Double-stranded molecule

In most organisms, the basic unit of nuclear DNA is a double-stranded molecule derived from those of both its ancestors, the father and the mother. The information it carries provides clues, therefore, not only to the genetic constitution of the organism but also on the characteristics it shares with its ancestors. 

DNA, mitochondrial (mt-DNA) A double-stranded molecule of DNA that controls the development and functioning of the mitochondrion containing it mt-DNA is passed along female lines. 

DNA (deoxyribonucleic acid) A double-stranded molecule held together by weak bonds between base pairs of nucleotides that encodes genetic information. The base sequence of each single strand can be deduced from that of its partner since base pairs form only between the bases A and T and between G and C. 

Hybridization Process of joining two complementary strands of DNA or one each of DNA and RNA to form a double-stranded molecule. 

Hybridization the process of a single-stranded nucleic acid molecule binding with a complementary single strand of nucleic acid to form a stable double-stranded molecule. Hybridization is temperature dependent, so DNA s that hybridize strongly at low temperature can be temporarily separated (denatured) by heating. 

DNA is a double-stranded molecule in which the structure of the second strand can be deduced from the structure of the first strand. The second strand is complementary (A s in the first strand match T s in the... 

In contrast to DNA, which is quite generally found in a double-stranded structure, RNA is generally, but not always, found in nature as a single-stranded molecule. There are, as always, exceptions, one of which we note below. Double-stranded RNAs as well as hybrid DNA RNA double-stranded molecules are found. 

Both endogenous and synthetic siRNAs are generated from double-stranded molecules and selection of the correct strand has to be determined. Generally, strand selection follows the so-called asymmetry rule. The asymmetry rule predicts that the siRNA strand with the less stably paired 5 end will be selected and... 

FIGURE 3.6 Annealing of two complementary strands of DNA to form a fully paired double-stranded molecule. 

DNA is a polydeoxyribonucleotide that contains many monodeoxy-ribonucleotides covalently linked by 3 ->5 -phosphodiester bonds. With the exception of a few viruses that contain single-stranded DNA, DNA exists as a double-stranded molecule, in which the two strands wind around each other, forming a double helix. In eukaryotic cells, DNA is found associated with various types of proteins (known collectively as nucleoprotein) present in the nucleus, whereas in prokaryotes, the protein-DNA complex is present in the nucleoid. 

While studying the structure of a small gene that was recently sequenced during the Human Genome Project, an investigator notices that one strand of the DNA molecule contains 20 A s, 25 G s, 30 C s, and 22 T s. How many of each base is found in the complete double-stranded molecule ... 

That the DNA content doubles prior to cell division was established by microspectrophotometry. It was clear that both daughter cells must receive one or more identical molecules of DNA. However, it was not known whether the original double-stranded DNA molecule was copied in such a way that an entirely new double-stranded DNA was formed or whether, as we now know to be the case, the two chains of the original molecule separated. The latter is called semiconservative replication, each of the separated strands having a new complementary strand synthesized along it to form the two identical double-stranded molecules. 

The DNA of a bacterial cell, such as Escherichia coli, is a circular double-stranded molecule often referred to as the bacterial chromosome. In E. coli this DNA molecule contains 4.6 million base pairs. The circular DNA is packaged into a region of the cell called the nucleoid (see Topic Al) where it is organized into 50 or so loops or domains that are bound to a central protein scaffold, attached to the cell membrane. Fig. la illustrates this organization, although only six loops are shown for clarity. Within this structure, the DNA is actually not a circular double-stranded DNA molecule such as that shown in Fig. lb but is negatively supercoiled, that is, it is twisted upon itself (Fig. lc) and is also complexed with several DNA-binding proteins, the most common of which are proteins HU, HLP-1 and H-NS. These are histone-like proteins (see below for a description of histones). 

Thermal melting refers to heating a DNA solution until the two strands of DNA separate, as shown in Figure 8-4. Conversely, a double-stranded molecule can be formed from complementary single stands. 

Like other DNA polymerases, reverse transcriptases are primer-and template-dependent. They also possess an RNase H activity (H stands for hybrid) that can degrade the RNA template after it is used for synthesis of the first DNA strand. The enzyme then can copy the first strand of DNA to make a double-stranded molecule. 

In an attempt to design a protocell, a Los Alamos group proposed a system essentially composed of non-enzymatic template replication coupled to micelle growth [55,56]. The micelle aggregate is assumed to incorporate from the medium precursors of lipids and template building blocks (monomers or oligomers). The authors assume that for this particular construct PNAs [57] would serve better because of their hydrophobic nature. It is assumed that single-stranded molecules face the hydrophilic anterior whereas double-stranded molecules immerse into the hydrophobic interior of the micelles. Alternation between these two states is assumed to facilitate replication. 

Base pair Unit of length for DNA work. Usually expressed as kb (kilobase) or kbp (kilo base pair). In the double-stranded molecule guanosine pairs with cytidine and adenosine with thymidine (or uridine in RNA). 

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