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Biochem Winter 2012 > Hemoglobin 1 > Flashcards

Hemoglobin 1 Flashcards

1
Q

Which protoporphyrin is found in heme?

A

IX

it has 4 methyl, 2 vinyl, and 2 proprioante side chains on the tetrapyrrole ring

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2
Q

Which part of rings open to bind? What do they bind to?

A

THere are two open positions on each side of the heme plane: 5th and 6th position
1 binds O2; 1 binds to side chain

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3
Q

Heme vs Hemin

A

heme (aka ferroprotoporphyrin) is +2, Hemin (ferriprotoporphyrin) is +3

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4
Q

What is Hb (ferrohemoglobin) ?

A

Oxygenated form of heme with +2 charge

ONly Ferrohemoglobin can bind Oxygen

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5
Q

What is the ferric +3 oxgenated form?

A

methemoglobin (HbM) (aka Ferrihemoglobin)-

CANNOT BIND oxygen

ferribHb

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6
Q

What is the structure of Hemoglobin?

A

A HETEROTETRAMER (2 diff types of chains, alpha and beta), circulating in RBC

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7
Q

What is the structure of Myoglobin? How many heme groups?

A

(single polypeptide with ONE heme group) A monomer in muscle cells

O2 gets transproted to muscle cells, faciliatetes O2 transport within muscle cells

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8
Q

What is Hemoglobin A?

A

Hemoglobin alpha2beta2 is normal

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9
Q

What genes can be on Chromosomes #16

A

zeta, alpha, alpha

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10
Q

What genes can be on Chromosomes #11

A

epsilon, Ggamma, Agamma, delta, beta

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11
Q

What are the gene clusters encoding the alpha and beta chains of human Hb on chromosome 16

A

zeta psi zeta, psi alpha 2, alpha 2, alpha 1, theta 1

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12
Q

GEne clusters encoding the alpha an beta chains of human Hb

A

Zeta epsilon, Ggamma, A gamma, Psibeta, , delta, beta

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13
Q

How many exons and introns does each chromsomes have on 11 and 16?

A

3 exons

2 introns

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14
Q

What are chains of Adult HbA1

A

alpha2 beta2

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15
Q

What are chains of Adult HBA2

A

alpha2 delta2

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16
Q

What is the name of fetal Hb? What are the chains?

A

HbF- alpha2 gamma2 (FETUS!)

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17
Q

What are the three embryonic HB

A

Hb Gower 1
Hb Gower 2
Hb Porland

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18
Q

Chains of Hb Gower 1

A

zeta2 epsilon2

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19
Q

Chains of Hb Gower 2

A

alpah2 epsilon2

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20
Q

Chains of Hb Portland

A

Zeta2 Gamma2

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21
Q

What does a heme group consist of?

A

an organic part, protoporyphyrin IX and iron atom.

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22
Q

Whawt does the porphyrin contain?

A

four pyrrole rings linked by 4 CH groups (methene bridges) in an alternating double-bond system.

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23
Q

What does Fe bind to?

A

four N (1-4 coordination position) int eh center of protoporphrin ring

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24
Q

What is the composition of the various normal hemoglobin molecules

A

two alpha (or alpha-like) polypeptide chains and two non-alpha polypeptide chains

Each polypeptide is the product of a separate gene, and is called the globin chain

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25
Q

how many Hemoglobin polypeptide chains are synthesized int eh life of a normal humanbeing?

A

6 distinct but chemically and functioanlly related chains

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26
Q

how many chains does each hb moleucle contin

A

either two alpha or two zeta cians

Zeta chains are ONLY syntehsized ruign first trimester of prenatal developetn

ti is replaced by alpha chain whos syntehsis contineus throughout fetal and adult life.

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27
Q

what ist the zeta chain synthesized?

A

only during first trimester of prenatal development. It is replaced by alpha chain

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28
Q

What are the four non alpha polypeptide chains

A

Beta, gamma, delta and epsilon

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29
Q

What two globins are the highest during embryonic development

A

zetaand epsilon

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30
Q

Which Hb coincides with teh shift in teh site of ERYTHROPOIESES form teh yolk sac to the liver and spleen?

