Lecture 12 - O2 Transport and Storage by Haemoglobin and Myoglobin Pt. II Flashcards

1
Q

What does the haem look like in deoxyhaemoglobin?

A

dished

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2
Q

What happens to the haem upon the formation of oxyhaemoglobin?

A

oxygen flattens the haem and pulls HisF8 and helix F toward the binding site

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3
Q

What will weaken oxygen binding?

A

anything that keep helix F away from the binding site

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4
Q

What are conformational changes?

A

shifts in the orientation of protein secondary elements

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5
Q

What are some mechanisms that work together to shift between T and R states

A
  • Allosteric regulation
  • pH
  • Physiological/genetic changes
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6
Q

What can change the balance of T & R state haemoglobin?

A

Conformational changes

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7
Q

When is co-operativity prominent?

A

In the presence of allosteric inhibitors of binding

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8
Q

What stabilises the T-state?

A

allosteric inhibitors BPG, CO2, and H+. this allows better cooperativity

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9
Q

What state is ‘stripped’ haemoglobin predominantly in in the absence of inhibitors?

A

R-state, shows little co-operativity

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10
Q

What is Haemoglobin allosterically controlled by?

A

2,3 - biphosphoglycerate (BPG)

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11
Q

How does BPG bind to deoxy-Hb?

A

electrostatic interactions

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12
Q

What does BPG do to Hb?

A

stabilises Hb in the deoxy T-state reducing oxygen affinity

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13
Q

How is BPG produced?

A

during respiration in peripheral tissues

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14
Q

What does BPG promote?

A

oxygen release where it is required

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15
Q

What does CO2 do to oxygen affinity?

A

reduce oxygen affinity

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16
Q

How does CO2 reduce the affinity of haemoglobin for O2?

A

The Bohr effect - elevated CO2 and lower pH (higher [H+]) in metabolising tissues both reduce the affinity of haemoglobin for O2

17
Q

How does lower pH decrease oxygen binding affinity?

A

favours protonation and stronger ionic interactions in the T-state

18
Q

How does CO2 reduce oxygen binding affinity directly?

A

binds to amino-terminal amino group stabilising the deoxy-Hb conformation in T-state

19
Q

What alternate isoforms of haemoglobin does Foetal haemoglobin have?

A

zeta equivalent to alpha, epsillon, and gamme equivalent to beta

20
Q

What differs between foetal and normal haemoglobin?

A

Different amino acid sequences of normal haemoglobin subunits alter their oxygen binding properties

21
Q

Does foetal or normal haemoglobin hold oxygen tighter?

A

foetal

22
Q

Why can foetal haemoglobin bind oxygen more tightly?

A

It is less sensitive to BPG

23
Q

Why is foetal haemoglobin less sensitive to BPG?

A

the gamma chain replaces the beta chain in foetal Hb. The gamma chain has a serine place of a histidine in the BPG binding site.

24
Q

What causes sickle cell haemoglovin?

A

The beta E6V variant of haemoglobin

25
Q

What is the consequence of sickle cell haemoglobin?

A

Sickle shape red blood cells get stuck in capillaries

26
Q

What is one benefit of sicle cell haemoglobin?

A

resistance to malaria

27
Q

What does the beta E6V variant of haemoglobin do?

A

enables an abnormal hydrophobic interaction between Hb tetramers

28
Q

When is the beta E6V variant particuarly exposed?

A

when in the deoxy haemoglobin form, as this causes polymerisation of Hb into chains that distort the RBC’s

29
Q

How does CRISPR-based therapy treat Sickle cell disease?

A

Up-regulation of foetal haemoglobin replaces faulty normal haemoglobin production

30
Q

How does Voxelotor treat sickle cell disease?

A

It is an oxygen affinity modulator, stabilises the oxygenated state, increases oxygen affinity