Double-stranded DNA dsDNA

The presence of conjugated double-bond systems in the purine and pyrimidine bases means that DNA and RNA absorb light in the ultraviolet region at 260 nm. For approximate determinations it can be assumed that a 50 /xg ml-1 solution of double-stranded DNA (dsDNA) has an absorbance of 1 at 260 nm. More exact quantitation can be obtained by comparing the ratio of the absorbance of the sample at 260 and 280 nm. The term optical density (OD) is often used in place of absorbance. Pure DNA preparations should have an OD 260/OD 280 of 1.8. Ratios less than this may indicate protein contamination while higher ratios may indicate the presence of RNA. 

The phage T4 (bottom left), one of the largest viruses known, has a much more complex structure with around 170 000 base pairs (bp) of double-stranded DNA (dsDNA) contained within its head. ... 

It is known that double-stranded DNA (dsDNA) is a relatively rigid strncture in standard conditions in physiologically relevant solutions like lx PBS buffer. For example, typical dsDNA has a... 

DNA replication begins with protein binding to the origin of replication, a unique sequence in the bacterial chromosome, causing a short region of double-stranded DNA (dsDNA) to unwind (Figure 11-2). 

This system separates double-stranded DNA (dsDNA) fragments with a length of 70 x 80 000 base pairs (bp) in gels of 3% to 0.1% agarose. For analysis of smaller-fragments (6000 to 1000 bp) PAGE systems are described in literature with 20-3% polyacrylamid. 

C4CiIm][PPg], a widespread IL, was recently used for fhe direcf exfraction of double-stranded DNA (dsDNA) [30]. The authors demonstrated that DNA may be extracted with high efficiency, >95%, while profeins and mefal-loproteins do nof inferfere extraction. The back-extraction of DNA info fhe aqueous phase wifh fhe efficiency of 30% was performed in fhe presence of phosphafe-cifrafe buffer solution (pH 4). 

CEC was used to separate double-stranded DNA (dsDNA) on microchips [58,152]. In these cases, Ci8-modified PMMA microchips were employed with ion-pair reverse phase chromatography and DNA fragments with different sizes were analysed by contact conductivity detection. 

Determination of the optimal experimental conditions for the atomic force microscopy (AFM) characterization of the surface morphology of a DNA electrochemical biosensor obtained using different immobilization procedures of calf-thymus double-stranded DNA (dsDNA) on a highly oriented pyrolytic graphite (HOPG) electrode surface. 

The electrochemical study of the in situ interaction of quercetin, adriamycin, DETA/NO and their metabolites with double-stranded DNA (dsDNA) immobilized on a glassy carbon electrode (GCE) surface. 

Perhaps the most well-recognized fluorescent dye for detection of DNA hybridization is ethidium bromide (EtBr). EtBr is a cationic phenanthridinium compound that can bind to DNA by intercalation. This dye has an excitation maxima at 518 nm when bound to double-stranded DNA (dsDNA). Excitation of EtBr is often done by use of an argon ion laser, making this fluorophore a viable choice for applications in optical sensors as well as confocal scanning laser microscopy and fluorometry [41]. The structure of ethidium bromide is shown in Fig. 6. 

The bacterial RNA polymerase has a subunit composition of ap>3 a, the a subunit being involved in correct initiation of transcription. Appropriate regulatory protein binding to the promoter region permits correct RNA polymerase binding, double-stranded DNA (dsDNA) unwinding and correct initiation of transcription. The dsDNA unwinds and the nascent RNA forms a transient RNA-DNA hybrid in the transcription bubble of unwound DNA that moves down the DNA. 

The procedure generally used for this step is the following the probe-coated electrode is immersed for a predetermined time in a stirred hybridization solution containing the DNA target, while holding [15,18-23] or not [25] the potential at + 0.5 V vs. Ag/AgCl. A double stranded DNA (dsDNA) or duplex is formed. This kind of hybridization scheme used for sequence specific purposes has problems of nonspecific adsorption of noncomplementary DNA on the transducer surface [23]. 

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