A

HbF (alpha2 gamma2)

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31
Q

What is ratio of beta to gamma globin chains at time of birth

A

1/3- 1/2 beta chains compared to gamma

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32
Q

When has beta synthesis reached its maximim adult rate and gamma chain synteheis noramllay reduced to 1% or less of the toatl Hb?

A

y 6 months

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33
Q

What are F cells?

A

the small amount of HbF present in normal adults is confiend to limited population of red cells caled F cells which also contain HbA

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34
Q

What chromosome/gene responsible for Myoglobin?

A

Mb gene on chromosome #22

Few human variants
Non-essential in mice

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35
Q

HOw different are G-gamma and A gamma?

A

By one residue!
G= glycine
A= alanine

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36
Q

What is Hb1Ac

A

by post-translational modification of HbA. While a small amt is present in every individual, tlevel may be significantly eleavted in patients with diabetes mellitus whose blood glucose levels are not well-controlled

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37
Q

How is HbA1C controlled?

A

HbA1c is formed by NONENZYMATIC addition f glucose (or glucose-6-phosphate) to an alpha-amino group and termed GLYCATION

Stable adduct is formed by the Amadori rearrangment of the ALDIMINE to KETIMINE

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38
Q

HOw is HBA1c useful clinically?

A

…to determine long term glucose levels in diabetic conditions since the STABLE GLYCATION BUILDS up over time, dependent on teh circulating glucose concentrations in blood

39
Q

What percent of the globin poplypeptide chains are folded in a right handed alpha hleical conformation?

A

~75%

8 major helical segments (A-H) in both myoglobinand beta chains and 7 chains in alpha chain

40
Q

Where do non-helical segments lie between?

A

the alpha helices and ends f chain

41
Q

What does the insdie fo the globin chain consist of?

A

almost entirely non-polar resides. Helical segments exhibit a priodic pattern of polar (exterior) and non-polar residues (interior)

42
Q

Where does Myoglobin have ioznied (polar) side chains ?

A

distributed all over the surface

43
Q

What about alpha nd beta globin chians/

A

polar groups on the surface of the molecules but in addition to non-polar pathches that allow them to combin with each other to form the alpha2- beta2 tetramer.

44
Q

How does large number of charged amino acids on the surface of Hb moleule, wtith hits spherical shape affet its solubliliy?

A

makes it very soluble

45
Q

Where does the heme group reside?

A

wihtin a non-polar crevice in the chain

46
Q

Describe the Hb structure

A

heme group in non-polar crvice in the chain

Highly polar proprionicacid side chains of heme lie on surface

rest of heme group is inside where it is surrounded by non-polar residues except for TWO HISTIDINES

47
Q

What are the funtions of the 2 Histidines

A

Irone atom of the heme is directly bonded to one Histidine (F8) - PROXIMAL HIS (5th coordination positiion)

the second (E7)- termed the distal HIS. This resduces affinity of myoglobin and Hb for CO

48
Q

What ist he fucntion fo the intricate folding of Hb and Mg

A

nature’s design for an oxygen carrier. Places heme in an environment that enables it to carry oxygen reversibly

In water, ferrous heme is very rapidly oxidized to ferric form (cannot bind oxygen); the non-polar heme bidning site provided by polypeptide chain protects the ferrous state of Fe from oxidatin to Ferric form

49
Q

What are the two interactions between teh alpha and beta chains

A

Little interaction b/w the two alpha hchains and two beta chains

  1. alpha1 - beta1 contact (and identical alpha 2- Beta 2) is one tyepe
  2. Alpha1- Beta 2, or Alpha2 -beta1

Majority of them are H-phobic in nature, although ionic interactions rae important in modualating the allosteric interactions

50
Q

Hb Quarternary Struvture

A

Dimer of Dimers

1 dimer of alpha 1- alpah2

1 dimer of beta 1- beta 2

4 hemes/tetramer (one heme per subunit)

51
Q

What are two ways oxygen is transported?

