Introduction
We often hear the words genes, DNA, RNA, genetics and so much more. Are all of these interrelated? How does an individual get their habits or genes from? What is the most basic level?
Well, all of this comes down to DNA. All your habits and genes are interrelated with DNA. What is it? Why does DNA have a negative charge? What is its structure? The organic materials called nucleic acids are present in the organisms in the form of DNA or RNA. The structure of DNA defines how the genes are made up in our bodies. As a matter of fact, it defines the genetic structure for the majority of organisms on the planet.
Let us help you understand the details of DNA.
What is DNA?
DNA stands for Deoxyribonucleic Acid, having a molecular structure that is unique. This can be found in both eukaryotic and prokaryotic cells of the organisms.
DNA is defined as a group of molecules that carry out the transmission of hereditary materials from parents to their offspring. This also holds true for viruses. Some viruses just contain RNA in the form of their genetic material, while for others DNA plays this role.
DNA is not just responsible for carrying genetic information. Along with this, it is also responsible for protein production in living beings. The DNA which is contained inside the nucleus of all organisms is defined as nuclear DNA. Most of the organisms’ genomes are handled by this, while the plastid DNA and mitochondrial DNA are responsible for handling the rest.
Mitochondrial DNA is the one that is stored inside the cell’s mitochondria. This is inherited by the child from their mother. There are approximately 16,000 mitochondrial DNA pairs present in the human body.
Discovery of DNA
The Swiss Biologist named Johannes Friedrich Miescher identified DNA in 1869 when he was conducting his research on white blood cells. Following this, the experimental data provided by Francis Crick and James Watson lead to the discovery of double helix structure.
Types of DNA
DNA is mainly found in three different types, namely:
A-DNA: This one is similar to the B-DNA form, and is a right-handed double helix structure. During extreme conditions of desiccation, dehydrated DNA takes the A form. Following this, the protein binding leads to the removal of solvent from the DNA.
B-DNA: This is a right-handed helix structure and is the most common DNA form. Under normal physiological conditions, this one exists the most.
Z-DNA: In this, the structure is a left-handed helix. It plays some role or the other in the regulation of genes.
What is the Structure of DNA?
The strands of a DNA molecule are made up of a long chain of monomer nucleotides. A deoxyribose sugar molecule has a phosphate group attached, as well as one of four nitrogenous bases: two purines (adenine and guanine) and two pyrimidines (cytosine and thymine). The phosphate of one nucleotide and the sugar of the next establish covalent connections, forming a phosphate-sugar backbone from which the nitrogenous bases protrude. One strand is held together by hydrogen bonds between the bases; the order of these bonds is specific which means adenine only links with thymine, and cytosine only with guanine.
From the inside, the DNA molecule is extraordinarily stable, allowing it to serve as a template for both DNA replication and the synthesis of the related RNA (ribonucleic acid) molecule (transcription). A gene is a segment of DNA that directs the creation of a certain protein by a cell.
DNA is split into two single strands, each of which serves as a template for the formation of a new strand. The principle (hydrogen-bond pairing) that is used in the double helix, is also used to copy the new strands. One of the original strands and one new strand are found in each of the two new double-stranded DNA molecules. The essential to stable genetic inheritance is "semiconservative" replication.
Within a cell, DNA is arranged into chromosomes, which are dense protein-DNA complexes. Chromosomes are present in the nucleus of eukaryotes, however, DNA can also be found in mitochondria and chloroplasts. In prokaryotes, which lack a membrane-bound nucleus, DNA is present in the cytoplasm as a single circular chromosome. Extrachromosomal DNA, or plasmids, are autonomous, the self-replicating genetic material found in some prokaryotes, such as bacteria, and a few eukaryotes. Plasmids have been widely utilized to research gene expression in recombinant DNA technology.
Viruses can have single-stranded or double-stranded DNA or RNA as their genetic material. Retroviruses contain their genetic material in the form of single-stranded RNA and create the enzyme reverse transcriptase, which can convert RNA into DNA. G-quadruplexes, four-stranded DNA structures, have been discovered in guanine-rich regions of the human genome.
The DNA structure can be aptly explained with an example of a twisted ladder. This structure is called a double-helix. The DNA is a nucleic acid, and these are all further made up of nucleotides.
Each nucleotide further contains components namely sugar, nitrogen bases, and phosphate groups. Nucleotides are linked together by sugar and phosphate groups leading to the formation of each DNA strand.
There are mainly four types of nitrogen bases namely, Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). Following this, the coiling up of DNA takes place leading to the formation of chromosomes.
Functions of DNA
All the hereditary information is carried out by genetic material called DNA. The small segments of DNA are called genes, which consist mainly of 250-2 million base pairs. DNA leads to the formation of proteins, which are the structural molecules for many organisms. Along with genetic information storing, DNA carries out the following functions:
Replication Process: Under this, the transfer of genetic information from parent cell to daughter cells takes place, leading to equal distribution of DNA during the cell division process.
