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DNA condensation refers to the process of compacting DNA molecules in vitro or in vivo. [1] Mechanistic details of DNA packing are essential for its functioning in the process of gene regulation in living systems. Condensed DNA often has surprising properties, which one would not predict from classical concepts of dilute solutions.
In nature, DNA can form three structures, A-, B-, and Z-DNA. A- and B-DNA are very similar, forming right-handed helices, whereas Z-DNA is a left-handed helix with a zig-zag phosphate backbone. Z-DNA is thought to play a specific role in chromatin structure and transcription because of the properties of the junction between B- and Z-DNA.
The organization of DNA presents a remarkable biological challenge: human DNA can reach 2 meters [1] and is packed into the nucleus with the diameter of 5-20 µm. [2] At the same time, the critical cell processes involve complex processes on highly compacted DNA, such as transcription, replication, recombination, DNA repair, and cell division.
The solenoid structure's most obvious function is to help package the DNA so that it is small enough to fit into the nucleus. This is a big task as the nucleus of a mammalian cell has a diameter of approximately 6 μm, whilst the DNA in one human cell would stretch to just over 2 metres long if it were unwound. [6]
All living cells contain both DNA and RNA (except some cells such as mature red blood cells), while viruses contain either DNA or RNA, but usually not both. [15] The basic component of biological nucleic acids is the nucleotide, each of which contains a pentose sugar (ribose or deoxyribose), a phosphate group, and a nucleobase. [16]
Many regions of the DNA are transcribed with RNA as the functional form: rRNA: Ribosomal RNA are used in the ribosome. tRNA: Transfer RNA are used in the translation process by bringing amino acids to the ribosome. snRNA: Small nuclear RNA are used in spliceosomes to help the processing of pre-mRNA. gRNA: Guide RNA are used in RNA editing.
Telomeric repeat–containing RNA (TERRA) is a long non-coding RNA transcribed from telomeres - repetitive nucleotide regions found on the ends of chromosomes that function to protect DNA from deterioration or fusion with neighboring chromosomes. TERRA has been shown to be ubiquitously expressed in almost all cell types containing linear ...
[21] [22] Both RNAi and an exosome-dependent RNA degradation process contribute to heterochromatic gene silencing. These mechanisms of Schizosaccharomyces pombe may occur in other eukaryotes. [23] A large RNA structure called RevCen has also been implicated in the production of siRNAs to mediate heterochromatin formation in some fission yeast. [24]