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Biosci 203 > Biological Gas Transport > Flashcards

Biological Gas Transport Flashcards

1
Q

What are the three necessary components?

A
  • A surface for gas exchange
  • A system for efficiently moving solutions
  • An efficient oxygen transport protein
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2
Q

Over approximately what distance does gas exchange occur over in alveoli?

A

0.3 micrometres

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3
Q

The concentration of Hb in an erythrocyte is…

A

5mM

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4
Q

What is the lifetime of an erythrocyte?

A

120 days

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5
Q

Why is packaging of Hb in erythrocytes essential?

A

To decrease viscosity to keep viscosity at a physiologically reasonable level

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6
Q

Per 100mL, what is the amount of oxygen with and without Hb?

A

Without - 0.3mL

With - 20mL

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7
Q

The alpha chain is encoded on which chromosome?

A

16

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8
Q

The beta chain is encoded on which chromosome?

A

11

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9
Q

Why is three different forms of Hb required in humans?

A

So the body can respond to the different oxygen sources at different phases of development and the different property demands

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10
Q

Erythrocytes originate from what?

A

Reticulocytes, which in turn come from Stem Cells

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11
Q

State the number of amino acids in the alpha chain

A

141

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12
Q

State the number of amino acids in the beta chain

A

146

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13
Q

Embryonic Hb is synthesised in…

A

The Yolk Sac

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14
Q

Fetal Hb is synthesised in…

A

The Liver

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15
Q

Adult Hb is synthesised in the…

A

Flat bones

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16
Q

At birth our Hb is…

A

Roughly 50% of both HbF and HbA

17
Q

Why is steric intereference in the Hb molecule important?

A

To prevent Fe2+ from oxidising into the more stable Fe3+, as this would bind the oxygen too tightly for efficient oxygen transport.

18
Q

Steric intereference in our Hb is created by…

A

The distal histidine, which prevents vertical binding of oxygen

19
Q

How is Hb assembled?

A

Spontaneously at quick rates

20
Q

What is the Hill coefficient?

A
  • An expression of the level of co-operativity

- The gradient of the oxygen binding curve around p50

21
Q

What is p50?

A

The concentration of oxygen when 50% of binding sites are occupied
This is typically 26-28mmHg for Hb

22
Q

What are the 3 models which have been used to explain the homotropic effect?

A
  • The two state concerted model
  • The sequential model
  • The stereochemical model (qualitative)
23
Q

Describe the two state concerted model

A
  • Quantitative with near perfect experimental fit
  • Theorises that there are two quaternary structures of Hb with different binding affinity - T (low) and R (high)
  • Both forms are present in equilibrium, with altering quantities of each form
24
Q

Describe the sequential model

A
  • Quantitative with near perfect experimental fit
  • Theorises that during oxygenation the quaternary structure will go through a series of subunit changes, with each changing slightly as oxygen is bound. These forms range from T (tense) state, when no oxygen is bound, to R (relaxed) when all subunits have oxygen bound
25
Q

Describe the stereochemical/Perutz model

A
  • Qualitative
  • Based on X-ray structure of oxy and deoxy structures
  • Says that the binding of oxygen to haem group makes the gap where a tyrosine is sitting smaller, forcing it out, and hence breaking ionic bonds between the neighbouring subunits, increasing the affinity of the neighbouring subunit to oxygen
  • Does not specify if all subunits are activated simultaneously or sequentially
26
Q

Name some heterotropic allosteric inhibitors of Hb

A

Cl-, H+, 2,3DPG

27
Q

What is the Bohr effect?

A

The lowering of pH reduces the oxygen affinity of Hb through the allosteric inhibition of Hb by H+

The impact of pH is linear over the human physiological pH range.

28
Q

When is 2,3DPG bound to Hb?

A

Under normal conditions there are equal amounts of Hb and DPG produced and Hb is usually bound by DPG

29
Q

How does DPG lower the oxygen affinity of Hb?

A

By stabilising the beta subunits in the deoxygenated form

30
Q

How is 2,3DPG synthesised?

A

It is formed only in red blood cells, and is a side product of Glycolysis

It is formed from 1,3DPG by a mutase, and can re-enter the glycolytic pathway by being converted by phosphatase into 3PG.

31
Q

What is the difference between the gamma and beta chains of Hb?

A

One of the Histidines of the beta subunit structure is changes to a Serine (OH group not ionizable at normal pH).

This results in the binding site of DPG being less charged, so it binds less tightly.

32
Q

What is the effect of temperature to Hb in humans?

A

An increase in termperature lowers the oxygen affinity of Hb

This is useful for an increased oxygen delivery during exercise

Biosci 203 (7 decks)

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