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This blog will enrich your knowledge about the Genetic Material that is DNA and RNA, including nucleoside, nucleotide and the facts behind being genetic.

At a GLANCE

We all have heard the comment about our looks and our every morphological character during our childhood. For example, suppose you have hazy eyes like your father. In that case, the comment is like, ‘you must be on your father.’ Including that we all have a common question during our childhood why doggy gives birth to dog only and cow gives birth to cow only? Isn’t it?

So, there must be something which every baby gets from their parents in a gift which makes them resemble their parents. This resemblance can be in the form of looks or any disease or any disorder anything. For more clearance, the recent global hot topic about looks of Aryan khan (son of Shah Rukh Khan), Ibrahim Ali Khan (son of Saif Ali Khan) almost looks similar to their fathers. The reason behind all these resembling characteristics is the Genetic Material they got from their fathers as a gift.

The genes are responsible for all the changes in our body, whether they are good or bad. Gene is the basic functional and physical unit of heredity. Heredity in biological terms is the process by which our biological parents pass down physical and mental qualities. And genetics is the branch that deals in detail with all these cases.

Genetic material (DNA and RNA)

We all are aware of the fact that DNA and RNA are genetic materials that are responsible for all the genetic processes. This genetic material is located exclusively in the Nucleus. In contrast, in prokaryotes where no defined nucleus is present, this genetic material is scattered in the cytoplasm. The structure of the DNA and RNA plays a significant role in genetic inheritance. Now the basic query about DNA and RNA is,

Why are only these molecules genetic material?

If one genetic material is available, then what is the need for another?

Nucleotides and nucleosides are the building blocks of DNA and RNA. As we have already discussed, a nucleotide comprises a phosphate group, pentose sugar, and nitrogenous base. In contrast, a nucleoside is lacking the phosphate group. There are two types of nitrogenous bases present in the composition of DNA, namely purines and pyrimidines.

this image gives the broad distribution off the nitrogenous bases present in the genetic material, nucleoside and nucleotides — NITROGENOUS BASES

DNA (Deoxyribose Nucleic Acid)

Deoxyribose nucleic acid is the structure of nucleotide that lacks the 2’ OH group. DNA is the acidic structure present in the Nucleus, which is primarily named Nuclein by Friedrich Miescher in 1869. The structure of DNA is the polynucleotide structure because it is a well-arranged collection of many nucleotides. The nucleotide structure is composed of sugar, phosphate group, and nitrogenous bases. Sugar and phosphate group forms the backbone of DNA while nitrogenous bases are arranged in it. Among all, purines and pyrimidines form complementary structures in DNA.

Complimentary structure means purines attached to the pyrimidines in opposite directions like steps through Hydrogen bonding. The complementary base pairs found in DNA are adenine pair with thymine (A=T) in double bond and guanine pair with cytosine in triple bond (G≡C). These nitrogenous bases are attached through Hydrogen-bond with each other. The formed polymer structure has at one end a free phosphate group at 5’ end of the sugar, that is 5’- end. Similarly, at the other end of the polymer, the sugar has free 3’-OH. Two nucleotides linked together via 3’-5’ phosphodiester bond to form dinucleotide and polynucleotide accordingly.

Further, James Watson and Francis Crick proposed the Double Helix Model of DNA based on X-ray diffraction analysis. Due to the complementary nature, if we know one sequence, then the second sequence of the double helix is predictable. Parent sequence acts as a template for the synthesizing strand. Still, DNA as genetic material is not confirmed, so Watson and crick describe the central dogma of DNA in molecular biology.

Central Dogma of DNA (Double Helix)

The double helix model includes two polynucleotide chains. These chains show anti-parallel polarity; that is, one stand is 3’→5’ direction; hence other will be 5’→3’ direction. The bases pair through hydrogen bond A=T and G≡C. the complementary arrangement of the bases form a uniform distance between two base pairs which is 0.34nm.

The structure looks like a twisted ladder in the right-hand direction, and the one turn is termed as pitch, and it is 3.4 nm. Each turn possesses approximately ten base pairs. The stacking of the planes of base pairs is seen in DNA structure. According to Francis crick, genetic information flows from DNA to RNA to Protein.

image describe about the flow of genetic information from DNA to RNA to protein. — **Flow of Genetic Information**

In some viruses, this process can be reversed that is from RNA to DNA. DNA is a negatively charged body, and this negative charge is due to the phosphate group in DNA.

Histone Protein

The average length of typical mammalian DNA is around 2 meters long. How is this long polymer packed in the cell?

In eukaryotes and even in prokaryotes without well-defined Nucleus, DNA is not fully scattered in the whole cell. The negatively charged DNA is packed with the positively charged Histone proteins in the region known as the nucleoid. Histone is the set of positively charged basic proteins that is rich in basic amino acids. Similarly, DNA is wrapped around many histone proteins and form a structure called a Nucleosome.

Repeating units of nucleosome form network chromatin which is thread like-colored bodies in the Nucleus. That structure looks like marbles on the string. This structure is packaged to form chromatin fiber. Chromatin fiber is further condensed and coiled during the metaphase of cell division, resulting in chromosome formation.

Chromatin has some regions; the first is loosely packed, known as euchromatin, with light color, and transcriptionally active. And the second one is tightly packed heterochromatin with dark color. Heterochromatin is transcriptionally inactive.

After all this clarification still, the genetic identity of the DNA is not confirmed; hence some experiments are performed to confirm its genetic identity. After proving of genetic identity of the DNA, it is also confirmed that the first genetic material was RNA. And DNA is evolved from RNA. DNA cannot directly convert into RNA; hence, it is converted into mRNA first via transcription and then mRNA into protein via translation.

The various experiments confirm DNA as genetic material and not protein. We will discuss those in the next blog till you stay connected with us.

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