A Level Biology Revision "Haemoglobin and the Oxygen Dissociation Curve"

Summary

This video from Free Science explores hemoglobin's role in oxygen transport. It explains how red blood cells' biconcave shape and lack of a nucleus facilitate oxygen carriage. Hemoglobin, with its four polypeptide chains, can bind up to four oxygen molecules. The oxygen dissociation curve, depicted as an S-shaped graph, illustrates hemoglobin's affinity for oxygen, which increases with each oxygen molecule bound due to positive cooperativity. This ensures efficient oxygen delivery to tissues and its release where needed.

Takeaways

• 🩸 The primary role of hemoglobin is to transport oxygen in the mammalian circulatory system.
• 🔵 Red blood cells, or erythrocytes, have a biconcave shape that facilitates rapid oxygen diffusion due to their large surface area to volume ratio.
• 🌐 Each erythrocyte contains approximately 300 million molecules of hemoglobin, an oxygen-carrying protein.
• 🧬 Hemoglobin is composed of four polypeptide chains, each associated with a heme group containing an iron ion (Fe2+) that can bind to oxygen.
• 🔗 Hemoglobin's ability to bind oxygen is reversible, allowing it to release oxygen when necessary, forming oxyhemoglobin.
• 📈 The oxygen dissociation curve illustrates the relationship between the percentage saturation of hemoglobin with oxygen and the partial pressure of oxygen.
• 🆙 At low partial pressures of oxygen, hemoglobin has a low affinity for oxygen, but this affinity increases once oxygen molecules start binding.
• 🔄 The structural change in hemoglobin upon oxygen binding, known as positive cooperativity, enhances the affinity for additional oxygen molecules.
• 🏋️ In active tissues with low oxygen partial pressure, hemoglobin releases oxygen, which is essential for cellular respiration.
• 🏃‍♂️ During intense exercise, such as in muscle tissue, the partial pressure of oxygen can be so low that all oxygen molecules may be released from hemoglobin.

Q & A

What is the primary role of hemoglobin in the mammalian circulatory system?

The primary role of hemoglobin is to transport oxygen within the mammalian circulatory system.

How is the structure of erythrocytes adapted for oxygen transport?

Erythrocytes have a biconcave structure, which provides a large surface area to volume ratio, allowing oxygen to diffuse in and out rapidly.

How many molecules of hemoglobin does each erythrocyte contain?

Each erythrocyte contains around 300 million molecules of the oxygen-carrying protein hemoglobin.

Why do erythrocytes lose their nucleus before entering circulation?

The absence of a nucleus in erythrocytes allows for more of their volume to be available to carry hemoglobin.

What is the composition of a hemoglobin molecule?

A hemoglobin molecule consists of four polypeptide chains, two shown in red and two in blue, each bound to a heme group.

What is the role of the iron ion Fe2+ in hemoglobin?

The iron ion Fe2+ in the heme group of hemoglobin allows each heme molecule to bind with one molecule of oxygen.

What is the term for hemoglobin when it binds to oxygen?

When hemoglobin binds to oxygen, it is referred to as oxyhemoglobin.

How is the oxygen dissociation curve measured?

The oxygen dissociation curve is measured by plotting the percentage saturation of hemoglobin with oxygen on the y-axis against the partial pressure of oxygen on the x-axis.

What does the S-shaped curve of the oxygen dissociation curve indicate?

The S-shaped curve, or sigmoid curve, indicates that hemoglobin has a low affinity for oxygen at low partial pressures and a high affinity at high partial pressures.

What is meant by the term 'positive cooperativity' in the context of hemoglobin?

Positive cooperativity refers to the phenomenon where the binding of one oxygen molecule to hemoglobin increases the affinity of the remaining heme groups for oxygen, facilitating the binding of additional oxygen molecules.

How does the partial pressure of oxygen affect the saturation of hemoglobin in the body?

In the alveoli, where the partial pressure of oxygen is high, hemoglobin is around 97% saturated. As red blood cells move into body tissues with lower oxygen partial pressure, oxygen molecules are unloaded from hemoglobin to support aerobic respiration.

What happens to the quaternary structure of hemoglobin when an oxygen molecule unloads?

When an oxygen molecule unloads from hemoglobin, the quaternary structure of the molecule changes, decreasing the oxygen affinity of the remaining heme groups.