A
  1. as oxygen in solution

2. in reversible chemical combination with the Hb of RBCs

52
Q

HOw much oxygen can be transported in plasma? In whole blood?

A

In plamsa, due to limited solubility of oxygen
only 0.3 mL O2/ 100mL

Whole blood, 18-20 mL O2 (60x greater b/c of the presence of Hb in teh RBs

53
Q

What is oxyhemoglobin and deoxyhemoglobin?

A

Hb comibned with O2 is oxyhemoglobin (Fe2+)

Deoxyhemoglobin (Fe2+) when oxyhemoblogin reversibly lose its O2

54
Q

What are the required physiological properties of Hb?

A
  1. Great Solubility (34% mg/100mL) or 5mM in RBC
  2. Transport large quantities of O2
  3. Uptake and release of Oxygen at apporpriate partial pressures of O2
    - must be saturated with O2What in lungs
    - -must release sufficient amounts of O2 in the tissues
  4. Good Buffer
55
Q

What gives Hb great solubility?

A
  • spherical shape

- polar groups on surface of molecule

56
Q

How much O2 can be transported

A

-18-20 mL O2/100 mL blood (cf 0.3 O2/100 mL H20)

57
Q

what kind of shape foes the hemogloglobin diss curve have?

A

sigmoidal shape

58
Q

What kind of shape does the myoglobin shpae have?

A

Hyperbolic

59
Q

order of Oxygen affinisty between Hb, Mb, cyt oxidase

A

Cyt Oxidase> Mb > Hb

60
Q

What is P50 for Mb and Hb

A

Mb = 1-5 mmHg (1-5 torr)

Hb = 26 mm Hg (26 torr)

61
Q

What is ARTERIAL Oxygen Tension

A

about 100 torrs

62
Q

What is mixed venous oxygen tesnion

A

about 50 torrs

63
Q

what is minimum oxygen tenstion for cytochrome enzymes?

A

4-5 torrs

64
Q

What is the venous circulatio oxygen tenstion?

A

about 40 mmHG, oxyhemoglobin dissociates and oxygen is readily made avaialable to cells

65
Q

What does the Hill coefficient measure?

A

The cooperativity of O2 binding

nH for Hb is about 2.8

the nH for Mb is 1.0 b/c there is single polypeptride chain and NO COOPERATIVITY

66
Q

What are the required phsyiogical properties of Hb

A
  1. Great Solubility 34% (mg/100mL) or 5mM in RBC
    spehrical shape
    polar gorups on surface of molecuels
  2. Transport large quantities of O2 (free gas solubility)); 18-20 ml O2/100 mL blood
  3. Uptake and release of oxygen at appropriate partial pressures of O2
    - must be satruated with O2 in the lungs
    - must release sufficient amounts of O2 in the tissues
  4. Good buffer
67
Q

What are two ways Oxygen is transported in the blood

A
  1. As oxygen in solution

2. in reversible chemical combination with the Hb of RBCs

68
Q

How much oxyen can plasma transprot>

A

0.3 ml O2/100 mL

69
Q

How much oxygen can WHOLE BLOOD transprot?

A

18-20 ml O2

Oxygen carryign capacity of whole blood is >60x greater than that of plamsa b/c of the presence of Hb in teh RBC

70
Q

For any given PO2, is the Y higher for myoglobin or for hemoblogin? Wha tis the P50 of each?

A

Y is higher for myoglobin (myoglobin has a higher affinity for Oxygen than does Hb);

Oxygn affinit can be characterized by qauantitiy called P50.

P50 Mb= 1-5 mm Hg (1-5 torr)

P50 Hb = 26 torrq

71
Q

What is the oxygen tentsion in venous circulation when oxyhemoblogin dissociates an doxygen in readily made available to cells?

A

40 mm Hg

72
Q

What factors decrease Hb Affinity for Oxygen?

A 
H+ (lower pH)
CO2
BPG
Cl-
Temp
73
Q

What is the effect of low pH (higher Hydrogen ion concentration) on oxygen affingty for Hb? For Mb?

