Hemoglobin and Myoglobin Flashcards
1
Q
where in the body does Hb bind O2
A
- in the alveoli of the lungs
2
Q
where in the body does Hb deliver O2
A
- to tissues throughout the body
3
Q
how does Hb assist in maintaining acid-base balance in the body
A
- binding some CO2 produced by metabolism
- releasing CO2 when Hb reaches the lungs
4
Q
function of Hb dependent upon
A
- partial pressure gradients of O2 or CO2
5
Q
partial pressure of a gas equal to
A
atmospheric pressure x fraction of atmosphere composed of that gas
6
Q
significance of different of partial pressure between lungs, tissues, and blood
A
- driving force for gas exchange
7
Q
myoglobin synthesized where
A
- inside muscle cells
- skeletal muscle, smooth muscle, cardiac muscle
8
Q
function of myoglobin
A
- stores oxygen in muscle cells for use at times of high metabolic demand
9
Q
myoglobin content varies by
A
- skeletal muscle fiber type
- IA > IIA > IIB
10
Q
percentage and type of helix found in myoglobin
A
- 80% alpha helical
11
Q
order of structure in myoglobin
A
- closely packed tertiary structure
12
Q
heme in structure of myoglobin
A
- single heme molecule covalently bound
13
Q
myoglobin binding of oxygen
A
- binds one O2 molecule at heme
14
Q
molecule on inside of heme ring
A
- Fe2+
15
Q
heme ring hydrophobic or hydrophilic
A
- hydrophobic
16
Q
polypeptide chains hemoglobin
A
- 2 alpha
- 2 beta
17
Q
polypeptide chain in myoglobin
A
- single polypeptide chain
18
Q
amount of O2 bound by hemoglobin
A
- can bind 4O2 at once
19
Q
hemoglobin interactions between subunits
A
- strong hydrophobic interactions between alpha 1 and beta 1
- and alpha 2 and beta 2
- weaker polar interactions between a1B1 and a2B2
20
Q
HbA composition
A
- a2B2
- quaternary higher order conformation
21
Q
significance of HbA
A
- glycosylation is marker for chronically elevated blood sugar
22
Q
HbA2 composition
A
- a2 delta 2
23
Q
HbF composition
A
- a2y2
24
Q
thalassemias
A
- imbalance in globin chain synthesis
25
what forms coordinate covalent bonds to Fe2+ in heme
- pyrrole rings
26
purpose of hydrophobic chains from pyrrole rings
- interact with a/B globin chains to stabilize heme binding
27
class of pigments that heme belongs to
- porphyrins
28
binding curve of myoglobin
- hyperbolic
| - single constant affinity for O2
29
P50 of myoglobin
- 2.8 torr
30
binding curve of hemoglobin
- sigmoidal
| - changing affinity for O2 over the binding curve
31
P50 of hemoglobin
- 26 torr
32
P50 definition
- the partial pressure of O2 at which 50% of O2 binding sites are occupied
33
two conformation of Hb
- taught
| - relaxed
34
taught conformation favors which form
- deoxy
| - O2 release
35
relaxed conformation favors which form
- oxy
| - O2 binding
36
O2 regulation of hemoglobin
- affects equilibrium between T and R forms
| - positive allosteric regulator of Hb O2 binding
37
movements of proximal and distal histidines cause
- attached alpha helices to move
| - causes conformational change at interface of each aB dimer in the Hb molecule
38
2,3-DPG on hemoglobin binding curve
- shifts right
39
2,3-DPG acts on hemoglobin
- stabilized T (deoxy) state
| - allow Hb-bound-O2 to dissociate and supply O2 to tissues operating at a high metabolic rate
40
2,3-DPG and hypoxia
- makes O2 release by Hb more responsive to hypoxia
| - allows more O2 release at low pO2
41
physiological changes that cause change in 2,3-DPG levels
- COPD
- high altitude
- chronic anemia
- pregnancy
42
Haldane effect
- high pO2 increases binding of O2 to Hb
- less binding of H+ and CO2
- O2 is affecting the affinity of Hb for CO2/H+
- more CO2 delivery to the lungs from tissues
43
Bohr Effect
- high CO2 and high protons
- protons (due to lower pH) in RBCs bind to Hb
- favor T state, favoring O2 release to the tissues
- CO2/H+ are affecting the affinity of Hb for O2
- more O2 release to tissues from lungs
44
increase in pH favors
- O2 binding
| - shifts left
45
decrease in pH favors
- O2 release
| - shifts right
46
fetal hemoglobin versus adult hemoglobin A
- fetal hemoglobin has a higher affinity for oxygen
47
HbF and 2,3-DPG
- binds 2,3-DPG very poorly because cavity is not as positively charged
48
O2 released by maternal HbA
- bound by fetal HbF
| - transported to fetal tissue
49
the most common Hb variant associated with significant pathology in the Us
- B^s variant
- caused by mutation at position 6 of beta globin gene
- changes Glu to Val
50
individuals homozygous for B^s allele or heterozygous for B^s and B-thalassemia allele
- produce significant amount of HbS
| - have sickle cell disease
51
importance of deoxy HbS
- forms long polymers within the erythrocyte
| - shortens lifespan of RBCs
52
competitors of Hb A at the iron binding site
- cyanide (CN-)
- carbon monoxide (CO)
- nitrogen dioxide (NO2)
- hydrogen sulfide (H2S)
- all inhibit oxygen binding
53
effect of competitors of HbA on iron
- do not change oxidation status of iron
| - remains Fe2+
54
carboxyhemoglobin
- stable complex of carbon monoxide and heme in Hb
| - forms more readily than oxyhemoglobin
55
importance of electronic environment of distal (O2-binding) side of heme
- prevents oxidation of Fe2+ to Fe3+ by the bound O2
| - would result in O2 release
56
mutations that change any of the 3 amino acids on the distal side of heme result in
- result in hereditary methemoglobinemia
57
hereditary methemoglobinemia characterized by
- cyanosis
| - brown color to blood
58
hereditary causes of methemoglobinemia
- mutations in PPP, especially G-6-PD deficiency
| - mutations in cytochrome b5 reductase
59
role of glutathione
- normally reduces reactive oxygen species thereby preventing formation of methemoglobin
60
deficiency of methemoglobinemia may not present until
- challenged by increased levels of activated O2 species
61
cytochrome b5 reductase importance
- reduces Fe3+ in methemoglobin to Fe2+
