DNA - Deoxyribonucleic Acid

What is DNA

DNA or Deoxyribonucleic acid is a molecule that has hereditary information about plants and animals. It is fundamental for the building and maintenance of any organism. All the cells of any living organism contain DNA. DNA is responsible for storing and passing the heredity information and the characteristic features from one generation to another. It holds the information for the building of all types of proteins in any form.

The Discovery of DNA

The discovery of the structure of DNA was led by Francis Crick and James Watson. It was discovered in 1953. Rosaline Franklin's work inspired them. He was the first to discover that DNA structure is made up of two spirals. Before his discovery, it was found out by Gregor Mendel that inherited entities exist. These entities are now known as genes.

DNA is the unit that maintains the characteristics of all organisms. Moreover, DNA is passed from one organism to their offspring while they reproduce; this is just a part of DNA from the parent organisms of the offspring. As a result, the offspring acquires the traits of their parent organisms; these include structural and functional characteristics. Consequently, offspring resemble their parents, and the scope of changes is also there, which ensures diversity of life.

Formation of the DNA

DNA is a twisted, double helix-shaped molecule that is complex in nature and is in the form of a ladder shape. The strand of DNA comprises A, T, G, and C. A, G, C, and T stand for adenine, guanine, cytosine, and thymine respectively. Long sequences of A, T, G, and C are present, which are known as the four bases of DNA. These are nitrogen bases that have a fixed pairing pattern. These bases are used to pair together to form a ladder-like structure of DNA.

The bases follow a standard way to pair themselves with each other. The bases always pair as A and T; C and G. All the base pairs are joined with the hydrogen bonds. The beginning of the strand of DNA is known as 5' (Five Prime), and the end is known as 3' (Three Prime).

The information stored in the code form is predicted using the sequence in which the bases are arranged. In humans, almost 99 percent of the DNA is the same and different sequences of the bases determine the information necessary for the maintenance and building of the organism.

The Structure of DNA

Long-chain of monomer nucleotides makes the complex strands of the DNA molecule. The deoxyribose molecule of sugar is attached to a phosphate group and one of the nitrogen bases in the DNA. These nitrogen bases are two purines which are adenine and guanine, whereas two pyrimidines are cytosine and thymine. The phosphate of one nucleotide is connected to the sugar of another nucleotide. Hence, connecting the two nucleotides with each other, this process forms a sugar-phosphate backbone. From the sugar-phosphate backbone, nitrogen bases protrude. The hydrogen bonds hold the two strands together. There is a fixed order of bonding in between A, T, G, and C. The bonding is such that adenine always bonds with thymine and guanine bonds with cytosine.

Major Functions of the DNA

DNA is responsible for carrying information from generation to generation. The major functions of the DNA which is the most vital molecule in organisms include:

1. Genetic information is stored in DNA in the coded form.
2. DNA has the function of directing protein synthesis.
3. DNA is responsible for determining the genetic code of the organism.
4. DNA controls heredity, evolution, metabolic activities, and differentiation.

Functions of DNA

The complex molecule DNA, which is responsible for functions such as storing genetic information, monitoring protein synthesis, and controlling heredity while maintaining diversity. Since it is a significant molecule, it is essential to know how DNA functions. The configuration of DNA is generally very stable. DNA is like a template for the DNA molecules which are newly formed. Additionally, it also acts as the standard for the production of RNA molecules. Gene is the DNA segment responsible for protein synthesis in a certain manner according to the code.

The Replication of DNA

DNA replication happens by the separation of the DNA strands. Each of the separated DNA strands is now the template for the new DNA strand. The new strand is formed by following the same pattern of the hydrogen bonds, which form the double helix. The formation of two DNA molecules takes place using the original DNA. These new DNA molecules comprise a new strand and an old strand. This replication of DNA is known as the semi conservative replication of the DNA. As a result of this type of replication, genetic traits are inherited stably.

Arrangement of DNA inside the Cell

Inside a cell, DNA is present in the chromosomes, which are dense proteins. The location of DNA in the cell varies on whether the organism is eukaryotic or prokaryotic. Usually, DNA is located in the nucleus of the cell in the eukaryotic organisms, but it is also present in the mitochondria and chloroplasts. However, since prokaryotic organisms lack a well-defined nucleus, DNA is present in the form of a single chromosome. This chromosome is circular and is directly present in the cytoplasm of the cell.

DNA in Different Organisms

In some of the prokaryotic organisms, plastids are present. These are autonomous extra chromosomal DNA which acts as self-replicating genetic material. DNA or RNA is present in the viruses, and the genetic material can be single or double-stranded. The material which governs the genetics is present in the form of single-stranded RNA in retroviruses. These produce reverse enzyme transcriptase, which is capable of generating DNA strands from RNA. The human genome has areas rich with guanine where four-stranded DNA is found. This DNA is known as G-quadruplexes.