A

Hb- decreases affinity

Mb- no effect

74
Q

How can you distinguish affect of CO2 vs pH on Hb oxygen dissociation cuve?

A

maintain a constant buffered pH, which both contribute to the effect

75
Q

In aerobic metabolism, how many equivalents of CO2 are produced per O2 consumed?

A

In aerobic metabolism, 0.8 equivalents of VO2 are produced per O2 consumed

About 75% of the shift caused by an increasess in pCO2 is the result of H+ generated in teh folloiwng reaction

76
Q

Some CO2 is carried by Hb to the lungs in teh form of what???

A

CARBAMATE! the unionized alpha amion groups of HB cn react reversibley with CO2

77
Q

What is the mechanism of the Bohr Effect?

A

About 0.5 H+ is taken up by Hb for each molecule of O2 that is released
Hb is an improtant physiological bufer and as a reuslt, pH of venous blood changes very little evne though in rapidly meatboizing tisseus much CO2 and acid are produced

78
Q

What type fo Hb (oxygenated or not) is able to take up H+

A

Deoxygenated!

79
Q

What three gorups int eh Hb molecule acct for much of the Borh effect?

A

Side chains of

  1. His 146 bet
  2. His 122 alpha
  3. Alpha-amino group of the alpha chain

The immediate environents become more NEGATIVELY charnged in the Deoxyhemoglobin b/c of changes in quaternary sructure induced by rlease of O2.

80
Q

If pKa higer or lower in deoxy Hb

A

pKA is higher in Deoxy Hb (affinity for proton is higher)

81
Q

Is Deoxy Hb a stronger or weaker acid

A

Weaker!

82
Q

When is BGP produced normally?

A

as an off-shoot of the glycolytic metabolism fo the red cell

Increases at high Altitudes, (low ambient O2) nd in certain metabolic conditions

83
Q

How many binding sits are tehre for DPG on Hb

A

ONly ONE binding site

84
Q

What is the net charge of DPG at physiologial level?

A

Minus 4-5 net negative charge

85
Q

When is 2,3 BPG Elevated? (what conditions)

How is 2,3, BPG maintained?

A

Anemia

Hypoxia (high altitude)

2.3 BPG lost in blood stored in citrate-glucose

Maintained with inosine via ribose

86
Q

Where is the single binding site of DPG on Hb

A

in the central cavity

87
Q

What happens when Hb is oxygenated?

A

BPG is extruede bc central cavity becomes too small

88
Q

Does HbF have stronger or weaker affinity for O2?

A

Stronger

89
Q

Why does HbF have a higher affinity for Oxygen?

A

b/c it Binds to BPG less strongly than HbA and consequently has a higher oxygen affinity in red cells

Higher O2 affinity optimizes teh transfer of oxgen form teh maternal tot eh fetal circualtion

Gamma chain has a Ser substituted for His at position 143, losing pos charge and inteactino with negative DPG

90
Q

What deos increase in Cl- concnetration affect Hb binding

A

shiftes O2 dissociation curve to teh right

Cl- ions may further brace the deoxy -state b forming additional salkt bridges

91
Q

What does an increase in Temperature do to oxygen affinity and Hb and Mb

A

shift right!

Decreases Oxygen affinity and therefore incerases the P50.

Affects BOTH myoglobin and Hb.

92
Q

Describe the characteristics of Hb alpha chain

A

like myoglobin

Alpha chain by itself has a high oxygen affinity, a HYPEBOLIC oxygen dissociation curve, and oxygen binding characteristics tha tare insensitive to pH, CO2 concentration and BPG levels

93
Q

Dexcribe characteristics of isoalted Beta chain of Hb

A

form tetramer, B4, which is called Hemoblin H

B4 entirely lacks the allosteric prperites of Hb.

The cooperative effets also disappear if the Hb molecule is split n half to alpha beta units

94
Q

Dexcribe characteristics of isoalted Beta chain of Hb

A

form tetramer, B4, which is called Hemoblin H

B4 entirely lacks the allosteric prperites of Hb.

The cooperative effets also disappear if the Hb molecule is split n half to alpha beta units

Biochem Winter 2012 (10 decks)

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