Metals in Biology

A molecule that binds to a metal ion, typically with a lone pair of electrons.

The strength of the bond between a metal ion and a ligand is determined by the charge of the metal ion. A higher charge results in a stronger bond.

Amino acids with side chains that can act as ligands. Examples include histidine, methionine, cysteine, and acidic amino acids.

The structure of a protein can create a specific environment to hold metal ions in place for specific functions.

Essential elements for life, found as cations (positive ions) in biological systems.

Sodium and potassium, major metals in cells, maintain charge balance and create concentration gradients for important cellular functions.

A protein pump that uses ATP to move sodium ions out of the cell and potassium ions into the cell, establishing and maintaining concentration gradients.

The movement of sodium back into the cell is coupled with the transport of sugar, utilizing the energy stored in the Na+ gradient.

An enzyme found in red blood cells that catalyzes the reversible conversion of carbon dioxide (CO2) and water (H2O) into carbonic acid (H2CO3).

The carbonic anhydrase reaction takes place in red blood cells and facilitates the efficient transport of CO2 from the muscles to the lungs for exhalation.

In red blood cells, carbonic anhydrase catalyzes the formation of carbonic acid (H2CO3) from CO2 and water. This reaction lowers the pH of the blood.

The formation of carbonic acid in red blood cells causes a decrease in pH, which leads to the release of oxygen from hemoglobin (Hb).

In the lungs, carbonic anhydrase catalyzes the conversion of carbonic acid (H2CO3) back to CO2 and water. This reaction consumes carbonic acid and raises the pH (making it more alkaline).

The active site of carbonic anhydrase contains a zinc ion (Zn2+) that acts as a Lewis acid to facilitate the reaction.

The rate-determining step in the carbonic anhydrase reaction is the deprotonation of water to produce a hydroxyl ion (OH-), which acts as a nucleophile.

In the presence of carbonic anhydrase, the deprotonation of water is accelerated, making the reaction diffusion-controlled, which means the enzyme is very efficient.

Magnesium (Mg2+) is a common ion found in many enzymes, particularly those involved in nucleotide-dependent reactions. It assists in the breaking of phosphate bonds within nucleotides.

Calcium (Ca2+) plays a crucial role in cell signaling processes. Its movement across cell membranes triggers a cascade of biochemical events. For example, muscle contraction involves Ca2+ influx through voltage-gated channels.

Molybdenum (Mo) is a vital trace metal, particularly in nitrogen fixation. It's a component of the FeMo-cofactor, an active site for nitrogenase, the enzyme responsible for converting atmospheric nitrogen into ammonia.

Manganese (Mn) is crucial for the process of oxygen production in plants. It's found at the catalytic site of the water-splitting enzyme, specifically a Mn4Ca cluster, where water molecules are oxidized to generate oxygen.

Iron (Fe) plays a pivotal role in electron transfer and oxygen metabolism. It forms part of various proteins like heme and iron-sulfur clusters. These structures allow iron to shuttle electrons and participate in oxygen transport and activation.

Copper (Cu) is found in proteins involved in electron transfer, oxygen transport (like hemocyanin), and oxygen activation. Its ability to shift between different redox states makes it ideal for these functions.

Nickel (Ni) forms the active site of bacterial hydrogenases, enzymes responsible for catalyzing hydrogen reactions. It plays a crucial role in the mechanism by which these enzymes transfer hydrogen atoms.

Cobalt (Co) is a component of vitamin B12, a vital cofactor for enzymes involved in methionine synthesis, a crucial process for building proteins.

Haemoglobin is a protein responsible for oxygen transport in the blood. It consists of four polypeptide chains (globins) and four heme groups. Each heme group contains an iron atom that can bind to one oxygen molecule.

The four polypeptide chains of haemoglobin are arranged in pairs, with two alpha chains and two beta chains. These chains are similar but not identical.

Haemoglobin uses a heme group, which contains an iron atom (Fe(II)), to bind to oxygen reversibly. This means that oxygen can bind and be released, allowing for efficient oxygen transport.

The binding of oxygen to one heme group in haemoglobin makes it easier for the other heme groups to bind to oxygen. This is called cooperativity and contributes to efficient oxygen delivery.

Haemoglobin exists in two states: T-state (tense) and R-state (relaxed). The T-state has lower affinity for oxygen, while the R-state has higher affinity. The transition between these states is influenced by oxygen binding.

The binding of oxygen to the heme group causes a conformational change in the haemoglobin molecule, shifting it from the T-state to the R-state. This change is amplified by the cooperativity of the subunits.

The sigmoidal shape of the oxygen binding curve of haemoglobin reflects the cooperative nature of oxygen binding. This means that haemoglobin is more efficient at taking up oxygen in areas of high oxygen concentration and releasing oxygen in areas of low oxygen concentration.

Myoglobin is a protein found in muscle tissue. It has a high affinity for oxygen and serves as an oxygen storage molecule. Myoglobin's oxygen binding curve is hyperbolic, unlike haemoglobin's sigmoidal curve.

The process that breaks down glucose to generate energy in the form of ATP. Occurs in the mitochondria of eukaryotic cells.

The organelle where respiration takes place in eukaryotic cells. It's composed of an inner and outer membrane.

A series of chemical reactions within the mitochondria that break down glucose and produce energy carriers.

The molecule that stores and releases energy in cells. It's like a tiny battery for the cell.

The difference in electrical potential across a membrane. In respiration, a proton gradient is established across the mitochondrial membrane.

A protein complex embedded in the inner mitochondrial membrane that uses the proton gradient to generate ATP. It's like a turbine that harnesses the energy of the proton flow.

A group of protein complexes (I-IV) involved in electron transport during respiration. They act like a relay team, passing electrons down a chain to release energy.

An electron carrier protein found in the ETC. Its heme group contains iron and is involved in electron transfer, like a delivery truck for electrons.

Cooperative O2 binding in hemoglobin is caused by interactions between different subunits within the tetramer. The change in conformation of one subunit affects the others, impacting O2 binding affinity. The molecule exists in two states - tense (T) with low affinity and relaxed (R) with high affinity. The binding of one O2 molecule to a subunit promotes the transition to the R state, leading to increased affinity in the other subunits.

Movement of the His residue and changes in protein conformation can be observed when comparing the X-ray structures of O2-bound and free hemoglobin. This confirms the structural basis for cooperative O2 binding.

Bioenergetics examines the storage and release of energy in biological systems. This field focuses on two primary processes: photosynthesis and respiration.

Photosynthesis is the process of converting light energy into chemical energy in the form of simple sugars. This occurs in plants and some bacteria. It utilizes light energy to split water molecules, producing oxygen and storing energy in organic molecules.

Photosynthesis and respiration represent a continuous cycle. Photosynthesis captures energy from sunlight and stores it in organic molecules. Respiration then releases this stored energy through the breakdown of these molecules.

Electron transfer through complexes I-IV in the mitochondria releases energy from the breakdown of organic molecules during respiration. The final electron acceptor is oxygen, forming water.

Electron transfer through photosystems I and II in the chloroplasts captures light energy and stores it in organic molecules during photosynthesis. These reactions involve the transfer of electrons and the formation of energy-carrying molecules like ATP and NADPH.