Hydrogen-bonded double helix complementary

Given two complementary strands of DNA containing 100 base pairs each, calculate the ratio of two separate strands to hydrogen-bonded double helix in solution at 300 K. Hint The formula for calculating this ratio is where A is the... 

Section 28 8 The most common form of DNA is B DNA which exists as a right handed double helix The carbohydrate-phosphate backbone lies on the outside the punne and pyrimidine bases on the inside The double helix IS stabilized by complementary hydrogen bonding (base pairing) between adenine (A) and thymine (T) and guanine (G) and cytosine (C)... 

Transcription Transcription is the process of forming a complementary m-RNA strand from the DNA. This process occurs in the cell nucleus. To begin, an enzyme helps the DNA double helix to break apart and uncoil slightly. This allows RNA nucleotide bases to form complementary hydrogen bonds to the DNA bases. In essence, the m-RNA is reading the DNA code. For example, let s imagine a short section of DNA with the following sequence ... 

FIGURE 1 5.22 Complementary hydrogen bonding in the DNA double helix. Hydrogen bonds in the thymine-adenine (T—A) and cytosine-guanine (C—G) pairs stabilize the double helix. 

DNA synthesis takes place by a mechanism of complementary autoreplication. DNA is present in nearly all biological systems (with the exception of certain phages) as a double helix, formed by poly-desoxyribonucleotides, linked together by complementary hydrogen bonds between base pairs (A-T) (G-C), twisted aroxmd a common axis. Under the influence of a special enzyme, polymerase, it can unwind into single polynucleotides, each of which becomes a template for formation of the complementary chain. This process is shown diagrammatically in Fig. 1. 

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 1.5 The DNA double helix. Two complementary polynucleotide chains running in opposite directions can pair through hydrogen bonding between their nitrogenous bases. Their complementary nucleotide sequences give rise to structural complementarity. 

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. 

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. 

Thus, each purine is specifically linked to a pyrimidine by either two or three hydrogen bonds. The result of these interactions is that each nucleotide recognizes and bonds with its complementary partner. This specific base-pairing means that the two strands in the DNA double helix are complementary. Wherever adenine appears in one strand, thymine appears opposite it in the other wherever cytosine appears in one strand, guanine appears opposite it in the other. We shall see later the significance of base pairing... 

---