Double helix complementary strands

The DNA isolated from different cells and viruses characteristically consists of two polynucleotide strands wound together to form a long, slender, helical molecule, the DNA double helix. The strands run in opposite directions that is, they are antiparallel and are held together in the double helical structure through interchain hydrogen bonds (Eigure 11.19). These H bonds pair the bases of nucleotides in one chain to complementary bases in the other, a phenomenon called base pairing. 

DNA arrays utilize this biopolymer s well-known ability to dimerize (the double helix) - single-stranded DNA can associate with a complementary single-stranded DNA (or RNA), the binding being entirely dependent on the linear sequence of DNA monomers (nucleotides). Many commercial companies will chemically synthesize any desired sequence of DNA, thus sufficiently long synthetic DNAs can be readily prepared to be cross-linked to arrays as probes. 

DNA is composed of two complementary strands wound around each other in a double helix. The strands are antiparallel the bases of each strand face the interior and hydrogen bond to their... 

Double helix (Section 28.8) The form in which DNA normally occurs in living systems. Two complementary strands of DNA are associated with each other by hydrogen bonds between their base pairs, and each DNA strand adopts a helical shape. 

FIGURE 12.1 DNA replication yields two daughter DNA duplexes identical to the parental DNA molecule. Each original strand of the double helix serves as a template, and the sequence of nucleotides in each of these strands is copied to form a new complementary strand by the enzyme DNA polymerase. By this process, biosynthesis yields two daughter DNA duplexes from the parental double helix. 

In 1953, James Watson and Francis Crick made their classic proposal for the secondary structure of DNA. According to the Watson-Crick model, DNA under physiological conditions consists of two polynucleotide strands, running in opposite directions and coiled around each other in a double helix like the handrails on a spiral staircase. The two strands are complementary rather than identical and are held together by hydrogen bonds between specific pairs of... 

Molecules of DNA consist of two complementary polynucleotide strands held together by hydrogen bonds between heterocyclic bases on the different strands and coiled into a double helix. Adenine and thymine form hydrogen bonds to each other, as do cytosine and guanine. 

Barton and coworkers have shown that proteins can in fact modulate the DNA electron transfer [168]. Methyltransferases are enzymes that recognize distinct DNA sequences, e.g., 5 -G CGC-3, and effect methylation by extrading the target base cytosine ( C) completely out of the DNA duplex while the remainder of the double helix is left intact. The methyltransferase Hha 1-DNA complex is a well-characterized example, revealing that the structure of the DNA is significantly but locally distorted [169,170]. In a recent study, Raj ski et al. used DNA duplex 20 containing the M.Hha I binding site between two oxidizable 5 -GG-3 sites [168] (Fig. 20). The duplex contains a complementary strand, selectively 5 -modified with a Rh intercalator that can function as a photooxidant. Upon... 

DNA is organized into two strands by the pairing of bases A to T and G to C on complementary strands. These strands form a double helix around a central axis. 

Base pair (bp) The four nucleotides in the DNA contain the bases adenine (A), guanine (G), cytosine (C), and thymine (T). Two bases (adenine and thymine or guanine and cytosine) are held together by weak bonds to form base pairs. The two strands of human DNA are held together in the shape of a double helix by those bonds between base pairs. For example, the complementary nucleic acid base sequence to G-T-A-C that forms a double-stranded structure with the matching bases is C-A-T-G. 

The two complementary strands of the DNA double helix run in antiparallel directions (Fig. 4-1). The phosphodiester connection between individual deoxynucleotides is directional. It connects the 5 -hydroxyl group of one nucleotide with the 3 -hydroxyl group of the next nucleotide. Think of it as an arrow. If the top strand sequence is written with the 5 end on the left (this is the conventional way), the bottom strand will have a complementary sequence, and the phosphate backbone will run in the opposite direction the 3 end will be on the left. The antiparallel direc-... 

Double-stranded DNA exhibits complementarity in forming the double helix. The complementary sequences have opposite polarity that is, the two chains run in opposite directions as in the following illustration ... 

Although relatively few structural studies of the interstrand GG adduct [42, 45, 46] have been reported, the data presented reveal the structural distortion to be significantly different from that of the intrastrand adduct. The prime feature of this adduct is the cross-linking between the two strands at GC sequences, thereby causing a kink in the double helix. In this instance, however, the kink is towards the minor groove, with a value of -47° (Fig. 4.3). Another feature of this adduct not present in the other intrastrand adducts is the complementary cytosine bases extruding from the lesion site. 

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