DNA: Full Form, Definition Structure, Function, Diagram, Facts, Discovery

DNA Definition:

DNA is a group of molecules that carry and transmit hereditary materials, or genetic instructions, from parents to offspring.

What is DNA?

Full-Form of DNA

The full form of DNA is Deoxyribonucleic Acid.

DNA meaning: DNA is a molecule that contains the information required for the synthesis of all the elements of life, its functioning, and reproduction. Made of two long chains spiralled into a double helix in a linear formation made up of nucleotides, which are comprised of sugarphosphate molecules and nitrogenous bases, namely adenine, thymine, cytosine, and guanine.

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The relevance and application of DNA are in its accurate interpretation of the body by carrying the information that gives an organism its features. In replication and gene expression, DNA is responsible for conveying hereditary traits to future generations and for the execution of detailed biological factors that are vital to existing life forms. Therefore, DNA is a critical biological molecule contributing to the genetics and molecular biology concepts of population and species variation and the carrying out of these species on earth.

Who discovered DNA?

The distinct double helix structure of DNA was not discovered until 1953 and was formulated by James Watson as well as Francis Crick. The authors of the model used XRD photographs of DNA provided by Rosalind Franklin and Maurice Wilkins. Franklin’s work proved helpful in the elucidation of the molecular conformation of DNA, its being helical, as well as its dimensions.

Discoveries made by Watson, Crick, Franklin, and Wilkins are considered one of the key events in the biological sciences. They identified the structure of DNA molecules, the storage of genetic information and how it can be passed from one generation to another, hence revolutionising genetics, heredity and molecular biology.

Types of DNA

DNA has the potential to exist in different conformations, mainly in terms of how the double helix is coiled and the relative positioning of its building blocks.

Here are the main types of DNA structures:

A-DNA:

A-DNA has a righthanded coil and is more compact than B-DNA though it has a longer pitch than B-DNA. It occurs under low humidity conditions or some specific sequences of DNA and RNA. A-DNA has approximately 11 base pairs per turn and is less frequently found in organisms; however, its importance is observed in molecular biology and biotechnology.

B- DNA

This type of DNA is the most common and stable in solutions that mimic the physiological state of the organism. B-DNA is righthanded with a twist of about 10.5. This is the version of DNA that is encountered in most biological processes and interactions.

Z-DNA:

Z-DNA is lefthanded and is less common than righthanded B-DNA and A-DNA. It forms under special physiological conditions or when the sequence of bases is separated by purines and pyrimidines in turns. Z-DNA has a zigzag structure of the backbone and is more destabilized than B-DNA and A-DNA. It is involved in gene regulation and it maps in regions of the genome being transcribed.

DNA Structure

The structure of DNA is listed below

Double Helix Model

Explanation of the double helix structure:

The main shape of the DNA molecule is in two chains that are coiled into a helix; a spiral staircase. It is with the help of such a structure that the DNA can compactly store all the genetic information entrusted to it and remain stable.

Contributions of Watson and Crick:

Application of xray diffraction came through Rosalind Franklin and Maurice Wilkins whose data supported James Watson and Francis Crick to formulate the DNA double helix in the year 1953. Their model was beautiful in that it was unambiguous in illustrating how genetic information is both coded and copied.

DNA double helix:

The DNA double helix has two antiparallel strands that are connected through hydrogen bonds present between two related nitrogenous bases. In the first strand, adenine is paired with thymine while in the second strand, cytosine is paired with guanine thus making pairing of the base complete.

Components of DNA

Nucleotides:

The nucleotides also known as the units of DNA make up the DNA molecule. Each nucleotide contains a phosphate group, a deoxyribose sugar molecule, and one of four nitrogenous bases; adenine, thymine, cytosine or guanine.

Structure of a nucleotide

A nucleotide has three components:

Sugar: In nucleotides, the sugar part can include deoxyribose in the case of DNA or ribose in the case of RNA. This is because; deoxyribose contains one less oxygen atom as compared with ribose, thus making DNA more stable.

Phosphate Group: This group is made of just one phosphorus atom and there, it links four oxygen atoms. It links the sugar moiety of the two adjacent nucleotides forming the backbone of the nucleic acid polymer.

Nitrogenous Base: In nucleotides, nitrogenous bases form four types. In DNA these are adenine (A), thymine (T), cytosine (C) and guanine (G) The bases paired together are A with T and C with G. In RNA, thymine is replaced by uracil, hence RNA has uracil (U) instead of T. These bases are paired particularly (A with T/U, and C with G) to transcribe genetic information.

