Questions and Answers
What is the primary function of calcium in bone and teeth?
Buffering body Ca2+ and phosphate ions, as controlled by hormonal action
How does magnesium participate in the regulation of nucleotides and polynucleotides?
As a counterion to the negatively charged ROPO3H- groups
What is the coordination sphere of magnesium in its complex with phosphate anions?
[Mg(H2O)6]2+, [Mg(H2O)5]2+, or [Mg(H2O)4]2+ with one or two phosphate oxygen atoms, respectively
What is the role of magnesium in the structure of RNA and DNA?
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What is the primary form of adenosine diphosphate (ADP) and adenosine triphosphate (ATP) in the cell?
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What is the unique role of magnesium in the plant kingdom?
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What is the composition of the mineral apatite found in bone and teeth?
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How does calcium participate in regulatory processes in the cell?
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What is the difference in the biological roles of calcium and magnesium?
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What is the role of calcium in the action of extracellular enzymes?
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Study Notes
Methylcobalamin
- Involved in the metabolism of methane-producing bacteria
- Transfers CH3 groups to Hg II, TlM, Pel, and Au I
- Converts elemental mercury into the highly toxic methylmercury ion CH3Hg+
Vitamin B12
- Has a planar tetradentate ligand with amido-type nitrogen atoms
- Models have been synthesized and studied, such as bis(dimethylglyoximato) complexes
- Successfully models the reducibility to the cobalt(I) state and the formation and reactions of cobalt-carbon bonds
Carboxypeptidase
- Zinc ion is bound in a distorted tetrahedral environment with two histidine nitrogen atoms, one glutamate carboxyl oxygen atom, and a water molecule as ligands
- Substrate binding occurs with the carbonyl oxygen atom of the peptide linkage replacing the water molecule in the coordination sphere of the zinc ion
- Key step in the mechanism involves the peptide bond breaking with formation of an acid anhydride, followed by rapid hydrolysis of the anhydride
Copper Metalloenzymes
- More than 20 have been isolated, but structure and function are not well understood
- Examples include ascorbic acid oxidase, cytochrome oxidase, and tyrosinases
- Catalyze oxidations, such as the oxidation of ascorbic acid to dehydroascorbic acid
Calcium
- Essential for the action of extracellular enzymes and participates in many regulatory processes
- Complexed by the side-chain carboxyl groups of proteins, with additional bonding to peptide carbonyl groups and hydroxyl groups
- Found in bone and teeth, with a composition similar to the mineral apatite
Magnesium
- Plays biological roles that are very different from those of calcium
- Acts as a counterion to negatively charged ROPO3H- groups in nucleotides and polynucleotides
- Helps to stabilize the three-dimensional structure of RNA and DNA and is crucial to the proper functioning of the genetic machinery of the cell
- Exists in complexes with ADP and ATP, and is the central atom of chlorophyll
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Description
This quiz covers the chemistry of methylcobalamin, its involvement in methane-producing bacteria metabolism, and its role in converting elemental mercury into toxic methylmercury ion.
