Molecular Biology
John C Watkinson, Raymond W Clarke, Louise Jayne Clark, Adam J Donne, R James A England, Hisham M Mehanna, Gerald William McGarry, Sean Carrie in Basic Sciences Endocrine Surgery Rhinology, 2018
Each DNA molecule is packaged into a chromosome by complex folding of the DNA around proteins. Diploid human cells contain 22 pairs of autosomes (1 to 22) and a pair of sex chromosomes (XX or XY) that determines the sex of the organism. One of each pair of chromosomes is maternally inherited and the other is paternally inherited. Each chromosome has a distinctive shape, size and banding pattern, but have the common appearance of two arms apparently separated by a constriction. The centromere is microscopically recognizable as the central constriction separating the chromosome into a long arm (q for queue) and a short arm (p for petit), but its biological role lies in anchoring the chromosome to the mitotic spindle for segregation during cell division. The ends of the chromosomes are capped by telomeres, which are specialized structures containing unique simple repetitive sequences. They maintain the structural integrity of the chromosome and provide a solution for complete replication of the extreme ends of the chromosome. The conventional nomenclature for chromosomal locus assignment is given by the chromosome number, followed by the arm and finally the position on the arm, for example, 3p21 indicates position 21(two-one) on the short arm of chromosome three.
Nucleic Acids
Danilo D. Lasic in LIPOSOMES in GENE DELIVERY, 2019
The size of a genome can vary from small chromosomes of a virus containing around 5000 base pairs (bp), to around 4 million for Escherichia coli, while the 46 human chromosomes contain coding for almost 105 different proteins encoded in about 3 billion bp. It is estimated that approximately 10 trillion cells of the human body contain about 100,000 genes each. Differential transcription of genes during embriogenesis and between different cell types and organs is responsible for maintaining the specialization of the cell types. However, in humans around 97% of the DNA does not code for any proteins. It is likely that this DNA, which is often called junk DNA, is not (completely) wasteful and that it contains important information about temporal and structural events, such as regulation of gene expression. Some of it forms telomers which protect the ends of chromosomes and centromers which are attachment sites for spindles. Gene regulators turn on the right genes, at the right places, at the right times and allow, in addition, genes to be switched on and off by some environmental factors, such as concentration changes of some peptides, proteins, hormones, or simple molecules, like sugars. Some of the DNA stretches may act as membrane (nuclear matrix) attachment sites, while others may be important in DNA packaging. The length of the junk DNA varies from species to species. For instance, salamanders have 40 times longer DNA than humans while puffin fish have an eight-fold shorter genome than similar vertebrates (Holmes, 1995).
Role of Histone Methyltransferase in Breast Cancer
Meenu Gupta, Rachna Jain, Arun Solanki, Fadi Al-Turjman in Cancer Prediction for Industrial IoT 4.0: A Machine Learning Perspective, 2021
During DNA packaging, basic proteins – histones – play a reported mark as a chromatin component in the nucleus of eukaryote cells, where they bind with DNA and further proceed the DNA for packaging into smaller units designated as nucleosomes that display their role in gene regulation. The unwounded chromosomal DNA length varies. Diploid cell DNA of humans is about 1.8 meters, shows wounded association on the basic proteins, and has approximately 0.09 mm (90 micrometers) of chromatin. During the mitotic process, the human diploid cell undergoes condensation and duplication, resulting in about 120 mm of chromosome. Histone modifications are directly correlated with gene regulation functions, including ADP-ribosylation, methylation, acetylation, ubiquitination, and citrullination.
Large extracellular vesicles carry most of the tumour DNA circulating in prostate cancer patient plasma
Published in Journal of Extracellular Vesicles, 2018
Tatyana Vagner, Cristiana Spinelli, Valentina R. Minciacchi, Leonora Balaj, Mandana Zandian, Andrew Conley, Andries Zijlstra, Michael R. Freeman, Francesca Demichelis, Subhajyoti De, Edwin M. Posadas, Hisashi Tanaka, Dolores Di Vizio
We were aware that DNA may be fragmented during DNA extraction [33] and that the working range of the Bioanalyzer chip used in the above experiments is limited in measuring DNA fragments larger than 10,000 bp. Therefore, in order to determine the size of un-sheared vesicular DNA, we lysed EVs directly in agarose plugs and resolved EV DNA by PFGE [26]. Resolution of high molecular weight DNA, which was possible with this method, revealed that L-EVs contain DNA fragments up to 2 Mega base pair (Mbp) (Figure 2(a)). In addition, DNA fragments in the size range of 100 Kbp–2 Mbp were enriched in L-EVs compared to whole cells and were undetectable in S-EVs (Figure 2(a,b)). This suggests a distinct process of DNA packaging in L-EVs. Resolution of lower molecular weight DNA using the same method demonstrated that the DNA extracted with the kit exhibited significantly smaller size (~10 kbp) than the un-sheared DNA extracted in agarose plugs, suggesting that the use of a commercial kit for DNA extraction shreds the DNA (Figure 2(c)).
Recent advances in targeting protein arginine methyltransferase enzymes in cancer therapy
Published in Expert Opinion on Therapeutic Targets, 2018
Emily Smith, Wei Zhou, Polina Shindiapina, Said Sif, Chenglong Li, Robert A. Baiocchi
The structural unit of the chromosome provides a platform for packaging approximately 1.8 m of DNA into the nucleus no more than 10 μm in diameter. DNA wound about the histone structural proteins form the nucleoprotein supra-structure known as chromatin. Four histone proteins (H2A, H2B, H3, and H4, and associated isoforms) assemble into an octamer forming a core about which nuclear DNA is wound in ~150 base pair loops, forming the nucleosome. The dynamic association between DNA and this histone core determines the degree of accessibility of transcriptional machinery to DNA and accounts for fine-tuned regulation of gene expression. Chromatin structure ranges from tightly packed, condensed heterochromatin to a more relaxed, open, euchromatin state. The restricted availability of DNA in heterochromatin generally correlates with more repressed transcriptional activity, whereas a more loosely packed euchromatin state allows for the binding of polymerase machinery, resulting in active transcription. Covalent modifications of specific nucleotides and histone amino acid residues are controlled by a wide array of epigenetic enzymes [2].
Chromosome aberration in typical biological systems under exposure to low- and high-intensity magnetic fields
Published in Electromagnetic Biology and Medicine, 2020
Emanuele Calabrò, Hit Kishore Goswami, Salvatore Magazù
It is known that the most crucial stage of mitotic division is the interphase wherein each very long chromatin thread (actually, chromatid) becomes a chromosome by way of replication of DNA and the immediate influence becomes operative of coiling and condensation so as to result in making compact chromosome. This packaging of DNA by tortuously folding and compacting into shaping a thick rod-shaped chromosome with two chromatids continues until early metaphase. It is precisely at this stage that alignment of chromosomes along the direction of the applied magnetic field was observed after exposure, such as it appears in Figures 7c–d and 9b. These changes have been the most common and repeated results observed in root tip preparations of both garlic and broad bean.
Related Knowledge Centers
- Cell Division
- DNA
- DNA Condensation
- Eukaryote
- Genome
- Histone
- S Phase
- Chaperone
- Transcriptional Regulation
- Metaphase