Haemoglobin

Question 1

What is haemoglobin?

Answer 1

-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

Question 2

What is a haem group?

Answer 2

-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

Question 3

What is the reversible reaction for oxyhemoglobin?

Answer 3

Haemoglobin + oxygen = oxyhaemoglobin

THIS IS A REVERSIBLE REACTION

Question 4

What is meant by the term loading?

Answer 4

-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

Question 5

What is meant by the term unloading?

Answer 5

-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

Question 6

What is myoglobin? State it’s structure and function

Answer 6

-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

Question 7

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

Answer 7

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

Question 8

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

Answer 8

-Oxygen concentration
-the greater the concentration of dissolved oxygen in cells, the higher the partial pressure

Question 9

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

Answer 9

Concentration of carbon dioxide in a cell

Question 10

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

Answer 10

-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

Question 11

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

Answer 11

-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

Question 12

What does an oxygen dissociation curve show?

Answer 12

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

Question 13

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

Answer 13

every haemoglobin molecule is carrying the maximum 4 molecules of oxygen

Question 14

What does 0% saturation mean on an oxygen dissociation graph?

Answer 14

none of the haemoglobin molecules are carrying any oxygen

Question 15

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

Answer 15

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

Question 16

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

Answer 16

Haemoglobin has a low affinity for oxygen which means it releases oxygen rather then combines with it, giving it a low saturation of oxygen

Question 17

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

Answer 17

-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.

Question 18

What is the purpose of co-operative binding?

Answer 18

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

Question 19

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

Answer 19

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.

Question 20

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

Answer 20

-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

Question 21

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

Answer 21

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

Question 22

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

Answer 22

• 5% 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

Question 23

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

Answer 23

-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)

Question 24

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

Answer 24

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

Question 25

How is haemoglobinic acid produced?

Answer 25

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

Question 26

Explain the purpose and the process of the chloride shift

Answer 26

-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.

Question 27

What happens when the blood reaches the lungs?

Answer 27

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

Question 28

What is the Bohr effect?

Answer 28

-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