DNA – Simple and Accurate Pictorial Analysis

In this article, we will discuss DNA in a simple and easy way and try to understand it from zero level. So just read this article patiently.

Also, the site also has articles on other important information related to DNA (all links are given below), so read them all for better understanding.

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| What is DNA?

DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Almost every cell in a person’s body has the same DNA. Most of the DNA is located in the nucleus of the cell, which is why it is called nuclear DNA, but a small amount of DNA can also be found in the mitochondria, where it is called mitochondrial DNA.

Remember – mitochondria are structures within cells that convert energy from food into a form that cells can use.

| The information in DNA is stored as a code composed of four chemical bases : adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA contains about 3 billion bases, and more than 99 percent of those bases are the same in all people.

This is the reason that all human beings are the same except for a few characteristics. The sequence of these bases determines the information available to build and maintain an organism, just as the letters of the alphabet appear in a certain order to form words and sentences.

Overall , DNA is made up of nucleotides and each nucleotide has a base, either adenine, thymine, cytosine, and guanine.  And each base is attached to a sugar molecule and a phosphate molecule . [We are going to understand further how all this happens.]

That is to say, together, a base and a sugar molecule and a phosphate molecule are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral shape called a double helix. 

The structure of the double helix is ​​somewhat ladder-like, with the base pair forming the ladder’s steps and the sugar and phosphate molecules forming the vertical sidepiece of the ladder.

Note – DNA bases (ie adenine, thymine, cytosine and guanine) bind with each other. Thymine with adenine and guanine with cytosine combine to form units called base pairs.

One important thing about DNA is that it can replicate itself, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is important when cells divide because each new cell needs an exact copy of the DNA present in the old cell.

But the question comes, how did all this happen and how did we come to know about it, so let’s understand everything from the beginning.

Also read – What is a thymus gland?

| Discovery and understanding of DNA

Human beings and plants from generation to generation have been giving birth to humans and plants like themselves. In such a situation, it was naturally a matter of curiosity for the scientists that how all this happens, the body remembers how its ancestors were and all that information has to be filled by default in the coming child.

Scientists knew that genetic properties are present in our genes and they are in the cell. Gregor Mendel did a lot of testing and study on it in the middle of the 19th century. Gregor Mendel is credited with discovering the basic principles of heredity.

But even then, it took almost 100 years to understand DNA, between 1940 and 1960, a systematic information was established in this regard. In the course of the discovery of DNA, how different things were found, and the mystery was revealed; It is very interesting to know this. Let us understand from the beginning.

| What material is the cell made of?

In the mid-18th century, scientists were looking for answers to the question, what material is a cell made of? One of them was Johann Friedrich Meischer, who worked in the laboratory of a German chemist, Ernst Felix Hohpözeller. 

He knew that cells were made of proteins, and he wanted to break them down into simpler pieces. In 1869 Meischer was working with dead and broken cells.

know more– What are cells?

He added an enzyme called pepsin to his sample. In fact, an enzyme is a substance that accelerates a chemical process. 

In the case of pepsin, it breaks down large atoms of proteins into smaller pieces. But Meisher noticed that there were some substances in the cell on which pepsin had no effect.

The substance which had no effect was isolated by Meisher and carried out some chemical tests on it. And in this way Meisher found phosphorus molecules in that substance.

Because this substance (which contained phosphorus) was found in the nucleus of the cell. Meischer named this new substance as nuclein.

However, before that, Meischer’s mentor Hohpözeler had once found phosphorus in living tissue (lecithin) . This time when his disciple found phosphorus in the cell, Hohpözeler researched it for two consecutive years to see for himself and he discovered phosphorus in yeast .

However, the substance that Höhpözeller found was somewhat different from Meisher’s, so they were given different names. 

The substance in which Meisher found phosphorus could be easily obtained from the thymus gland, a part of animals. Hence it was named ‘ Thymus Nuclein ‘. Whereas Hohpözeller’s substance could be obtained from ‘ yeast ‘ hence it was named ” yeast nuclein “.

Also read – Difference between prokaryotic and eukaryotic cells [illustrated]

| The relationship between proteins and nuclein …

Meischer also discovered that the nuclein released from the salmon ‘s sperm cell was bound to a very simple protein , which he named ‘ protamine ‘.

