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Biochemistry > Hemoglobin > Flashcards

Hemoglobin Flashcards

1
Q

T/F Oxygen is soluble in water

A

F, it isn’t that’s why you need hemoglobin

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2
Q

Major form of hemoglobin in adults

A

Hb A

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3
Q

Hb A composition

A

4 polypeptide chains (2 alpha and 2 beta held together via non-covalent interactions)
. Each chain has regions of alpha-helical structure and hydrophobic heme binding pocket

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4
Q

Hemoglobin tetramer

A

Composed of 2 identical dimers, alpha-beta 1 and 2
. Chains in dimer held by hydrophobic interactions
. Dimers held together by polar bonds

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5
Q

Deoxyhemoglobin

A

. T (taut) structure
. 2 alpha-beta dimers interact via ionic and H bonds that constrain movement of polypeptide chain
. Low oxygen affinity form

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6
Q

Oxyhemoglobin

A

. R (relaxed) structure
. Binding of O2 to hemoglobin causes rupture of some polar bonds between alpha-beta dimers allowing movement
. High-oxygen-affinity form

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7
Q

T/F there is a small amount of oxygen dissolved in plasma blood

A

T, but it is physiologically insignificant

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8
Q

How many O2 molecules can Hb bind?

A

4, one at each heme

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9
Q

Pulse oximetry

A

Noninvasive, indirect method of measuring O2 saturation of arterial blood based on light absorption difference by R and T Hb

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10
Q

Partial pressure needed to achieve half-saturation of binding sites (P50)

A

26 mmHg for Hb, 1 mmHg for myoglobin

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11
Q

How many O2 molecules can myoglobin carry?

A

1

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12
Q

Myoglobin O2-dissociation curve shape and why

A

Hyperbolic shape reflecting that myoglobin reversible binds a single molecule of O2

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13
Q

What is Mb designed to do?

A

Bind O2 released by Hb at low pO2 in muscle

. Releases o2 w/in muscle in response for O2 demand

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14
Q

When is oxygen dissociation curve Hb steepest and why?

A

. At O2 concentrations that occur in tissue

. Permits O2 delivery to respond to small changes in pO2

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15
Q

What shape O2-dissociation curve for Hb?

A

Sigmoidal, indicating subunit cooperative binding

. Allows unloading at areas of low pO2

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16
Q

Cooperative binding

A

. Binding of an O2 molecules at 1 heme inc. O2 affinity of remaining heme groups in same tetramer
. Heme-heme interaction

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17
Q

Allosteric effectors

A

. affects the ability of Hb to reversible bind to O2
. PO2
. PH in environment
. PCO2
. 2,3,-BPG
. Bind to one site on Hb and affect binding of O2 to heme groups at other sites on Hb

18
Q

T/F Myoglobin is NOT effected by allosteric effects

A

T

19
Q

Net effect of structural changes of heme groups

A

Affinity of Hb for the last O2 bound is 300 times greater than 1st bound O2

20
Q

Where is O2 loaded and unloaded onto Hb

A

. Loaded in lungs where [O2] is high and Hb is saturated

. Unloaded in peripheral tissues for oxidative metabolism

21
Q

Bohr effect

A

. Release of O2 from Hb enhanced when pH is lowered/when there is increase pCO2
. Dec. pH and inc. pCO2 shift curve right to stabilize T form
. Inc. pH and dec. pCO2 shift the curve to the left and stabilize R

22
Q

concentration of H and CO2 in capillaries of metabolically active tissues compared with alveolar capillaries of lungs

A

Concentration is higher in metabolically active tissues than alveolar capillaries where CO2 is released into air

23
Q

Carbonic anhydrase

A

Coverts CO2 to carbonic acid

CO2 + H2O -> H2CO3 -> spontaneously lose H to become HCO3 + H

24
Q

Major blood buffer

A

Bicarbonate

25
Q

How does Bohr effect happen?

A

Ionizable groups (His side chains) that have higher pKa in deoxy Hb than in oxyHb
. Inc. in [protons] and decrease in pH causes ionizable groups to be protonated and able to form ionic bonds or salt bridges
. Stabilize deoxyHb decreasing O2 affinity

26
Q

When inc. protons and lower pO2 the equilibrium is shifted _____ favoring

A

Right, deoxyHb

27
Q

When inc. in pO2 or dec. protons, the equilibrium is shifted ____ favoring ____

A

Left, oxyHb

28
Q

2,3-BPG

A

. Most abundant organic P in RBCs
. Concentration of 2,3-BPG in rbcs is approx. equal to concentration of Hb
. Synthesized from intermediate in glycolysis

29
Q

How does 2,3 BPG bind and what does binding do?

A

. Decreases O2 affinity by binding to T Hb but not R Hb

. Stabilizes T confirmation

30
Q

Where does 2,3-BPG bind?

A

. Pocket formed by 2 beta-globin chains in center of T form tetramer
. Pocket has many pos. Charged amino acids that form ionic bonds w/ Neg. charged P groups on 2,3-BPG

31
Q

How is 2,3-BPG expelled from Hb?

A

Oxygenation

32
Q

Which does oxygen-dissociation curve move w/ 2,3-BPG

A

. Presence reduces Hb affinity shifting curve right

. Helps release O2 in tissue partial pressure

33
Q

When does [BPG] inc?

A

. In response to chronic hypoxia (COPD or high altitudes)

. Chronic anemia

34
Q

How long does it take rbcs to restore depleted 2,3-BPG after being transfused from a bank?

A

6-24 hours

35
Q

2 ways CO2 is transported as:

A

. bicarbonate

. Carbamate

36
Q

How is carbamate carried?

A

. Bound to N-terminal group of Hb forming carbaminoHb

Hb-NH-COO + H

37
Q

How does CO2 affect oxygen dissociation curve?

A

. Stabilizes T form dec. O2 affinity shifting curve right

38
Q

WHen does CO2 dissociate from Hb?

A

Released in breath

39
Q

CO binding to Hb

A

. High affinity
. Binds to 1+ heme sites shifting Hb to R conformation and remaining sites bind O2 that don’t have CO
. Called carboxyHb
. Shifts curve left and changes from sigmoidal to hyperbola
. Affect Hb unable to release O2 in tissues

40
Q

How many times greater is CO affinity over O2 affinity?

A

220 time greater

41
Q

How does CO toxicity result?

A

. Combo of tissue hypoxia and direct CO-mediated damage at cellular level

42
Q

How is CO toxicity treated?

A

100% O2 at high pressure to dissociate CO from Hb

Biochemistry (64 decks)

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