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biochemistry Jonklaas > Test 2: Hemoglobin and Myoglobin > Flashcards

Test 2: Hemoglobin and Myoglobin Flashcards

1
Q

where is myoglobin located

A

in muscles

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2
Q

where is hemoglobin located

A

in red blood cells

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3
Q

describe the Hb subunits

A

4 subunits that are homologous to MB

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4
Q

which structure was the 1st one discovered by x ray cyrstallography

A

myoglobin

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5
Q

how man helices does myglobin have

A

8 alpha helices labeled a through H

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6
Q

what are the differences between myoglobin and hemoglobin

A
  • myoglobin is a monomer, Hb is a tetromer of 4 Mb like homo subunits
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7
Q

describe the Hb subinits

A

2 alpha globin and 2 beta globin

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8
Q

who solved Hb structure

A

Max perutz

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9
Q

what is heme

A

protoporphyrin IX + Fe+2 + Mb

  • in Hb each subinits has a heme proesthetic group
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10
Q

what does it mean by prosthetic group

A

it means the non amino acid portion of a protein that is required

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11
Q

what does the heme group do in hemoglobin

A

in each of the 4 subinits it binds oxygen in the lungs and releases it in tissues

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12
Q

what does the heme group do in Mb

A

stores and releases oxygen for muscle activity

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13
Q

what does the Fe+2 do in the heme

A

responsible for binding to oxygen and it switches between different oxidation states

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14
Q

what doe His E7 do the binding pcoket of heme

A
  • forces any ligand to bind to Fe(II) at a bent angle
  • bent allows for O2 ot bind FE(II) on heme reversibily
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15
Q

what is holding the heme in place

A

hydrophobic interactions

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16
Q

what bond is holding the heme in place to each Hb subinits/ Mb in proximal His

A

coordinate covalent bond to His F8

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17
Q

which His is directly binded to the Iron

A

His F8 proximal

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18
Q

what does His 8 do

A
  • bonded to iron
  • anchor iron
  • positions the heme group
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19
Q

what is the role of His E7

A
  • does not directly bind to the iron
    -stabilzie O2 molecule
  • reduces harmul molecules like CO
  • binds O2 bent to stabilize it
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20
Q

pls describe CO poisioning

A
  • CO has a strong affinity for Fe+2 and when binded linerly and it prefers linear binding it is 20,000 stronger than O2
  • but steric hinderance of His e7 reduces the effect
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21
Q

why is CO, CN, NH3, NO, and H2S bad

A

bind in place of ocygen on a heme in complex IV of ETC

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22
Q

what happens when the O2 gets oxidized to FE+3 in Hb and Mb

A
  • ## gives Methemoglobin ( brown)
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23
Q

what is important about MetHB and MetMB when binding

A
  • they can’t bind O2
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24
Q

what enzyme can reduce Fe+3 to Fe+2

A

diaphorase

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25
Q

how can Fe+3 be formed

A
  • 2 hemes w/out a protein come and autoxidize through intermediate ( O2 bridge between two Fe(II) centers)
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26
Q

what prevents FE+3 from being formed

A
  • bulky groups around heme
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27
Q

what is the Mb O2 binding eqiation

A

Mb+ O2 = MbO2

28
Q

what is the equation for the fraction of Mb bound to O2

A

Y = O2/ O2= Kd

29
Q

what is Kd in the Mb fraction equation

A

Kd is the dissociation constant
affnity of Mb for oxygen

30
Q

low Kd means what and High kd means what

A

low kd = higher affinity
high Kd= lower affinity

31
Q

what curve does Myoglobin show

A

hyperbolic curvewhat

32
Q

what is the 1/2 saturaiton of Mb

A

p50( 1/2 sat ) = 2.8 torr

33
Q

does Mb give a lot or less O2

A

little O2 over a normal physiolgogical range

34
Q

what happens with O2 in Mb during exercise

A
  • O2 doesnt transport fast enough
  • PO2 falls low allowing Mb to release O2
  • YO2 drops from 0.97 to 0.91
35
Q

what does each Hb subinit have

A

heme and O2 binding site

36
Q

why does Hb transport O2 from lungs to tissues

A

because O2 diffusion in larger animals is poor so they need Hb to do it

37
Q

what is the structure of Hb

A

dimer of 2 alpha and 2 beta
(ab)^2 dimer

38
Q

what happens when O2 binds to Hb

A

there is a conformational change in the quaternary strucrure and Mb does not have this

39
Q

what are the 2 states of Hb

A

deoxy- tense T state
oxy - R state (relaxed)

40
Q

what does the switch between states invovle

A

15o twist
- rotation between ab dimer pairs

41
Q

describe the affinity for T and R state

A
  • T = low O2 affinity
  • R = high O2 affinity
42
Q

how does O2 binding Hb effect T to R state switch

A
  • communication cannot be electronic bc hemes are too far apart
43
Q

what AA is present in T state

A

lys 82

44
Q

what is the structural change that happens during T state

A
  • heme groups are slightly distored bc iron is pulled out of the plane
  • 4 subinits are more tight together
45
Q

structural change in R state

A
  • o2 pulls the iron INTO the plane
  • salt bridges are broken allowing the subunit units to move freely
46
Q

why is iron pulled out of the plane in the porphyrin ring

A

iron is in a high spin state making it too large to fit within the plane

47
Q

why is iron pulled into the plane for R state

A
  • change int he iros electronic congiruation, reducing its size and allows it to move in
48
Q

how does His f8 move in T and R

A
  • T pulls slugly downward
    R- pulls it along with it caues a domino effect causing a shift in th eentire protein structure
49
Q

what bonds are present in T state

A
  • H bonds and ion pairs (Not present in R state)
50
Q

why is it difficult for T to bind the 1st O2

A

His E7 and Val E11 block access to heme
- HIs E7 is connected to the iron and t is at bent angle

51
Q

how many angstroms is FE+2 out in T state

A

0.6

52
Q

what happens when the 1st O2 binds

A

pulls FE+2 back itno the heme plane wich is R state

53
Q

what does His F8 pull

A

the F helix like a lever and then it movesw

54
Q

what happens when F helix moves

A

ab pairs rotate with respect to each other meaning a change in the Quat structure of Hb

55
Q

what happens in the A1-b2 and a2-b2 binding

A

equivalent h bonds and ion pair act like knobs

56
Q

when we are shiftig between T to R what happens to His e7 and val e11

A

move out of the way so theo2 has more access to the heme

57
Q

where does the energy to breka the ion pairs and H bonds in the t state come from

A

the energy in the formation of Fe-o2 bond formation drives the transition from T to R

58
Q

what mechanism did we jsut describe

A

the perutz mechanism

59
Q

Hb in r state has what curveq

A

sigmoidal because we have +ve cooperativity ( Rstate and T state binding curve)

60
Q

what is positive cooperativity

A

binding of a molecule increases the likelihood that additional molecules will bind to other binding sites

61
Q

pls expain the + cooperativity

A
  • low affinity T state o2 can’t bind
    2. 1st o2 binds to one of the 4 subunits caues the ionic = hbonds to disrupt
  • transition to R state due to the hemoglobin to move in and causes the other subinits to bind
    4. the curve is then sigmoidal
62
Q

whyis Hb an ideal O2 transport protein

A

S shaped YO2 curvew

63
Q

what is the p50 for Hb

A

26 torr

64
Q

in lungs what does the p02 =

A

100 torr

65
Q
A

biochemistry Jonklaas (8 decks)

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