Functioning of DNA in Humans

All functions in the human body are performed based on the proteins, which are encoded by the genes. For example, alpha globin is a protein built based on the instructions coded in the HBA1 human gene. The alpha-globin is the component of the haemoglobin which is a protein responsible for carrying oxygen in the red blood cells. Another example of a human gene with a crucial function of synthesizing a protein identifies the odour through the nose. This protein is known as the olfactory receptor.

DNA Sequencing

The sequence of the bases in DNA is found out using a technology which is known as DNA Sequencing. The researchers utilize this technology to obtain the order of genes, chromosomes, or genomes in a DNA sequence.

Where is the DNA Located

Every cell in the body of each organism comprises DNA. The DNA is present in two locations which are in the nucleus of the cell and the mitochondria. The nuclear DNA is located in the nucleus of the cell, and mitochondrial DNA is located in the mitochondria. Mitochondria are responsible for the conversion of energy from food to the form that the body can utilize by the body to perform its functions.

Properties of the DNA

• DNA consists of two types of helices right-handed and left-handed. Right-handed and left-handed helices differ in the stability of the DNA. The most stable DNA is of B - conformation with right-handed helices.
• DNA strands separate on heating and hybridize on cooling.
• The melting temperature is the temperature at which DNA strands separate from each other, and it varies for each sequence.
• The arrangement of the DNA sequence is according to order in which the amino acids in the protein are present, which is true for all organisms.
• DNA holds complex genetic information for a longer time as it is a stable molecule.

Types of DNA

DNA is classified into two types based on its location. These types are nuclear DNA and mitochondrial DNA.

Nuclear DNA

• The location of this DNA is the nucleus of the cell.
• It has two copies in each cell.
• Nuclear DNA comprises linear chromosomes with open ends.
• Nuclear DNA contains 46 chromosomes which include 3 billion nucleotides.
• These are diploid in nature and are inherited from two parents.
• The nuclear DNA has a mutation rate of 0.3 %.

Mitochondrial DNA

• The location of this DNA is in the mitochondria of the cell.
• It has over 100 - 1000 copies in each cell.
• The structure of mitochondrial DNA is closed and circular.
• There are 16,569 nucleotides in human mitochondrial DNA.
• These are haploid and are inherited only from the mother.
• The rate of mutation is higher in mitochondrial DNA when compared with the nuclear DNA.

Forms in which the DNA exists

The major forms in which DNA exists are as stated below:

B - DNA: It is one of the most common DNA forms that were originally found by using X-ray diffraction of the sodium salt of DNA fibres. This experiment was done at 92% relative humidity.

A - DNA: It was found while conducting analysis using X-ray diffraction. This experiment was done at 75 % relative humidity.

Z - DNA: It is of a zigzag pattern, and its structure is of left-handed doubling helical.

C - DNA: It was found while using the ions Li+ and Mg2+. This experiment was conducted at 66 % relative humidity.

D - DNA: It is a very rare variant of the DNA that consists of eight base pairs for each helical turn.

E - DNA: It is DNA that is of eccentric and extended form.

DNA Testing Method

DNA in any human depicts their heritage and hence is capable of predicting the diseases and their risks. There are various applications of the DNA tests, which include diagnosing genetic diseases and predicting whether a person is carrying a genetic mutation that can be passed to their children. Another crucial function of DNA tests is to predict genetic disorders and check the risk of genetic disease in the person. For example, gene mutations such as BRCA1 and BRCA2, which are breast and ovarian cancers, can be diagnosed if the person does a DNA test.

Genetic tests or DNA tests have consequences; hence people often undergo genetic counselling, which gives people an advantage as they can understand the results better.

Many undergo DNA tests to find their family tree and know who their ancestors were.

Grooves in the DNA Structure

1. A DNA molecule consists of two grooves that are asymmetric in nature. These grooves are present because due to the structure of DNA, which is double-helical. The two grooves are such that one of them is smaller as compared to the other.
2. DNA consists of the phosphate, sugar, and base groups. The force of the bonds of these groups is such that the base group form a 120-degree angle instead of a 180-degree angle. This geometrical configuration is the reason for its asymmetric structure.
3. When the backbones are far apart, larger grooves known as major grooves are formed, while the backbones are close enough to smaller grooves known as the minor grooves.
4. One of the major applications of grooves is to determine the DNA sequence as the major and minor grooves show their edges.
5. Proteins should be able to recognize the DNA sequence to follow for the proper functioning of cells and the body. Hence the recognition is critical.

How is Important DNA

• DNA is a little, though a significant part of living organisms. Life wouldn't have existed, and everything would have been abiotic without DNA.
• DNA is responsible for making life diverse so that each living being is different and special.
• DNA makes organisms functional and alive.
• DNA controls the major cell functions and even cell division.
• The study of DNA has benefitted people excel in the fields like agriculture, virology, genealogy, and forensic science.

Conclusion

The development and discovery of DNA have opened doors to new possibilities in various fields like agriculture, medicine, and research. DNA is crucial for our existence and also for the existence of all biotic elements. Hence it is important to study and understand its structure and function to develop technologies that would help us excel in various fields.