Complementary base pairing in DNA

Fig. 9.11 The complementary base-pairs in DNA interact through hydrogen bonds. The backbones of each strand in DNA consists of sugar units (to which the bases are attached) connected by phosphate groups.

Complementary base pairing in DNA. Adenine (a purine) always pairs with thymine (a pyrimidine) guanine (a purine) always pairs with cytosine (a pyrimidine). 

What data obtained from the chemical analysis of DNA supported the idea of complementary base pairing in DNA proposed by Watson and Crick ... 

Complementary base pairs in DNA are linked through the formation of... 

The hydrogen-bonding interactions that occur between complementary base pairs in DNA. 

In molecular biology, a set of two hydrogen-bonded nucleotides on opposite complementary nucleic acid strands is called a base pair. In the classical Watson-Crick base pairing in DNA, adenine (A) always forms a base pair with thymine (T) and guanine (G) always forms a base pair with cytosine (C). In RNA, thymine is replaced by uracil (U). 

FIG U RE 3.4 Watson-Crick base pairing in DNA. Adenine is complementary to thymine, and guanine is complementary to cytosine. 

In complementary base pairing within DNA, G pairs with C and A with T. Thus the answer is CGAATCAT. 

The gully complementary nature of the base pairs in DNA means that each strand can act as a blueprint for the other. Assisted by the enzyme DNA polymerase, the DNA molecule can be unzipped and replicate itself exactly by the assemblage of new nucleotides from the cell s pool. This process is known as semiconservative replication because the two identical DNA molecules produced consist of one original and one new strand of DNA. DNA is able to replicate itself, which is essential to the process of cell division. As a result, an exact copy of the cell s genetic instructions can be handed on to the next generation of cells. 

The normal base pairs in DNA. Adenine in one polynucleotide chain pairs with thymine in the complementary chain guanine pairs with cytosine. A-T base pairs are joined by two hydrogen bonds G-C base pairs are Joined by three hydrogen bonds. 

The specific, complementary base pairing in the double-helical structures of DNA and RNA (Figure 1.9) is what gives rise to the ability to translate and proliferate this genetic information. 

Adenine-guanine base pairs occupy more space than is available in the interior of the double helix, whereas cytosine—thymine base pairs are too small to span the distance between the sites to which complementary bases are bonded. One would not normally expect to find such base pairs in DNA. 

Fig. 10.12 The left-hand diagram shows two units in one strand of DNA DNA is composed of condensed deoxyribonucleotides and the four possible nucleobases are adenine (A), guanine (G), eytosine (C) and thymine (T). The right-hand diagrams illustrate how complementary base pairs in adjacent strands in DNA internet through hydrogen bonding. (See also Figure 10.15.)...

The right-hand diagrams illustrate how complementary base pairs in adjacent strands in DNA interact through hydrogen bonding. (See also Fig. 10.16, p. 323.)... 

RNA is made from DNA in a process that is similar to the way in which DNA replicates itself. A portion of DNA is uncoiled by helicase and RNA is assembled along the unzipped strands of DNA, using the same complementary base pairs as DNA, except that uracil replaces the thymine. As in DNA replication, the RNA sequence that forms has the complementary base pairs of the DNA gene. The DNA sequence on the next page would form the complementary RNA sequence shown. 

A FIGURE 21.15 Base Pairing in DNA The bases in nucleic acids are complementary. Each pyrimidine base pairs with only one purine base (G with C, A with T) via specific hydrogen bonds that occur between the two bases. 

The Watson-Crick model portrays the double-stranded DNA molecule as a right-handed helix. This means that when the molecule is viewed from one end the top surface of the helix spirals towards the right. Each turn of the helix contains ten base-pairs, measures 3.4 nm in length and corresponds to the major periodicity (Section 4.5) attained by X-ray crystallography. The distance of 0.34 nm occupied by one nucleotide is consistent with the experimental minor periodicity. The two helical strands are held together by the hydrogen bonds between complementary base-pairs. In addition, within a polar environment vertical hydrophobic... 

The complementary base pairs in the centre of the double-stranded DNA structure are planar yet perpendicular to the plane of the sugars in the backbone. The optimum... 

In the human cell there are 23 pairs of chromosomes containing approximately 3000 million base pairs of DNA. Short sequences of DNA, perhaps with as few as 20 nucleotide units and sometimes radiolabeled, can be obtained either by chemical synthesis (gene machine) or from cloning. These short sequences can be used to probe for a complementary sequence by looking for the position to which they bind to any DNA sample under investigation, from blood for example. Such probes can detect as little as 100 fg of DNA and are the basis of forensic genetic fingerprinting tests. 

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