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Chapter 22: Problem 53

What structural feature do hemoglobin, cytochrome c, and chlorophyll have in common?

Short Answer

Expert verified
Hemoglobin, cytochrome c, and chlorophyll all have a porphyrin ring structure with a metal ion at the center as a common structural feature.

Step by step solution

01

Identify Common Structural Feature

All three molecules, hemoglobin, cytochrome c, and chlorophyll, contain a heterocyclic ring known as a porphyrin. This porphyrin ring is a large, nitrogen-containing ring with a metal ion at its center.
02

Describe Function of Metal Ion

The metal ion at the center of the porphyrin ring plays a crucial role in the function of each molecule. In hemoglobin and cytochrome c, it is an iron (Fe) ion, whereas in chlorophyll it is a magnesium (Mg) ion. This metal ion allows the molecules to participate in electron transfer or oxygen binding.
03

Explain Importance of Porphyrin Ring

The porphyrin ring structure facilitates the molecules' role in biological processes. Hemoglobin's role in oxygen transport, cytochrome c's role in electron transport during cellular respiration, and chlorophyll's role in photosynthesis are all supported by the presence of this ring.

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Key Concepts

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

Hemoglobin Structure
Hemoglobin is a crucial protein found in red blood cells, responsible for carrying oxygen from the lungs to tissues throughout the body and facilitating the return transport of carbon dioxide. The structure of hemoglobin is composed of four polypeptide chains, each containing a heme group with a central iron (Fe) ion within a porphyrin ring. The iron is vital as it binds to oxygen molecules.
  • The porphyrin ring structure in hemoglobin allows for the reversible binding of oxygen, enabling efficient oxygen transport.
  • The heme groups are embedded in a globular protein, which ensures proper positioning for the iron to interact with oxygen.
The ability of hemoglobin to carry oxygen is influenced by its quaternary structure; changes in pH and the presence of other molecules like carbon dioxide can impact oxygen binding affinity.
Cytochrome c Function
Cytochrome c plays a key role in the electron transport chain, which is part of cellular respiration in the mitochondria. The electron transport chain is a series of complexes that generate ATP, the primary energy currency in cells, through a process known as oxidative phosphorylation.
  • The central iron ion of cytochrome c's porphyrin ring can alternate between a reduced (Fe2+) and oxidized (Fe3+) state, allowing it to transfer electrons between protein complexes within the mitochondrial membrane.
  • As electrons are transferred from cytochrome c to the next complex, protons are pumped across the membrane, creating a gradient that drives ATP synthesis.
Through the function of cytochrome c, and pivotal involvement of the porphyrin ring and its iron ion in electron transfer, cells can produce the energy necessary for survival.
Chlorophyll and Photosynthesis
Chlorophyll is the pigment that gives plants their green color and is vital for photosynthesis, the process by which plants convert light energy into chemical energy. Chlorophyll molecules have a porphyrin ring with a central magnesium (Mg) ion that plays a critical role in capturing light energy.
  • During photosynthesis, chlorophyll absorbs light, which excites the electrons of the magnesium ion, initiating the process of converting light to chemical energy.
  • There are different types of chlorophyll, such as chlorophyll a and b, which absorb light at slightly different wavelengths, increasing the range of light energy that can be harvested by a plant.
This initiation by chlorophyll's porphyrin ring is the first step in a series of energy conversion events that result in the synthesis of glucose, which plants use as an energy source, and oxygen, which is released into the atmosphere.
Metal Ions in Proteins
Metal ions are essential for the function of a variety of proteins. The presence of a metal ion can be critical to a protein's structure and catalytic ability, often by stabilizing charged intermediates or by acting directly as an electron donor or acceptor.
  • Some common metal ions in proteins include iron, zinc, magnesium, and copper, each serving distinct roles in different biochemical processes.
  • The structure of metalloproteins is often specifically adapted to the geometry and coordination preference of the incorporated metal ion.
In the context of the porphyrin ring, the metal ion is integral to the molecule's function, where in hemoglobin it binds oxygen, in cytochrome c it facilitates electron transfer, and in chlorophyll it absorbs light for photosynthesis. The precise mechanisms by which these metal ions operate are finely tuned to support life's complex biochemical systems.

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