Mutations: Under this process, changes take place in DNA sequences.
Transcription
Cellular metabolism
Gene therapy
DNA fingerprinting
Why is DNA Negatively Charged?
Well, this is a question for many. Why does DNA have a negative charge? It happens because the nucleotides contain phosphate groups.
The bonds created between oxygen and phosphorus atoms are negative, which makes the phosphate backbone negative. In the complete DNA structure, the phosphate group contains only one oxygen atom that is negative. However, this makes the complete structure negative.
The hereditary substance in humans and virtually all other animals is DNA and ribonucleic acid (RNA). The DNA of virtually every cell in a person's body is identical. Although mitochondria contain a minor quantity of DNA, the cell nucleus (also known as nuclear DNA) contains the majority of DNA (where it is called mitochondrial DNA or mtDNA). Mitochondria are cellular structures that convert dietary energy into energy that can be used.
Adenine (A), guanine (G), cytosine (C), and thymine (T) are the four chemical bases that makeup DNA's coding (T). Human DNA is made up of around 3 billion bases, with over 99 percent of those bases being identical in all humans. Similar to how letters of the alphabet appear in a specific order to form words and sentences, the arrangement, or sequence, of these bases, affects the information accessible for creating and maintaining an organism.
To form a base pair, a base joins with a T base, and a C base joins with a G base. Each base is coupled by a sugar and phosphate molecule. A nucleotide consists of three components: base, sugar, and phosphate. A double helix is a spiral made up of two long strands that structure nucleotides. The rungs of the double helix are formed by the base pairs, while the sugar and phosphate molecules serve as the ladder's vertical side pieces.
The ability of DNA to replicate, or produce duplicates of itself, is one of its most important features. The base sequence can be duplicated using each strand of DNA in the double helix as a template. When cells divide, this is vital because each new cell must have an exact copy of the old cell's DNA.
FAQs on Why is DNA Negatively Charged?
1. Which part of the DNA molecule is responsible for its negative charge?
The overall negative charge of DNA is due to the phosphate groups that form the phosphodiester backbone of the molecule. Each phosphate group contains a negatively charged oxygen atom at physiological pH, giving the entire DNA strand a strong negative charge.
2. If DNA is negatively charged, why is it called an acid (Deoxyribonucleic Acid)?
DNA is considered an acid because the phosphate groups in its backbone can donate a proton (H+) in an aqueous solution, which is the definition of an acid. When it donates these protons, the phosphate groups are left with a negative charge. Therefore, its acidic nature is the very reason it is negatively charged in the neutral pH of a cell.
3. How does the negative charge of DNA enable its separation by gel electrophoresis?
The technique of gel electrophoresis uses an electric field to separate molecules. Since DNA has a consistent negative charge along its backbone, when placed in a gel and an electric current is applied, it will migrate towards the positive electrode (anode). This property is crucial as it allows different-sized DNA fragments to be separated; smaller fragments move faster through the gel matrix than larger ones.
4. How is the long, negatively charged DNA molecule packed into a tiny, compact nucleus?
The negative charge of DNA is neutralised by a group of positively charged proteins called histones. Histones are rich in basic amino acids like lysine and arginine, which have positive charges. The electrostatic attraction between the negative DNA backbone and the positive histones allows DNA to wrap tightly around them, forming a condensed structure known as chromatin, which fits inside the nucleus.
5. Is RNA also negatively charged like DNA? Explain why.
Yes, RNA (Ribonucleic Acid) is also negatively charged for the same reason as DNA. It possesses a sugar-phosphate backbone where the phosphate groups are deprotonated at physiological pH, imparting a net negative charge to the entire molecule. This charge is important for its interactions with other molecules, including ribosomes during protein synthesis.
6. What is the most common structural form of DNA found in living cells?
The most common structural form of DNA found under physiological conditions in living cells is B-DNA. This is the classic right-handed double helix structure described by Watson and Crick. Other forms, such as A-DNA and Z-DNA, can exist but are typically found under specific, often non-biological, conditions.
7. What are the key structural and functional differences between DNA and RNA?
While both are nucleic acids, DNA and RNA have several key differences:
- Sugar: DNA contains deoxyribose sugar, whereas RNA contains ribose sugar.
- Structure: DNA is typically a double-stranded helix, while RNA is usually single-stranded.
- Nitrogenous Bases: DNA uses Adenine (A), Guanine (G), Cytosine (C), and Thymine (T). RNA uses A, G, C, and Uracil (U) in place of thymine.
- Function: DNA's primary role is the long-term storage of genetic information, while RNA's roles are more diverse and immediate, including acting as a messenger (mRNA), transferring amino acids (tRNA), and forming part of ribosomes (rRNA).
