Adenine hydrogen-bonding

As with proteins, the nucleic acid polymers can denature, and they have secondary structure. In DNA, two nucleic acid polymer chains are twisted together with their bases facing inward to form a double helix. In doing so, the bases shield their hydrophobic components from the solvent, and they form hydrogen bonds in one of only two specific patterns, called base pairs. Adenine hydrogen bonds only with thymine (or uracil in RNA), and guanine pairs only with cytosine. Essentially every base is part of a base pair in DNA, but only some of the bases in RNA are paired. The double-helix structure... 

Each base hydrogen bonds strongly to only its complementary base.Adenine hydrogen bonds to thymine or to uracil guanine hydrogen bonds to cytosine. 

The DNA base pairs guanine (G), cytosine (C), adenine (A) and thymine (T). The uracil-2,6-diaminopyridine pair can also form three hydrogen bonds but has a much lower association constant than G-C. 

Nicotinamide, (S)-N-(a-methylbenzyl)-hydrogen bonding, 2, 111 Nicotinamide, N-phenyl-hydrogen bonding, 2, 111 Nicotinamide adenine dinucleotide in biochemical pathways, 1, 248 coenzyme system with NADH, 2, 121 reactions, 2, 382 reduction, 2, 281, 283... 

The side chain of Gin 28 forms two hydrogen bonds (b) to the edge of the adenine base of base pair T14-Al in the major groove of the DNA. (Adapted from J. Anderson et al.. Nature 326 846-852, 1987.)... 

Like Thr 124 and Thr 215, the Asn 69 and Asn 159 residues occupy equivalent positions in the two homologous motifs of TBP. By analogy with the symmetric binding of a dimeric repressor molecule to a palindromic sequence described in Chapter 8, the two motifs of TBP form symmetric sequence-specific hydrogen bonds to the quasi-palindromic DNA sequence at the center of the TATA box. The consensus TATA-box sequence has an A-T base pair at position 4, but either a T-A or an A-T base pair at the symmetry-related position 5, and the sequence is, therefore, not strictly palindromic. However, the hydrogen bonds in the minor groove can be formed equally well to an A-T base pair or to a T-A base pair, because 02 of thymine and N3 of adenine occupy nearly stereochemically equivalent positions, and it is sufficient, therefore, for the consensus sequence of the TATA box to be quasi-palindromic. 

Several classes of vitamins are related to, or are precursors of, coenzymes that contain adenine nucleotides as part of their structure. These coenzymes include the flavin dinucleotides, the pyridine dinucleotides, and coenzyme A. The adenine nucleotide portion of these coenzymes does not participate actively in the reactions of these coenzymes rather, it enables the proper enzymes to recognize the coenzyme. Specifically, the adenine nucleotide greatly increases both the affinity and the speeifieity of the coenzyme for its site on the enzyme, owing to its numerous sites for hydrogen bonding, and also the hydrophobic and ionic bonding possibilities it brings to the coenzyme structure. 

The two strands which make up DNA are held together by hydrogen bonds between complementary pairs of bases adenine paired with thymine and guanine paired with cytosine. The integrity of the genetic code (and of life as we know it) depends on error-free transmission of base-pairing information. 

Examine AT pair and GC pair, adenine-thymine and guanine-cytosine base pairs, respectively. Identify the hydrogen bonds in each. Are they the same as those you sketched Are the base pairs flat as normally drawn in textbooks, or are they significantly puckered or twisted ... 

DNA is made up ot two intertwined strands. A sugar-phosphate chain makes up the backbone of each, and the two strands are joined by way of hydrogen bonds betwen parrs of nucleotide bases, adenine, thymine, guanine and cytosine. Adenine may only pair with thymine and guanine with cytosine. The molecule adopts a helical structure (actually, a double helical stnrcture or double helix ). 

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