Haemoglobin

Question 1

What is another name for red blood cells?

Answer 1

Erythrocytes

Question 2

What are the three adaptations of the erythrocytes?

Answer 2

1. The biconcave structure provides a large surface area to volume ratio which increases and diffusion rate for oxygen to diffuse out of the blood rapidly
2. Contain many oxygen carrying haemoglobin
3. Contain no nucleus so that more of the volume of the erythrocyte can carry haemoglobin

Question 3

What does each haem prosthetic group in haemoglobin contain?

Answer 3

An Fe²+group

Question 4

What is it in the haem group that Oxygen binds to?

Answer 4

Fe 2²⁺

Question 5

How many oxygens can bind to one Hb?

Answer 5

4

Question 7

How many haem groups does each Hb contain?

Answer 7

4 in each poplypeptide chain subunit

Question 8

What is the equation for the formation of oxyhaemoglobin?

Answer 8

Hb + 4O₂ ⇌ Hb(O₂)₄

Question 9

What is the shape of the oxygen dissociation curve?

Answer 9

Sigmoidal, S-shaped curve due to cooperative binding

Question 10

Explain why at low pO₂ the oxygen dissociation graph is slow

Answer 10

At low pO₂ the Hb has a low oxygen affinity and so it is difficult for Hb to pick up and bind with oxygen

Question 11

Explain why it is easier for Hb to pick up oxygen 2 and 3 as shown on the oxygen dissociation curve

Answer 11

Cooperative binding- The oxygen affinity of Haemoglobin increases because when the first oxygen binds to Hb, it distorts and changes the shape of the molecule. This makes it easier for more oxygen to bind

Question 12

Why is it more difficult for the fourth oxygen to bind with Hb?

Answer 12

After three oxygens have binded to the haem groups in Hb, it is very dfficult for the fourth to bind, even at a high pO₂ it is difficult for Hb to become fully saturated.

Question 13

Give a difference between faetal haemoglobin and adult haemoglobin and a reason for this difference

Answer 13

DIFFERENCE:
Foetal Hb has a higher affinity for oxygen
REASON:
It needs to be able to bind to oxygen in a lower partial pressure in the placenta

Question 14

What is the role of Haemoglobin?

[3 marks]

Answer 14

• Hb binds to oxygen in the alveoli where there is a high pO₂ to form oxyhaemoglobin
• The oxygen is then released in the tissues where respiration is occuring

Question 15

Hb has a high affinity for oxygen in a [blank] partial pressure and will pick up and bind to oxygen e.g. in the alveoli

fill in the blank

Answer 15

high

Question 16

Hb has a low affinity for oxygen in a [blank] partial pressure and will release oxygen e.g. in respiring tissues

Answer 16

low

Question 17

What is the effect of a high partial pressure of carbon dioxide on the oxygen dissociation curve?

Answer 17

It shifts the curve to the right
(as in high pCO₂ Hb has a lower affinity for oxygen and so releases it more easily- the Bohr effect)

Question 18

Why is the Bohr effect important?

Answer 18

• In the lungs where there is a high partial pressure of oxygen and low partial pressure of carbon dioxide, Hb will have a higher affinity for oxygen and bind to oxygen more easily
• In respiring tissues there is a low partial pressure of oxygen and high partial pressure of carbon dioxide. Hb will have a lower affinity for oxygen and so will release oxygen into the respiring tissues more easily.

Question 19

How is around 5% of carbon dioxide transported around the body?

Answer 19

It directly diffuses into the blood plasma

Question 20

How is around 20% of carbon idoxide transported around the body?

Answer 20

Carbon dioxide reacts with haemoglobin to form carbaminohaemoglobin in a reversible reaction

Question 21

What does the reaction between carbon dioxide and haemoglobin form?

Answer 21

carbaminohaemoglobin

Question 22

How many carbon dioxide molecules can react with one molecule of haemoglobin?

Answer 22

Four

Question 23

How is majority of carbon dioxide transported around the body?

Answer 23

• in **high pCO₂, **Carbon dioxide diffuses into the erythrocytes and reacts with water to form carbonic acid
• the carbonic anhydrase enzyme in the erythrocytes catalyses this reaction
• The carbonic acid dissociates, forming the hydrogen carbonate ion (HCO₃^- and the hydrogen ion (H⁺
• The hydrogen carbonate ion diffuses out of the erythrocytes into the blood plasma, down the concentration gradient. The chloride ion diffuses into the erythrocyte to maintain the charge balance
• The hydrogen ion reacts with haemoglobin to form haemoglobinic acid

Question 24

What is the effect of the formation of carbonic acid in the red blood cells?

Answer 24

• It reduces the level of carbon dioxide in the red blood cells.
• This creates a steep concentration gradient for carbon dioxide and so increases the rate and efficiency of the diffusion of carbon dioxide into the red blood cells

Question 25

When **carbon dioxide** is in the **blood plasma** it is **[blank]** from the lungs when blood passes the **[blank]** ## Footnote **fill in the blanks**

Answer 25

* **exhaled** * **alveoli**

Question 26

**How** is the **oxygen dissociation curve different** for **foetal Hb** compared to **adult Hb**?

Answer 26

It is shifted more to the **left** (as foetal Hb has a higher affinity for oxygen than adult Hb so that it can bind to oxygen in the low pO₂ of the placenta)

Question 27

**Why** would it be **bad** if **foetal Hb** had a **MUCH high affinity** for oxygen than **adult Hb**

Answer 27

This would **prevent foetal Hb** from **releasing oxygen** into the **foetal tissues**

Question 28

**What else** makes the **oxygen binding** of **foetal Hb very efficient**?

Answer 28

* **Carbon dioxide** from the **foetus diffuses** into **maternal blood** * The carbon dioxide **lowers** the **oxygen affinity** of the **maternal haemoglobin** so that it **releases more oxygen** and transfers it to the blood of the foetus