haemoglobin Flashcards

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1
Q

what is haemoglobin?

A

-a protein that is present inside red blood cells. It is a large globular protein with a quaternary structure (made up of more then one polypeptide chain) made up of 4, 2 alpha and 2 beta chains
-each polypeptide chain is attached to a haem group

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2
Q

What is a haem group?

A

-haemoglobin’s prosthetic group, making it a conjugated protein
-it contains iron which gives it its high affinity for oxygen
-each haem group is attached to a chain, and combines with a single oxygen molecule which means that 1 haemoglobin molecule can carry 4 oxygen molecules altogether

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3
Q

What is the reversible reaction for oxyhemoglobin?

A

Haemoglobin + oxygen = oxyhaemoglobin

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4
Q

What is meant by the term loading?

A
  • Adding oxygen to haemoglobin
  • happens in the lungs because oxygen moves down the concentration gradient of the alveolar air space and into the erythrocytes (red blood cells)
  • the haemoglobin has an affinity for the oxygen and they become associated. There is no bond between them
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5
Q

What is meant by the term unloading?

A
  • the loss of oxygen from haemoglobin
  • happens in respiring tissues because oxygen moves down the concentration gradient from the erythrocytes (red blood cells) into the tissues where oxygen is constantly being used in aerobic respiration and it’s concentration remains low
  • as the haemoglobin releases the oxygen it dissociates
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6
Q

What is myoglobin? State it’s structure and function

A
  • A protein which acts as an oxygen store in muscle cells
  • Only has one poplypeptide chain and haem group
  • forms oxymyoglobin when it picks up oxygen from oxyhaemoglobin
  • it has a higher affinity for oxygen than haemoglobin
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7
Q

Describe the path of a molecule of oxygen from alveolus to aerobic respiration.

A

1) Oxygen loads onto haemoglobin in the lungs to make oxyhemoglobin

2) oxygen travels in the blood in the form of oxyhaemoglobin to the muscles

3) oxygen dissociates from the oxyhaemoglobin to associate with myoglobin to make oxymyoglobin

4) oxygen is stored in the muscles in the form of oxymyoglobin

5) oxygen is released when the muscles are working hard to allow aerobic respiration to continue for longer before switching to a anaerobic respiration

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8
Q

What is the partial pressure of oxygen (po2) a measure of?

A
  • Oxygen concentration
  • the greater the concentration of dissolved oxygen in cells, the higher the partial pressure
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9
Q

What is the partial pressure of carbon dioxide a measure of?

A

Concentration of carbon dioxide in a cell

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10
Q

Explain how haemoglobins affinity for oxygen varies depending on the partial pressure of oxygen.

A

-When there is a high partial pressure of oxygen, oxygen loads onto haemoglobin to form oxyhaemoglobin
-When there is a low partial pressure of oxygen, oxyhaemoglobin unloads it’s oxygen

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11
Q

Where in the body is there a high partial pressure of oxygen, and a low partial pressure of oxygen?

A

-alveoli have a high partial pressure of oxygen, allowing for oxygen to be loaded onto haemoglobin
-respiring cells have a low partial pressure of oxygen, so oxygen is unloaded from haemoglobin for respiration

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12
Q

What does an oxygen dissociation curve show?

A

-How saturated the haemoglobin is with oxygen at any given partial pressure

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13
Q

What does 100% saturation mean on an oxygen dissociation graph?

A

every haemoglobin molecule is carrying the maximum 4 molecules of oxygen

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14
Q

What does it mean when the partial pressure of oxygen is high on an oxygen dissociation graph?

A

Haemoglobin has a high affinity for oxygen, and it will readily combine with oxygen, so it has a high saturation

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15
Q

Describe and explain the shape of haemoglobin on an oxygen dissociation graph

A
  • has a sigmoid or ‘s’ shaped curve
  • the first part of the graph is because haemoglobin has a very low affinity for oxygen at low oxygen concentrations
  • when haemoglobin combines with the first oxygen molecule, its shape alters in a way that makes it easier for other molecules to bind too (known as cooperative binding)
  • as the haemoglobin starts to become saturated, it gets harder for more oxygen molecules to join
  • as a result the curve has a steep bit in the middle where it’s really easy for oxygen molecules to join, and shallow bits at the end where it’s harder. -When the curve is steep, a small change in partial pressure of oxygen causes a big change in amount of oxygen carried by the haemoglobin
  • at high partial pressure, there is a high affinity for oxygen and it is difficult to offload it, producing the flat part of the ‘S’ curve.
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16
Q

What is the purpose of co-operative binding?

A

It ensures that haemoglobin is very good at delivering large amounts of oxygen to the tissues if required

17
Q

Explain what the main difference between adult haemoglobin and fetal haemoglobin is?

A

Fetal haemoglobin has a higher affinity for oxygen (fetus’s blood is better at absorbing oxygen then its mothers) at the same partial pressure of oxygen.

18
Q

Explain the importance of fetal haemoglobin having a higher affinity oxygen then adult haemoglobin.

A

-the fetus gets its oxygen from its mother’s blood across the placenta
-by the time the mothers blood reaches the placenta, its oxygen saturation had decreased because some has been used by the mother
-for the fetus to get enough oxygen to survive its haemoglobin had got to have a higher affinity for oxygen so it take up enough
-if the two haemoglobins had the same affinity for oxygen, the fetus’ blood wouldn’t be saturated enough

19
Q

What other then the partial pressure of oxygen effects the haemoglobins affinity for oxygen?

A

The partial pressure of carbon dioxide
-the production of carbon dioxide during aerobic respiration increases the rate of oxygen unloading

20
Q

What are the 3 ways that carbon dioxide is carried in the blood?

A

% dissolved directly into the blood plasma
-15% combines with the amino groups in the polypeptide chains of haemoglobin forming a compound called Carbaminohaemoglobin
-80% diffuses into the red blood cells for conversion into hydrogencarbonate

21
Q

What enzyme does red blood cells contain and what reaction does it catalyse?

A

-carbonic anhydrase
-catalyses a reaction in which carbon dioxide forms a weak acid called carbonic acid

Carbon dioxide + water = carbonic acid (this is a reversible reaction)

22
Q

What are the products of the reaction of carbonic acid dissociating?

A

Carbonic acid = hydrogen ions + hydrogencarbonate (this is a reversible reaction)

23
Q

How is haemoglobinic acid produced?

A

An increase of hydrogen ions causes oxyhaemoglobin to unload its oxygen so that haemoglobin can take up the hydrogen ions, forming haemoglobonic acid (HHb)

24
Q

Explain the purpose and the process of the chloride shift

A

-it maintains the balance of charge between the red blood cells and the plasma
-the hydrogencarbonate ions diffuse out of the red blood cells and are transported into the blood plasma. To compensate for the loss of hydrogencarbonate ions from the red blood cells, chloride ions diffuse into the red blood cells.

25
Q

What happens when the blood reaches the lungs?

A

The low partial pressure of carbon dioxide causes some of the hydrogencarbonate ions and hydrogen ions to recombine into carbon dioxide and water. The carbon dioxide then diffuses into the alveoli and is breathed out

26
Q

What is the Bohr effect?

A

-When carbon dioxide levels increase, the dissociation curve ‘shifts’ to the right, showing that more oxygen is released from the blood (because the lower the saturation of haemoglobin with oxygen, the more oxygen is released)
-the hydrogen ions bind with oxyhemoglobin to form haemoglobin acid and oxygen (lowers haemoglobins affinity for oxygen and buffers pH reducing build up of H+)
-the oxygen then diffuses out of the red blood cell to respiring cells during exercise, due to the initial increase in co2