GENETIC MATERIALS, THEIR PROPERTIES, FUNCTIONS, STRUCTURE, AND THEIR REPLICATION
What is genetic material
The substance that is transformed from the parents to their offspring and help in providing them some kinds of resemblance between the parents and offspring or among the offsprings itself is called genetic material. Such genetic materials are found in the gene. DNA and RNA are the principle of genetic materials in living organisms. Basically, DNA is the genetic material in almost all the organisms except some viruses such as RNA virus which have RNA as their genetic material.
The genetic materials have three main functions as follows:
- It changes by the process of mutation
- It carries all the information needed for the proper functioning of the cells.
- It is capable to replicate and inherited to the offspring.
What is a gene
A gene is a unit of heredity that gets transformed from parents to their offspring. Gene is also called a segment of DNA molecule which encodes a character of an organism.
Properties of gene
- Genes are located in DNA which is situated in 23 pairs of the chromosome in human
- Genes occupy a specific position called locus in the chromosome
- Genes have two alleles. Contrasting alleles in the heterozygous and uniform alleles in the homozygous
- Genes are responsible for the genotype and phenotype of organisms.
- Genes multiply by the process called replication
- Genes are capable of modification by a process called mutation or recombination. The mutant genes differ in their original functions.
What are the Central and Revers Central Dogma
The unidirectional flow of genetic information from DNA to RNA(mRNA) and from mRNA to proteins is known as Central Dogma
Note:- The formation of mRNA from DNA is called transcription and from mRNA to protein is called translation
Reverse Central Dogma
Almost all the organisms have DNA as their genetic materials; however, some of the virus-like retroviruses contain RNA as their genetic material. Such virus contains an enzyme called reverse transcriptase that makes the flow of genetic information in reverse direction than that of the central dogma. That’s in the reverse central dogma, information flow from RNA to DNA and from DNA to mRNA and finally into protein. Thus their process of reverse central dogma helps in the formation of DNA from RNA.
From the illustration above, it is clear that the formation of DNA from mRNA is called reverse transcription and formation of mRNA from DNA is called transcription and from mRNA to protein is called translation.
Both DNA(Deoxyribonucleic Acid) and RNA (Ribonucleic Acid) are made up of nucleic acid. Therefore to study about the structure of DNA and RNA, the knowledge of nucleic acid is the must. So, let us discuss the nucleic acid first and then dive into the details about the structures of DNA and RNA.
The nucleic acid is the most important molecules in the life of living organisms. They are the macromolecules which are even larger than the proteins. The main elements that constitute the nucleic acid are carbon, oxygen, hydrogen, nitrogen, and phosphorus. As said above, there are two types of nucleic acids. They are DNA and RNA. Nucleic acids are the components of repositories and transmitters of genetic materials.
Structure of Nucleic Acid
Before talking about the structure of the nucleic acid, we won’t discuss nucleotide because nucleotides are the building blocks of nucleic acids. A nucleic acid is made up of three major components namely – base, sugar, and phosphate.
We can represent this stuff into a simple equation as below:
Nucleotide = base + sugar + Phosphate
Here, I want you to know so that you never mistake nucleotide with nucleoside. So, the nucleotide is formed by the combination of base + sugar + phosphate whereas nucleoside refers to only base + sugar
The three components of nucleotides are:
- Pentose sugar
- Nitrogenous bases
- Phosphoric acid
Let us talk about each of these three components in detail
- Pentose sugar – Pentose sugars are five-carbon sugar found in the nucleic acids. RNA and DNA both contain pentose sugar. RNA has ribose sugar and DNA has deoxyribose sugar. Ribose and deoxyribose sugar differ in their structures at C2 where deoxyribose has one oxygen less than the ribose which is clear from the name itself deoxyribose i.e. one oxygen-less.
- Nitrogenous base – The nitrogenous bases found in the nucleotides are aromatic heterocyclic compound. These nitrogenous bases are of two categories which are purine and pyrimidines.
- Purines – They have two carbon-nitrogen rings in their structures. Examples of purines include adenine and guanine. Adenine and guanine are represented by A and G respectively in short.
- Pyrimidine – They have one carbon-nitrogen rings in their structures. Pyrimidine includes cytosine (C), thymine (T), and Uracil (U). DNA contains only thymine but the RNA contains uracil and not thymine. Thymine and uracil differ in their structure by the presence or absence of the Methyl group (-CH3). This is the reason why thymine is also called methylated uracil.
- Phosphoric acid – It is called phosphoric acid because it contains a phosphate group. It helps in binding nucleic acids by phosphor-diester bond and forms a backbone of nucleic acid.
|Deoxyribonucleic acid (DNA)
|Ribonucleic Acid (RNA)|
|1. It is double-stranded, helix and spirally coiled in shape and structure.
2. It has deoxyribose sugar
3. The nitrogenous bases are adenine, guanine, cytosine, and thymine.
4. It is made up of a large number of the nucleotide in comparison to ribonucleic acid.
5. Purines and pyrimidines are present in equal proportion unlike in RNA.
6. Intracellular and extracellular are the two types of DNA.
7. DNA can replicate itself and form new DNA.
8. DNA is the primary hereditary material.
|1. It is single stranded and nonhelical.
2. It has ribose sugar.
3. The nitrogenous bases are adenine, guanine, cytosine, and uracil. Note that thymine is not found in RNA and Uracil is the place of thymine.
4. It is formed of less number of nucleotide.
5. Purine and pyrimidines are not in equal proportion.
6. There are three types of RNA – they are mRNA, tRNA, and rRNA.
7. RNA cannot replicate itself
8. RNA is not a hereditary material except in some viruses like ribovirus
Replication of DNA
Among the two types of genetic materials, RNA and DNA; only DNA can replicate itself. The details about the replication of DNA explained in the points below:
- Replication is always semi-conservative
- Replication begins at the sequences called origin.
- DNA synthesis is initiated by short segments of RNA called primers.
- The elongation of the DNA strand is always in the 5 prime to 3 prime direction.
- New DNA is synthesized from dNTPs; in the polymerization of DNA, two phosphates are cleaved from a d NTP and the resulting nucleotide is added to the 3 prime hydroxyl group of the growing nucleotide strand.
- Replication is continuous on the leading strand and discontinuous n the lagging strand.
- New nucleotide strands are made complementary and parallel to their template strands.
- Replication takes place at very high rates and is accurate due to precise nucleotide selection, proofreading, and repair mechanism.
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