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MFM > Structure and Function of Myoglobin and Hemoglobin > Flashcards

Structure and Function of Myoglobin and Hemoglobin Flashcards

1
Q

how many molecules of Hb in one RBC?

A

640 million molecules

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2
Q

main function of RBC?

A

transfer O2 from lungs to tissues

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3
Q

composition of hemoglobin

A

2 alpha chains and 2 beta chain tetramer with heme in each chain

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4
Q

what is heme?

A

the porphyrin protoporphyrin IX with Fe2+ chelated in its center

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5
Q

what does hemoglobin use to bind oxygen?

A

heme group, binds to ONLY Fe2+

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6
Q

what does oxidation of heme iron result in?

A

ferric iron (Fe3+) which produces methemoglobin

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7
Q

color of oxygenated-Hb

A

red

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8
Q

color deoxygenated-Hb

A

blue

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9
Q

describe Fe in heme

A

heme iron is Fe2+, and is bound to the nitrogen atoms of the 4 pyrol rings AND with a nitrogen atom in a histidine side chain of the globin (5th bond), and molecular oxygen makes 6th bond

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10
Q

what binds oxygen in heme?

A

Fe2+ ONLY, makes 6th bond with heme iron

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11
Q

what is cyanosis

A

hemoglobin becomes deoxygenated abnormally due to pulmonary and circulatory failure or severe anemia

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12
Q

what is congenital methemoglobinemia

A

mutation of proximal histidine to tyrosine that makes the heme iron accessible to oxidizing agents, that makes it unable to bind O2, or defective diaphorase that cannot fix the methemoglobin Hb

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13
Q

what is the result of oxidation of heme iron?

A

Fe2+ becomes Fe3+, making methemoglobin Hb that cannot bind O2

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14
Q

how is oxidized heme iron repaired?

A

diaphorase (methemoglobin reductase) repairs metHb by reducing Fe3+ to Fe2+

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15
Q

what occurs if there is a mutation in diaphorase?

A

metHb builds up in the cell (deoxygenated)

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16
Q

what is acquired methemoglobinemia?

A

oxidizing drugs like nitrites, dapsone, or benzocaine

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17
Q

how is cyanide poisoning treated?

A

amyl nitrite, which induces formation of methemoglobin in the blood which binds and sequesters cyanide in the blood

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18
Q

what is myoglobin?

A

relative of Hb in the muscle cells, only has one chain

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19
Q

shape of myoglobin graph?

A

hyperbolic, because it has a higher affinity for oxygen

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20
Q

function of myoglobin, how does that relate to its function

A

short term storage of O2 for muscle contraction, so the affinity for O2 is higher to keep it on the myoglobin (shift to left in graph)

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21
Q

how does the plot of hemoglobin relate to its function?

A

sigmoidal plot, hemoglobin transports oxygen from the lungs to the tissues, so it has a low affinity for O2 when the PO2 is low in the tissues, making release of O2 easier (why graph is shifted right related to myoglobin), also shows cooperative binding that binding of 1 O2 facilitates the rest

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22
Q

what occurs when PO2 is high? (like in the lungs)

A

Hb and myoglobin are both saturated with O2

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23
Q

what occurs when PO2 is low in Hb? (like in the tissues)

A

hemoglobin cannot bind O2 as well as myoglobin, so release of O2 is easier, Hb acts as transporter

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24
Q

what occurs when PO2 is low in myoglobin?

A

has a higher affinity for O2 so does not release it as readily

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25
Q

explain cooperative binding of O2 to Hb

A

when one O2 binds to one Hb subunit in its T form, it triggers a conformational change in the adjacent subunits, converting them to R form, so binding of 1 molecule facilitates binding of 2nd molecule and so on.

26
Q

why is cooperative binding advantageous?

A

when the blood is in high PO2 in lungs, oxygen easily binds to the 1st subunit and quickly fills up rest; then at low PO2 in tissues, first O2 molecule drops and quickly drops off the rest of the O2 - allows efficient and largest possible load of O2

27
Q

what agents affect O2 binding to Hb

A
  1. 2,3-BPG (bisphosphoglycerate)
  2. hydrogen ions (pH)
  3. CO2
28
Q

what occurs when there is high [H+], high CO2, and high 2,3-BPG?

A

the Hb curve shifts to the right (less affinity for O2, so more readily dropped off at tissues)

29
Q

what occurs when there is low [H+], low CO2, and low 2,3,-BPG?

A

the Hb curve shifts left (greater affinity for O2, so holds onto O2 more)

30
Q

what is the benefit of 2,3-BPG being a negative allosteric effector of O2 binding to Hb?

A

in the capillaries, Hb unloads 40% of its O2, whereas, if there was no 2,3-BPG, little would be released, so it decreases affinity for O2 so it can be released in the capillaries

31
Q

where is 2,3-BPG formed?

