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BIOC192 2022 > lecture 7 - oxygen transport: haemoglobin vs myoglobin > Flashcards

lecture 7 - oxygen transport: haemoglobin vs myoglobin Flashcards

1
Q

What is myoglobin?

A

A haem protein that stores and supplies oxygen to cardiac and smooth muscle.

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2
Q

The amount of myoglobin in human muscle allows for how much intense activity?

A

7 seconds

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3
Q

After myoglobin has released all of its available oxygen into the muscles, where must oxygen be sourced from?

A

The lungs

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4
Q

Where does haem bind to myoglobin?

A

In the globulin fold, which provides a pocket for haem binding

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5
Q

What is haem?

A

A prosthetic group/cofactor

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6
Q

What is the structure of a haem unit?

A

4 pyrrole rings connected in a plane with a central Fe2+ ion that can bond to protein (haemoglobin of myoglobin) and O2

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7
Q

What is the primary structure of myoglobin?

A

Made up of ~150 amino acids

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8
Q

What is the secondary structure of myoglobin?

A

Made up of 8 alpha-helices (named A to H), and connecting loops (AB, BC …)

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9
Q

What is the tertiary structure of the myoglobin protein?

A

Globin fold with a hydrophobic pocket

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10
Q

Where does haem bind on myoglobin?

A

His F8 (Histidine, the eighth amino acid in Helix F)

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11
Q

What is the location of His F8 on myoglobin?

A

A Histidine residue, the eighth amino acid on the F helix

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12
Q

What is the quaternary structure of myoglobin?

A

Is a monomeric (single polypeptide) chain so doesn’t technically have a quaternary structure

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13
Q

What is the structure of haem, when bound to oxygenated myoglobin?

A

4 pyrrole rings linked together in a plane with 4 coordinate bonds to Fe (II) via N atoms. The Fe then has two other coordinate bonds to O2 and the nitrogen atom of His F8 on myoglobin

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14
Q

What gives haem its characteristic red colour?

A

Molecular electronic orbitals of Fe2+ absorb complementary/opposite wave lengths of light

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15
Q

Is the binding of oxygen to haem reversible or irreversible?

A

Reversible

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16
Q

What part of the myoglobin protein does O2 break and reform interactions with?

A

His E7

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17
Q

What is the relationship expressed by the Beer-Lambert Law?

A

There is a linear relationship (direct proportionality) between the concentration and absorption of a solution

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18
Q

What is the colour of HbO2?

A

bright red

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19
Q

What is the colour of Hb (deoxyhaemoglobin)?

A

Dull red

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20
Q

What is the symbol for oxyhemoglobin?

A

HbO2

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21
Q

What is the symbol for deoxyhemoglobin?

A

Hb

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22
Q

How does His E7 affect O2 binding on myoglobin?

A

Distorts binding of gas molecules to Haem, reducing the binding affinity of oxygen to myoglobin, making it easier to release oxygen into a muscle cell.

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23
Q

How does lactate affect oxygen binding to myoglobin?

A

Reduces mygolbin’s affinity to myoglobin allosterically, shifting the binding curve to the right

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24
Q

How does lactate in muscles affect oxygen availability?

A

Lactate builds up in muscles promoting oxygen release from myoglobin, increasing O2 availability for respiration

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25
Q

What is the mechanism through which lactate affects oxygen binding in myoglobin and haemoglobin?

A

Allosteric control - lactate binds to an alternative site to the binding pocket

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26
Q

What is the shape of a myoglobin binding curve?

A

Hyperbolic

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27
Q

What is the relative O2 partial pressure when Mb becomes saturated with oxygen?

A

Low PO2

28
Q

What is the symbol for oxygen partial pressure?

A

PO2

29
Q

What is the unit of oxygen partial pressure?

A

Torr

30
Q

What is the PO2 in the lungs?

A

~100 Torr

31
Q

What is the PO2 in resting muscle?

A

~20 Torr

32
Q

Why is myoglobin considered a ‘backup’ store of O2 muscle cells?

A

It only releases O2 when PO2 is very low

33
Q

What is the equation for the oxygenation of myoglobin?

A

Mb + O2 ⇌ MbO2

34
Q

What does the availability of O2 to cellular proteins depend on?

