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MCP > L1_Hemoglobin > Flashcards

L1_Hemoglobin Flashcards

1
Q

Is myoglobin extra or intracellular?

A

Intracellular

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2
Q

What is a normal concentration of hemoglobin in the blood?

A

145g/L or 14.5g/dL

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3
Q

Why is hemoglobin needed?

A

Because solubility of O2 i blood is low and diffusion of O2 across tissue more than 1mm thick is not sufficient to support life

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4
Q

What is the typical O2 concentration in the following places: atmosphere, blood in alveolar capillaries, blood in muscle capillaries, cytoplasm of myocyte, Km of Cytochrome oxidase

A 
Atmosphere: 760 torr
Alveolar Capillaries: 100 torr
Muscle Capillaries: 20 torr
Myocyte Cytoplasm: 5 torr
Km of Cyt. Oxidase: <1torr
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5
Q

Where is the steepest gradient of O2 concentration?

A

between muscle capillaries and myocyte cytoplasm

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6
Q

O2 diffusion within the cell is facilitated by what?

A

myoglobin

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7
Q

Where is myoglobin most abundant?

A

muscle cells

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8
Q

How many alpha helices does myoglobin have?

A

8

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9
Q

What is the prosthetic group of myoglobin?

A

heme

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10
Q

What is ApoHb, what is holoHb?

A

Apo is HB tetramer with no heme, Holo is Hb tetramer with 4 hemes

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11
Q

In 1 molecule of HoloHb saturated with O2, how many heme molecules are there? Oxygen molecule? oxygen atoms?

A

4 heme
4 O2 molecules
8 O atoms

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12
Q

How many subunits does Hb have?

A

4 (2beta 2 alpha)

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13
Q

What 3D shape are the subunits of Hb arranged in?

A

Tetrahedron

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14
Q

What is a Hemoglobin protomer?

A

an alpha-beta dimer

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15
Q

What are the two different states that an Hb tetramer can exist in, which has a higher affinity for O2

A

T and R (R has a higher affinity for O2) 15 deg rotation between the two states

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16
Q

What type of structure is heme, what are its subunits, what are the substituent groups of these sub units?

A

Porphyrin Ring, 4 pyrole rings, The substituent groups are 4 methyl, 2 vinyl, and 2 propionate

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17
Q

What are the four Ns donated from heme to bind iron referred to as?

A

equatorial ligands

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18
Q

What AA from Hb acts as the 5th ligand? What type of ligand is this referred to as?

A

The proximal Histidine is an axial ligand

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19
Q

What provides the 6th ligand of Fe in Hb?

A

O2

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20
Q

What is the role of the distal histidine, what key functions does it have?

A

It hydrogen bonds with O2 which increases the affinity for O2, It also Decreases the affinity for CO because CO binds in a linear fashion that clashes with the distal histidine. It also may prevent oxidation of Fe by O2

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21
Q

Does hemoglobin have a higher affinity for O2 or CO, NO and H2S?

A

CO, NO, and H2S

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22
Q

list the correct oxidation state for the following: ferrous and Ferric

A 
Ferrous = 2+
Ferric = 3+
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23
Q

What is the color of DeoxyHb and OxyHb?

A

Deoxy - Dark Red

Oxy- Brilliant Scarlet

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24
Q

What is the oxidation state of Fe in MetHb? Can it bind O2?

A

3+, No

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25
Q

What does CN- do?

A

Inhibits Cytochrome Oxidase

26
Q

What happens to the Fe when it binds O2 (not oxidation state but structurally)?

A

Its bonds get shorter and it moves into the plane of the heme, this triggers a conformational change which destabilizes the T state

27
Q

What is the O2 pressure in venous and arterial blood?

A

venous 20-30 torr

Arterial 100 torr

28
Q

What shape are Hb and Mb binding curves

A

Hb - sigmoidal

Mb - hyperbolic

29
Q

What is the P50 of adult Hb and Mb?

A

Hb - 26 torr

Mb - 2.6 torr

30
Q

The cooperatively of O2 binding is a classical model for what type of interaction?

A

Allosteric

31
Q

Does Mb show allosteric effects?

A

No

32
Q

List the positive effectors of Hb and the negative effectors which are left and which are right shifting?

A

Positive: O2 (Left shifting, stabilize R)
Negative: BPG, CO2, H+, Cl- (right shifting, stabilize T)

33
Q

What is the definition of cooperativity?

