Cytosine hydrogen bonding

Two papers have attempted to compare the observed infrared lines of the base pairs in the region of the hydrogen-bond absorption with the calculated data. Rein and Svetina have calculated the proton vibrational states and relative transition probabilities for two guanine-cytosine hydrogen bonds. Their preliminary results seemed to be consistent with the absorption peak at 3489 cm (0.436 eV) reported by Pitha et for the hydrogen bond N-H stretching mode of... 

Hydrogen bonds hold the base pairs of double-stranded DNA together (see Section 25.4). Thymine hydrogen bonds with adenine. Cytosine hydrogen bonds with guanine. 

Complementary bases are nucleotide bases that form strong hydrogen bonds with one another. Adenine and th)nnme are complementary bases, as are adenine and uracil, and guanine and cytosine. Hydrogen bonding of complementary bases, called base pairing, is the key to nucleic acid structure and function (see Figure 25.11). 

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. 

Figure 7.7 Color codes for the recognition patterns at the edges of the base pairs in the major (a) and minor (b) grooves of B-DNA. Hydrogen-bond acceptors are red hydrogen-bond donors are blue. The methyl group of thymine is yellow, while the corresponding H atom of cytosine is white.

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 ). 

---