A

PO2 in the local environment and binding affinity of O2 to haemoglobin

35
Q

What is the quaternary structure of haemoglobin?

A

A tetramer - 4 globin proteins associated non-covalently

36
Q

What type of tetramer is haemoglobin?

A

α2β2 - 2 α-subunits and 2 β-subunits (though no beta strands, only alpha helices in secondary structure)

37
Q

How many haem units does each globin protein contain in Hb?

A

1

38
Q

What is the binding requirement of Hb?

A

Bind O2 in the vicinity of the lungs where the pO2 is ~100 Torr

39
Q

What is the release requirement of Hb?

A

Release O2 in the vicinity of peripheral tissues where the pO2 is ~20 Torr

40
Q

What is the shape of a Hb binding curve?

A

Sigmoidal

41
Q

What is the conformation of crystals in oxy-Hb in the aerobic zone?

A

Needle shaped

42
Q

What is the conformation of crystals in deoxy-Hb in the anaerobic zone?

A

Hexagonal plate-shaped

43
Q

What are the states of Hb, as described in both the concerted and sequential models?

A

T and R

44
Q

What is the T state of Hb?

A

Tense, low-activity, deoxygenated

45
Q

What is the R state of Hb?

A

Relaxed, high-activity, oxygenated

46
Q

Can subunits be in different states within 1 Hb molecule, according to the MWC/concerted model?

A

No - all subunits must be in the same state - T or R

47
Q

Can subunits be in different states within 1 Hb molecule, according to the KNF/sequential model?

A

Yes - one substrate (O2) binding induces a T -> R conformational change in only one subunit

48
Q

According to the MWC/concerted model, what happens to the equilibrium when each successive substrate (O2) binds?

A

Equilibrium shifts in favour of the R state

49
Q

According to the MWC, concerted model, what stabilises the T form?

A

Inhibitors

50
Q

According to the MWC, concerted model, what stabilises the R form?

A

Activators

51
Q

What is the principle of the KNF/Sequential model?

A

One substrate (O2) binding induces a T -> R conformational change in only 1 subunit. This conformational change influences the neighbouring subunits (cooperativity) making them more likely to bind substrate.

52
Q

What are the 2 Hb binding models?

A

MWC, concerted model & KNF, sequential model

53
Q

What Hb binding model explains negative cooperativity?

A

the KNF, sequential model

54
Q

Why does Hb have a sigmoidal binding curve?

A

Hb displays cooperativity - the binding of one O2 molecule with one Haem/globin facilities the binding of additional O2 to other binding sites/haem/globin

55
Q

Why do myoglobin and haemoglobin have differently shaped binding curves?

A

Hb displays cooperativity, but Mb does not because it is monomeric

56
Q

What state is deoxygenated Hb likely to be in?

A

Low oxygen affinity state - T state

57
Q

What state is oxygenated Hb likely to be in?

A

The high oxygen affinity state - R state

58
Q

What is the low oxygen affinity state?

A

T state

59
Q

What is the high oxygen affinity state?

A

R state

60
Q

What are the similarities between Mb and Hb?

A

Oxygen binds to haem, shfit from dull to brought red during O2 binding, allosteric control by other molecules such as lactate

61
Q

What are the differences between Hb and Mb?

A

tetramer vs monomer, sigmoidal vs hyperbolic binding curve, transport molecule vs tissue storage

62
Q

does myoglobin display the Bohr Effect?

A

No - as Mb is monomeric, allosteric binding of CO2 and H+ mean little change in Haem that affect O2 binding .

63
Q

Is Hb a homotetramer of heterotetramer?

A

Heterotetramer - it has 2 different a- and b- globins

64
Q

How does BPG affect myoglobin?

A

it doesn’t. cannot bind and cause effects like it does to Hb

65
Q

where does carbon monoxide bind to haemoglobin?

A

to the haem group as a competitive substrate to oxygen

66
Q

Is myoglobin allosteric?

A

No - is not under allosteric control because it is monomeric

67
Q

Why is Haem located in a hydrophobic binding pocket?

A

To prevent water oxidising Fe2+ to Fe3+

BIOC192 2022 (37 decks)

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