⭐️Exchange: Haemoglobin

Question 1

What is haemoglobin made of?

Answer 1

A quaternary protein molecule made of 4 polypeptides (two of which are alpha polypeptides and 2 are beta polypeptides) where each one is associated with a haem group which contains an Fe2+ ion.

Question 2

Where do oxygen molecules mind on a heamoglobin?

Answer 2

The bind to the Fe2+ of each polypeptide so each haemoglobin molecule can carry for O2 molecules

Question 3

What is affinity?

Answer 3

The degree to which a substance tends to bind with another

Question 4

What is loading and where does it occur?

Answer 4

The process of haemoglobin binding with oxygen and it takes place in the lungs

Question 5

What is unloading and where does it occur?

Answer 5

The process of haemoglobin releasing oxygen and it occurs in the tissues

Question 6

Give two things haemoglobin must do to be efficient in carrying out its role in transporting oxygen. How is it able to do these both?

Answer 6

• readily associating with oxygen at the surface where gas exchange takes place
• readily dissociating from oxygen at the tissues that require it

By changing its affinity for oxygen under different conditions

Question 7

How is haemoglobin able to change its affinity under different conditions? Give an example

Answer 7

As it’s shape is able to change in the presence of certain substances. For example, in the presence of carbon dioxide, the new shape of the haemoglobin molecule binds more loosely to oxygen which as a result causes the haemoglobin to release the oxygen

Question 8

Where is the affinity of haemoglobin high and where is it low?

Answer 8

High at gas exchange surfaces and low in respiring tissue

Question 9

Why do different haemoglobin molecules (from different organisms) have different affinities of oxygen?

Answer 9

Because each species produces a haemoglobin with a slightly different amino acid sequence so they each have different tertiary and quaternary structures and so different binding properties. Depending on its structure haemoglobin moelcules range from those with a high affinity for oxygen and those with a low affinity fro oxygen

Question 10

In the oxygen dissociation curve, why is the gradient of the curve initially shallow?

Answer 10

Because the shape of the Hb molecule makes it hard for the first Hb molecule to bind to one of the four sites because they are closely united so at low oxygen concentrations little oxygen binds

Question 11

In the oxygen dissociation curve, why does the graph steepen?

Answer 11

Because the binding o the first molecule changes the quaternary structure of the haemoglobin molecule causing its shape to change which makes it easier for other subunits to bind to an oxygen molecule.

Question 12

What is positive cooperativity in Hb?

Answer 12

Where it takes a smaller partial pressure of oxygen to bind the second molecule than it did the first one so as more oxygen binds, affinity increases

Question 13

In the oxygen dissociation curve, why does the graph plateau?

Answer 13

Because by now, the majority of binding sites are occupied so it’s less likely that a single oxygen molecule will find an empty site to bind to

Question 14

In the oxygen dissociation curve, what does it mean if:

• the graph is shifted to the left?
• the graph is shifted to the right?

Answer 14

• There is a greater affinity of Hb for oxygen so it loads oxygen readily but it unloads it less easily
• there is a lower affinity of Hb for oxygen so it loads oxygen less readily but it unloads it more easily

Question 15

What is bohr’s affect?

Answer 15

The fact that the greater the concentration of carbon dioxide, the more readily the Hb releases its oxygen

Question 16

How does the Bohr effect explain the behaviour of Hb in gas exchange surfaces?

Answer 16

Because in gas exchange surfaces, the concentration of co2 is low and oxygen is high so the affinity of Hb for oxygen is increased which means oxygen is readily loaded by Hb so the reduced co2 concentration means the oxygen dissociation curve is shifted to the left

Question 17

How does the Bohr effect explain the behaviour of Hb in gas in rapidly respiring tissues?

Answer 17

as here, the concentration of co2 is high and the affinity of haemoglobin for oxygen is reduced so oxygen is readily unloaded from the haemoglobin into the muscle cells and so the oxygen dissociation curve shifts to the right due to the increase in oxygen

Question 18

Why does a greater concentration of carbon dioxide cause haemoglobin to release its oxygen more readily?

Answer 18

Because dissolved carbon dioxide is acidic and the low pH causes the Hb to change shape

Question 19

Give the steps that take place following the loading, transport and unloading of oxygen

Answer 19

1. At the gas exchange surface, carbon dioxide is constantly being removed
2. The pH is slightly raised due to the low concentration of C02
3. The higher pH changes the shape of the Hb into one that enables it to load oxygen more readily
4. This shape also increases the affinity of haemoglobin for oxygen so it’s not released while being transported in the blood to the tissues
5. In the tissues, co2 is produced by respiring cells and this is acidic so the pH of the blood within the tissues is lowered
6. The lower pH changes the shape of the haemoglobin into one with a lower affinity for oxygen and so it releases its oxygen into respiring tissues

Question 20

What shift is the oxygen dissociation curve of a lugworm and what has led that to be the case?

Answer 20

Left shift as the lugworm isn’t very active and the oxygen form the sea water that circulates their burrows diffuse into their blood and then uses Hb to transport the oxygen. When the tide goes out and there’s no fresh water circulating, the oxygen in the burrow reduces so the lugworm has to extract as much oxygen from the water as possible. The left shift means the Hb if fully loaded even if there’s little oxygen in the environment

Question 21

What shift is the oxygen dissociation curve of a llama and why is this the case?

Answer 21

Left shift because the llama lives in high altitudes where atmospheric pressure and so partial pressure of oxygen is lower which makes it difficult to load the Hb with oxygen, hence, their Hb has got a higher affinity