DNA Structure and It's Details

You must have heard this many times “It is in my DNA” and wondered what does it actually imply? DNA is a hereditary material that is present in every living organism on our planet Earth. The genetic instructions are carried in these structures which are passed from one generation to another and are responsible for how that organism develops, grows, reproduces, and functions. So let us dig into some of the basics and details of this material.
Who discovered DNA – Contrary to the belief that DNA was discovered in the 1950s by biologist duo James Watson from the US and Francis Crick from England, DNA was discovered as early as 1869 when the Swiss biologist Johannes Friedrich Miescher was researching white blood cells. He was doing a series of research in which he found the existence of DNA, their main chemical components, and how they joined each other.
What is the full form of DNA – DNA stands for Deoxyribonucleic acid. If we bifurcate the word:

  • Deoxy means a missing oxygen atom
  • Ribo stands for Ribose sugar
  • Nucleic is present in the nucleus of cells
  • Acid – phosphate ion which is negatively charged and acidic

Components of the DNA molecule – The 3 components of a DNA molecule are carbon-sugar group, phosphate group, and a nitrogen base.
DNA Structure – DNA molecules are polymers which are built by linking together smaller molecules called monomers. The smallest units of DNA are called nucleotides, which is made of monomers. These nucleotide monomers bunch together to form a DNA molecule.
Nucleotides are composed of a nitrogen base, sugar group, and a phosphate group.  Sugar is the backbone of this structure. Nitrogen bases are of 4 types: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C)The nitrogen bases form a unit called “base pair” with each other, A pairs with T and C pairs with G.  Then these base pairs attach to a sugar molecule and a nitrogen molecule to form a nucleotide.
Each helix has a pitch of 3.4 nm that’s why the distance between any 2 base pairs is 0.34 nm. These nucleotides attach to each other forming 2 long strands, which run opposite to each other in a spiral shape to form a structure termed as a double helix. A double helix looks like a ladder whose rungs are made of nitrogen base and the 2 sides contain phosphate group and sugar group.
Where is DNA found – DNAs are mostly located in the nucleus of a cell (where they are termed as nuclear DNA) but a small amount of it is also present in mitochondria and known as mitochondrial DNA. Mitochondria are powerhouses of our body that convert the food we eat into the form cells can use to produce energy.
DNA Functions – The most important function of DNA is to carry genetic information from generation to generation coded in the way the nitrogen bases are arranged in the nucleotides. Some of the other functions of DNA include:

  • Cellular metabolism – The metabolic reactions of the cells is regulated by DNA which uses enzymes, hormones, and specific RNAs (Ribonucleic acid which is responsible for regulation and expression of genes) for this purpose.
  • Transcription – RNAs are produced from DNAs through the process of transcription
  • DNA Replication – Genetic information is passed from one cell to daughter cells and from one generation to the next. It produces carbon copies through replication.
  • Development of organisms – By the mechanism of the internal genetic clock, the development of organisms is controlled by the DNA molecules.
  • DNA FingerPrinting – The DNA sequence is unique for each individual and cannot match that of another individual. This property is useful in DNA fingerprinting, which is carried out to identify an individual through his or her DNA.

Types of DNA – There are 4 major forms of DNA that are double-stranded. They are connected by the interaction of complementary base pairs.

  • B-form DNA – This is the most common form of DNA in which 2 strands of DNA, each in a right-hand helix, are coiled around the same axis. The H-bonding between the bases holds the 2 strands together.
  • A-form DNA – This is similar to B-form DNA in the sense it is also a right-handed double-helical structure but is thicker and has a shorter distance between its base pairs. When a DNA is dehydrated, it takes the A form so that it can be protected from extreme conditions like desiccation. It can also be formed when protein binding removes the solvent from DNA.
  • Z-form DNA – This is the 3rd form of duplex DNA but is a left-handed helical structure. A sequence of alternating purines and pyrimidines form a zigzag structure in a Z-form DNA. It is present at the starting of a gene site hence it is assumed to play some role in gene regulation and transcription.

FAQ (Frequently Asked Questions)

  1. What is the relationship of chromosomes and DNA?

DNAs are very long structures, so long that they have to be packaged correctly to fit into cells. For this, they are coiled tightly into structures called chromosomes. Each chromosome has 1 DNA molecule and there are 23 pairs of chromosomes inside each cell’s nucleus of the human body.

  1. How many bases do humans have?

There are close to 3 billion bases in humans out of which 99% are the same in all humans.

  1. What are genes?

The way nitrogen bases are arranged in a DNA sequence forms genes. Genes are responsible for protein creation by the cells.

  1. What is DNA sequencing?

It is a technology to determine the order of bases in a DNA sequence. An important breakthrough was made in 2017 when the DNA sequencing of Egyptian mummies was done to find their genome-wide data.

  1. What is Chargaff’s rule?

This defines the grammar of DNA i.e. both strands of the nucleotide have a 1:1 ratio of pyrimidine and purine bases and amount of: A = T; C = G

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