topic 4.5 - transport of gases in the blood

Question 1

what is the main job of haemoglobin

Answer 1

to transport oxygen around the body

Question 2

transport of oxygen - how do the molecules bind?

Answer 2

• 1st oxygen molecule that binds alters the arrangement of the molecule
• easier for the following oxygen molecules to bind
• final O2 molecule binds a lot faster than first
• same process in reverse when oxygen dissociates from haemoglobin

Question 3

structure of haemoglobin and how it transports oxygen

Answer 3

• haemoglobin is a large globular protein
• made up of 4 peptide chains, each with an iron containing prosthetic group (haem group)
• can pick up 4 molecules of O2 in a reversible reaction to form oxyhaemoglobin

Hb + 4O2 ⇌ Hb4O2
haemoglobin + oxygen ⇌ oxyhaemoglobin

Question 4

transport of oxygen - how do the molecules bind? (positive cooperativty)

Answer 4

• 1st oxygen molecule that binds to iron alters the arrangement of the haemoglobin molecule
• easier for the following oxygen molecules to bind
• final O2 molecule binds a lot faster than first
• same process in reverse when oxygen dissociates from haemoglobin

Question 5

where is the partial pressure of oxygen high

Answer 5

• the lungs have a high pp of oxygen
• so oxygen binds rapidly with haemoglobin to form oxyhaemoglobin

Question 6

why does the percentage saturation of oxygen in the lungs not reach 100%

Answer 6

• most iron atoms are already bound to the oxygen molecules
• the probability of a collision between an unbound iron atom and oxygen molecule is low

Question 7

oxygen levels in body tissues

Answer 7

• relatively low
• concentration of oxygen in cytoplasm of RBC is higher than in the surrounding tissue
• hence, O2 moves out by diffusion down its concentration gradient
• haemoglobin gives up some of its O2

Question 8

Bohr effect

Answer 8

• in the presence of CO2 the affinity of haemoglobin for oxygen decreases so it is released
• hence, oxygen dissociates from haemoglobin and can be used in respiring tissues
• changes in carbon dioxide concentration result in changes in the curve - Bohr effect

Question 9

Bohr effect - haemoglobin and oxyhaemoglobin dissociation curve - increased CO2

Answer 9

• increase in CO2 causes curve to shift to the right
• oxygen associates less readily and dissociates more readily

Question 10

Bohr effect - haemoglobin and oxyhaemoglobin dissociation curve - decreased CO2

Answer 10

• decrease in CO2 causes curve to shift to the left
• oxygen associates more readily and dissociates less readily

Question 11

what happens when oxygen dissociates from haemoglobin?

Answer 11

• gets harder to remove the oxygen
• conc of oxygen in RBC when blood enters is low
• concentration of oxygen in cytoplasm of RBC is higher than in surrounding tissue
• hence oxygen moves into cells via diffusion down its concentration gradient

Question 12

what is myoglobin

Answer 12

• respiratory pigment found in muscle tissue of vertebrates
• small bright red protein

Question 13

structure of myoglobin and how this relates to its function

Answer 13

• similar to a single haemoglobin chain
• single polypeptide chain
• contains haem group which binds oxygen
• has a higher affinity for oxygen so becomes easily saturated
• once bound to oxygen, it doesn’t give up oxygen easily hence acts as an oxygen store

Question 14

similarities between haemoglobin and myoglobin

Answer 14

• both globular proteins
• both contain haem group/s

Question 15

differences between haemoglobin and myoglobin

Answer 15

• higher oxygen affinity in Mb
• haemoglobin carries oxygen to cells in body whereas Mb stores oxygen in muscle cells to be used as energy
• Hb has quarternary structure, Mb has tertiary structure
• higher conc of Hb in blood, higher conc of Mb in heart & muscle cells