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Cellular Composition > Proteins and ligands > Flashcards

Proteins and ligands Flashcards

1
Q

What is the function of myoglobin?

A

Stores (binds and releases) oxygen in the muscles

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2
Q

What kind of protein are haemoglobin and myoglobin?

A

Globular

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3
Q

What is the structure of foetal haemoglobin?

A
  • made up of two alpha chains and two gamma chains
  • Each chain binds a haeme group
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4
Q

What is the general structure of myoglobin?

A

Formed from one chain and one haeme group

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5
Q

What sort of coordinate complexes can Fe2+ form?

A

Penta and hexa

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6
Q

What type of ligand is haeme?

A

Polydentate

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7
Q

What are the 6 ligands haeme binds to?

A
  • 4 haeme nitrogens
  • 1 His side chain
  • 1 O2
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8
Q

What technique can be used to measure oxygen binding to myoglobin and haemoglobin?

A

A spectrophotometer

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9
Q

How does spectrophotometry allow oxygen binding to myoglobin and haemoglobin to be measured?

A
  • when bound to haeme the Fe2+ has some Fe3+ character
  • The change in electronic configuration of Fe2+ on binding O2 results in a colour change
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10
Q

What shape is the oxygen binding curve for haemoglobin?

A

Sigmoidal

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11
Q

What shape is the oxygen binding curve for myoglobin?

A

Rectangular hypobola

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12
Q

What does a small Kd mean in terms of binding and affinity?

A

A small Kd means tighter binding to a protein and a stronger affinity

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13
Q

What is Kd of a protein?

A

The concentration of ligand at which half the protein is bound to ligand

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14
Q

What represents the fraction of a protein bound to ligand?

A

Y

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15
Q

How can you calculate Y?

A

[Ligand]/Kd x [Ligand]

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16
Q

What is the effect of the binding curves of myoglobin and haemoglobin on O2 release?

A

The sigmodial shape of the Hb binding curve allows Hb to deliver around 10x as much O2 to exercising tissues as Mb

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17
Q

How many structural forms of Hb are there?

A

2

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18
Q

What are the two structural forms of Hb?

A

Deoxyhaemoglobin (Tense) and oxyhaemoglobin (Relaxed)

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19
Q

Which form (tense or relaxed) of Hb has a low affinity for O2 ?

A

Deoxyhaemoglobin (Tense)

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20
Q

How is cooperativity diagnosed?

A

Using a Hill plot

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21
Q

What feature does binding of O2 to haemoglobin show?

A

Positive cooperativity

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22
Q

What is positive cooperativity?

A

Binding of O2 to one subunit increases the bidning affinity of the other sites

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23
Q

What value of n from a Hill plot indicates no cooperativity?

A

1

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24
Q

What is P50?

A

The concentration of O2 required to occupy half the binding sites

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25
Q

Give a compound which can bind to Hb allosterically

A

2,3-bisphosphoglycerate

26
Q

Compare the binding of 2,3-bisphosphoglycerate in deoxy and oxy hb

A

Binds more tightly to deoxy-Hb than oxy-Hb

27
Q

When is 2,3-BPG over produced?

A

In response to:

  • high altitude
  • airway obstruction
  • congestive heart failure
28
Q

What is the effect of 2,3-BPG on T-state (deoxy) Hb?

What is the effect of this?

A

Stabilises T-state Hb. This increases the P50

29
Q

What are the structural similarities between haemoglobin and myoglobin?

A
  • Both can bind, transport, and detoxify nitric oxide (NO)
  • Both are globular proteins with tightly packed cores
  • Both contain haem
30
Q

What roles does nitric oxide have in the body?

A

It is a vasodilator and inhibitor of platelet aggregation

31
Q

What is the effect of binding of O2 on the atomic radius of Fe2+ in haeme?

A

When O2 is bound the Fe2+ has a smaller atomic radius

32
Q

Why does O2 in oxyhaemoglobin form a H bond with another His side chain?

