8-10 Haemoglobin & Oxygen Dissociation Curve (Cambridge AS & A Level Biology, 9700)

Summary

This video revisits the structure and function of red blood cells, focusing on hemoglobin, a globular protein responsible for oxygen transport. It explains how hemoglobin can bind to four oxygen molecules, forming oxyhemoglobin, and describes its dual properties: a high affinity for oxygen and a readiness to release it when needed. The video also covers the oxygen dissociation curve, showing how hemoglobin's oxygen saturation changes with different partial pressures of oxygen, and how this is crucial for supplying oxygen to body cells during respiration.

Takeaways

• 🔴 Hemoglobin is a globular protein, made up of four polypeptide chains, and each chain contains a heme group with iron that binds to oxygen.
• 🔍 Hemoglobin has a duality in its behavior: it has a high affinity for oxygen but also readily releases oxygen when needed.
• ⚖️ The binding of oxygen to hemoglobin forms oxyhemoglobin, with one hemoglobin molecule able to bind to four oxygen molecules (eight oxygen atoms).
• 🔄 The oxygen binding process is reversible, allowing hemoglobin to both attach to and release oxygen depending on the environment.
• 📉 The oxygen dissociation curve shows the relationship between partial pressure of oxygen and hemoglobin's oxygen saturation, creating a sigmoid (S-shaped) curve.
• 🌡️ Partial pressure of oxygen refers to the concentration of oxygen in a given area, affecting how much oxygen hemoglobin can carry.
• 💯 Oxygen saturation of hemoglobin is the percentage of oxygen bound to it. A red blood cell with fully bound oxygen has 100% saturation.
• 📊 At low partial pressures of oxygen, hemoglobin is less saturated, but at high partial pressures, it becomes fully saturated.
• 🎯 Hemoglobin releases more oxygen when the body cells have lower oxygen levels, especially in areas where the partial pressure of oxygen is low.
• 🫁 In the lungs, hemoglobin binds to oxygen due to the high partial pressure, and in the body cells, hemoglobin releases oxygen when partial pressure drops, facilitating oxygen transfer to tissues.

Q & A

What is hemoglobin and why is it referred to as a globular protein?

Hemoglobin is a protein found in red blood cells that carries oxygen. It is referred to as a globular protein because of its spherical shape and its solubility in water.

Why is hemoglobin considered a quaternary protein?

Hemoglobin is considered a quaternary protein because it is made up of four polypeptide chains: two alpha-globin and two beta-globin chains, each of which has a heme group.

What role does iron play in hemoglobin?

Iron is found in the heme group of hemoglobin, and it binds to oxygen. This interaction is crucial for oxygen transport and is also responsible for the red color of red blood cells due to the formation of iron oxide.

How many oxygen molecules can one hemoglobin molecule bind, and why?

One hemoglobin molecule can bind up to four oxygen molecules because it has four heme groups, each of which can attach to one oxygen molecule.

What is meant by the duality of hemoglobin?

The duality of hemoglobin refers to its ability to both strongly bind oxygen and readily release it when needed. Hemoglobin can hold onto oxygen when oxygen levels are high and release it when oxygen levels are low.

What is the oxygen dissociation curve, and what does it represent?

The oxygen dissociation curve is a graph that shows the relationship between the partial pressure of oxygen and the percentage saturation of hemoglobin with oxygen. It is typically S-shaped (sigmoid), indicating how hemoglobin binds oxygen under different oxygen concentrations.

What is meant by 'partial pressure of oxygen,' and how does it affect hemoglobin?

Partial pressure of oxygen refers to the concentration of oxygen gas in a particular area. Hemoglobin’s ability to bind or release oxygen depends on the partial pressure, with higher partial pressures leading to greater oxygen binding and lower partial pressures promoting oxygen release.

What is percentage saturation of oxygen in hemoglobin?

Percentage saturation refers to how full hemoglobin is with oxygen. For example, if hemoglobin is fully bound to four oxygen molecules, it is 100% saturated. If it has only two oxygen molecules, it is 50% saturated.

How does hemoglobin respond when exposed to areas with low partial pressure of oxygen?

In areas with low partial pressure of oxygen, such as body tissues using oxygen for respiration, hemoglobin releases a significant portion of its oxygen. This allows the cells to receive the oxygen they need.

What happens when red blood cells pass through the lungs versus body cells in terms of oxygen saturation?

In the lungs, where the partial pressure of oxygen is high, hemoglobin in red blood cells becomes fully saturated (100%) with oxygen. As these red blood cells pass through body cells where oxygen pressure is lower, hemoglobin releases oxygen, reducing its saturation.