Haemoglobin

Question 1

describe the structure of haemoglobin (5)

Answer 1

• protein with a quaternary structure
• made of 2 alpha + 2 beta globins
• each subunit contains a haem group
• each haem group containing an iron ion (Fe2+)
• each molecule can carry 4 oxygen molecules

Question 2

how is the structure of haemoglobin related to its function (3)

Answer 2

• oxygen can bind reversibly with haemoglobin ( bind to the prosthetic haem group)
• can bind to haemoglobin at respiratory surfaces
• can dissociate from haemoglobin at respiring tissues

Question 3

how can haemoglobin be written

Answer 3

Hb
or Hb(A) - adult haemoglobin

Question 4

equation for binding of Hb with oxygen

Answer 4

Hb + 4O2 <–> HbO8 (oxyhaemoglobin)

Question 5

describe what is the partial pressure of oxygen (pO2)

Answer 5

the measure of the concentration of oxygen in a particular area

Question 6

describe what is the percentage saturation of haemoglobin

Answer 6

how much oxygen is associated (bound) with haemoglobin

Question 7

generally describe and explain the oxygen dissociation curve

Answer 7

• at low partial pressure of oxygen less oxygen binds to haemoglobin
• at higher partial pressure of oxygen more oxygen binds to haemoglobin

Question 8

describe the oxygen dissociation curve in terms of what occurs at the lungs

Answer 8

• alveoli found at a partial pressure of around 13
• at high partial pressure haemoglobin is fully saturated with oxygen (become oxyhaemoglobin)

Question 9

describe the oxygen dissociation curve in terms of what occurs in respiring tissues

Answer 9

• tissues use oxygen for aerobic respiration
• low partial pressure of around 5
• oxygen dissociates from oxyhaemoglobin into the tissues until equilibrium is reached

Question 10

what shape is the oxygen dissociation graph

Answer 10

sigmoidal (S) shape

Question 11

what is the amount of oxygen association determined by

Answer 11

the partial pressure of oxygen

Question 12

why do different organisms have slightly different haemoglobins

Answer 12

due to slight differences in their sequence of amino acids

Question 13

why does changing the sequence of amino acids change the structure and function of haemoglobin

Answer 13

• alters the tertiary / quaternary structure
• changes affinity for oxygen
• matches the environmental conditions the organism lives in, with different partial pressures

Question 14

describe in terms of cooperative binding why the dissociation curve is sigmoidal shaped

Answer 14

(as partial pressure of oxygen increases…)
- When first oxygen molecule binds to one subunit of deoxyhaemoglobin, this is difficult
- binding changes the tertiary structure of Hb, increasing its affinity for oxygen
- second and third O2 molecules can now bind more easily
- fourth O2 molecules only binds at high partial pressure where there is a high probability of association

Question 15

describe, simply, the cooperative nature of oxygen binding

Answer 15

• first oxygen binds with difficulty to one subunit of deoxyHb, changing tertiary structure
• increases affinity for oxygen, makes it easier for further oxygens (2nd, 3rd + 4th) to bind

Question 16

what does the Bohr effect tell us

Answer 16

the effects of CO2 on the dissociation curve

Question 17

describe the effects of CO2 concentration on the dissociation of oxyhaemoglobin

Answer 17

• (at a given pO2) increased partial pressure of carbon dioxide reduces haemoglobins affinity for oxygen, so is more likely to dissociate oxygen
• organisms are able to meet their metabolic (energy) demand

Question 18

how does carbon dioxide change Hb affinity for oxygen

Answer 18

CO2 forms carbonic acid when dissolved within the water in blood, this higher PH will change the shape of the Hb, decreasing its affinity for oxygen

Question 19

how does CO2 change the dissociation curve

Answer 19

• higher PH created by the carbonic acid will shift the dissociation curve to the right

Question 20

which line on the dissociation curve will be furthest left

Answer 20

• line showing the alveoli
• least acidic conditions, as CO2 will diffuse out and not into the bloodstream
• blood will have a low ppCO2

Question 21

which line on the dissociation curve will be furthest right

Answer 21

• line showing respiring tissues
• most acidic conditions, respiration produces CO2
• blood will have a high pCO2

Question 22

describe how and why Llama Hb has adapted

Answer 22

• Llamas live in high altitude, this has a lower PO2
• Llama Hb has a high affinity for oxygen compared to human Hb
• this means Llamas can fully saturate their Hb in the lungs prior to tissue transport

Question 23

what is the function of myoglobin

Answer 23

oxygen storage

Question 24

role of myoglobin

Answer 24

enables aerobic respiration to continue once haemoglobin has dissociated its oxygen

Question 25

where is myoglobin found

Answer 25

cardiac and skeletal muscle tissues

Question 26

features of myoglobin (3)

Answer 26

- is a single polypeptide with one haem group - very high affinity for oxygen, higher than Hb - only dissociate oxygen at very low tissue P.O2

Question 27

does myoglobin engage in cooperative binding

Answer 27

no because only one oxygen can bind to it (contains only one haem group)