Question

All of the following can bond with hemoglobin except a. \(\mathrm{HCO}_{3}^{-}\) b. \(\mathrm{O}_{2}\). c. \(\mathrm{H}^{+}\). d. \(\mathrm{CO}_{2}\). e. NO.

Short answer

The correct answer is a. \(\mathrm{HCO}_{3}^-\) (Bicarbonate ion), as it is not known to bond with hemoglobin.

Step-by-step solution

List the molecules that bond with hemoglobin

Hemoglobin is known for its capability to bond with the following molecules: 1. Oxygen (\(\mathrm{O}_2\)) 2. Carbon dioxide (\(\mathrm{CO}_2\)) 3. Protons/hydrogen ions (\(\mathrm{H}^+\)) 4. Nitric oxide (NO)

Compare the given options with the known list

Now that we have the list of known molecules that bond with hemoglobin, let's compare it to the given options: a. \(\mathrm{HCO}_{3}^{-}\) (Bicarbonate ion) b. \(\mathrm{O}_{2}\) (Oxygen) c. \(\mathrm{H}^{+}\) (Proton/Hydrogen ion) d. \(\mathrm{CO}_{2}\) (Carbon dioxide) e. NO (Nitric oxide)

Identify the option that does not bond with hemoglobin

Comparing the list of known molecules that bond with hemoglobin, we can see that option (a) Bicarbonate ion (\(\mathrm{HCO}_3^-\)) is not in the list. Therefore, the correct answer is: a. \(\mathrm{HCO}_{3}^-\) (Bicarbonate ion)

Key concepts

Hemoglobin and Oxygen Transport

Hemoglobin, a protein found in red blood cells, is critically important for oxygen transport in the body. It has the vital role of carrying oxygen from the lungs to the tissues and organs that require it for cellular respiration. The oxygen molecules bind to the iron atoms within the hemoglobin molecule, enabling each hemoglobin unit to transport up to four molecules of oxygen.

To understand this process, imagine hemoglobin as a bus with four seats reserved for oxygen passengers. Once hemoglobin reaches oxygen-rich areas of the lungs, the 'seats' get occupied by oxygen molecules. As the blood circulates and passes through the oxygen-hungry tissues, these molecules disembark, delivering the essential gas for the production of energy within cells.
The efficiency of oxygen transport is influenced by factors such as the pH level of the blood and the presence of carbon dioxide, which can cause hemoglobin to release oxygen more readily. This relationship between oxygen release and the acidity or carbon dioxide level in the blood is known as the Bohr effect.

Hemoglobin and Carbon Dioxide Transport

While hemoglobin is widely recognized for its role in oxygen transport, it also plays a key part in carbon dioxide transport from the tissues back to the lungs for exhalation. Carbon dioxide, a waste product of metabolism, is transported in the blood in three main ways: dissolved directly in the blood plasma, converted into bicarbonate ions (\(\mathrm{HCO}_3^-\)), or bound to hemoglobin.

When \(\mathrm{CO}_2\) is produced by cells, it diffuses into red blood cells, where it can bind to hemoglobin to form carbaminohemoglobin. However, this is not a permanent bond; when the red blood cells reach the lungs, \(\mathrm{CO}_2\) is released from the hemoglobin due to the higher oxygen concentration and low \(\mathrm{CO}_2\) levels. It is then expelled as we exhale. Interestingly, the presence of \(\mathrm{CO}_2\) lowers the blood's pH, promoting the release of oxygen from hemoglobin – another example of the Bohr effect in action.

Hemoglobin and Acid-Base Balance

The acid-base balance in the blood is a delicate equilibrium that is crucial for normal physiological functions. Hemoglobin contributes to maintaining this balance by its ability to bind to protons (\(\mathrm{H}^+\)), which are released during metabolic processes and can affect the blood's pH. When hemoglobin releases oxygen, it becomes more acidic and readily accepts \(\mathrm{H}^+\) ions, thus preventing a decrease in blood pH.

Hemoglobin's ability to buffer the blood also involves its interaction with bicarbonate ions, although it cannot directly bind to \(\mathrm{HCO}_3^-\). Instead, the enzyme carbonic anhydrase in red blood cells rapidly converts \(\mathrm{CO}_2\) and water into \(\mathrm{HCO}_3^-\) and hydrogens ions. The bicarbonate then diffuses into the plasma, playing a central role in the bicarbonate buffer system, which is essential for maintaining blood pH within its narrow range of normalcy. Hemoglobin's functional flexibility allows it to act as a transporter of gases and also as an acid-base buffer, facilitating the complex regulatory mechanisms that keep our internal environment stable.