Transport Of Oxygen By Heamoglobin

Question 1

what is an oxygen dissociation curve?

Answer 1

• when haemoglobin is exposed to different partial pressures of oxygen it does not bind evenly
• the oxygen dissociation curve shows the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen

Question 2

Changing structure of haemoglonbin?

Answer 2

• the closely United shape of the haemoglobin molecules makes it difficult for the first oxygen molecule to bind to one of the sites on its four polypeptide subunits so the graph is initially shallow
• the binding of the first oxygen molecule changes the quaternary structure of the haemoglobin making it change shape making so it’s easier for other subunits to bind
• after third molecule it becomes harder for the fourth to bind as the majority of the binding sites are occupied so its less likely a single oxygen molecule will find an empty site to bind to this means the gradient of the curve reduces and flattens out

Question 3

which factors should you keep in mind when using oxygen dissociation curves?

Answer 3

• the further to the left the curve is the greater the affinity of haemoglobin for oxygen
• the further to the right the curve is the lower the affinity of haemoglobin for oxygen

Question 4

how does the loading, transport and unloading of oxygen work?

Answer 4

• at the gas exchange surface carbon dioxide is constantly being removed
• the pH is slightly raised due to the low concentration of carbon dioxide
• the higher pH changes the shape of haemoglobin into one that enables it to load oxygen readily
• this shape also increases the affinity of haemoglobin for oxygen so its not released while being transported in the blood to the tissues
• in the tissues carbon dioxide is produced by respiring cells
• carbon dioxide is acidic in solution so the pH of the blood within the tissue is lowered
• the lower pH changes the shape of haemoglobin into one with lower affinity for oxygen
• haemoglobin releases its oxygen into the respiring cells

Question 5

what happens to haemoglobin in humans?

Answer 5

• the haemoglobin becomes saturated with oxygen as it passes through the lungs
• not all oxygen molecules are filled to their max of four molecules so the overall saturation of haemoglobin molecules at atmospheric pressure is normally 97%
• when this haemoglobin reaches a tissue with a low respiratory rate only one will normally be released
• this means that blood returning to the lungs will contain haemoglobin that is still 75% saturated with oxygen
• if a tissue is very active three oxygen molecules will be unloaded form each haemoglobin molecule

Question 6

what happens to haemoglobin in lung worms?

Answer 6

• the lung worm is not very active as it spends almost all of its life in a u shaped burrow under sea water that circulates through its burrow
• oxygen diffuses into the lung worms blood from the water and it uses its haemoglobin to transport oxygen to its tissues
• when the tide goes out the lungworm can no longer circulate a fresh supply of oxygenated water thorough its burrow meaning the burrow contains less oxygen as it is used up
• the lung worm has to extract as much oxygen as possible from the water in the burrow so it can survive until the tide covers it again

Question 7

what is positive cooperativity?

Answer 7

• it takes a smaller increase in the partial pressure of oxygen to bind the second oxygen molecule than it did to bind he first
• binding to the first molecule makes binding to the second one easier so the gradient of the curve steepens

Question 8

how does carbon dioxide affect haemoglobins affinity for oxygen at the gas exchange surface?

Answer 8

• the concentration of carbon dioxide is low because it diffuses across the exchange surface and is excreted from the organism
• the affinity of haemoglobin for oxygen is increased which coupled with the high concentration for oxygen in the lungs means that oxygen is readily associated with haemoglobin
• this means the oxygen dissociation curve shifts to the left

Question 9

how does carbon dioxide affect haemoglobins affinity for oxygen at rapidly respiring tissues?

Answer 9

• the concentration of carbon dioxide is high so the affinity of haemoglobin for oxygen is reduced which coupled with the low concentration of oxygen in the muscles means that oxygen is readily unloaded from the haemoglobin into the muscle cells
• this means the oxygen dissociation curve shifts to the right

Question 10

how do you ensure that there is always sufficient oxygen for respiring tissues?

Answer 10

• the more active the tissue the more oxygen is unloaded
• the higher the rate of respiration the more carbon dioxide the tissue produces
• the lower the pH the greater the haemoglobin shape change
• the more readily oxygen is uploaded the more oxygen is available for respiration

Question 11

what happens to haemoglobin in lung llama?

Answer 11

• they live at high altitudes where the atmospheric pressure is lower so the partial pressure of oxygen is also lower meaning it is difficult to load haemoglobin with oxygen
• llamas also have a type of haemoglobin that has a higher affinity for oxygen than human haemoglobin so the oxygen dissociation curve is shifted to the left of the human oxygen dissociation curve