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Chapter 21: Problem 20

Why are \(\mathrm{CN}^{-}\) and \(\mathrm{CO}\) toxic to humans?

Short Answer

Expert verified
CN- (cyanide ion) and CO (carbon monoxide) are toxic to humans because they interfere with cellular respiration, preventing cells from producing the necessary energy for survival. CN- binds to cytochrome c oxidase (complex IV) in the mitochondria, blocking the electron transport chain and halting ATP production. CO, on the other hand, competes with oxygen for binding sites on hemoglobin, impairing oxygen transportation to cells and reducing ATP production. Both CN- and CO, therefore, affect the ability of cells to produce ATP and can cause significant harm to the human body.

Step by step solution

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1. Introduction to CN- and CO

CN- (cyanide ion) and CO (carbon monoxide) are toxic to humans because they can interfere with the cellular respiration process, preventing cells from producing the energy necessary for survival. Let's dive deeper into the specific ways in which each of these molecules disrupts cellular respiration.
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2. CN- and Cellular Respiration

In the human body, CN- is toxic because it can bind to an enzyme called cytochrome c oxidase (complex IV) found in the mitochondria. This enzyme is an essential component of the electron transport chain, a series of chemical reactions that generate adenosine triphosphate (ATP) – the primary energy source for cells. When CN- binds to the cytochrome c oxidase, it blocks the enzyme from transferring electrons to oxygen, ultimately preventing the formation of water and halting the electron transport chain. As a result, cells can't produce ATP, leading to a lack of energy and eventually causing cell death and tissue damage.
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3. CO and Cellular Respiration

CO is also a potent toxicant that affects cellular respiration. CO is structurally similar to molecular oxygen (O2), and this similarity allows CO to bind with hemoglobin, the protein in red blood cells responsible for carrying oxygen from the lungs to the tissues. However, CO binds to hemoglobin with an affinity that is over 200 times greater than that of oxygen, making it extremely difficult for oxygen to compete with CO for binding sites on hemoglobin. As a result, when there is a significant amount of CO in the environment, the hemoglobin in red blood cells will predominantly bind with CO rather than oxygen. This means less oxygen can be transported to cells and used in the electron transport chain, impairing ATP production and leading to tissue hypoxia. In summary, both CN- and CO can interfere with cellular respiration, affecting the ability of cells to produce ATP – a critical energy source required for cell function and survival. CN- binding to the cytochrome c oxidase in the electron transport chain and CO competing with oxygen for binding sites on hemoglobin ultimately lead to a lack of energy at the cellular level and can cause significant harm to the human body.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Cytochrome c Oxidase
Cytochrome c oxidase is the last enzyme in the respiratory electron transport chain of mitochondria. It plays a pivotal role in cellular respiration by facilitating the transfer of electrons from cytochrome c to oxygen, which is reduced to water. This step is crucial as it maintains the flow of electrons through the chain, allowing for the creation of a proton gradient across the mitochondrial membrane.

During this process, protons are pumped from the mitochondrial matrix to the intermembrane space, storing energy that is later utilized by ATP synthase to generate ATP from ADP and inorganic phosphate. When toxic substances like cyanide (CN-) bind to cytochrome c oxidase, they inhibit this oxygen transfer, impeding ATP production and resulting in potential cellular dysfunction and death.
Electron Transport Chain
The electron transport chain is a series of proteins and molecules embedded within the mitochondrial inner membrane. It serves as the final stage of cellular respiration, following glycolysis and the Krebs cycle. Electrons derived from nutrients are transferred through these proteins, resulting in the release of energy.

As electrons cascade from one component of the chain to another, this energy is used to pump protons across the membrane, creating an electrochemical gradient known as the proton motive force. ATP synthase uses this gradient to synthesize ATP. Interruptions in the electron transport chain, such as those caused by poisons like cyanide or carbon monoxide, can lead to severe energy deficits, as the chain is integral to most of the ATP generated in aerobic organisms.
ATP Production
ATP, or adenosine triphosphate, is the energy currency of the cell, produced predominantly through the process of oxidative phosphorylation within the mitochondria. The ATP synthase enzyme relies on the proton motive force to add an inorganic phosphate to ADP, forming ATP.