A

in RBC from glycolytic intermediate 1,3-BPG

32
Q

when would 2,3-BPG concentration increase in the blood?

A

hypoxic conditions like COPD, severe anemia, and high altitude

33
Q

what happens to the sigmoid graph in hypoxic conditions?

A

it would shift right to optimize O2 release in the tissues

34
Q

what is the process of storing blood for donation?

A

storage causes loss of 2,3-BPG, bc no active glycolysis, so to prevent ATP depletion, glucose, adenine, phosphate, and other glycolytic intermediates are added

35
Q

what occurs in an acidic environment?

A

as the pH goes down, CO2 content goes up due to Bohr effect, therefore Hb decreases affinity for O2, because when O2 binds Hb, protons are released from Hb

36
Q

what occurs in a basic environment?

A

CO2 goes down, and pH goes up, so Hb increases affinity for O2 binding, thus releasing a proton molecule

37
Q

what occurs when CO2 is produced by metabolic processes?

A

it is hydrated to become H+ and HCO3-, so when Co2 increases, H+ increases, making pH go down

38
Q

what occurs when Hb binds oxygen with relation to pH, and what occurs when protons bind Hb

A

Hb binding of O2 causes a release of protons, helping a basic environment to increase [H+], when [H+] is high, H+ binds Hb, causing the release of O2

39
Q

what is the effect of CO2 on Hb?

A

CO2 decreases affinity of Hb to O2, as CO2 increases, H+ increases, so pH goes down, making H+ bind to Hb as a negative allosteric effector and Hb releases O2, some CO2 covalently binds to Hb

40
Q

what is carbamate hemoglobin?

A

when CO2 is covalently bound to Hb

41
Q

difference between fetal Hb and adult Hb

A

fetal Hb has higher affinity for O2 than adult Hb because histidine is replaced by serine, so 2,3-BPG binds less tightly to HbF than to HbA

42
Q

what does it mean that 2,3-BPG binds less tightly to HbF than HbA?

A

indicates that O2 will have a higher affinity for HbF than HbA, so the HbF can easier draw O2 from maternal blood

43
Q

what would the sigmoid graph of HbF compared with HbA look like?

A

the HbF would be shifted to the left compared with HbA

44
Q

what is sickle cell or hemoglobin S?

A

genetic disorder, is recessive

45
Q

difference between sickle cell trait versus disease?

A

heterozygous individuals are asymptomatic and have the trait only, homozygous individuals are symptomatic and have the actual disease

46
Q

pathology of hemoglobin S

A

a single mutation of glutamine to valine at position 6 of beta globin makes a sticky patch, so the Hb molecules form aligned polymers, causing the abnormal aggregation that makes the sickle shape

47
Q

why is hemoglobin S detrimental?

A

the polymerization causes RBC to not be able to deform to fit in narrow capillary lumen, and aggregate in the capillaries to occlude BF

48
Q

treatment for sickle cell

A

hydroxyurea helps to increase expression of fetal hemoglobin HbF

49
Q

composition of HbF

A

2 alpha and 2 gamma units

50
Q

what is hemoglobin C?

A

single mutation of glutamine to lysine at the position 6 of beta globin, HbSC has higher tendency for HbS to polymerize

51
Q

what is thalassemia?

A

unequal production of alpha or beta globin of Hb (alpha-thalassemia or beta thalassemia)

52
Q

how does thalassemia major result?

A

severe form, from homozygous mutation in the beta globin gene

53
Q

how does thalassemia minor form?

A

milder form, heterozygous mutation in beta globin gene

54
Q

consequence of thalassemia?

A

instability or aggregation, bc RBC don’t form properly and cannot carry sufficient O2, results in anemia that BEGINS IN CHILDHOOD AND LASTS THROUGH LIFE

55
Q

how to dx hemoglobinopathies?

A

electrophoresis, isoelectric focusing, and ion exchange chromatography to separate Hb variants and mutants, then CBC, protein analysis, and DNA analysis (RFLP - restriction fragment length polymorphisms)

56
Q

what is the 6th amino acid in HbA?

A

Glu (- charge)

57
Q

what is the 6th aa in HbS?

A

Val (neutral)

58
Q

what is the 6th aa in HbC?

A

lysine (+)

59
Q

where would the Hb variants show up on Hb electrophoresis?

A

HbA would travel closer to the anode (+), HbC would be closer to the cathode (-), HbS would be in the middle

60
Q

what is HbA1c?

A

glycated Hb normally present 4-6% of the HbA fraction, glucose is nonenzymatically attached to primary aa groups of globin polypeptide

61
Q

what is HbA1c directly proportional to?

A

levels of blood glucose concentrations over previous 3-6 weeks

MFM (39 decks)

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