General characteristics of DNA:
1. DNA (or Deoxyribonucleic Acid) is a long polymer of deoxyribonucleotides.
2. The number of nucleotides present in a DNA determines the length of DNA.
3. A pair of nucleotides (such as: A-T and G-C) in a DNA is called a base pair.
4. The number of base pairs in a DNA also determines the length of DNA.
5. The length of DNA varies in different organisms, such as in Escherichia coli the length of DNA is 4.6 × 106 bp (or base pair), and haploid content of human DNA is 3.3 × 109 bp.
6. DNA was first identified by Friedrich Meischer in 1869 and he named it as ‘Nuclein’.
7. DNA is hydrophilic (or water loving) in nature.
8. It is an acidic substance present inside the nucleus of the cell.
9. The two polynucleotide chain of DNA are not identical to each other, they are either complementary to each other due to their base pairing property.
- The complementary base pairing of DNA helix satisfies Chargaff’s rule, which states that, the DNA of an organism should always have a 1:1 stoichiometric ratio of purines and pyrimidines i.e., the amount of adenine should always be equal to the amount of thymine (A=T) and the amount of guanine should always be equal to the amount of cytosine (C=G).
- In a DNA the genetic information is present on one of the two strands called as the template strand or non-coding strand while the other strand is called as coding strand.
Central dogma theory:
The Central dogma theory is proposed by Francis Crick, which states that the genetic information flows from DNA to RNA to Protein. Thus it means that DNA produces RNA (by the process called transcription) and RNA produces protein (by the process called translation)
DNA —Transcription–→ RNA —Translation–→ Protein
Types of DNA
There are three different types of DNA, these are explained elaborately below:
- It is the most common Watson-Crick proposed double helical model of DNA.
- In B-DNA the two strands are coiled in right-handed fashion.
- The diameter between the helix in it is 2.37nm.
- Rise per base pair in it is 0.34nm.
- The distance per complete turn (or pitch) in it is 3.4nm.
- The number of base pairs per complete turn in it is 10.
- Topology of its major groove is wide and deep.
- Topology of its minor groove is narrow and shallow.
- In A-DNA the two strands are also coiled in right-handed fashion.
- The diameter between the helix in it is 2.55nm.
- Rise per base pair in it is 0.29nm.
- The distance per complete turn (or pitch) in it is 3.2nm.
- The number of base pairs per complete turn in it is 11.
- Topology of its major groove is narrow and deep.
- Topology of its minor groove is broad and shallow.
- In Z-DNA the two strands are coiled in left-handed fashion.
- The phosphodiester backbone of Z-DNA is arranged in a zig-zag pattern.
- It is discovered by Rich, Nordheim and Wang in 1984.
- The diameter between the helix in it is 1.84nm.
- Rise per base pair in it is 0.37nm.
- The distance per complete turn in it is 4.5nm.
- The number of base pairs in it is 12.
- Topology of its major groove is flat.
- Topology of its minor grove is narrow and deep.