Mass Transport

Question 1

Describe the structure of haemoglobin

Answer 1

Globular, water soluble
-consists of four polypeptide chains, each carrying a haem group (quaternary structure)

Question 2

describe the role of haemoglobin

Answer 2

-present in the red blood cells
-oxygen molecules bind to the haem groups and are carried around the body to where they are needed in respiring tissues

Question 3

name 3 factors affecting oxygen-haemoglobin binding

Answer 3

-partial pressure/concentration of oxygen
-partialpressure/concentration of carbon dioxide
-saturation of haemoglobin with oxygen

Question 4

how does the partial pressure of oxygen affect oxygen-haemoglobin binding?

Answer 4

as partial pressure of oxygen increases, the affinity of haemoglobin for oxygen also increases, so oxygen binds tightly to haemoglobin. When partial pressure is low, oxygen is released from haemoglobin

Question 5

how does partial pressure of carbon dioxide affect oxygen-haemoglobin binding

Answer 5

-as partial pressure of carbon dioxide increases, the conditions become acidic causing haemoglobin to change shape. The affinity of haemoglobin for oxygen therefore decreases, so oxygen is released from haemoglobin. This is known as the Bohr effect

Question 6

how does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding?

Answer 6

It is hard for the first oxygen molecule to bind. Once it does, it changes the shape to make it easier for the second and third molecules to bind, known as positive cooperativity. It is then slightly harder for the fourth oxygen molecule to bind because there is a low chance of finding a binding site

Question 7

explain why oxygen binds to haemoglobin in the lungs

Answer 7

-partial pressure of oxygen is high
-low concentration of carbon dioxide in the lungs, so affinity is high
-positive cooperativity (after the first oxygen molecule binds, binding of subsequent oxygen molecules is easier).

Question 8

explain why oxygen is released from haemoglobin in respiring tissues

Answer 8

-partial pressure of oxygen is low
-high concentration of carbon dioxide in respiring tissues, so affinity decreases

Question 9

what do oxyhaemoglobin dissociation curves show?

Answer 9

saturation of haemoglobin with oxygen (in %), plotted against partial pressure of oxygen (in kPa), Curves further to the left to show the haemoglobin has a higher affinity for oxygen

Question 10

how does carbon dioxide affect the position of an oxyhaemoglobin dissociation curve?

Answer 10

curve shifts to the right because haemoglobins affinity for oxygen has decreased