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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
What is the mechanism through which lactate affects oxygen binding in myoglobin and haemoglobin?
Allosteric control - lactate binds to an alternative site to the binding pocket
26
What is the shape of a myoglobin binding curve?
Hyperbolic
27
What is the relative O2 partial pressure when Mb becomes saturated with oxygen?
Low PO2
28
What is the symbol for oxygen partial pressure?
PO2
29
What is the unit of oxygen partial pressure?
Torr
30
What is the PO2 in the lungs?
~100 Torr
31
What is the PO2 in resting muscle?
~20 Torr
32
Why is myoglobin considered a ‘backup’ store of O2 muscle cells?
It only releases O2 when PO2 is very low
33
What is the equation for the oxygenation of myoglobin?
Mb + O2 ⇌ MbO2
34
What does the availability of O2 to cellular proteins depend on?
PO2 in the local environment and binding affinity of O2 to haemoglobin
35
What is the quaternary structure of haemoglobin?
A tetramer - 4 globin proteins associated non-covalently
36
What type of tetramer is haemoglobin?
α2β2 - 2 α-subunits and 2 β-subunits (though no beta strands, only alpha helices in secondary structure)
37
How many haem units does each globin protein contain in Hb?
1
38
What is the binding requirement of Hb?
Bind O2 in the vicinity of the lungs where the pO2 is ~100 Torr
39
What is the release requirement of Hb?
Release O2 in the vicinity of peripheral tissues where the pO2 is ~20 Torr
40
What is the shape of a Hb binding curve?
Sigmoidal
41
What is the conformation of crystals in oxy-Hb in the aerobic zone?
Needle shaped
42
What is the conformation of crystals in deoxy-Hb in the anaerobic zone?
Hexagonal plate-shaped
43
What are the states of Hb, as described in both the concerted and sequential models?
T and R
44
What is the T state of Hb?
Tense, low-activity, deoxygenated
45
What is the R state of Hb?
Relaxed, high-activity, oxygenated
46
Can subunits be in different states within 1 Hb molecule, according to the MWC/concerted model?
No - all subunits must be in the same state - T or R
47
Can subunits be in different states within 1 Hb molecule, according to the KNF/sequential model?
Yes - one substrate (O2) binding induces a T -> R conformational change in only one subunit
48
According to the MWC/concerted model, what happens to the equilibrium when each successive substrate (O2) binds?
Equilibrium shifts in favour of the R state
49
According to the MWC, concerted model, what stabilises the T form?
Inhibitors
50
According to the MWC, concerted model, what stabilises the R form?
Activators
51
What is the principle of the KNF/Sequential model?
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
What are the 2 Hb binding models?
MWC, concerted model & KNF, sequential model
53
What Hb binding model explains negative cooperativity?
the KNF, sequential model
54
Why does Hb have a sigmoidal binding curve?
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
Why do myoglobin and haemoglobin have differently shaped binding curves?
Hb displays cooperativity, but Mb does not because it is monomeric
56
What state is deoxygenated Hb likely to be in?
Low oxygen affinity state - T state
57
What state is oxygenated Hb likely to be in?
The high oxygen affinity state - R state
58
What is the low oxygen affinity state?
T state
59
What is the high oxygen affinity state?
R state
60
What are the similarities between Mb and Hb?
Oxygen binds to haem, shfit from dull to brought red during O2 binding, allosteric control by other molecules such as lactate
61
What are the differences between Hb and Mb?
tetramer vs monomer, sigmoidal vs hyperbolic binding curve, transport molecule vs tissue storage
62
does myoglobin display the Bohr Effect?
No - as Mb is monomeric, allosteric binding of CO2 and H+ mean little change in Haem that affect O2 binding .
63
Is Hb a homotetramer of heterotetramer?
Heterotetramer - it has 2 different a- and b- globins
64
How does BPG affect myoglobin?
it doesn’t. cannot bind and cause effects like it does to Hb
65
where does carbon monoxide bind to haemoglobin?
to the haem group as a competitive substrate to oxygen
66
Is myoglobin allosteric?
No - is not under allosteric control because it is monomeric
67
Why is Haem located in a hydrophobic binding pocket?
To prevent water oxidising Fe2+ to Fe3+

BIOC192 2022 (37 decks)

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