DNA: Types, Discovery, Structure, Replication, Function

What is DNA? You might have heard this term in various crime investigation shows and cartoons. But do you understand what it exactly means? 

DNA is nothing but molecule groups that are responsible for carrying and transmitting the genetic and hereditary materials from generation to generation, ideally from parents to offsprings, and from the offsprings to theirs, and so on.

Nucleic acids are contained in all the organisms in the structure of RNA or DNA. These acids are organic and are formed by combining the sugar molecules, nitrogenous bases and phosphate groups. Inside a series sequence, these combinations can be linked by multiple bonds. That is how DNA is structured. 

In this article, we will discuss everything related to DNA in detail while having a good look at other concepts.

What is DNA?

DNA, also known as Deoxyribonucleic acid, is an organic chemical consisting of genetic instructions and information for protein synthesis. DNA can be seen in most cells of all living creatures. It is a vital part of reproduction, where genetic heredity occurs. Therefore, the main objective is to transfer the inheritance from the older generation to future generations.

Additionally, the same thing happens with viruses. Most of these entities contain DNA or RNA, which can act as their genetic material. For example, many viruses have DNA as their genetic material, whereas the others may have RNA instead of DNA. HIV (Human Immunodeficiency Virus) has RNA, but it will turn into DNA after it gets attached to the host cell.

In addition, DNA plays a key role in protein production. Nuclear DNA is nothing but the DNA present within each cell’s nucleus. The name of the organism in which these cells are contained is eukaryotic organisms. It is capable of coding most of the organism’s genomes. Meanwhile, the plastid and mitochondrial DNA takes care of the rest.

Furthermore, the DNA contained in the cell’s mitochondria is called mitochondrial DNA, which has been inherited from the mothers to their children. We can find approximately 16,000 mitochondrial DNA base points if we take humans. Likewise, plastids are capable of having their DNA. They also play a crucial role in photosynthesis.

Types of DNA

DNA is an organic compound that has a unique molecular structure. It can be seen in all eukaryotic and prokaryotic cells. There are three different types of DNA. They are:

1. A-DNA

A-DNA is right-handed DNA. It has a double helix structure. The A form of this DNA type is mainly formed because it can protect the DNA while there are any occurrences of extreme conditions, namely desiccation. Mostly this type is obtained by dehydrated DNA. The protein binding around it helps remove the solvent from DNA. Therefore, because of this, it takes an A form.

2. B-DNA

B-type DNA is considered the most common form of DNA conformation. It consists of a right-handed helix structure. Moreover, under normal psychological conditions, it is very common to see that much DNA possesses a B-type conformation.

3. Z-DNA

This DNA type is left-handed DNA. Here, a double helix is present, with the wind in a zigzag pattern to the left. Alexander Rich and Andres Wang invented the Z-DNA. Multiple reports claim that the Z-type DNA was found during the start of the gene. Therefore, one can believe that it might have some crucial roles to play in regulating genes.

Discovery of DNA

Johannes Fredrich Miescher, a Swiss biologist, first discovered DNA in 1869 while researching white blood cells. Later on, the DNA’s double helix structure was recognised by James Watson and Francis Crick using the experimental data.

Ultimately, the results have proven that DNA is solely responsible for containing genetic instructions in organisms.

Structure of DNA

Let us have a look at the following DNA structure, which represents various DNA parts:

We should know that the DNA consists of nucleotide bases and a sugar-phosphate backbone. The nucleotide bases include cytosine, guanine, thymine and adenine.

One can think of the DNA structure as a twisted ladder. The structure of DNA is seen as a double helix. DNA is a nucleic acid. Moreover, all nucleic acids are constructed upon nucleotides.

Furthermore, the molecules of DNA are composed of nucleotides. Every nucleotide contains various other substances, namely nitrogen bases, phosphate groups, and sugar.

In addition to that, DNA’s basic building block includes nucleotides. These are a nitrogen group, a phosphate group, and a sugar group. The main function of phosphate and sugar groups is to link the nucleotides with one another to form all the strands of DNA.

