Deoxyribonucleic Acid (DNA)

DNA (Deoxyribonucleic Acid) is the molecule that carries the genetic instructions for all living things — humans, animals, plants, and even bacteria.

Think of DNA as the instruction manual or blueprint that tells your body how to grow, how to function, and what traits you have (like eye color, height tendencies, and more).

DNA is made of repeating units called nucleotides, which link together to form a long, twisted, ladder-like structure known as the double helix. Each DNA molecule contains genes, which store information needed to make proteins that keep the organism alive and functioning.

Characteristics of DNA

• The full form of DNA is Deoxyribonucleic acid, which stands for 'deoxy', which stands for missing oxygen, 'ribo' stands for ribose sugar, 'nucleic' represents the nucleus of a cell, and 'acid' represents the acidic nature of DNA due to phosphorus.
• DNA is present in each cell (except for some viral species, RBCs, sieve cells, etc.) and is passed down from parents to their offspring.
• DNA is a form of nucleic acid and is one of the four major macromolecules that make up the living system.
• In eukaryotic cells, it is found in the nucleus of the cell, whereas in prokaryotes, it is found free-floating in the cell cytoplasm.
• DNA is also found in mitochondria, chloroplasts, and in smaller forms called plasmids in certain bacterial species.

Nucleotides

Nucleotides are the basic unit of the genetic material. Every nucleotide contains three parts: a phosphate group (one phosphorus bond to four oxygen particles), a sugar backbone (deoxyribose or ribose), and nitrogenous bases.

Features of Nucleotides are given below:

• The nitrogen bases are adenine (A), thymine (T) in the case of DNA, guanine (G), cytosine (C), and uracil (U) in the case of RNA. Together, these act as the "letters" that make up the hereditary code of our DNA.
• Nucleotides are joined together to form two long strands that twist to form a structure called the double helix.
• On the off chance that you consider the double helix structure as a ladder, the phosphate and sugar particles would be the sides, while the base pairs would be the steps.
• The bases on one strand pair with the bases on another strand: Adenine matches with thymine in DNA or uracil in RNA (A-T/U), and guanine matches with cytosine (G-C).

Properties of DNA 

DNA shows the following main characteristics;

• It is made up of two strands that are held together by a hydrogen bond to form a double helical structure.
• DNA can have hundreds to millions of nucleotides in it.
• The largest human chromosome is chromosome no. 1 with around 220 million base pairs.
• The smallest human chromosome is chromosome no. 21 with around 45 million base pairs.
• The backbone of DNA is formed when multiple units of sugar are joined by phosphodiester bonds.
• The sugars are held together by phosphate groups in such a manner that there are phosphodiester connections between the third and fifth carbon atoms of adjacent sugar rings. These are the 3′-end (three prime end) and 5′-end (five prime end) carbons.
• The two DNA strands will have opposite polarity, i.e., if one strand is 3'-end to 5'-end, then the other will be 5'-end to 3'-end.
• Chargaff's rule states that "the amounts of adenine (A) and thymine (T) are usually similar, as are the amounts of guanine (G) and cytosine (C).

DNA as the Genetic Material 

Under ordinary cell conditions, RNA goes through hydrolysis nearly multiple times quicker than DNA, which makes DNA a more stable particle. So, overall, DNA is the chosen genetic material because; 

• DNA is more easily repaired.
• DNA Information is more stable to the activity of enzymes.
• Double-stranded and allows double-checking for any errors.

Structure of DNA

The DNA structure represents a helical ladder and is depicted as a double helix. It is a nucleic corrosive, and all nucleic acids are comprised of nucleotides. The structure of the DNA molecule is made up of units called nucleotides.