Hydrogen bonds between bases: Complementary nitrogenous base pairs in DNA hydrogen bond with each other. Adenine has two hydrogen bonds with the molecules of thymine, and cytosine has three hydrogen bonds with guanine. These effects assist in maintaining the double helix formation of the DNA molecule and also in the unwinding and replication of the DNA molecule during the process of cell division.

Function of DNA

The functions of DNA are discussed below:

Genetic Information Storage

Information in DNA is held in the form of nucleotide base pairs namely adenine, thymine, cytosine and guanine. These bases pair only (AT and CG), and they create a language or a code that determines how large protein structures and other actions in a cell are to be constructed.

DNA Replication

Semiconservative replication: In the process of DNA replication, one strand of the parent DNA molecule acts as the model against which a new strand is synthesized. This process ensures that in every newly synthesized DNA molecule, of them, one is the old strand and the other a new one.

Enzymes involved:

Key enzymes in DNA replication include: Key enzymes in DNA replication include:

• DNA polymerase: replicates and duplicates DNA and can attach a new nucleotide to the existing chain.

• Helicase: negatively impacts the various faces in that it unwinds the double helix of DNA splitting the two strands.

• Ligase: joins the newly synthesized Okazaki fragments on the lagging stand.

Transcription and Translation

Process of transcription: Transcription therefore generally means using DNA as a mould to produce RNA. RNA polymerase has an affinity for a concrete segment of the DNA (promoter) to embrace and release two threads of DNA and cause the synthesis of an RNA molecule from one of the DNA threads. There is also the RNA molecule called messenger RNA or mRNA; it can transport the DNA’s genetic information towards the ribosomes.

Process of translation

Translation is the process in which information in mRNA is read to form proteins. It happens in the ribosomes and is the process by which tRNA molecules bring an amino acid to the form and position it according to the nucleotide sequence of mRNA specifying the protein. The ribosome moves along the mRNA sequence deciphering it in sets of three symbols called codons, which correlate with different amino acids. The building block of a protein is a polypeptide chain that is composed of amino acids and its conformation makes up a functional protein.

DNA and Heredity

Genes and Chromosomes

Genes are small portions of DNA through which the body acquires instructions to make proteins or functional RNA. These genes are located on chromosomes; these are threadlike structures of the nucleus that contain hereditary material. Organisms have 46 chromosomes which are found in 23 pairs, each of which is inherited from one of the parents.

DNA Mutations and Repair

The DNA mutations and repair is discussed below

Types of DNA Mutations

Point Mutations:

These affect a gene with a single change of the nucleotide base pair forming the DNA sequence. There are three main types of point mutations: There are three main types of point mutations:

Substitution:

It involves the substitution of one nucleotide for another; in the process of translation this may lead to a change in the amino acid added to the growing protein chain.

Insertions:

Additional bases are added to the DNA code, which changes a later set of three bases, or codon, and, consequently, all the amino acids following the mistake.

Deletions:

The nucleotides are cut out from the string and the reading frame is shifted so in addition to having the amino acid chain extended, it will not be functional.

Frameshift Mutations:

These are occasioned by shifts in the reading frame of the genetic code through either the addition or omission of nucleotides. This distorts the human ability to synthesize a usable protein that is coded from the genetic message, and more often than not the end product is a nonfunctional protein.

Causes of Mutations

1. Spontaneous Mutations:

These occur stochastically in DNA replication or in other cellular processes for which DNA polymerase or other enzymes operating during DNA synthesis are erroneous.

2. Environmental Factors:

Some more causes of mutation include radiation like UV light and ionizing, some chemicals like tobacco smoke, pollutants, and, some viruses.

DNA Repair Mechanisms

Cells have several mechanisms to repair damaged DNA

1. Mismatch Repair:

Reacts to two main sources of DNA damage; errors arising from DNA replication where wrong base pairing is done, for instance, AG as opposed to AT.

2. Excision Repair:

They are classified into two;

• Base Excision Repair (BER): Repairs minor size modifications on individual bases that may encompass oxidation, deamination, or alkylation. The incorrect base is removed and the accurately matching base is put back in by DNA polymerase and ligase.

• Nucleotide Excision Repair (NER): Smooth largescale DNA damage, for example by UV radiation or some chemicals. This is an excision process whereby a part of the DNA strand with the lesion is removed, and a repair is done using the healthy strand.

3. Recombinational Repair:

This mechanism aids in the repairing of doublestrand breaks if one strand is replaced with another with the aid of an undamaged similar sequence; the homologous DNA. This repair is necessary to maintain genomic stability and prevent the formation of chromosomal rearrangements.

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