Phosphorus

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What is Phosphorus?

Phosphorus is the 15th element in the periodic table, in Group 5. It is apparent in two forms, distinguishable by their characteristic colour (white phosphorus and red phosphorus). Almost all of the phosphorus that we know of is derived from phosphoric acid, which is especially the case in biological systems.

Sources of Phosphate

Bones are an extremely good source of phosphate with approximately 0.5% of the human body being composed of phosphorus, almost all of which is in the form of calcium phosphate in the bones.

What is the Importance of Phosphorus?

Phosphorus is a vital element in the composition of many structures in the human body, and also in other living organisms. It is involved therefore in many processes that are vital for the survival of an organism.
Phosphorus is a fundamental element in living tissues:

The Association of Phosphates with Lipids

Phosphates form an essential component of cell membranes. The hydrophilic heads contain a phosphorylated glycerol subunit (i.e. a glycerol molecule with a phosphate group attached) [1].

Phosphate Component in Nucleic Acids

DNA is composed of nucleosides, which contain a phosphate group, hence the sugar-phosphate backbone in DNA. The energy to replicate DNA comes from the cleavage of two phosphates from the ddNTPs that it is composed of, as such providing energy. This forms the phosphodiester bonds between the nucleosides. Similarly, RNA also has these two phosphate groups which are cleaved during the process of transcription for the formation of mRNA.

The Involvement of Phosphate in Metabolism

ATP is considered to be the energy currency of the cell. Some processes involve instead GTP. These molecules are hydrolysed to ADP and Pi, and GDP and Pi respectively. These molecules provide the energy by cleaving off one of the three phosphate groups.

The Importance of Phosphates in Cell Signalling

Cell SignallingPhosphorylation cascades are vital to many processes that involve signal transduction. Phosphorylated molecules, in particular proteins, are very heavily involved in these pathways. These phosphorylation cascades are very heavily dependent on kinases which add phosphate groups to proteins [2].

In cell signalling, trimeric G-proteins contain an α-subunit which binds GTP, and when activated, it releases the GDP and binds GTP. The α-subunit is also an ATP-ase, so cleaves a phosphate group yielding GDP and inorganic phosphate  [3]. This is the mechanism by which the G-protein inactivates.
2 key proteins that are activated by trimeric G-proteins are:-

Radioactive labelling

The radioactive isotope P-32 is used to label DNA strands which have been isolated by using a kinase derived from a bacteriophage which utilises ATP for the addition of a P-32 molecules onto the 5’ end of the DNA molecule. This can also be achieved by using DNA polymerase to replicate the DNA in the presence of the ddNTPs labelled with P-32, which are then incorporated into the DNA. Hence, the P-32 can act as a DNA marker  [4].

Other processes in which phosphate is involved

References

  1. [Alberts B., Johnson A., Lewis J., Raff M., Roberts K. and Walter P. (2007) Molecular Biology of The Cell, 5th edition, New York: Garland Science, Taylor and Francis Group.]
  2. [Alberts B., Johnson A., Lewis J., Raff M., Roberts K. and Walter P. (2007) Molecular Biology of The Cell, 5th edition, New York: Garland Science, Taylor and Francis Group.]
  3. [Alberts B., Johnson A., Lewis J., Raff M., Roberts K. and Walter P. (2007) Molecular Biology of The Cell, 5th edition, New York: Garland Science, Taylor and Francis Group.]
  4. [Alberts B., Johnson A., Lewis J., Raff M., Roberts K. and Walter P. (2007) Molecular Biology of The Cell, 5th edition, New York: Garland Science, Taylor and Francis Group.]
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