The double helical structure of DNA exists in at least six different types A to E and Z. Among these, B, A, and Z forms are important.
DNA molecules are huge in size. On an average, a base pair of B-DNA with a thickness of.34 nm has a molecular weight of 660. The term kilobase pair (Kb = 1,000 base pairs) is common in the DNA structure. The number of base pairs and the length of DNA (contour length) varies from species…
DNA is among the largest known. It is difficult to isolate DNA without fragmentation. The entire DNA of bacteria, such as Escherichia coli, has a molecular weight of 2.6 × 109. Viral DNAs range in size from about 1 to 350 × 106. The residue weight of a single nucleotide is 300 to 350. Thus,…
The double helical structure of DNA was proposed by James Watson and Francis Crick in 1953 (Noble Prize, 1962). The structure of DNA double helix is comparable to a twisted ladder as shown in Figure 5.3. The salient features of Watson and Crick model of DNA are given below. DNA molecule consists of two helical polynucleotide…
Erwin Chargaff, in late 1940s, quantitatively analysed the DNA hydrolysates from different species. The important conclusions drawn by him are the following: Table 5.4 DNA Composition of Human Liver The double helical structure of DNA derives its strength from Chargaff’s rule. Single-stranded DNA, which is usually single stranded, does not obey Chargaff’s rule. However, double-stranded…
The monomeric deoxynucleotides in DNA are held together by 3′-5′-phosphodiester bond. DNA structure is often represented in a shorthand form as shown in Figure 5.2. A DNA molecule is made of two chains of several thousands of linked nucleotides. Each nucleotide consists of a phosphate group, a pentose (= a sugar with five carbon atoms and…
The backbone of a DNA molecule consists of deoxyribose linked by phosphodiester bridges. The 3′ hydroxyl of the adjacent sugar moiety of one deoxyribonucleotides is joined to the 5′ hydroxyl of the adjacent sugar by an internucleotide linkage called a phosphodiester bond.
DNA is a polymer of deoxyribonucleotides and is found in chromosomes, mitochondria, and chloroplasts. The nuclear DNA is bound to basic proteins called histones. DNA is present in every nucleated cell and carries the genetic information. The human body contains 0.5 gm of DNA.
Nucleoside monophosphate possesses only one phosphate moiety (AMP and TMP). The addition of second or third phosphate to the nucleoside results in nucleoside diphosphate (e.g. ATP). The additional phosphates are linked by acid anhydride bonds possessing high-energy group potential. These bonds yield about 7 Cal/mol on hydrolysis.