Question

Which transition metal atom is present in each of the following biologically important molecules: (a) hemoglobin, (b) chlorophylls, (c) siderophores, (d) hemocyanine.

Short answer

The transition metal atoms present in each of the biologically important molecules are: (a) Hemoglobin - Iron (Fe), (b) Chlorophylls - Magnesium (Mg), (c) Siderophores - Iron (Fe), and (d) Hemocyanin - Copper (Cu).

Step-by-step solution

(a) Hemoglobin

Hemoglobin is a protein responsible for carrying oxygen in the blood of vertebrates. The transition metal atom present in hemoglobin is Iron (Fe). Iron is a part of the heme group, which is responsible for binding to oxygen and allowing the hemoglobin molecule to transport oxygen throughout the body.

(b) Chlorophylls

Chlorophylls are photosynthetic pigments found in plants, algae, and photosynthetic bacteria. They play an essential role in converting light energy into chemical energy through the process of photosynthesis. The transition metal atom present in chlorophyll molecules is Magnesium (Mg). Magnesium is located at the center of the chlorophyll molecule, helping to capture and transfer light energy for photosynthesis.

(c) Siderophores

Siderophores are small molecules produced by certain bacteria and fungi to sequester iron from their environment. They have a high affinity for iron and are involved in iron acquisition, storage, and transport. The transition metal atom present in siderophores is Iron (Fe). The siderophores bind to iron, allowing the organisms to take up the essential nutrient from their surroundings.

(d) Hemocyanin

Hemocyanin is an oxygen-carrying protein found in some invertebrates, such as crustaceans and mollusks. It is an alternative to hemoglobin, which is commonly found in vertebrates. The transition metal atom present in hemocyanin is Copper (Cu). Hemocyanin contains copper ions in its active site, which binds to oxygen and allows the protein to transport oxygen throughout the organism's body.

Key concepts

Hemoglobin and Iron

Hemoglobin is a critical protein found in the blood of vertebrates. Its main role is to transport oxygen from the lungs to various tissues and organs in the body. The fascinating part of hemoglobin's structure is the presence of iron (Fe). This transition metal atom is housed within a component known as the heme group. The iron ion allows hemoglobin to bind oxygen effectively. When you breathe in, oxygen molecules attach to the iron in the heme group of hemoglobin.
This loading of oxygen not only supports the transportation of oxygen but also facilitates its release at needed sites. Essentially, the iron acts as a ferry, loading oxygen at the lungs and unloading it at tissues requiring oxygen for metabolism. Through this sophisticated mechanism, hemoglobin and its iron atoms play a vital role in sustaining life by enabling cellular respiration.

Chlorophyll and Magnesium

Chlorophyll is the iconic green pigment found in plants, algae, and some bacteria. It is crucial for the miracle of photosynthesis, where light energy is converted into chemical energy, enabling the synthesis of nutrients from sunlight. At the heart of chlorophyll is a magnesium (Mg) ion. This transition metal atom is central to chlorophyll's ability to capture light.
The role of magnesium is pivotal; it helps maintain the structural stability of the chlorophyll molecule. Additionally, it plays a key role in the absorption and transfer of photon energy. Through this energy transfer process, chlorophyll contributes essentially to the conversion of light energy into chemical energy, which is stored in strong energy-carrying molecules such as ATP and NADPH. Hence, magnesium is indispensable for life on Earth due to its involvement in the photosynthetic process.

Siderophores and Iron

Siderophores are an intriguing group of molecules that some bacteria and fungi produce to obtain iron from their environment. Iron is vital for many biochemical processes, but it is often unavailable directly in nature due to its tendency to form insoluble complexes. Siderophores solve this problem by binding iron ions tightly.
These molecules act like highly specific iron scavengers, capable of sequestering even minute amounts of iron from their surroundings. Once captured, the iron-siderophore complex can be transported back into the organism, where the iron is utilized for cellular processes such as respiration and DNA synthesis. This clever mechanism ensures that microorganisms have access to essential iron, even in environments where it is scarce.

Hemocyanin and Copper

Hemocyanin is different from the better-known hemoglobin, primarily found in invertebrates like mollusks and crustaceans. Instead of iron, hemocyanin relies on copper (Cu) ions to bind and transport oxygen. This protein gives the blood of these creatures a distinctive blue color when oxygenated.
Copper in hemocyanin functions by binding oxygen between two copper ions when the invertebrate breathes in. This binding facilitates the transfer of oxygen throughout the organism's body. Unlike hemoglobin, where oxygen binds to a heme group centered around iron, in hemocyanin, it’s the copper ions that directly interact with the oxygen molecules. This difference illustrates the diversity of biological systems in nature, demonstrating how different life forms have adapted to utilize varied transition metals for essential biological functions.