Haemoglobin (oxygen dissociation curve, Bohr effect, adaptations) | A Level Biology

Summary

This video explains the role of hemoglobin in oxygen transport within the body. Hemoglobin is a protein made of four subunits, each containing a heme group that binds oxygen. The oxyhemoglobin dissociation curve illustrates how hemoglobin’s affinity for oxygen varies with oxygen concentration, showing high affinity in the lungs and low affinity in tissues. The Bohr effect explains how increased carbon dioxide reduces hemoglobin’s affinity for oxygen, aiding oxygen release in active tissues. The video also explores how different organisms adapt their hemoglobin to their environments, such as fetal hemoglobin, which binds oxygen more readily in low-oxygen conditions.

Takeaways

• 😀 Red blood cells are specialized to carry oxygen through the protein hemoglobin, which consists of four subunits and a heme group containing iron (Fe2+).
• 😀 Hemoglobin binds to oxygen in the lungs to form oxyhemoglobin, a reversible process, unloading oxygen in tissues with lower oxygen concentration.
• 😀 The oxyhemoglobin dissociation curve shows the relationship between partial pressure of oxygen (x-axis) and hemoglobin saturation with oxygen (y-axis).
• 😀 The S-shaped curve indicates that hemoglobin's affinity for oxygen increases after the first oxygen molecule binds due to cooperative binding.
• 😀 In the lungs, high oxygen concentration increases hemoglobin’s affinity for oxygen, while in tissues, low oxygen concentration leads to easier oxygen unloading.
• 😀 Carbon dioxide causes the oxyhemoglobin dissociation curve to shift to the right (Bohr effect), lowering hemoglobin’s oxygen affinity in tissues for increased oxygen unloading.
• 😀 The Bohr effect benefits oxygen unloading during activities like exercise when CO2 levels rise and pH drops.
• 😀 Hemoglobin structure can differ between organisms based on environmental adaptations, with variations in amino acid sequences leading to changes in shape and oxygen affinity.
• 😀 Hemoglobin curves shifted to the left indicate a higher affinity for oxygen, which is useful in low oxygen environments, like fetal hemoglobin in the placenta.
• 😀 Hemoglobin curves shifted to the right reflect a lower oxygen affinity, benefiting organisms that need more oxygen in their tissues, such as those with a high metabolic rate.
• 😀 Organisms are adapted to their environments through variations in hemoglobin structure, enhancing survival by optimizing oxygen uptake and delivery based on environmental needs.

Q & A

What is the primary function of red blood cells?

Red blood cells are specialized to carry oxygen throughout the body.

What is hemoglobin and what role does it play in red blood cells?

Hemoglobin is a protein found in red blood cells, made up of four subunits. It binds to oxygen, allowing red blood cells to carry oxygen from the lungs to tissues and unload it where it's needed.

How is hemoglobin's structure related to its function?

Hemoglobin has a ternary structure, meaning it is made of four polypeptide subunits. Each subunit contains a heme group with an iron ion (Fe²⁺), which binds to oxygen, enabling hemoglobin to carry it efficiently.

What is the oxyhemoglobin dissociation curve and why is it important?

The oxyhemoglobin dissociation curve shows the relationship between the partial pressure of oxygen and the percentage saturation of hemoglobin with oxygen. It is important because it illustrates how oxygen binds and unloads from hemoglobin in different conditions, such as in the lungs and tissues.

Why is the oxyhemoglobin dissociation curve shaped like an 'S'?

The curve is 'S' shaped due to the cooperative nature of oxygen binding. As one oxygen molecule binds to hemoglobin, it changes the shape of the protein, making it easier for subsequent oxygen molecules to bind.

How does the partial pressure of oxygen influence hemoglobin's oxygen affinity?

In areas with high oxygen concentration (like the lungs), hemoglobin has a high affinity for oxygen and binds it efficiently. In areas with low oxygen concentration (like tissues), hemoglobin has a lower affinity, allowing oxygen to unload where it’s needed for respiration.

What is the Bohr effect and how does it affect oxygen unloading?

The Bohr effect occurs when increased carbon dioxide in the blood lowers pH, which reduces hemoglobin's affinity for oxygen. This helps oxygen unload more readily in tissues, especially during activities like exercise when oxygen demand increases.

How can the oxyhemoglobin dissociation curve shift in response to changes in carbon dioxide levels?

An increase in carbon dioxide shifts the oxyhemoglobin dissociation curve to the right, lowering hemoglobin's affinity for oxygen, thus promoting oxygen unloading in tissues.

How do different organisms have adapted hemoglobin to their environments?

Different organisms may have variations in hemoglobin structure to better suit their environments. For example, some organisms have hemoglobin with a higher affinity for oxygen, useful in low-oxygen environments, while others have hemoglobin with a lower affinity, suited to active or high-metabolism environments.

What is the significance of fetal hemoglobin having a higher affinity for oxygen than adult hemoglobin?

Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin, which allows the fetus to absorb oxygen from the mother’s blood across the placenta, even when the oxygen concentration in the mother's blood is lower.