Function of Haemoglobin in Oxygen Carriage

Question 1

Regarding genetic defects in haemoglobin (true or false):

Genetic defects in haemoglobin are the least common of all genetic disorders

Answer 1

False. Genetic defects in haemoglobin are the most common of all genetic disorders.

Question 2

Regarding genetic defects in haemoglobin (true or false):

Sickle cell disease is caused by a single base mutation in the β globin gene

Answer 2

True

Question 3

Regarding genetic defects in haemoglobin (true or false):

Normally equal quantities of α and β chains are produced

Answer 3

True. A problem with either the α or β globin gene leads to an excess of one type of chain being produced. Excess globin chains precipitate causing haemolysis and anaemia.

Question 4

Regarding genetic defects in haemoglobin (true or false):

α-thalassaemia is usually due to deletions of one or more α genes

Answer 4

True. This has varying degrees of clinical severity. 4-gene deletion is incompatible with life.

Question 5

Regarding genetic defects in haemoglobin (true or false):

β-thalassaemia is most often apparent at birth

Answer 5

False. β-thalassaemia usually becomes apparent at between three to six months of age, when the switch to adult HbA takes place.

Question 6

Regarding haemoglobin (true or false):

Each haem binds to one iron atom

Answer 6

True

Question 7

Regarding haemoglobin (true or false):

Each haemoglobin molecule carries two oxygen molecules

Answer 7

False. One haem group binds reversibly to one molecule of oxygen, so each haemoglobin molecule binds four oxygen molecules

Question 8

Regarding haemoglobin (true or false):

Methaemoglobin formation is due to oxidation of Fe3+ to Fe2+

Answer 8

False. Iron can be oxidized from the ferrous (Fe2+) to the ferric (Fe3+) form. As Fe3+ it is unable to combine with oxygen. Methaemoglobin is an oxidized derivative of hemoglobin.

Question 9

Regarding haemoglobin (true or false):

2,3-DPG binds to the β-chains of haemoglobin

Answer 9

True

Question 10

Regarding haemoglobin (true or false):

The presence of carboxyhaemoglobin increases the Hüfner constant

Answer 10

False. Hüfner’s constant is the amount of oxygen (in ml) carried by each gram of haemoglobin. Different values have been obtained for this constant, with those found experimentally consistently lower than the theoretical value. This is believed to result from the presence of small percentages of other forms of haemoglobin, such as COHb, in in-vivo samples.

Question 11

The oxyhaemoglobin dissociation curve is shifted to the right with (true or false):

An increase in temperature

Answer 11

True

Question 12

The oxyhaemoglobin dissociation curve is shifted to the right with (true or false):

An increase in carbon monoxide

Answer 12

False. CO has an affinity for haemoglobin that is 300 times that of oxygen. It shifts the oxy-haemoglobin dissociation curve to the left. The most common source of CO is tobacco smoke.

Question 13

The oxyhaemoglobin dissociation curve is shifted to the right with (true or false):

An increase in 2,3-DPG

Answer 13

True

Question 14

The oxyhaemoglobin dissociation curve is shifted to the right with (true or false):

Fetal haemoglobin

Answer 14

False. HbF has a greater affinity for O2 than HbA.

Question 15

The oxyhaemoglobin dissociation curve is shifted to the right with (true or false):

Anaemia

Answer 15

True

Question 16

Regarding investigations into, and manufacture of, alternative means of O2 delivery (true or false):

Perfluorocarbons promise to provide an alternative means of oxygen delivery

Answer 16

False. Perfluorocarbons were investigated. However, while initial results seemed promising, this research has been abandoned because of adverse effects caused by the emulsified perfluorocarbon preparation required for clinical use.

Question 17

Regarding investigations into, and manufacture of, alternative means of O2 delivery (true or false):

Using stroma-free haemoglobin extracted from erythrocytes is problematic because Hb dissociates into α/β dimers after extraction

Answer 17

True. α/β dimers are non-functional and can cause nephrotoxicity.

Question 18

Regarding investigations into, and manufacture of, alternative means of O2 delivery (true or false):

Genetic engineering techniques have been used to produce large quantities of stabilized haemoglobin

Answer 18

True. Genetic engineering techniques have been used to insert a modified haemoglobin gene into E.coli plasmids, which then produce stabilized haemoglobin in large quantities.

Question 19

Regarding investigations into, and manufacture of, alternative means of O2 delivery (true or false):

Free haemoglobin has a much shorter intravascular half-life than an erythrocyte

Answer 19

True. This can lead to raised bilirubin levels. Free haemoglobin is also an excellent scavenger of nitric oxide and the resulting vasoconstriction may be the cause of hypertension seen in some phase 1 clinical trials.