Even though the electron transport chain and ATP production are incredibly efficient, this system requires a continuous supply of oxygen and the proper functioning of all involved enzymes. Compounds that disrupt this process, such as cyanide, can therefore have immediate and fatal consequences as ATP production halts. Without ATP, vital cellular processes cannot occur, leading to cell death.
Hemoglobin Oxygen Binding
Hemoglobin is the oxygen-transporting protein found in red blood cells. It consists of four subunits, each with a heme group capable of binding one molecule of oxygen. The binding and release of oxygen by hemoglobin are regulated by the oxygen concentration, pH, and presence of other molecules like CO2.

However, certain gases, such as carbon monoxide (CO), can compete with oxygen for binding sites on hemoglobin due to their similar structure. CO's higher affinity for the binding sites significantly reduces oxygen delivery to tissues, compromising cellular respiration which relies on oxygen for ATP production. This can lead to severe hypoxia and organ failure. Hence, understanding hemoglobin's oxygen-binding capacity is essential for grasping how crucial steady oxygen supply is for our well-being and survival.

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Most popular questions from this chapter

Draw all the geometrical isomers of \(\mathrm{Cr}(\mathrm{en})\left(\mathrm{NH}_{3}\right)_{2} \mathrm{BrCl}^{+} .\) Which of these isomers also have an optical isomer? Draw the various isomers.

Give formulas for the following. a. hexakis(pyridine)cobalt(III) chloride b. pentaammineiodochromium(III) iodide c. tris(ethylenediamine)nickel(II) bromide d. potassium tetracyanonickelate(II) e. tetraamminedichloroplatinum(IV) tetrachloroplatinate(II)

Molybdenum is obtained as a by-product of copper mining or is mined directly (primary deposits are in the Rocky Mountains in Colorado). In both cases it is obtained as \(\mathrm{MoS}_{2}\), which is then converted to \(\mathrm{MoO}_{3}\). The \(\mathrm{MoO}_{3}\) can be used directly in the production of stainless steel for high-speed tools (which accounts for about \(85 \%\) of the molybdenum used). Molybdenum can be purified by dissolving \(\mathrm{MoO}_{3}\) in aqueous ammonia and crystallizing ammonium molybdate. Depending on conditions, either \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{Mo}_{2} \mathrm{O}_{7}\) or \(\left(\mathrm{NH}_{4}\right)_{6} \mathrm{Mo}_{7} \mathrm{O}_{24} \cdot 4 \mathrm{H}_{2} \mathrm{O}\) is obtained. a. Give names for \(\mathrm{MoS}_{2}\) and \(\mathrm{MoO}_{3}\). b. What is the oxidation state of Mo in each of the compounds mentioned above?

Compounds of \(\mathrm{Sc}^{3+}\) are not colored, but those of \(\mathrm{Ti}^{3+}\) and \(\mathrm{V}^{3+}\) are. Why?

Consider the following data: \(\begin{aligned} \mathrm{Co}^{3+}+\mathrm{e}^{-} \longrightarrow \mathrm{Co}^{2+} & \mathscr{E}^{\circ} &=1.82 \mathrm{~V} \\\ \mathrm{Co}^{2+}+3 \mathrm{en} \longrightarrow \mathrm{Co}(\mathrm{en})_{3}^{2+} & K &=1.5 \times 10^{12} \\\ \mathrm{Co}^{3+}+3 \mathrm{en} \longrightarrow \mathrm{Co}(\mathrm{en}) 3^{3+} & K &=2.0 \times 10^{47} \end{aligned}\) where en \(=\) ethylenediamine. a. Calculate \(\mathscr{E}^{\circ}\) for the half-reaction $$ \mathrm{Co}(\mathrm{en})_{3}^{3+}+\mathrm{e}^{-} \longrightarrow \mathrm{Co}(\mathrm{en})_{3}^{2+} $$ b. Based on your answer to part a, which is the stronger oxidizing agent, \(\mathrm{Co}^{3+}\) or \(\mathrm{Co}(\mathrm{en})_{3}{ }^{3+}\) ? c. Use the crystal field model to rationalize the result in part b.
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