Cellular Biology

Nucleic Acid Polymerization



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Nucleic acids are the vital genetic blueprint, messengers and builders of the cellular world. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the genetic material of cells. Prior to cell division, a new copy of the DNA genome must be made. And in order for our cells to make proteins, RNA must be created from the DNA template. Here's a summary of how new nucleic acid molecules are built.

* What Are DNA and RNA Made of? *

Nucleotides are the building blocks of nucleic acids. Each nucleotide is a monomer of nucleic acid and consists of 3 portions:

* a pentose sugar (ribose)
* one or more phosphate groups
* one of five cyclic nitrogenous bases

* Phosphate-Sugar Backbone *

Nucleotides are linked together by covalent bonds between phosphate of one nucleotide and sugar of next. These linked monomers become the phosphate-sugar backbone of nucleic acids. Nitrogenous bases extending from this phosphate-sugar backbone like teeth of a comb.

* The Nucleic Acid Ladder *

Hydrogen bonds form between specific bases of two nucleic acid chains, forming a stable, double-stranded DNA molecule. The structure is analogous to a ladder, with the two deoxyribose-phosphate chains as side rails and the base pairs, linked by hydrogen bonds, forming the rungs.

* How Are Nucleotides Put Together Into Nucleic Acids? *

Nucleic acid synthesis is an anabolic polymerization process. Anabolic reactions build bigger molecules and require energy. Polymerization is the process of taking nucleotide monomers and putting them together into polymers (large molecules composed of many monomers).

These three-phosphate nucleotide building blocks of DNA and RNA bring their own energy for polymerization within their phosphate bonds. When the triphosphate bond of the nucleotide is broken, it contributes the energy required add another nucleotide to the growing nucleic acid.

* What Do Nucleic Acids Do? *

The three main activities that nucleic acids are involved in are:

1. Replication: The duplication of genetic material.
2. Transcription: Passing the genetic code of DNA onto RNA molecules.
3. Translation: RNA following DNA's instructions for building proteins from amino acids.

* Replication: Before a cell divides, it must make a copy of its DNA so that both parent and daughter cells have a complete copy of genetic information. This process of copying the double-stranded DNA molecule is called replication.

* Transcription: This is the process by which a DNA sequence is copied to produce a complementary strand of RNA. In other words, it is the transfer of genetic information from DNA into RNA.

* Translation: Ribosomes (which contain rRNA) make proteins from the messages encoded in mRNA. Proteins are polymers made of monomer units called amino acids. Each three nucleotide group of the nucleic acid, called a codon, encodes one amino acid. This triplet code of genetic instructions for a polypeptide chain is 'written' in the DNA as a series of 3-nucleotide 'words,' and this is the genetic code.

* Sources *

Bauman, R. (2005) Microbiology.
Park Talaro, K. (2008) Foundations in Microbiology.

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