Later , in 1879, another student of Hohpözler , Albrecht_Kossel, studied Mescher’s nuclein . Kausil’s main objective was to understand the relationship between proteins and nuclein.

Kossel did research on this and he too found nuclein attached to a protein. But this protein was not as simple as Mesher’s protamine but rather complex. Kausil named his protein ‘ Histone ‘. [‘Histone’ means ‘cell’ in Greek.] It has even been established that the pairing of nuclein and protein together forms nucleoprotein.

Kausil easily separated histones (i.e. proteins) and nuclein. He found that the two were linked because the nuclein was acting as an acid and the histones were acting as bases. And we all know that acids and bases react with each other. 

Nuclein being an acid, it got its name nucleic-acid. (Now you must have understood where nucleic acid came from.) In this way, the nucleic obtained from the thymus gland came to be called ‘ thymus nucleic-acid ‘ and the nucleic obtained from yeast came to be called ‘ yeast nucleic-acid ‘.

Also read – 15+ DNA Facts that everybody should know

Search for Purines and Pyrimidines…

By now it was known that nuclein is an acid, now it was left to understand what kind of atoms of nucleic-acids are and how they are related to each other. To understand this, Kausil thought of breaking them into smaller pieces by chemical processes.

For this, Kausil and his students worked for years on nucleic-acids and they were able to identify some of its components. Some molecules were made of double-rings. There was a molecule at each angle of the double-ring. (You can see in Figure 1) Counting will give nine angles and nine molecules. In this, four molecules will be of nitrogen and the rest will be molecules of carbon.

Kausil discovered two substances with such a structure, which are known as purines . Each substance was part of a nucleic-acid. One of these was called guanine (G) and the other adenine (A) . The difference between the two is that adenine has an additional nitrogen molecule and guanine has additional nitrogen and oxygen molecules. [Which you can see in Figures 2 and 3.]

During further research, Kausil also found fragments of nucleic-acids that were simpler than both purines. Simple in the sense that their atom (unlike purines) had only one ring of six molecules. Such a single ring is called a pyrimidine . As you can see in Figure 4, it has only 2 nitrogen molecules. And the other four angles have carbon molecules.

Kausil found two pyrimidines in the fragments of Thymus nucleic-acid . One of them is called cytosine (c) and the other is called thiamine (t) . Cytosine has one extra nitrogen and one extra oxygen, and thiamine has two extra oxygen molecules and one extra carbon atom. (As you can see in Figure 5 and Figure 6.)

After much research, the difference between the atoms of nucleic-acids of thymus and yeast was discovered. Both had purines (guanine and adenine), but thymus nucleic acid had two pyrimidines (cytosine and thiamine), while yeast nucleic acid had (cytosine and uracil).

In fact, another pyrimidine was found in yeast nucleic-acids, which was similar to thymine yet different from it. This pyrimidine is known as uracil (u) .

The difference between thymine and uracil is that thymine has one extra carbon molecule whereas uracil has two extra oxygen molecules. There is no extra carbon molecule in it. [As you can see in Figure 7.]

Fact – Kausil received the Nobel Prize in Medical Sciences in 1910 for this unprecedented research work in the field of nucleic acids.

| The sugar in nucleic acid…

Even in nucleic acids ‘purines and pyrimidines’ had become evident. But Kausil was not satisfied with this because Kausil found some sugar-like substance in the nucleic acid, but what it was, Kausil could not tell him. A Russian-American chemist who worked with Kausil led the research on what it was; Phoebius Eran Theodore Lieven .

He disintegrated the atoms of yeast nucleic acids and found in one part of them an atom of sugar, which Kausil had previously expressed.

However, chemists knew that living tissue contained a six-carbon sugar called glucose . But it is in nucleic acid, it was not known. So, researching yeast nucleic acids, Lieven found sugar, but it contained only five carbon molecules. And in its atom, along with carbon, there were ten hydrogen molecules and five oxygen molecules.

This information was not enough, as those molecules could combine in different samples to form eight different sugars. Each of these sugars had different properties. Now Leevan had to find out what sugar he had found in the yeast nucleic-acids . In 1909, Levon recognized the correct sugar. It was known as ‘Ribose ‘.

Similarly, Leevan also found a five-carbon sugar fragment in thymus nucleic-acids. But the five-carbon sugar of thymus nucleic-acids was quite unique. And the chemists knew nothing about him.

