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Integrated Exam 3/9 > Biochem - Globins > Flashcards

Biochem - Globins Flashcards

1
Q

What do hemoglobin and myoglobin do to O2’s reactivity?

A

reduce it

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2
Q

2 reasons for O2 transport proteins:

A
  • reduces O2 activity
  • gets more solubility in the blood
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3
Q

Oxidation vs reduction

A

O: loss of e- (increase in oxidation #)
R: gain of e- (decrease in oxidation #)

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4
Q

Oxidant vs reductant

A

O: accepts e-‘s (oxidation state decreases)
R: donates e-‘s (oxidation state increases)

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5
Q

Example of powerful oxidant

A

oxygen

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6
Q

How do hemoglobin and myoglobin affect oxygens reactivity?

A

reduce it by forming a protective environment around it so it cant react

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7
Q

Hemoglobin picks up _____, so it acts as a biological _____

A

protons
buffer

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8
Q

What are heme iron’s two oxidation states?

A

Fe2+ (ferrous)
Fe3+ (ferric)

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9
Q

How many bonds can ferrous iron form?

A

6 bonds
- 4 bonds with the nitrogens of the pyrrole rings
- 1 bond with the histidine of the globin chain
- 1 bond with oxygen

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10
Q

Carbon monoxide binds
_____ more tightly than oxygen

A

200-fold

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11
Q

T/F: Ferric iron doesnt bind to oxygen?

A

True

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12
Q

O2 doesn’t bind to protein components, it binds to _____ groups

A

prosthetic

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13
Q

What is an example of prosthetic groups?

A

vitamins

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14
Q

What is the heme prosthetic group derived from?

A

precursors in the body (NOT vitamins)

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15
Q

Heme structure

A
  • forms 4 pyrroles (because of the 4 nitrogens)
  • 1 central iron
  • flat
  • bulk of molecule is hydrophobic/nonpolar
  • one edge that is polar (because of the proprionic acid groups)
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16
Q

Myoglobin structure:

A
  • 153 amino acids (80% in α helix form)
  • overall nonpolar molecule
  • has 1 polar surface (between histidines)
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17
Q

Heme and myoglobin:

A
  • Heme slides into a pocket between E and F helices
  • Histidine in helix F binds heme iron (proximal His)
  • Histidine in helix E binds O2 (distal His)
  • the surface between the 2 histidine portions is POLAR (prevents H2O from entering and oxidizing the iron)
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18
Q

Which residue does histidine bind to the heme iron?

A

Residue position 93

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19
Q

Histidine in helix F:

A
  • proximal His (more anterior when looking at a 3D structure)
  • binds heme iron
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20
Q

Histidine in helix E:

A
  • distal His (more posterior when looking at a 3D structure)
  • binds O2
  • actually makes contact with O2, unlike prox. histidine
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21
Q

Hemoglobin structure:

A
  • heterotetramer
  • 2α and 2β subunits (so hemoglobin can bind up to 4 O2)
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22
Q

How many oxygen can hemoglobin vs myoglobin bind?

A

H: 4 oxygens
M: 1 oxygen

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23
Q

What is the sequence identity btwn Hb and Mb?

A

17%

24
Q

What is the sequence identity btwn α and b globins?

A

40%

25
Q

Structural conservation between globin chains is greatest at which structural level?

A

tertiary

26
Q

Forms of Hemoglobin in the Human Circulatory System:

A
  • 92.5% HbA1 α2b2 (alpha 2 beta 2)
  • 2.5% HbA2 α2δ2 (alpha 2 delta 2)
  • 5% HbA1c α2 (b-NH-Glc)2
    overall: 95% adult hemoglobin is in blood, 5% is HbA1
27
Q

Forms of Hemoglobin in the Fetal/Embryonic Circulatory System:

A

Fetus:
- HbF α2γ2 (alpha 2 gamma 2)

Embryo:
- Hb Gower ζ2ε2 (zeta 2 epsilon 2)
- Hb Portland ζ2γ2 (zeta 2 gamma 2)

28
Q

Fetal development and clinical manifestations

A
  • when beta chains replace gamma chains at birth, visible manifestations become observed (not affected during embryonic development, because no beta chains in the embryo)
  • disorder to alpha chains is expressed during fetal development
29
Q

Quaternary Structure of Hemoglobin:

A
  • non covalent assembly of polypeptide chains
  • has a distinctive hole in middle of structure
  • when treated with urea, becomes 2 alpha-beta dimer “halfs”
30
Q

Myoglobin-O2 binding equation

A

Y = fraction of Mb with O2 bound

pO2 = partial pressure of O2

Kd = equilibrium dissociation constant

note: if pO2 > Kd : Y=1 (this is why shape of binding curve plateau’s at 100% binding)

note: if pO2 < Kd : Y = pO2/Kd

31
Q

Myoglobin-O2 binding continued

A
  • Kd and affinity are inversely related
  • Low Kd = high binding strength (affinity)
  • Low K-1 (slow and small) = high affinity (results in more bound species)
32
Q

Myoglobin-O2 binding shifts

A

if curve shifts to right:
- Kd increases (bc bigger pO2 value)
- affinity for O2 decreases

if curve shifts to left:
- Kd decreases
- affinity for O2 increases

33
Q

Why is Mb binding simpler than Hb binding?

A
  • Mb is a single O2 binding to a single polypeptide chain
  • Hb binding equation has exponents
  • Hb shape is sigmoidal
34
Q

Hemoglobin-O2 binding equation

A

N = cooperativity (hill coefficient)

35
Q

Does Hb display positive or negative cooperativity?

A

positive cooperativity (when the binding on one ligand stimulates the binding of another)

36
Q

In Hb, the last O2 bind with _____ greater affinity than the first O2

A

100-fold

37
Q

What are the 2 reasons positive cooperativity is ideal?

A
  • it fully loads partial pressures in the lung
  • it significantly unloads partial pressure in tissues
38
Q

O2 binding properties - Hb/Mb

A
  • Hb releases O2 to tissues
  • Mb within the cells of the tissues picks it up
  • at the level where Hb releases O2, Mb binds (bc it has high affinity at those partial pressures)
39
Q

When O2 binds to DeoxyHb, how many degrees is the orientation shifted to become OxyHb?

A

15 degrees

40
Q

Hb movement at the atomic level

A

Deoxy state: iron is “puckered out”
Oxy state: iron is flush (gets pulled into the ring)

41
Q

Another name for DeoxyHb

A

T state

42
Q

Another name for OxyHb

A

R state

43
Q

Histidine in DeoxyHb vs OxyHb

A

Deoxy:
+ charged His
pKa 8 (high pKa = weak acid = stronger binding to proton)

Oxy:
neutral His
pKa 6 (normal His pKa = releases the proton)

44
Q

Relationship between O2 and protons in Hb

A
  • inversely related
  • O2 binds to Hb, protons come off
  • protons bind to Hb, O2 comes off
    overall: protons influence the affinity of Hb for O2
45
Q

pH effect: protons and O2

A
  • High proton concentrations decrease pH values
  • proton binds -> decreased pH
  • decreased pH = right shift
  • right shift = increased Kd
  • increased Kd = lower affinity for O2
46
Q

What happens when CO2 binds to Hb?

A
  • right shift
  • lower affinity O2
  • is used as a way to get more O2 to tissues
47
Q

Where does BPG bind?
What is net charge of BPG?
What does it do?
How does BPG affect affinity for O2?

A
  • central cavity of Hb
  • -5
  • stabilizes deoxyHb
  • lowers affinity for O2
48
Q

Fetal Hb has a _____ affinity for BPG and a _____ affinity for O2 when compared to maternal Hb

A
  • lower
  • higher
49
Q

T/F: Fetal Hb and maternal Hb have a similar relationship to Hb and Mb

A

TRUE

50
Q

The globin gene family is thought to have evolved through a series of…

A
  • gene duplications
  • random mutational drift
51
Q

Sick cell hemoglobin (HbS) is a balanced polymorphism with good and bad characteristics

A

bad: sickle cell disease
good: resistance to malaria

52
Q

What is the malaria parasite known as?

A

Plasmodium falciparum

53
Q

In HbS, what amino acid can substitute Glutamic acid at position 6 of beta globin chains?

A
  • Valine (non-polar substituting polar)
  • Val can fit between Leu and Phe hydrophobic pockets
  • Causes Hb to go through polymerization (distorts RBC, causes the “sickle” shape)
54
Q

Tendency to polymerize is favored by which state?

A
  • T state
55
Q

What factors favor polymerization (“sickling”)?

A
  • High proton concentration
  • Low O2
  • Low pH

Integrated Exam 3/9 (8 decks)

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