Deoxyribonucleic acids is the full meaning or form of DNA. DNA is a molecule that makes up the human body. It is used to identify the lineage of ancestors and family members. This type of anus explains the physical relationship between humans and their parents. DNA plays a vital role in our bodies. The DNA functions in the body’s genetic functions. It also controls the protein synthesis. Primarily, DNA’s most important function is to use the genetic code in order to encode the sequences of amino acids found in the routine. In other words, DNA is the medium by which any creature or human is born.
The structure of DNA determines the function. This is useful in understanding its function. The nucleotides are the fundamental building blocks of DNA, as we have already stated. These nucleotides consist of a 5-carbon sugar, a Phosphore Group, and a Nitrogenous Base. Each strand of DNA is made up of sugars and phosphates, which combine nucleotides. Base pairs are formed when two DNA strands come together. The following nitrogenous bases can be paired together: AT and CG. The weak bonds between gases and hydrogen bonds (also known as hydrogen bonds) allow them to contact each other. These bonds can be easily broken or repaired.
For a DNA test, some samples may be taken from your body. It can also be used to take blood, skin, or ulcer liquid samples. Let’s just say that amniotic fluid, also known as ulnar fluid, is the liquid found around the fetus during pregnancy. You can also collect samples from the inside cheeks of the person conducting the DNA test. These samples can be tested by accredited laboratories. These laboratories can perform DNA tests for a fixed fee, which can range from 10 to 40 thousand. The report can be obtained within 15 days.
There are three major types of DNA: double-stranded, connected by interactions between base pairs. These forms are known as A-form, Z-form and B-form DNA.
Watson and Crick combined the information from DNA’s base composition, dinucleotide structures, and the observation that X-ray crystallography suggested an helical periodicity in their 1953 model of a double helical DNA structure. Two strands of DNA were proposed by Watson and Crick — each in a right hand helix, wound around the same axis. H-bonding (in anti conformation), holds the two strands together, as illustrated in Figure 184.108.40.206.1.
Major groove Major groove
Minor groove Minor groove
If pyrimidine is always paired with purine, bases can fit in the double-helical model. From Chargaff’s rules, the two strands will pair A with T and G with C. This pairs a keto base with an amino base, a purine with a pyrimidine. There can be two H-bonds between A and C, while three can form between G or C.
These are the complementary base pairs. This base-pairing scheme instantly suggests a way of replicating and copying the genetic information.
These two strands do not appear in a side-by-side arrangement. This would be known as aParanemic jointInstead, the two strands are wrapped around the same helical direction and intertwine with each other (which is known as aThe plectonemic coil). This intertwining has one consequence: the DNA cannot be separated without it rotating. One turn of DNA is required for each “untwisting”.
Dimensions of the B-form (the most frequent) of DNA
- 0.34 nm, between bp, 3.4 nm per turn. About 10 bp each turn
- 1.9 nm (about 2.0 nm or 20 Angstroms) in diameter
Major and minor grooves
Figure 2.5.2d2.5.2d shows that the major groove is larger than the minor groove in DNA. Many sequence-specific proteins interact with the major groove. The major groove is where the N7 and C6 purines groups, as well as the C4- and C5 pyrimidines groups, face. They can therefore make contact with specific amino acids in DNA binding proteins. Specific amino acids can be used as H-bond acceptors and donors to form H-bonds that are specific to specific nucleotides within the DNA. The minor groove also contains H-bond acceptors and donors. In fact, some proteins can bind to specific minor groove proteins. Base pairs stack with some rotation.
There are three types of duplex nucleic acids. B-form is the most common form and can be found in DNA at physiological salt concentrations and neutral pH. This is the right-handed, double helical structure that we are referring to. For RNA-DNA duplexes, and RNA–RNA duplexes, a thicker right-handed duplex has been described with fewer base pairs. This is known as A-form nucleic acids.
The third form of duplex DNA is a left-handed version with a strikingly different helical structure. This Z DNA can be formed using a combination of purines and pyrimidines (e.g. GCGCGC is especially important in negatively supercoiled DNA. Only a small portion of DNA found in cells exists in the Z format. Although it has been tempting to suggest that this structure may be involved in regulation of some cell function (e.g transcription or regulation), there is no conclusive evidence.
The main difference between A and B-form nucleic acids is in the conformation for the deoxyribose sugar rings. It is located in the C2’ endoconformation of B-form, while it is in A-form’s C3′-O-C1′ atom. Figure 220.127.116.11.4 shows that if you look at the plane created by the C4’-O-C1’ atoms of deoxyribose the C2’ atom is higher than the plane in C2′ endoconformation. In the C3’ endoconformation the C3’ atom is higher than the plane. This conformation places the 5′- and 3’hydroxyls (both esterified with the phosphates linking the next nucleotides), closer together than in the C2 endoconformation (Figure 2.16). This reduces the distance between adjacent nucleotides by approximately 1 Angstrom in A/form relative to B-form nucleic acids (Figure 18.104.22.168.4). Figure 22.214.171.124.4: Syn and anti conformations of the base relative to the sugar in nucleotides.
The placement of the base-pairs in the duplex is another major difference between A and B-form nucleic acids. B-form’s base-pairs are nearly centered above the helical direction (Figure 126.96.36.199.4), while A-form has them displaced from the central axis to be closer to the major groove. In A-form, the result is a ribbon-like shelix with a cylindrical core.
Z-DNA is a completely different duplex structure. The two strands are arranged in left-handed, helices. There is also a pronounced ZIG-ZAG (hence its name). Z-DNA forms when DNA is in an alternating sequence of purine-pyrimidine such as GCGCGC. The G and C nucleotides can be in different conformations which leads to the zigzag pattern. The G nucleotide is the most important difference.
It contains the sugar in C3′ endoconformation (like B-form nucleic acids and A-form DNA), and the guanine ring in the synconformation. This puts the guanine back above the sugar ring, which is in contrast to the anticonformation found in A- and A-form nucleic acids. The base in the anticonformation puts it in a position that it can easily form H-bonds to the complementary base on its opposite strand. Z-DNA’s duplex must accommodate the distortion caused by the G nucleotide during the synconformation. Z-DNA’s adjacent nucleotide has cytosine that is in “normal” C2′ endo. This anticonformation is not possible. Figure 188.8.131.52.5: B-form (left), A-form (middle) and Z-DNA (right). (CC BY-SA 4.0; Mauroesguerroto)
Even the classic B-DNA structure is not uniform. A duplex oligonucleotide crystal X-ray difffraction analysis shows that each sequence has a unique structure. To optimize base stacking, these variations in B-DNA could differ in the propeller twist between bases within a pair, or in the 3 ways 2 consecutive base pairs can move relative each other: roll, slide, twist.
|Helix sense||Right-Handed||Right-Handed||Left Handed|
|base pairs per turn||10||11||12|
|Vertical rise per bp||3.4 A||2.56 A||19 A|
|Rotation per bp||+36deg||+33deg||-30deg|
|Helical diameter||19 A||19 A||19 A|