In the year 1929, Lieven understood the characteristics of this five-carbon sugar. Its molecular structure was exactly like ‘ribose’ but one oxygen molecule was missing in it.

Since it was missing an oxygen molecule, Levon named this sugar ” deoxyribose .” Where ‘deoxy’ meant ‘a lack of oxygen’. Its structure looks something like this.

Thus it could now be clearly seen that out of the two types of nucleic-acids, the yeast nucleic-acid atom contained ribose and uracil . Whereas the thymus nucleic-acid atom contained deoxyribose and thymine .

Chemists called yeast nucleic-acids as ” ribonucleic-acids (RNA) ” and thymus nucleic-acids as ” diribonucleic-acids (DNA) “. And this is what we know as RNA and DNA respectively.

We read above that both RNA and DNA contain a substance that contains phosphorus. It later became clear that phosphorus molecules were not found alone in nucleic acids. They are always part of a group that also contains hydrogen and oxygen molecules. This mixture is called phosphate group and we can call them (ph) in short. Which looks something like this.

understand in detail – Difference between RNA and DNA

All in all, now all the components were separately clarified. The sugar had become clear. The phosphate molecule had become apparent. And adenine, thymine/uracil, cytosine, and guanine became evident as bases. 

This is called a nucleotide. And many nucleotides together make up the structure of DNA. Leevan tried to understand how nucleic-acids are formed by combining all these pieces. And now we are going to understand the same.

Purines and pyrimidines are associated with ribose or deoxyribose. And all this is associated with the phosphate group. 

Remember here that when purines and pyrimidines and phosphorus groups combine with ribose, it is called ribonucleic-acid (RNA) and when purines and pyrimidines and phosphorus groups combine with deoxyribose, it is called called diribonucleic acid (DNA) .

Remember here too that DNA contains adenine (A), thymine (T), cytosine (C) and guanine (G), Whereas in the atoms of RNA, everything else is the same, only uracil (u) is there in place of thymine (T).

Also read – DNA Test [Genetic Testing]: What, How, Meaning and Benefits..!

| structure of DNA

Now if we remember, we read in the definition of DNA above that DNA is made up of nucleotides and each nucleotide has a base, it can be any of adenine, thymine, cytosine and guanine. . And each base is attached to a sugar molecule and a phosphate molecule. [Let us understand how all this happens.]

Nucleotides are arranged as shown in the given figure. Here Phosphate means Phosphate group and Sugar means Ribose or Deoxyribose. And Base means purines and pyrimidines. Where Purines come from Adenine and Guanine and Pyrimidines come with Thymine, Uracil and Cytosine.

This structure of the nucleotide repeats over and over again and forms a ladder-like structure. It happens that first it repeats itself on one side, where the sugar and phosphate groups combine to form a strand, and then it repeats itself in the opposite direction to the other strand.  This Strand (ie both the pillars of the ladder) is called Sugar Phosphate Backbone .

In this process the bases of both the sides bind with hydrogen bonds to form base pairs . These Base Pairs look like ladder poles. And we have also discussed above that these base pairs bind to each other under a certain rule, that is, adenine (A) always associates with thymine (T) and cytosine (C) always with guanine (G). Joins. You can understand by looking at the given picture.

In this way DNA is prepared. Hope you understand how DNA was discovered and how it came into existence. Remember here that this structure was propounded by Lewell. However, Lewell’s structure was fully confirmed in 1938 by a Scottish chemist, Alexandre Robertus Taud. For which he also got the Nobel Prize.

As soon as the understanding of DNA was established, many techniques related to it expanded, and we got many secrets related to our life which would not have been found otherwise. 

Today , many systems like DNA Sequencing , Genomics, Gene Editing and DNA Testing have been developed and new dimensions are being added to it.

Links of other articles related to DNA are being given, for better understanding, must read them and share our articles…

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References,
How we came to know about DNA – Isaac Asimov, Hindi translation, Arvind Gupta
https://www.nigms.nih.gov/education/Booklets/the-new-genetics/Documents/Booklet-The-New-Genetics.pdf#page=11
https://www.genome.gov/about-genomics/fact-sheets/Deoxyribonucleic-Acid-Fact-Sheet
https://www.genome.gov/about-genomics/fact-sheets/