|
Non B-DNA
Non-B DNA is DNA in any conformation other than the canonical (B-DNA) conformation, the most common form of DNA found in nature at neutral pH and physiological salt concentrations. Non-B DNA structures can arise due to various factors, including DNA sequence, length, supercoiling, and environmental conditions. Non-B DNA structures can have important biological roles, but they can also cause problems, such as genomic instability and disease. Types of Non-B DNA Non-B DNA can be classified into several types, including A-DNA, Z-DNA, H-DNA, G-quadruplexes, and Triplexes (Triple-stranded DNA Triple-stranded DNA (also known as H-DNA or Triplex-DNA) is a DNA structure in which three oligonucleotides wind around each other and form a triple helix. In triple-stranded DNA, the third strand binds to a Nucleic acid double helix#Helix geomet ...). A-DNA is a right-handed double helix structure for RNA-DNA duplexes and RNA-RNA duplexes that is less common than the more well-known B-DNA ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
B-DNA
In molecular biology, the term double helix refers to the structure formed by double-stranded molecules of nucleic acids such as DNA. The double helical structure of a nucleic acid complex arises as a consequence of its secondary structure, and is a fundamental component in determining its tertiary structure. The structure was discovered by Rosalind Franklin and her student Raymond Gosling, Maurice Wilkins, James Watson, and Francis Crick, while the term "double helix" entered popular culture with the 1968 publication of Watson's '' The Double Helix: A Personal Account of the Discovery of the Structure of DNA''. The DNA double helix biopolymer of nucleic acid is held together by nucleotides which base pair together. In B-DNA, the most common double helical structure found in nature, the double helix is right-handed with about 10–10.5 base pairs per turn. The double helix structure of DNA contains a ''major groove'' and ''minor groove''. In B-DNA the major groove is wider th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
A-DNA
A-DNA is one of the possible double helical structures which DNA can adopt. A-DNA is thought to be one of three biologically active double helical structures along with B-DNA and Z-DNA. It is a right-handed double helix fairly similar to the more common B-DNA form, but with a shorter, more compact helical structure whose base pairs are not perpendicular to the helix-axis as in B-DNA. It was discovered by Rosalind Franklin, who also named the A and B forms. She showed that DNA is driven into the A form when under dehydrating conditions. Such conditions are commonly used to form crystals, and many DNA crystal structures are in the A form. The same helical conformation occurs in double-stranded RNAs, and in DNA-RNA hybrid double helices. Structure Like the more common B-DNA, A-DNA is a right-handed double helix with major and minor grooves. However, as shown in the comparison table below, there is a slight increase in the number of base pairs (bp) per turn. This results in a smal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Z-DNA
Z-DNA is one of the many possible double helical structures of DNA. It is a left-handed double helical structure in which the helix winds to the left in a zigzag pattern, instead of to the right, like the more common B-DNA form. Z-DNA is thought to be one of three biologically active double-helical structures along with A-DNA and B-DNA. History Left-handed DNA was first proposed by Robert Wells and colleagues, as the structure of a repeating polymer of inosine–cytosine. They observed a "reverse" circular dichroism spectrum for such DNAs, and interpreted this incorrectly to mean that the strands wrapped around one another in a left-handed fashion. The relationship between Z-DNA and the more familiar B-DNA was indicated by the work of Pohl and Jovin, who showed that the ultraviolet circular dichroism of poly(dG-dC) was nearly inverted in 4 M sodium chloride solution and that the structure of poly d(I–C)·poly d(I–C) was in fact a right-handed D-DNA conformation. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
H-DNA
Triple-stranded DNA (also known as H-DNA or Triplex-DNA) is a DNA structure in which three oligonucleotides wind around each other and form a triple helix. In triple-stranded DNA, the third strand binds to a B-form DNA (via Watson–Crick base-pairing) double helix by forming Hoogsteen base pairs or reversed Hoogsteen hydrogen bonds. Structure Examples of triple-stranded DNA from natural sources with the necessary combination of base composition and structural elements have been described, for example in Satellite DNA. Hoogsteen base pairing A thymine (T) nucleobase can bind to a Watson–Crick base-pairing of T-A by forming a Hoogsteen hydrogen bond. The thymine hydrogen bonds with the adenosine (A) of the original double-stranded DNA to create a T-A*T base-triplet. Intermolecular and intramolecular interactions There are two classes of triplex DNA: intermolecular and intramolecular formations. An intermolecular triplex refers to triplex formation between a duple ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
G-quadruplex
In molecular biology, G-quadruplex secondary structures (G4) are formed in nucleic acids by sequences that are rich in guanine. They are helical in shape and contain guanine tetrads that can form from one, two or four strands. The unimolecular forms often occur naturally near the ends of the chromosomes, better known as the telomeric regions, and in transcriptional regulatory regions of multiple genes, both in microbes and across vertebrates including oncogenes in humans. Four guanine bases can associate through Hoogsteen hydrogen bonding to form a square planar structure called a guanine tetrad (G-tetrad or G-quartet), and two or more guanine tetrads (from G-tracts, continuous runs of guanine) can stack on top of each other to form a G-quadruplex. The placement and bonding to form G-quadruplexes is not random and serve very unusual functional purposes. The quadruplex structure is further stabilized by the presence of a cation, especially potassium, which sits in a centr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triple-stranded DNA
Triple-stranded DNA (also known as H-DNA or Triplex-DNA) is a DNA structure in which three oligonucleotides wind around each other and form a triple helix. In triple-stranded DNA, the third strand binds to a Nucleic acid double helix#Helix geometries, B-form DNA (via Base pair, Watson–Crick base-pairing) double helix by forming Hoogsteen base pairs or reversed Hoogsteen hydrogen bonds. Structure Examples of triple-stranded DNA from natural sources with the necessary combination of base composition and structural elements have been described, for example in Satellite DNA. Hoogsteen base pairing A thymine (T) nucleobase can bind to a Base pair, Watson–Crick base-pairing of T-A by forming a Hoogsteen base pair, Hoogsteen hydrogen bond. The thymine hydrogen bonds with the adenosine (A) of the original double-stranded DNA to create a T-A*T base-triplet. Intermolecular and intramolecular interactions There are two classes of triplex DNA: intermolecular and intramolecula ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
