Identification of the living and the dead
Jason Payne-James, Richard Jones in Simpson's Forensic Medicine, 2019
The molecule of DNA has two strands of sugar and phosphate molecules that are linked by combinations of four bases, adenine, thymine, cytosine and guanine, forming a double helix structure. Only about 10 per cent of the molecule is used for genetic coding (the active genes), the remainder being ‘silent’. In these silent zones, there are between 200 and 14,000 repeats of identical sequences of the four bases. Sir Alec Jeffreys found that adjacent sequences were constant for a given individual and that they were transmitted, like blood groups, from the DNA of each parent. The statistical analysis of DNA identification is extremely complex and it is important that any calculations are based upon the DNA characteristics of a relevant population and not upon the characteristics of a ‘standard’ population somewhere else in the world. Forensic genetics developed from protein-based techniques and brought with it the term ‘DNA fingerprinting’, this being based on restriction fragment length polymorphisms (RFLPs) of high-molecular-weight DNA. Development of analytical techniques resulted such as the amplification of much smaller short tandem repeat (STR) sequences using the polymerase chain reaction (PCR) which soon replaced RFLP analysis and became standard in genetic identification. STR multiplexes are now available which simultaneously amplify up to 30 STR loci from as little as 15 cells or fewer. The huge volume of information associated with the great range of observed STR genotypes allows for genetic individualisation (with the exception of identical twins).
Histone Interactions with DNA
Lubomir S. Hnilica in The Structure and Biological Function of Histones, 1972
Increase in the temperature of a solution containing DNA leads to a disruption of the bonds stabilizing the double stranded form of the DNA helix. Disruptive effects similar to the above can also be observed if a DNA solution is exposed to extreme pH values or if the interactions between the individual bases are modified by replacing the water with organic solvents. The denaturation of DNA normally proceeds in three overlapping steps. These are (1) the collapse of hydrogen bonded structures (mostly between AT and GC base pairs), (2) the disruption of base stacking, and (3) complete strand separation. The stability of the DNA double stranded structure depends partly on the base composition of the DNA (the stability increases with its G + C content) and partly on the molecules associated with the DNA. The pH and ionic strength of the solvent also contribute substantially to the stability of double stranded DNA. It exceeds the scope of this monograph to discuss in detail the multiple aspects of DNA denaturation. In addition, these have been reviewed by other investigators.850,851
The Nuclear Matrix and the Organization of Nuclear DNA
Isaac Bekhor, Carol J. Mirell, C. C. Liew in Progress in Nonhistone Protein Research, 1985
Numerous control experiments have been done to diminish the possibility that nascent DNA is artifactually binding to the nuclear matrix during the extraction procedures by virtue of features unique to replicating DNA. Reconstruction experiments have demonstrated no preferential affinity of matrix components for single-stranded DNA, or nascent DNA, or replicating chromatin, or nascent DNA complexed with matrix proteins, when added at any (or all) of the extractions steps.30,35,36 Autoradiographic experiments have shown that the same percentages of nuclei and matrices are labeled, eliminating the possibility of a random adherence of extracted nascent DNA to all matrix structures.36 We have been able to generate labeled single-stranded DNA in nuclei in situ enzymatically. This single-stranded DNA was not enriched in nuclear matrix preparations which were clearly enriched for nascent DNA.36Size analysis showed that nascent DNA is not simply protected by matrix components; the replicating DNA sequences are as sensitive to nuclease digestion as is the nonreplicating DNA after removal of the histones (References 30 and 35 and unpublished data).
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
Chromosomes are molecules composed of the deoxyribonucleic acid (DNA) that represents the genetic material of a living being. In human beings, there are 22 pairs of chromosomes and 2 sex chromosomes for a total of 46. DNA is an organic polymer composed of monomers that are called nucleotides. They consist of a phosphate group and a nitrogenous base linked to deoxyribose by the so-called N-glycoside bond. The nitrogenous bases that can be used in nucleotide formation are adenine, cytosine, guanine and thymine disposed in base pairs of adenine-thymine (A-T) and guanine-cytosine (G-C) that in aqueous solutions are linked one each other by hydrogen bonds forming a double helix structure because of the repulsions between the negative charge of phosphate groups. This double helix structure is bound to proteins (the histones) that have positively charged amino acids in order to bind the DNA which is negatively charged and is wrapped around the core of histone of eight protein subunits forming the nucleosome. About 200 base pairs of DNA are coiled around each histone. This coil is untwisted generating a negative superturn per nucleosome that is the active chromatin.
The roles of epidermal growth factor receptor in viral infections
Published in Growth Factors, 2022
Infectious spleen and kidney necrosis virus (ISKNV) is a member of family Iridoviridae that infects more than 50 species fishes. It comprises of a single linear, double-stranded DNA enclosed by icosahedral capsid. Outbreak of ISNNV causes serious economic losses in aquaculture industry. A recent study by Niu et al. (2021) has reported that EGFR mediates endocytosis of ISKNV in vitro and in vivo. Treatment of gefitinib inhibits ISKNV entry to Chinese perch brain (CPB) cells by suppressing EGFR/PI3K pathway and viral-induced cytoskeleton rearrangement (Figure 2(h)). In the in vivo study using largemounth bass, gefitinib inhibited ISKNV infection and diminished pathogenicity as evidenced by lower degree of hyperaemia and bleeding in spleen and liver (Niu et al. 2021).
Common mutations of interest in the diagnosis of amyotrophic lateral sclerosis: how common are common mutations in ALS genes?
Published in Expert Review of Molecular Diagnostics, 2020
Benedetta Perrone, Francesca Luisa Conforti
Genetic testing for SOD1, TARDBP, and FUS genes includes first and second-generation DNA sequencing methods. Sanger sequencing is the ‘first-generation’ DNA sequencing method, widely used in ALS diagnosis, first emerged in 1977 [110]. Sanger Sequencing is known as the chain termination or the dideoxynucleotide or the sequencing by synthesis method. It consists of using one strand of the double-stranded DNA as a template to be sequenced. This sequencing is made using chemically modified nucleotides called dideoxynucleotides (dNTPs). These dNTPs marked for each DNA bases by ddG, ddA, ddT, and ddC also include a fluorescent marker (A is indicated by green fluorescence, T by red, G by black, and C by blue). The fluorescent dideoxynucleotides (dNTPs) are used for elongation of nucleotide, once incorporated into the DNA strand they prevent the further elongation. Then, we obtain DNA fragments ended by a dNTP with different sizes and fragments, separated according to their size by capillary electrophoresis. A laser within the automated machine used to read the sequence detects a fluorescent intensity that is translated into a ‘peak’ revealing heterozygous or homozygous variants within a sequence [111].
Related Knowledge Centers
- Nucleic Acid
- Polymer
- Polynucleotide
- Protein
- Rna
- Virus
- Lipid
- Nucleic Acid Double Helix
- Genetics
- Reproduction