Table of Contents
What is DNA?
DNA which stands for deoxyribonucleic acid, is present in the chromosomes of living cells. The molecule carries genetic instructions, important for the growth, reproduction, functioning, and development of living organisms and some viruses. The structure of DNA is a long, double-stranded molecule, composed of four types of nucleotides.
Discovery of DNA
The discovery of DNA came into effect in 1869 by Swiss biochemist Friedrich Miescher. He successfully isolated the nuclein from the nuclei of white blood cells. In the early 20th century the concept of DNA as hereditary material was unclear to scientists. It was believed earlier that proteins are responsible for carrying genetic information.
Later, in 1952 it was discovered through the Hershey Chase experiment, that not protein, but DNA was responsible for carrying the genetic information.
The structure of DNA was discovered in 1953, by Francis Crick and James Watson. This was the turning point in the discovery of DNA structure. The use of Rosalind Franklin’s X-ray diffraction images proposed the double-helix model of DNA. The discovery led to the reveal of how genetic information is stored and replicated.
Do Check: DNA Full Form
What is DNA made of?
DNA being a polymer, is made up of many smaller units, known by nucleotides. The nucleotides are the building blocks of DNA. the nucleotide is made of 3 major components – a phosphate group, deoxyribose sugar, and a nitrogenous base. Mentioned below is the brief of these components.
- Phosphate group – This phosphate group is attached to the 5’ end of the sugar molecule. It forms the backbone of the DNA structure.
- Deoxyribose sugar – The name itself suggests, that the sugar molecule lacks oxygen at the 2’ position. The deoxyribose sugar is a 5’ carbon of the sugar molecule.
- Nitrogenous base – It is a part of nucleotide that has 4 base pairs, namely – adenine, guanine, thiamine, and cytosine. These base pairs combine together in a specific way like – adenine with thiamine(A-T), and guanine with cytosine(G-C). Hence, they help in carrying genetic information in this manner.
These base pairs are bonded together with hydrogen bonds, giving a double-helix structure to the DNA.
Also Check: Chemical Constitution of DNA
Chemical Structure of DNA
The DNA structure is often observed as ladder-like, giving a double helix structure. The backbone of the ladder is composed of sugar and phosphate groups of each nucleotide, linked by a phosphodiester bond.
The two strands of DNA run antiparallel to each other, which means they run in opposite directions. One strand runs from 2’ to 5’ end, while the other runs opposite from 5’ to 2’ end.
This is important for DNA replication and transcription.
The double helix structure is stabilized by hydrogen bonds, which are present between the nitrogenous bases. There is a 3.4 nm pitch between each helix. Based on these calculations, the distance between consecutive base pairs (i.e., hydrogen-bonded bases of opposite strands) is 0.34 nm.
The DNA coils up forming chromosomes. These chromosomes consist of a single molecule of DNA in it. A human cell’s nucleus contains around twenty-three pairs of chromosomes. Additionally, DNA plays a crucial role in cell division.
How do DNA Sequences Work?
Protein synthesis relies on genetic information encoded in DNA sequences. Transcription and translation are the two main steps in this procedure.
Transcription
In this process, a segment of DNA is copied into messenger RNA. This is done by the enzyme RNA polymerase. Here are the steps of transcription in brief.
- First-step gene expression occurs in the nucleus of eukaryotic cells (or the cytoplasm in prokaryotes).
- As RNA polymerase binds to the promoter region of DNA, it unwinds the double helix, revealing template DNA.
- The next step is for RNA polymerase to make a complementary RNA strand.
- This is done using uracil instead of thymine in the DNA template.
- Upon reaching a termination sequence in the transcription process, the newly formed mRNA is released.
- Messenger RNA leaves the nucleus once processed and awaits translation to produce proteins.
Translation
In this process, the stored information in DNA is converted into protein. The process starts with transcription as the first process, where DNA is copied into mRNA.
- The mRNA moves to ribosomes, starting the translation process.
- The role of ribosomes is to read the mRNA in triplets and name them as codons.
- An amino acid is associated with each codon.
- tRNA molecules transport amino acids to the ribosome, where they are linked together to form polypeptide chains.
- The folding of this chain results in the formation of a functional protein.
DNA Function
The sequence of nitrogenous bases in DNA carries hereditary information. The sequences formed by A,T,G,C decide the formation of proteins in the body. These proteins help in different functions of the body. Proteins are constructed from amino acids, composed of three nitrogenous bases, called codons.
- DNA sequences such as “ATG” code for methionine, while “TGG” code for tryptophan. An organism’s genome consists of all the instructions for building and maintaining the organism, which is the entire sequence of DNA.
- In forensic science, DNA is used to identify individuals based on their unique genetic makeup.
- It is possible to establish paternity, identify disaster victims, and link suspects to crime scenes by using DNA profiling, which is also called DNA fingerprinting.
- Besides forensic science, the DNA sequences has helped in crop improvement, crime solving, and biodiversity.
- DNA sequence determines the type of disease in living organisms as well.
FAQs on DNA Structure
What is DNA?
DNA stands for deoxyribonucleic acid, a molecule that is responsible for carrying hereditary information. It determines traits and is present in nearly all living things
What is the structure of DNA?
The structure of DNA is a double-helix structure, resembling a ladder-like structure. The sides of the ladder are made of sugar-phosphate backbone. The rungs are pairs of nitrogenous bases- A,T,G,C standing for adenine, thymine, guanine, and cytosine respectively.
What are the base pairing rules in DNA
The pairing of the base pairs is as follows- Adenine pairs with thiamine - A-T. Guanine pairs with Cytosine - G-C.
What is the difference between DNA and RNA?
DNA and RNA differ in a few criteria like, DNA has a double strand, whereas RNA has a single strand. DNA contains deoxyribose sugar, whereas RNA uses uracil instead of thymine.
What is a gene?
A gene is a piece of DNA that is responsible for encoding a specific protein or RNA molecule.
