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Flashcards in Hemoglobin and myoglobin Deck (23)
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1
Q

Polar gases (e.g. HS and NH3) are more soluble in water.

Nitrogen, O2, and CO2 are

A

nonpolar

insoluble in water; they’re transported via hemoglobin and myoglobin

2
Q

What causes hemoglobin (Hb) to bind O2 in the lungs but release it at the tissue?

A

Lungs have a higher pH

At the tissues, Hb picks up CO2 and H+ to deliver back to the lungs

3
Q

Which binds O2 more tightly - Hb or Mb?

A

Mb binds to O2 more tightly

Its affinity is unaffected by pH change or modifying molecules

4
Q

Heme is a prosthetic functional group in both Hb and Mb. What is its structure?

A

Protoporphyrin IX ring with a ferrous ion (Fe2+) at its center.

The Fe2+ makes 4 bonds to the ring, a 5th bond to a His, and a 6th bond to a single molecule of O2. It can move in or out of the plane of hte ring

5
Q

While both Mb and Hb are similar and have a heme group in the center, what is thei rmajor difference?

A

Mb is a monomer

Hb is a heterotetramer: 2 a-globin subunits, 2 B-globin subunits ; each subunit has a central heme group

6
Q

equilibrium dissociation constant (Kd)

A

[ligand] at which half of the available ligand binding sites are occupied.

It’s essentially Km - the higher Kd, the lower affinity

7
Q

The binding curve for Mb is ___, which suggests that Mb has

A

hyperbolic, sugesting that Mb has only one binding site for its ligand (O2).

As the pressure of O2 increases, binds very rapidly to Mb until binding sites become limiting.

8
Q

The Kd of myoglobin is called

A

P50

9
Q

The shape of Hb’s binding curve is ___, indicating ___

A

sigmoidal, indicating cooperative binding for O2 subunits

Binds slow at first, but as the O2 pressure increases, binding rate increases until they all get filled

10
Q

A curve shifted to the right signifies

A

higher Kd –> weaker affinity

That’s why Hb’s curve is shifted to the right

11
Q

Hb’s tense vs relaxed state

A

R state: The His is positioned such that the Fe2+ is in the plane of the ring and has a high affinity for binding O2

T state: The His is positioned such that it pulls the Fe2+ out of plane; lower O2 affinity

12
Q

__ bonds are broken when Hb switches from R state to T state.

A

8 bonds = 6 are interchain between diff subunits; 2 are intrachain

13
Q
A
14
Q
A
15
Q

How does the transition from T to R state occur?

A

Each O2 that binds one of the heme groups breaks 2 of the ionic bonds, making it easier for the next Fe2+ to bind O2

This goes on until all 4 subunits bound an O2

16
Q

What molecules affect O2 binding in Hb and how?

A
  • Increases Hb’s affinity for O2
    • O2
    • CO
  • Decreases affinity
    • H+ (acidity)
    • CO2
    • BPG

Things that increase affinity shift the curve to the left; decreasing affinity shfits right

17
Q

Why does H+ and lower pHs decrease Hb’s O2 binding affinity?

A

It favors ionization and strengthens the ionic interactions of the T state

18
Q

When O2 enters the plasma from the tissues, it can have one of 3 fates:

A
  • 10% dissolves in the plasma and goes to the lungs
  • In the RBC, 23% forms an adduct with hemoglobin –> carbaminohemoglobin
  • In the RBC, ~70% is converted with water into bicarbonate (HCO3-) and H+ by carbonic anhydrase.
    • –> HCO3- and H+ are transported to the plasma, then lungs where they’re converted back to CO2 and water
    • H+ acidifies the system to decrease O2 binding affinity
19
Q

How does CO cause flu-like symptoms (headache, nausea, vertigo), seizures, coma, and death?

A
  • Binds Hb MUCH more tightly than O2 and doesn’t let go
  • Stabilizes the R state, which prevents O2 from being released into the tissue

Tx: pure oxygen

20
Q

Methemoglobinemia

A
  • Fe2+ oxidation to Fe3+ –> methemoglobin (MetHb), which won’t carry O2
  • Death; Infants will get blue baby syndrome
  • Causes:
    • Exogeneous oxidizing drugs (benzocaine, dapsone) increases
    • Nitrate-containing compounds (bismuth nitrate) or well water containing ntirates
21
Q

What is the strongest modifier of O2 binding affinity?

A

2,3-Bisphosphoglycerate (BPG) from glycolysis

  • Decreases affinity of Hb for O2 so tissues can work
22
Q

What happens when someone living at sea level travels to the mountains?

A

Their BPG is too low –> Hb is only 87% saturated in the lungs, so not enough O2 will get into the tissues

Tiredness, dizziness, nauseous

After a few days, you adapt by increasing you BPG

23
Q

Adult hemoglobin vs fetal

A

Adult: 2 a-globin subunits and 2 B-globin

Fetal: 2 a-globin subunits and 2 y-globin subunits

  • y-subunit: 2 serines replace 2 His in the B subunits –> HbF is lower affinity for BPG and thus a higher affinity for O2

That way, if mom experiences a rapid decrease in oxygen, fetus will be spared