8.4 Transport of oxygen and carbon dioxide in blood

Question 1

What is haemoglobin?

Answer 1

red pigment that carries oxygen: large globular conjugated protein made up of 4 peptide chains, each with an iron-containing haem prosthetic group

Question 2

What forms when oxygen binds with haemoglobin?

Answer 2

binds quite LOOSELY to haemoglobin, forming oxyhaemoglobin

Hb + 4O2 = Hb(O2)4

= sign means reversible reaction

Question 3

What are oxygen levels like in erythrocyte cells when blood enters capillaries in lungs?

Answer 3

relatively low
–> makes a steep conc gradient between inside erythrocyte and air in alveoli
–> oxygen moves into cell and binds to haemoglobin

Question 4

What is special about the arrangement of haemoglobin?
What is this phenomenon called?

Answer 4

as soon as one oxygen molecule binds to haem group, the molecule changes shape, making it easier for the next oxygen molecules to bind

–> Positive Cooperativity

Question 5

What happens to the conc gradient after one oxygen molecule binds to haemoglobin?

Answer 5

steep diffusion gradient is maintained as free oxygen conc in erythrocyte stays low

–> occurs until all haemoglobin is saturated with oxygen

Question 6

What are oxygen levels like in erythrocyte cells when blood reaches the body cells?

Answer 6

Concentration of oxygen in cytoplasm of body cells is lower than that of erythrocytes
–> oxygen moves out of erythrocytes and into the body cells, down a conc gradient

Question 7

What does it mean when haemoglobin has affinity for oxygen?

Answer 7

the amount of partial pressure of oxygen needed to saturate the haemoglobin molecule

Question 8

What is partial pressure of oxygen?

Answer 8

amount of oxygen in tissue pO2
–> measured in kPa

Question 9

When partial pressure for oxygen is high, what occurs?

Answer 9

Ventilation= lung tissue have high pO2

–> more oxygen is able to associate with haemoglobin molecules to be transported

Question 10

When partial pressure for oxygen is low, what occurs?

Answer 10

In respiring tissue, pO2 is low

–> oxygen dissociates from oxyhaemoglobin and diffuses to respiring cells

Question 11

Oxygen dissociation curve

Answer 11

S-shaped curve
–> Hb saturation with O2 % is not directly proportional to pO2

Question 12

How does haemoglobin’s ability to associate with oxygen change as it gets more saturated?

Answer 12

First oxygen molecules associates and changes the conformation of haemoglobin

This makes it easier for the 2nd and 3rd oxygen molecules to associate

However, it is difficult to associate the 4th oxygen molecule (curve plateau below 100%)

Question 13

Effect of different partial pressures of oxygen on affinity of Hb for oxygen?

Answer 13

At low partial pressure of oxygen,
- Hb oxygen saturation is low, so Hb has a low affinity for O2

At high partial pressure of oxygen,
- Hb oxygen saturation is high so Hb has a low affinity for O2

Question 14

Why would high altitude animals not respire efficiently at low altitudes

Answer 14

low altitude= pO2 higher than high altitude
–> Llama haemoglobin has higher affinity for oxygen than human haemoglobin ( curve is more shifted to the left)

–> At high partial pressure of oxygen, llama haemoglobin would not dissociate oxygen to respiring tissues

Question 15

What is the affinity of fetal haemoglobin like?

Answer 15

since a fetus is completely dependent on its mother to supply it with oxygen, oxygenated blood from mother runs close to deoxygenated fetal blood

Fetal Hb has a higher affinity for oxygen than adult haemoglobin at each point,
–> removes oxygen from maternal blood as they pass each other

Question 16

What is the bohr effect?
Where is it important?

Answer 16

As the partial pressure of CO2 rises, haemoglobin gives up oxygen more easily

–> in active tissue with high partial pressure of CO2, haemoglobin can give up oxygen more readily
–> in lungs where the proportion of CO2 in air is low, oxygen binds to haemoglobin molecules easily

Question 17

How is carbon dioxide transported to the lungs?

Answer 17

About 5% is carried dissolved in plasma

10-20% combined with amino groups in polypeptide chains of haemoglobin
–> carbaminohaemoglobin

75-85% converted into HCO3- hydrogen carbonate ions in cytoplasm of red blood cells

Question 18

How are the hydrogen carbonate ions formed?
(equaiton)

Answer 18

CO2 reacts slowly with water to form carbonic acid (H2CO3)
–> acid dissociates to form hydrogen ions & hydrogen carbonate ions)

CO2+H2O = H2CO3 = H+ + HCO3-

Question 19

Why is most of the CO2 transported through the RBC?

Answer 19

blood plasma, reactions occur slowly

In the cytoplasm of RBCs, there are high levels of enzyme CARBONIC ANHYDRASE

Question 20

Function of carbonic anhydrase

Answer 20

enzyme catalyses the reversible reaction between CO2 & water to form carbonic acid
–> carbonic acid dissociates to form the H+ & HCO3-

Question 21

What happens to the H+ ions produced?

Answer 21

they bind with haemoglobin in red blood cells
–> forms haemoglobonic acid (causes haemoglobin to release all the oxygen it is carrying

Question 22

What happens to the hydrogen carbonate ion produced?

Answer 22

Negatively charged HCO3- ions move out of the blood cell into the plasma via diffusion (down conc gradient)

chloride ions move into erythrocytes to maintain electrical balance
–> chloride shift

Question 23

What happens to some CO2 that escapes being broken down by carbonic anhydrase enzyme?

Answer 23

They bind directly with the haemoglobin, forming
–> carbaminohaemoglobin

Question 24

When blood reaches the lung tissue, how does carbon dioxide help with gas exchange?

Answer 24

low conc of CO2 in lung tissue = carbonic anhydrase catalyses the reverse reaction by breaking down carbonic acid (H2CO3) into CO2 + H2O

Hydrogen carboante ions diffuse back into the blood cells and react with hydrogen ions to form carbonic acid

Question 25

What happens asa result of carbonic acid being broken down in the lung tissue?

Answer 25

free CO2 is released, diffusing out of blood into lungs

Chloride ions diffuse out of the red blood cells and back into the plasma

Question 26

What does haemoglobin act as during gaseous exchange?

Answer 26

a buffer and prevents changes in pH by accepting H+ ions
–> pH would go down making conditions too acidic for catalyst to work