Transport of Oxygen (A-level Biology)
Transport of Oxygen
Haemoglobin
- The haemoglobins are a group of chemically similar molecules found in many different organisms.
The Structure of Haemoglobin
- Haemoglobin is a water soluble gobular protein that has a quaternary structure. This means that it consists of more than one polypeptide chain.
- The structure of Haemoglobin consist of four polypeptide chains. Two chains are ⍺-polypeptides (alpha) and two chains are β-polypeptides (beta).
- Each of the polypeptide chains are associated with a haem group. Each haem group contains an Fe2+ ion which can combine with an oxygen molecule (O2).
- Each haemoglobin molecule can therefore carry four oxygen molecules.
- Fetal haemoglobin has a different affinity for oxygen, compared to adult haemoglobin. This is to allow the foetus to survive at a low partial pressure.
- Fetal haemoglobin needs to be very good at absorbing oxygen. By the time oxygen reaches the placenta, the oxygen saturation of the blood has decreased.
- β-polypeptides (beta) chains are uncommon. Instead, the haemoglobin molecule is made up of two ⍺-polypeptide (alpha) chains and two γ-polypeptide chains (gamma).
Role of Haemoglobin
- Haemoglobin is found in red blood cells (erythrocytes). Haemoglobin allows red blood cells to transport oxygen from the lungs to all other parts of the body.
- When haemoglobin combines with oxygen, oxyhaemoglobin is formed.
The Transport of Oxygen By Haemoglobin
- The association (or loading) of oxygen is the process by which haemoglobin binds with oxygen. In humans, oxygen association occurs in the lungs.
- After oxygen association, the red blood cells transport the oxygen. Oxygen is transported from the lungs to the rest of the body.
- The dissociation (or unloading) of oxygen is the process by which oxygen is released from haemoglobin. In humans, oxygen dissociation occurs at cells which require oxygen, where haemoglobin returns to the lungs in order to bind to oxygen again.
- Affinity is the degree to which one substance combines with another. Haemoglobin has different affinities for oxygen molecules under different conditions.
- When oxygen concentration is high, haemoglobin has a high affinity for oxygen. This means that it will readily associate with oxygen and will dissociate with it less easily.
- When oxygen concentration is low, haemoglobin has a low affinity for oxygen. This means that it will readily dissociate with oxygen and will associate with it less easily.
- Haemoglobin changes its affinity for oxygen by changing its shape when in the presence of certain substances. For example, in high carbon dioxide (CO2) concentration, haemoglobin has a low affinity for oxygen, whereas in low CO2 concentration, haemoglobin has a high affinity for oxygen.
- Having changing affinities for oxygen means that oxygen is only associated/dissociated where necessary. This makes haemoglobin efficient at transporting oxygen because oxygen is readily associated at the gas exchange surface (the lungs) and readily dissociated at the tissues which need it.
Oxyhaemoglobin Dissociation Curves
- The partial pressure of oxygen is a measure of oxygen concentration. Partial pressure is measured in kilopascal (kPa).
- The greater the concentration of dissolved oxygen in a cell, the greater the partial pressure.
- Haemoglobin has different affinities for oxygen depending on its partial pressure. Haemoglobin will readily associate more tightly with oxygen if the partial pressure of oxygen is high and will readily dissociate with oxygen if the the partial pressure of oxygen is low. These two processes are known as loading and unloading.
- The process of respiration uses up oxygen. This decreases partial pressure, in turn decreasing affinity of oxygen for haemoglobin. As a result, oxygen gets released to respiring tissues where needed.
- Oxyhaemoglobin dissociation curves are S-shaped. They show the relationship between the partial pressure of oxygen and the saturation of haemoglobin with oxygen.
- Saturation can have an effect on affinity.
- Gradient of the curve is initially shallow. This is because the shape of haemoglobin makes it hard for the first oxygen molecule to bind to one of the four sites. This explains why haemoglobin has a low affinity for oxygen at low partial pressure of oxygen.
- Gradient of the curve steepens as the second and third oxygen molecules bind. The binding of the first oxygen molecule causes the structure of the haemoglobin to change, and this change in shape makes it easier for the second and third oxygen molecules to bind.
- Gradient of the curve flattens and levels off. Although it should be easier for the fourth oxygen molecule to bind to haemoglobin, it is actually harder because three out of four binding sites are occupied. This makes it less likely that an oxygen molecule will find a site to bind to.
The Effects of Carbon Dioxide Concentration
- Haemoglobin has a lower affinity for oxygen at higher partial pressures (concentrations) of carbon dioxide, causing oxygen to be released. This is known as the Bohr effect and explains why haemoglobin has different affinities at different areas in the body.
- Dissolved carbon dioxide is acidic. When carbon dioxide is present, it lowers the pH of the area and causes the haemoglobin to change shape.
- Respiring cells produce carbon dioxide, and this increases the partial pressure of carbon dioxide. This reduces the affinity of haemoglobin for oxygen, and as there is also a low partial pressure of oxygen at the respiring cells, oxygen is dissociated from haemoglobin.
- At the gas-exchange surface (the lungs), the partial pressure of carbon dioxide is low because here it is removed from the organism. This increases the affinity of haemoglobin for oxygen, and as there is also a high partial pressure of oxygen in the lungs, oxygen is readily associated to haemoglobin.
- The Bohr effect refers to shifts to the oxyhaemoglobin dissociation curve. An increase in partial pressure of carbon dioxide will shift the S-curve to the right, whereas a decrease in partial pressure of carbon dioxide shifts the curve to the left.
Haemoglobin in Different Organisms
- Different species have different types of haemoglobin. These haemoglobins have different oxygen transport properties which are adapted to the environment of each animal.
