Haemoglobin

Question 1

What shape is the oxygen dissociation curve?

Answer 1

sigmoid/s-shaped

Question 2

Why is it hard for the first O2 to bind to Hb?

Answer 2

because the haem groups are in the middle of haemoglobin molecule

Question 3

What impact does increasing CO2 have on the oxyhaemoglobin disassociation curve?

Answer 3

shifts the curve to the right, meaning affinity is reduced and O2 is given up more readily

Question 4

Describe the quaternary structure of haemoglobin

Answer 4

2 PAIRS of polypeptides (alpha and beta) join to make a spherical protein. Each polypeptide contains a haem group

Question 5

Explain how binding of oxygen affects the shape of haemoglobin

Answer 5

• Hard for first oxygen to bind as haem groups are in the middle of the haemoglobin molecule
• First oxygen causes a conformational change in the haemoglobin (change in shape) making it easier for the second and third molecules to bind
• Harder to reach final binding site so fourth oxygen binds less easily

Question 6

Define dissociate

Answer 6

Oxygen ‘unbinding’ from haemoglobin

Question 7

Briefly outline the role of haemoglobin

Answer 7

• Hb binds/associates with oxygen in areas with high pO2
• transported and unloaded/dissociates in areas with low pO2

Question 8

How would DNA lead to different haemoglobin molecules having different affinities for oxygen?

Answer 8

• Different sequence of bases
• Different primary structure
• Different shape
• so different affinities

Question 9

Comment on the saturation of haemoglobin with oxygen at high partial pressures

Answer 9

Hb is highly saturated

Question 10

Describe and explain the shape of the oxyhaemoglobin dissociation curve

Answer 10

In low partial pressures haemoglobin has a low affinity for oxygen (dissociates oxygen more easily), the curve is shallow
Curve becomes steeper as the affinity for oxygen increases
Curve levels off at nearly 100% saturation at high partial pressures of oxygen

Question 11

Explain how, with reference to haemoglobin, animals are adapted to their environment

Answer 11

An animal that lives in an environment with low partial pressure of oxygen will have haemoglobin with a high affinity for oxygen, the curve is to the left - this allows fully saturated haemoglobin at low partial pressures of oxygen

Question 12

Where in the body is there a high partial pressure of oxygen?

Answer 12

in the lungs

Question 13

What saturation and colour is deoxyhaemoglobin?

Answer 13

0% it is a bluey-red colour

Question 14

How does a rise in temperature impact the oxygen dissociation curve?

Answer 14

it moves it to the right (oxygen is given up more readily)

Question 15

Define associate

Answer 15

Oxygen binding to haemoglobin

Question 16

Define affinity

Answer 16

How readily haemoglobin will bind to oxygen

Question 17

Describe the structure of haemoglobin (4 marks)

Answer 17

Primary - sequence of amino acids;
Secondary - H bonds, beta pleated sheet/alpha helix;
Tertiary - ionic, disulphide bridges, H bonds. 3D shape;
Quaternary - 4 polypeptide chains, 4 haem groups
it is globular and water soluble

Question 18

What does partial pressure mean?

Answer 18

The concentration of a gas

Question 19

Why does CO2 reduce the affinity of Hb to O2?

Answer 19

Dissolved CO2 lowers the pH, meaning it is more acidic. This causes the Hb to change shape and therefore lowers the affinity of Hb to O2

Question 20

How would the haemoglobin in animals living at high altitudes differ from those at lower altitudes?

Answer 20

• higher affinity for oxygen.
• because the air at higher altitudes has a much lower partial pressure than at sea level.

Question 21

How would the haemoglobin in animals with a higher metabolic rate differ from those with a low metabolic rate?

Answer 21

• dissociates with oxygen very easily.
• allows oxygen to be quickly and easily supplied to the cells for use in respiration.

Question 22

Why would an oxyhaemoglobin curve that is shifted to the right be beneficial to an organism?

Answer 22

• oxygen binds less easily/lower affinity for oxygen
• more oxygen given up more easily
• for respiration

Question 23

Why is the Bohr effect beneficial?

Answer 23

• Hb affinity for O2 reduced
• O2 given up more readily for aerobic respiration

Question 24

How would a physiological change during exercise allow excess CO2 to be released whilst pCO2 PER BREATH stays constant?

Answer 24

• increased breathing rate
• same pCO2 but breaths more frequent