A

allostery in which what is happening at one site promotes the same thing happening at another identical site, generally a property of multimeric proteins

34
Q

What has a higher affinity for O2 purified/stripped deoxy Hb or Deoxy Hb in whole blood?

A

Purified

35
Q

How may molecules of BPG bind a HB tetramer?

A

1

36
Q

What is the P50 of Hb without BPG?

A

3torr

37
Q

What is the function of BPG?

A

To basically set the midpoint for Hb such that the steep part of the binding curves falls in between the POs in the lungs and tissues

38
Q

what is the SO2 in arterial blood compared to venous blood?

A

Arterial 95%

Venous 43%

39
Q

Where does BPG bind Hb?

A

It binds symmetrically between the two beta chains in the T-state

40
Q

What short term adaptation does the body make to adjust to high altitudes?

A

Increase the BPG concentration

41
Q

Does the Bohr effect modulate the affinity of Mb?

A

No

42
Q

What is the Bohr effect?

A

Higher pH/ lower H+ concentration increases the affinity for O2 (Lungs). Lower pH/ Higher H+ concentration decreases affinity for O2 (Tissue)

43
Q

Does the binding of O2 to Hb make it a stronger acid or base?

A

Acid - releases protons

44
Q

What role does CO2 play in the bohr effect?

A

CO2 spontaneously forms Bicarbonate and H+ which lowers O2 affinity in tissues and helps unload hemoglobin. In the lungs, PO2 is high so Hb binds and produces H+ which combines with the bicarbonate to form CO2 which is blown off

45
Q

How does CO2 directly interact with Hb?

A

It can bind the N-termini of Hb subunits which stabilizes the T-state and the release of O2 in tissues.

46
Q

How does fetal hemoglobin compare to adult hemoglobin with respect to affinity for O2, P50, and affinity for BPG?

A

Higher affinity for O2, Lower P50 (15), and lower affinity for BPG

47
Q

How many CO2 molecules can bind to one Hb tetramer?

A

4

48
Q

What are the 3 normally observed hemoglobins?

A 
Hemoglobin A (alpha2beta2)
Hemoglobin A2 (alpha2delta2)
Hemoglobin F (alpha2gamma2)
49
Q

What are the consequences of a mutation causing a change in a surface residue?

A

With the exception of sickle cell Hb, these mutations usually have no clinical manifestation.

50
Q

What are the consequences of a mutation causing a change in an internally located residue?

A

These mutations often destabilize the Hb structure and/or alter its O2 binding function. Persons with unstable Hb often suffer from hemolytic anemia

51
Q

Describe what happens in a patient with methemoglobinemia

A

A mutation near the O2 binding site can favor heme oxidation generating methemoglobin. Methemoglobin is not an effective O2 carrier, moreover the ferric iron moves into the plane of the heme, promoting the conformational changes which increase the affinity of the other subunits in the molecule so they do not release O2. Patients suffering from this will appear to have bluish skin, a condition known as cyanosis.

52
Q

Describe the mutation that causes HbS

A

A mutation at position 6 of the beta chain causes a glutamate to Valine switch.

53
Q

What do homozygotes for HbS suffer from?

A

Sickle-Cell Anemia which is a form of hemolytic anemia.

54
Q

What is an advantage of being a heterozygote for HbS?

A

73% reduced rate of contracting malaria. They usually live a normal life although there erythrocytes have a shorter than normal lifetime.

55
Q

What does the Hbs mutation cause?

A

it causes HbS to aggregate and polymerize in to rigid extended fiber that span the length of the cell.

56
Q

Of the two Valine molecules in Hbs, how many contact a neighboring molecule during polymerization?

A

1

57
Q

Describe the subunit composition of HbC, and its properties

A

has a subunit composition alpha2beta2. The same residue mutated in HbS is mutated to a Lysine. HbC does not polymerize like HbS but does protect against malaria

58
Q

Describe the subunit composition of HbH, and its properties

A

subunit composition of beta4, it bind oxygen bery tightly and non-cooperatively hence providing very inefficient O2 delivery

59
Q

Describe the subunit composition of HbBarts

A

gamm4, like HbH it displays high affinity and non-cooperativity which results in poor delivery to tissues.

60
Q

What would be the order that Hbs, HbC, and HbA would travel down a gel? shortest to longest distance traveled

A

HbC, HbS, HbA

MCP (5 decks)

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