1
Introduction

The discipline of bioinorganic chemistry is concerned with the function of metallic and most of nonmetallic elements in biological processes. Also, it is the study of the chemistry, structure, and reactions of the metalloprotein molecules belonging to the living cell.

The precise concentrations of different ions, for instance, in blood plasma indicate the importance of these ions for biological processes, (Table 1-1).

Table 1-1 Ion Concentration in Extracellular Blood Plasma

Such elements fall into four broad classifications: the polluting, contaminating, beneficial, and essential elements.

• Polluting elements: Pb, Hg, and Cd
• Contaminating elements: vary from person to person
• Beneficial elements: Si, V, Cr, Se, Br, Sn, F, and Ni
• Essential elements: H, C, N, O, Na, Mg, K, Ca, P, S, Cl, Mo, Mn, Fe, Co, Cu, Zn, and I (Fig. 1-1).

Figure 1-1 Distribution of elements essential for life (Cotton and Wilkinson, 1980).

Twenty-five elements are currently thought to be essential to warm-blooded animals (Table 1-2).

Table 1-2 Percentage Composition of Essential Elements in Human Body

Essentiality has been defined according to certain criteria:

• A physiological deficiency appears when the element is removed from the diet.
• The deficiency is relieved by the addition of that element to the diet.
• A specific biological function is associated with the element.

Every essential element follows a dose–response curve, shown in Fig. 1-2. At lowest dosages the organism does not survive, whereas in deficiency regions the organism exists with less than optimal function.

Figure 1-2 The dose-response curves of selenium and fluoride.

The ten ions classified as trace metal are Fe, Cu, Mn, Zn, Co, Mo, Cr, Sn, V, and Ni, and the four classified as bulk metals are Na, K, Mg, and Ca. The nonmetallic elements are H, B, C, N, O, F, Si, P, S, Cl, Se, and I.

Biological Roles of Metal Ions

What are the general roles of metal ions in biological systems?

The general roles of metal ions in biological systems are summarized in Table 1-3.

Table 1-3 Role of Metal Ions and Examples

Metals in biological systems function in a number of different ways:

• Groups 1 and 2 metals operate as structural elements or in the maintenance of charge, osmotic balance, or nerve impulses.
• Transition metal ions that exist in single oxidation states, such as zinc (II), function as structural elements in superoxide dismutase and zinc fingers or as triggers for protein activity, e.g., calcium ions in calmodulin or troponin C.
• Transition metals that exist in multiple oxidation states serve as electron carriers, e.g., iron ions in cytochromes or in iron–sulfur clusters of the enzyme nitrogenase or copper ions in azurin and plastocyanin.
• As facilitators of oxygen transport, e.g., iron ions in hemoglobin or copper ions in hemocyanin.
• As sites at which enzyme catalysis occurs, e.g., copper ions in superoxide dismutase or iron and molybdenum ions in nitrogenase.
• Metal ions may serve multiple functions, depending on their location within the biological system, so that the classifications in Table 1-3 are somewhat arbitrary and/or overlapping.

Proteins: Formation, Structures, and Metalloproteins

This section is designed to introduce the chemistry of proteins. The text broadly includes where and how the proteins are formed, along with the structure and formation of metalloproteins.

Following the introduction of organelles and their functions within the cell, the discussion will be concerned with the general structure of deoxyribonucleic acid (DNA) and how the nucleus maintains its control of cell growth, division, and formation of [messenger, transfer, and ribosomal ribonucleic acid (mRNA, tRNA, rRNA)]. This is followed by how mRNA and tRNA master the formation of proteins within a cell. Then, primary, secondary, tertiary, and quaternary structures of the formed proteins and the factors that control each of these structures are discussed.

Specific points about the ligation of various metal ions to different amino acids within the proteins are made, and the binding stabilities of various metal ions toward different amino acids are arranged.

The general formulas, side chains, and corresponding names of the common natural α-amino acids, the formation of the peptide chain from the amino acids, and the physiological roles of proteins are described.

The chemistry of the prosthetic and cofactors is explored. Enough basic biochemistry is presented to enable the student to understand the discussions that follow.

Organelles and Their Functions

Identify the organelles and their functions within the cell.

• Cells are the building blocks of all living things.
• There are similarities in the appearance, chemical constituents, and activities of all cells (Fig. 1-3).

  Figure 1-3 (a) Animal cell and (b) plant cell.

• Different structures within the cell are called organelles.
• Each organelle has an important, specific function in the cell.
• The mitochondria are responsible for conversion of food into usable energy (metabolism):
  • They contain enzymes for cell metabolism.
  • More than 50% of the energy produced by mitochondrial oxidation of carbohydrates is recaptured as adenosine diphosphate (ADP) and converted into adenosine triphosphate (ATP).
  • The derived energy is trapped in ATP molecules (Scheme 1-1).

    Scheme 1-1 Derived energy is trapped in adenosine triphosphate molecules (ATP).

  • ATP can diffuse rapidly throughout the cell, delivering energy to sites where it is required for cellular processes.
• In green plants, chloroplasts contain chlorophyll molecules and other pigments.
  • Chlorophyll and other pigments in chloroplasts absorb light energy from the sun and use it to produce ATP, glucose, and...