- Species living in environments with low oxygen concentrations will have haemoglobin with a higher affinity for oxygen. Their oxygen dissociation curve would be to the left of a human’s.
- Species living in environments with high oxygen concentrations and that are also very active will have haemoglobin with a lower affinity for oxygen. Their oxygen dissociation curve would be to the right of a human’s.
In conclusion, we have covered it’s definition and the structure of haemoglobin as well as it’s role in transporting oxygen all over the body. Haemoglobin is an important protein involved in oxygen and carbon dioxide transport, pH regulation, and the prevention of genetic disorders related to hemoglobin. Its study is essential in understanding the biology of the circulatory system and the impact of genetic mutations on human health.
FAQs
Hemoglobin (often spelled haemoglobin) is a protein found in red blood cells that is responsible for carrying oxygen from the lungs or gills to the body’s tissues and organs. It is a globular protein that is made up of four subunits, each containing a heme group, which binds to oxygen. The heme group contains an iron atom, which binds to oxygen in the lungs or gills and releases it in the body’s tissues.
In addition to its role in oxygen transport, hemoglobin also plays a role in the transport of carbon dioxide from the body’s tissues back to the lungs or gills for removal from the body. This is because hemoglobin can also bind to carbon dioxide and other waste products, allowing them to be carried away from the tissues.
Hemoglobin is essential for the proper functioning of the circulatory system and overall health. Any disruption in its production or function can lead to serious health problems, including anemia and oxygen deprivation in the body’s tissues.
In A-level Biology, the structure of haemoglobin is often described as a quaternary protein structure. It is made up of four polypeptide chains, with each chain containing a heme group. The four polypeptide chains are classified as two alpha chains and two beta chains. The alpha and beta chains are arranged in pairs, with each pair forming a subunit of the protein.
Each heme group within a subunit can bind to one molecule of oxygen, and the binding of oxygen to one heme group can affect the binding of oxygen to the other heme groups within the same subunit. This is known as cooperative binding, and it allows hemoglobin to effectively bind to and release oxygen as needed by the body’s tissues.
The amino acid sequences of the alpha and beta chains of hemoglobin are encoded by separate genes, which can undergo mutations that affect the structure and function of the protein. For example, mutations in the gene that encodes the beta chain can lead to the production of abnormal forms of hemoglobin, such as sickle cell hemoglobin, which can cause health problems such as sickle cell anemia.
The transport of oxygen refers to the movement of oxygen from the atmosphere to the cells of an organism, where it is used in cellular respiration to produce energy.
The transport of oxygen is important in A-level Biology as it is a fundamental process in the survival and metabolism of living organisms. It is essential for the production of energy and the maintenance of vital bodily functions.
The different types of oxygen transport in the body include:
Dissolved Oxygen: oxygen that is dissolved in the blood plasma.
Hemoglobin: a protein in red blood cells that binds to oxygen and carries it to the cells.
Myoglobin: a protein in muscle cells that stores oxygen for cellular respiration.
Hemoglobin transports oxygen through the binding of oxygen molecules to the iron atoms in the hemoglobin molecule. The binding of oxygen to hemoglobin causes a change in the shape of the hemoglobin molecule, allowing it to pick up more oxygen as it travels through the lungs. When the hemoglobin reaches the cells, the oxygen is released and used in cellular respiration.
The factors that affect the transport of oxygen include:
Concentration of Oxygen: the higher the concentration of oxygen, the more oxygen that can be transported by hemoglobin.
Altitude: at higher altitudes, the air pressure and oxygen concentration decreases, making it harder for hemoglobin to transport oxygen.
Temperature: higher temperatures increase the solubility of oxygen in the blood, making it easier for hemoglobin to transport oxygen.
Acidity: changes in the acidity of the blood can affect the ability of hemoglobin to bind to oxygen.
A deficiency in oxygen transport can lead to a range of health problems, including:
Anemia: a condition where there is a reduction in the number of red blood cells or a decrease in the hemoglobin content of the blood.
Hypoxia: a condition where there is a decrease in the supply of oxygen to the tissues and organs.
Ischemia: a condition where there is a restriction of blood supply to a particular part of the body.
The oxyhaemoglobin dissociation curve is a graph that illustrates the relationship between the partial pressure of oxygen (pO2) in the blood and the saturation of hemoglobin with oxygen (SO2). It shows how much oxygen is bound to hemoglobin at different pO2 levels.
The curve is sigmoidal in shape, meaning that the rate of oxygen binding to hemoglobin increases as the pO2 increases until a certain point, after which it levels off. This point is known as the plateau region or the saturation point, where almost all of the hemoglobin is fully saturated with oxygen. The curve then starts to decline steeply as the pO2 increases further, indicating that hemoglobin is becoming less efficient at binding to oxygen.
Understanding the oxyhaemoglobin dissociation curve is important in the diagnosis and treatment of respiratory disorders, such as chronic obstructive pulmonary disease (COPD), as it helps to determine how much oxygen is being delivered to the body’s tissues and how efficiently hemoglobin is binding to and releasing oxygen.
Oxygen transport can be improved through a range of interventions, including:
Exercise: regular physical activity can improve the efficiency of the cardiovascular system, increasing the amount of oxygen that is transported to the cells.
Improved respiratory function: improving respiratory function, for example, through breathing exercises, can increase the amount of oxygen that is inhaled and transported to the cells.
Increased hemoglobin production: increasing the production of hemoglobin, for example, through diet and supplements, can improve the transport of oxygen.
Understanding the oxyhemoglobin dissociation curve is important in the diagnosis and treatment of respiratory disorders, such as chronic obstructive pulmonary disease (COPD), as it helps to determine how much oxygen is being delivered to the body’s tissues and how efficiently hemoglobin is binding to and releasing oxygen.
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