Haemoglobin

Question 1

Why can’t oxygen be carried in the blood as it is

Answer 1

Solubility of oxygen in aqueous solutions is low

More efficient to have the oxygen-carrying molecule haemoglobin

Question 2

How many molecules of haemoglobin does an erythrocyte carry

Answer 2

300 million

Question 3

Haemoglobin

Answer 3

A quaternary protein
Composed of four subunits
Each containing a haem group (Fe2+)
Has an affinity for oxygen
Carries oxygen in the blood

Question 4

Affinity

Answer 4

Chemical attraction

Question 5

What is formed when oxygen and haemoglobin combine

Answer 5

Oxyhaemoglobin

Question 6

Percentage saturation of haemoglobin

Answer 6

Oxygenated haemoglobin/Maximum saturation x 100

Question 7

Partial pressure of oxygen

Answer 7

The amount of oxygen in a mixture of gas or solution

pO2/kPa

Question 8

Lower pO2

Answer 8

Less haemoglobin saturated with oxygen

Question 9

Where is the low partial pressure of oxygen

Answer 9

Tissues/respiring cells

Around 5kPa at rest

Question 10

Where is the high partial pressure of oxygen

Answer 10

In lungs
Around 16kPa
In capillaries around 13.16kPa

Question 11

Loading/association

Answer 11

When oxygen is taken up by haemoglobin

Question 12

Unloading/dissociation

Answer 12

When oxygen is released/given up by haemoglobin

Question 13

When is oxygen unloaded

Answer 13

In low oxygen concentrations
Low pO2/kPa
So it can be used by respiring cells/tissues

Question 14

When does Hb have a higher affinity for oxygen

Answer 14

At high partial pressures of oxygen

Question 15

Explain the cooperative nature of oxygen loading

Answer 15

The first oxygen molecule binding to Hb alters its three D tertiary structure
Exposing the 2nd and 3rd binding sites
So it is easier for the 2nd and 3rd oxygen molecules to bind and load

Question 16

Oxygen dissociation curve name of shape

Answer 16

Sigmoid

Question 17

Hb maximum saturation

Answer 17

98%

When red blood cells pass through the pulmonary capillaries

Question 18

Explain the importance of the pO2 in tissues

Answer 18

Low due to aerobic respiration

Hb has a lower affinity for O2 at lower pO2 so oxyhaemoglobin starts to break down and oxygen is unloaded

Question 19

How does the oxygen dissociation curve provide evidence for the cooperative nature of oxygen loading

Answer 19

At low pO2 there is little increase in saturation as oxygen increases
Then a rapid increase as it gets easier for 2nd and 3rd oxygen molecules to bind

Question 20

Explain the effect of increased respiration on oxygen dissociation

Answer 20

Tissue cells respire anaerobically
Reducing the dissolved oxygen in the surrounding tissue fluid
Reducing partial pressure to a level lower than normal
Oxygenated blood with fully saturated haemoglobin unloads oxygen more readily
Due to Hb now having a lower affinity to oxygen because of low kPa
More oxygen unloaded at respiring cells for respiration to provide ATP for muscle contraction

Question 21

What is the effect of carbon dioxide in the blood

Answer 21

Dissolves in the blood
Making it more acidic and lowering pH
Since Hb is a protein the change in pH slightly alters its tertiary structure
So it has a lower affinity to O2 at high levels of pCO2

Question 22

Explain the Bohr shift

Answer 22

Higher than normal pCO2 causes oxygen dissociation curve to shift to the right
CO2 makes blood more acidic so changes the shape of the protein Hb
Reducing its affinity to oxygen
And decreasing the saturation for the same pO2
Since the pO2 will be high at respiring cells, more oxygen will be unloaded
To be used for aerobic respiration to produce ATP
To meet the demands of oxygen of the organisms cells

Question 23

Explain the relationship between surface area to volume ratio of mammals and the effect of this on the oxygen dissociation curve of their Hb

Answer 23

Smaller mammals have a greater surface area to volume ratio
So more more heat lost per unit mass
Smaller mammals have a greater rate of respiration/metabolism
Oxygen is required for this aerobic respiration
So Hb unloads oxygen more readily at the tissues because has a lower affinity for oxygen

Shifts to right

Question 24

What does a steep oxygen dissociation curve mean

Answer 24

Oxygen unloaded more readily in small decreases of oxygen

Question 25

Advantage of the oxygen dissociation curve of a foetus being to the left of its mother

Answer 25

Higher affinity so loads more oxygen
At low partial pressures of oxygen
Oxygen can move from the mother to the foetus

Question 26

Explain lugworm haemoglobin

Answer 26

Live in burrows in sand, water fills up hole when tide changes
Use oxygen that diffuses into it from surrounding water
Hb will have a higher affinity for oxygen
So can saturate Hb at low partial pressures
Since between tides the pO2 will be low
Tissues still have a slightly lower pO2
Steep curve means oxygen will be unloaded rapidly at tissues when required even when only small changes in pO2

Question 27

Explain how oxygen is loaded and transported and unloaded in the blood

Answer 27

Hb has a high affinity for oxygen
Carries oxygen as oxyhaemoglobin in the red blood cells
Association/loading occurs in the lungs
At high partial pressures of oxygen
Unloaded/dissociation occurs at respiring tissues
At low partial pressures of oxygen
Caused by a higher concentration of carbon dioxide and a reduced affinity

Question 28

Explain the relationship between Foetal and Adult haemoglobin

Answer 28

Different tertiary structure
Foetal has a higher affinity for oxygen at low partial pressures of oxygen
Like those in the womb
Meaning oxygen can still get to the foetus even if there is little oxygen left in the mothers blood
Once born foetal Hb breaks down in the first few months
And is replaced by adult Hb
Which has a decreased affinity for oxygen
So more oxygen is unloaded at the respiring cells/tissue
So more aerobic respiration to produce the energy in the form of ATP needed for things like growth and movement