A

It stabilises the O2-Fe2+ interaction

33
Q

What is the formula for Kd?

A

[protein] x [ligand]/ [protein bound to ligand]

34
Q

Compare the P50 of myoglobin and haemoglobin binding to O2

A

Myoglobin has a P50 of 2 tor whilst haemoglobin has a P50 of 26 tor

35
Q

How does binding of O2 to one subunit of haemoglobin affect the Kd of the other subunits of haemoglobin?

A

Reduces Kd

36
Q

What is on the y axis of a Hill plot?

A

Log (Y/1-Y)

37
Q

What is on the x axis of a Hill plot?

A

log(pO2)

38
Q

Is deoxy-Hb referred to as tense or relaxed?

A

Tense

39
Q

Does relaxed Hb have a high or low affinity for oxygen?

A

High

40
Q

Which form of haemoglobin is favoured when the [O2] is low?

A

T state

41
Q

Which form of Hb is favoured when [O2] is high?

A

R state

42
Q

Which form of Hb binds O2 more tightly?

A

R state

43
Q

What happens to the equilibrium between T state and R state Hb when O2 binds?

A

The equilibirum shifts from favouring the T state to favouring the R state

44
Q

Which state of Hb does 2,3-BPG bind more tightly to?

A

T state

45
Q

What happens to oxygen release if [2,3-BPG] is increased?

A

More O2 is released

46
Q

Does foetal Hb bind to 2,3-BPG as tightly as Hb?

A

No

47
Q

Where does 2,3-BPG bind on Hb?

A

At the interface of β1 and β2 subunits

48
Q

Which form of Hb do H+ preferentially bind to?

A

deoxy/T state

49
Q

What is the effect of increased [H+] on O2 release?

A

If [H+] increases more O2 is released

50
Q

Where does the formation of HCO3- occur?

A

In red blood cells in the capillaries of tissues

51
Q

Where does formation of CO2 from HCO3- occur?

A

In red blood cells in the capillaries of the lungs

52
Q

Outline how Bohr shift occurs

A
  • CO2 diffuses into RBCs where it combines with H2O to form HCO3- and H+
  • H+ binds to oxy-Hb causing O2 to be released
  • HCO3- diffuses into plasma and circulates until reaches the lungs
  • in lungs more oxy-Hb is formed so H+ are released
  • H+ combines with HCO3- to form H2O and CO2
  • CO2 diffuses out of red blood cells into lungs
53
Q

Which amino acids do salt bridges which stabilise the T state of Hb form between?

A
  • Lys40 forms a salt bridge to His146 which in turn also forms a salt bridge with Asp94
  • These salt bridges occur between subunits
54
Q

Why are the salt bridges only formed between the amino acid residues in the T state?

A

Only in the T state are the 3 residues correctly orientated to enable the formation of 2 salt bridges

55
Q

At a lower pH what is the effect of the fractional saturation curve?

A

It is shifted to the right so Hb binds O2 less tightly

56
Q

What are the 2 ways red blood cells carry CO2?

A
  • as HCO3-
  • Formation of carbamate
57
Q

How can CO2 form carbamate?

A

It can bind directly to the amino terminal groups of Hb

58
Q

How does formation of carbamate reduce the P50 of Hb for O2?

A

Carbamate participates in salt bridges which help to further stabilise the T state

59
Q

What conditions reduces the affinity for O2 the most?

A

Low pH and prescence of CO2

60
Q

Which mutation causes sickle cell anaemia?

A

β E6V

61
Q

How does sickle cell anaemia confer some resistance to malaria?

A

It reduces the half life of red blood cells so helps to break the life cycle of the plasmodium

62
Q

How does sickle cell anaemia cause problems?

A
  • mutation produces a hydrophobic patch on the surface of Hb
  • this causes β subunits to stick together
  • Hb aggregates into fibres

Cellular Composition (15 decks)

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