Nucleic acids and chromatin
Nucleic acids and chromatin

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1.3 Nucleic acids and the flow of genetic information

The ‘flow’ of information from an organism's genome to the synthesis of its encoded proteins is referred to as the central dogma and emphasises the crucial roles that nucleic acids play within the cell (Figure 2). The synthesis of proteins (translation) is directed by the base order in mRNA, copied directly from that in the DNA of the genes by transcription. Translation involves RNAs in the form of the ribosome and tRNAs. In this unit we will be focusing on the relationship between the molecular components of nucleic acids, the structures they form in the cell and how they interact with proteins. We will also examine the approaches used to analyse these structures and discuss how the unique properties of nucleic acids have been exploited as molecular tools.

In those organisms that have large genomes, there is a balance between the necessary compaction of large amounts of genetic material within the confines of the cell and enabling sufficient access to this material for the operation of the cell's maintenance and expression systems. Evolutionarily, this balance has been successfully achieved in the eukaryotes through the emergence of the histones.

Figure 2
Figure 2 The roles of nucleic acids in the cell. (a) The central dogma describes the flow of genetic information in the cell. (b) Replication of DNA. (c) Transcription of DNA to give mRNA, tRNAs and rRNAs. (d) Translation of mRNA in protein synthesis involves rRNAs in the ribosome and tRNAs.

These proteins are complexed with DNA as chromatin, and it is in this form that eukaryotic DNA is packaged in the nucleus. We will complete this unit by discussing histones and their roles in both genome packaging and expression.

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