There are four types of nitrogen bases. They are as follows:

• Cytosine (C)
• Guanine (G)
• Thymine (T)
• Adenine (A)

All these bases are capable of pairing with each other in the below-mentioned way: Cytosine (C) with Guanine (G) and Adenine (A) with Thymine (T).

Moreover, these base pairs are fundamentally useful for the double helix structure of the DNA. Therefore, this order defines the instructions of the DNA or the genetic code.

Chargaff’s Rule

A biochemist named Erwin Chargaff found that the number of nitrogenous bases in the DNA contained equal amounts. The C’s amount is equal to G’s, while the amount of A will be equal to T.

A = T;C = G

In simple words, the DNA present in any cell from any living creature should contain a 1:1 ratio of pyrimidine and purine bases.

DNA Replication

DNA replication is a major technique that happens during cell division. Its other name is semi-conservative replication. During this process, DNA is capable of making a copy itself.

The following is the diagrammatic representation of DNA replication:

DNA replication procedure occurs using three simple stages. They are:

Stage 1: Initiation

DNA replication starts at a point called the origin of replication. In this stage, the two DNA strands get segregated using the DNA helicase, which eventually forms the replication fork.

Stage 2: Elongation

The elongation stage is the next, followed by the invitation one. Here, the nucleotides present on the template strands are read by the DNA polymerase III. After doing so, it generates a new strand simply by adding the complementary nucleotides. For instance, there will be an addition of Thymine on the complementary strand if it reads an Adenine on the template strand.

Moreover, gaps will be formed when nucleotides are added to the lagging strand. These gaps are referred to as Okazaki fragments. Ultimately, such nicks or gaps are sealed by ligase.

Stage 3: Termination

The last stage is the termination sequence. It is contained opposite to the origin of replication. The termination sequence eliminates the replication process. The TUS protein, aka Terminus Utilisation Substance, is capable of binding to the terminator sequence and halting the movement of DNA polymerase.

Function of DNA

Genes in the DNA are seen as tiny segments and contain about 250 to 2 Million pairs. For one amino acid, three nitrogenous base sequences strand. It happens for a polypeptide molecule.

Polypeptide chains can fold in secondary, tertiary and quaternary structures to form multiple proteins. Various protein types can be formed because of the presence of different organisms. Proteins are considered the main structural and functional molecules in many organisms. In addition to the strong genetic instructions, DNA can be involved in the following processes:

• Gene Therapy
• DNA Fingerprinting
• Cellular Metabolism
• Transcription
• Mutations
• Replication process

Reason for DNA as Polynucleotide Molecule

DNA is sometimes referred to as a polynucleotide molecule. It is because the molecules of DNA are majorly composed of deoxythymidylate (T), deoxycytidylate (C), deoxyguanylate (G) and deoxyadenylate (A). These are combined to create long chains known as a polynucleotide. Ultimately, according to the structure of DNA, the DNA has two chains of polynucleotides.

Conclusion

To conclude, DNA is a scientific study of molecule groups attached to your cells that consists of the hereditary information of your parents. In the modern world, a DNA test is done to confirm the parent-offspring pair. In addition, police perform DNA tests to find thieves and murderers.

Hence, we have seen everything related to DNA structure while understanding the other interlinked concepts. 

Frequently Asked Questions

1. What is DNA, and what does DNA stand for?

 A. DNA stands for Deoxyribonucleic acid. It is a hereditary material present in every living organism. The major purpose of DNA is to carry the genetic instructions and information on to future generations. It starts from parents and gets passed on to their offspring, their offspring, and so on.

2. Mention the three major DNA types.

A. The three types of DNA are:

• A-DNA: It is right-handed DNA that contains a double helix.
• B-DNA: This DNA is a right-handed helix one and is a common one.
• Z-DNA is a left-handed double helix DNA with a zigzag pattern.

3. Point out the difference between DNA and RNA.

A. In general, RNA can be seen as a single-stranded molecule having a shorter nucleotides chain. Meanwhile, DNA is considered a double-stranded molecule containing a long chain of molecules. Another major difference is that DNA can self-replicate, whereas RNA cannot.