight (8) a-helices [A-H]; four of these helices are terminated by proline residues.
66
Beta 2
Tyr145
Residue
(-OH)
Beta 2
Val98
Carboxyl
(=O)
68
Transport protein efficient in both binding and unloading because it has a sigmoidal binding curve
69
What defines beta thal minor
one gene defective
beta thal trait
70
Alpha 2
Val93
Carboxyl
(=O)
Alpha 2
Tyr140
Residue
(-OH)
71
E7
Distal Histidine, Protects the heme and forces O2 to bind with an angle
72
Alpha 1
Lys127
Residue
(NH3+)
Alpha 2
Arg141
Cterm
(COO-)
73
What is the mutation for St. Etienne?
Cause? Mechanism?
β His (F8) to Gln
• This change results in Hb variant known as
St. Etienne.
• This variant does not hold on to its heme
because Gln does not coordinate well with
the ferrous atom in the heme, opening the
hydrophobic crevice for polar solvent.
74
β2 (His146)'s residue interacts with \_\_\_\_\_of the same β2 by
charge-charge interaction and with _______ of the
α1 through charge-charge interactions.
Asp; Lys 40
76
What are the AA are involved in binding 2,3 BPG?
Lys82, His143, His2,
and the N-terminal amino group of the β-
chains
77
F8
Proximal Histidine, binds Fe (II)
79
How do higher levels of 2,3 BPG in RBCs affect Hb structure?
Stabilizes dHb structure
80
For Mb overall, approximately \_\_\_% of the
polypeptide chain is in a-helical structure
75%
81
2,3 BPG is a(n)\_\_\_\_\_\_ ______ of hemoglobin that regulates long-term changes in oxygen affinity.
allosteric effector
83
Transport protein efficient in binding but inefficient in unloading (hyperbolic bind curves)
85
In deoxy Hb, the C-terminus of β2 (His146) lies
atop helix C in α1 (residues 36-42) and is held in
place by a network of ______ and\_\_\_\_\_\_\_\_\_\_.
hydrogen bonds; salt bridges (ionic interactions)
86
87
In deoxy Hb, the C-terminus of ________ lies
atop helix C in α1 (residues 36-42) and is held in
place by a network of hydrogen bonds and salt
bridges (ionic interactions).
β2 (His146)
88
What is the mutation for HbC
β6 Glu to Lys
89
Transport protein efficient in unloading but inefficient in binding (hyperboloic binding curves)
91
At what concentration of O2 will the concentration
of MbO2 equal the concentration of
unoccupied Mb?
At a given concentration of O2 that is
sufficient to saturate 50% of all available
myoglobin binding sites
92
Binding of BPG acts to:
lower the oxygen affinity of Hb.
93
Alpha 2
Tyr140
Residue
(-OH)
Alpha 2
Val93
Carboxyl
(=O)
94
95
What is the mutation for G. Makassar?
What does it cause? By what mechanism?
β6 Glu (Helix A) to Ala
• Changes in helix A of β6 from Glu to Ala
produces insignificant sickling.
• This is because Ala, due to its small size,
probably does not fit in the hydrophobic
EF pocket of the β chain very well.
96
What is the symbol for Hb Barts?
(γ4)
97
Alpha 2
Arg141
Residue
(NH3+)
Alpha 1
Val1
N-terminus
(NH3+)
98
What is the mutation for Hammersmith?
Cause? Mechanism?
β 42 Phe (CD1) to Ser
## Footnote
• This variant is unstable and loses its heme.
• This is explained by the fact that replacement of
the more hydrophobic amino acid residue Phe with
Ser, which is hydrophilic and polar, opens the
pocket for water and results in loss of heme.
99
If two α genes are defective, the individual
is designated as
having α thalassemia
trait.
100
Alpha 2
Arg141
Cterm
(COO-)
Alpha 1
Lys127
Residue
(NH3+)
101
The heme groups, with their oxygen binding sites, are all
close to the surface of the molecule, but not close to one
another. What does this imply (regarding cooperative oxygen binding)
cooperative oxygen binding cannot be attributed to heme-heme interaction
102
F4
Leucine, Heme contact
103
Hemoglobin (Hb) transports ___ from
lungs to tissues and to transports \_\_\_\_
and ___ from tissues to lungs.
O2; H+; CO2
104
Alpha 2
Arg141
Residue
(NH3+)
Alpha 1
Asp 126
Residue
(-O-)
105
Effects of CO2 on O2 Binding
## Footnote
Some \_\_\_\_\_\_is transported out of
the erythrocytes and is carried dissolved in the
blood serum. A portion reacts directly with
hemoglobin, binding to the N-terminal amino
groups of the chains to form \_\_\_\_\_\_\_.
Some of this bicarbonate is transported out of
the erythrocytes and is carried dissolved in the
blood serum. A portion reacts directly with
hemoglobin, binding to the N-terminal amino
groups of the chains to form carbamates
106
How do you equate oxygen saturation in Mb?
107
Beta 1
His146
Residue
(+)
Beta 1
Asp94
Residue
(COO-)
108
Beta 1
His146
C-terminus
(COO-)
Alpha 1
Lys40
Residue
(NH3+)
109
CD1
Phenylalanine, Heme contact
110
How are the tertiary and quarternary structural changes in Hb connected?
changes in tertiary structure that accompany oxygen binding can be tolerated up to a certain point before the T-R switch occurs. Whenever one sit is occupied on each of the two alpha-beta dimers. the molecule as a whole adopts the R quarternary structure.
111
Alpha 2
Val1
N-terminus
(NH3+)
Alpha 1
Arg141
Residue
(NH3+)
112
Mb and Hb in which the iron has been
oxidized chemically to Fe+3 does not bind
oxygen; it binds \_\_\_\_.
Water