The structure of DNA is described below:

• A nucleotide is made up of three parts, i.e., sugar, phosphate, and nitrogen bases. The bases A, T, G, and C are held by the sugar-phosphate complex to form the DNA strands.
• The two strands of DNA are arranged in opposite polarity.
• These strands are kept together by the hydrogen bond that is available between the two corresponding nitrogenous bases.
• There are 10.5 base pairs per turn of the helix, and the pitch of every helix is 3.4 nm. Subsequently, the distance between two back-to-back base matches (i.e., hydrogen-bound bases of the opposite strands) is 0.34 nm.
• The helix is right-handed, meaning that the chains rotate counter clockwise as they approach an observer observing the longitudinal axis.
• On one end of a strand, an exposed 5′-hydroxyl group is found, frequently with connected phosphates, whereas the other end has a free 3′-hydroxyl group present.
• The two strands are arranged oppositely to each other. This structure is best explained by the double-helical model given by Watson and Crick.

Types of DNA

The following are some most common types of DNA found:

Nuclear DNA (nDNA): The eukaryotic cells have a nucleus that contains the genetic material of the cell, i.e., the DNA. This form of DNA that controls all the general characteristics of a cell is called nuclear DNA.

Mitochondrial DNA (mtDNA): Mitochondria are semi-autonomous as they possess their own DNA, RNA, and ribosomes. This DNA is called mitochondrial DNA, and it usually comes from the mother in the case of sexually reproducing organisms.

A-DNA: A-DNA is a right-handed double helix with 11 bases per turn and a 2.3 nm diameter. It forms under dehydrated conditions and is more compact than B-DNA.

B-DNA: B-DNA is the most common form of DNA found in cells. It has a right-handed helix, 10 bases per turn, and a 1.9 nm diameter.

C-DNA: C-DNA is also a right-handed double helix with 9.3 bases per turn and a 1.9 nm diameter. It forms under specific laboratory conditions.

D-DNA: D-DNA is a rare form of DNA that lacks the Guanine (G) base. It has 8 base pairs per turn and a 2.3 nm diameter.

E-DNA: E-DNA is an extended, right-handed helix with 7.5 bases per turn and a 2.3 nm diameter. It is another rare structural variant.

Z-DNA: Z-DNA is a left-handed helix with a distinctive zig-zag backbone. It contains 12 bases per turn and has a 1.8 nm diameter. It can form in regions with alternating purines and pyrimidines.

DNA Replication

DNA replication is the process by which the DNA makes its copy. In this process, the two strands break to make two templates on which new opposite strands are formed. That means 1 double helical DNA will give rise to two new double helical DNAs. As in the new DNA, one strand comes from the parent DNA; the process is therefore called semi-conservative. DNA replication involves the following steps;

There are three steps of the Replication of DNA that are given below:

1. Initiation: When the two strands of DNA separate to mark the beginning of the process.
2. Elongation: When new bases are paired with the parental strand to form the new strand.
3. Termination: When the newly attached base pair is joined by the sugar-phosphate backbone, the process terminates, thus forming a new double helix of DNA.

RNA vs DNA 

Some of the common differences between DNA and RNA are mentioned here:

Importance of DNA 

DNA contains the information that is fundamental for a living being to develop, function, and reproduce.

• DNA assists your body with development. The cells read this code on three bases all at once to create proteins that are fundamental for development and growth.
• Each combination of three nucleotide bases codes for an amino acid, which is the structural block of proteins.
• Proteins are the main functional unit that directly and indirectly are associated with all the functions of living systems when synthesised correctly.

History of DNA

• In 1869, Friedrich Miescher identified a substance in the nuclei of human WBC, which he named "nuclein".
• In 1919, based on Miescher's work, Phoebus Levene proposed the "polynucleotide" model of nucleic acid.
• Based on Levene's work, Erwin Chargaff and Oswald Avery delved into the gene structure and composition.
• Erwin Chargaff has the "Chargaff's rule" for A, T, G, and C arrangement and composition.
• In 1953, James Watson and Francis Crick gave the double helix model of DNA with the help of X-ray crystallography done by Rosalind Franklin and Maurice Wilkins.

Related Articles:

• Why is DNA Negatively Charged?
• Diagram of DNA Replication
• Difference Between Gene and DNA
• Difference Between DNA and RNA