Criteria for becoming a unequivocal genetic material

A molecule that can act as genetic material must fulfill the following criteria :

(i)   It should chemically and structurally stable.

Stable

(ii)  It should be able to generate it own replica (replication).
(iii) It should provide the scope for slow mutations that are
      required for evolution.
(iv) It should be able to express itself in the form of
      Mendelian characters.

The genetic material should be stable enough not to change with different stages of life cycle, age or with change in physiology of organism.

~ Check out : Which is a better genetic material, DNA or RNA?

The RNA

RNA is a long polymer of ribonucliecotides. And a ribonucliecotide is made up of a Ribose sugar, phosphate and bases such as Adenine, Guanine, Cytosine and Uracil. Well, RNA was discovered with DNA by Friedrich Meischer and termed them as 'nuclein'. Ribonucleic acid (RNA) is a polymeric molecule implicated in various biological roles in coding, decoding, regulation, and expression of genes.

RNA was the first genetic material. There are evidences to suggest that essential life processes, such as metabolism, translation, splicing etc. evolved around RNA. RNA used to act as a genetic material as well as a catalyst. There are some important biochemical reactions in living systems that are catalysed by RNA catalyst (ribozyme) and not by protien enzyme e.g., Ribonucleases R (Cleavage), Snurps (splicing), Peptidyl transferase (peptide bond formation).
But RNA being a a catalyst was reactive and hence unstable. Therefore, DNA has evolved from RNA with chemical modifications that makes it more stable. DNA being double stranded and having complementary strand further resists changes by evolving a process of repair.
RNA is adapter, structural molecule and in some cases catalytic. So from the above discussion it is very much clear both RNA and DNA can function as genetic material, but DNA being stable is preferred for storage of genetic material. For the transmission of genetic information RNA is better material.

Types of RNA

Name of the RNA	Location inside the cells	Features	Amount from total RNA	Functions
mRNA (m-messenger)	In the cytoplasm.	mRNA is the most heterogeneous of the 3 types of RNA in terms of both base sequence and size.	5%	It carries the genetic code copied from the DNA during transcription in the form of triplets of nucleotides called codons.
rRNA (r-ribosomal)	In ribosomes.	Ribosomes are composed of a large subunit called the 50S and a small subunit called the 30S, each of which has its own rRNA molecules.	80%	rRNAs combine with proteins in the cytoplasm to form ribosomes, which act as the site of protein synthesis and has the enzymes needed for the process. These complex structures travel along the mRNA molecule during translation and facilitate the assembly of amino acids to form a polypeptide chain. They bind to tRNAs and other molecules that are crucial for protein synthesis.
tRNA (t-transfer)	Mainly cytoplasm.	tRNA is the smallest of the 3 types of RNA having about 75-95 nucleotides.	15% (well 100-80+5 =15)	tRNAs are an essential component of translation, where their main function is the transfer of amino acids during protein synthesis.

For more details on specific RNA check the next post.

Well How do the life originated, give your own opinions after watching the video below in the comments.

The DNA

DNA is a long polymer of deoxyribonucleotides. It is an acidic substance
present in nucleus. DNA was first identified by Friedrich Meischer in 1869.
He named it as "Nuclein". Altmann found these substances to be acidic in
nature, hence he named it nucliec acid.

The length of DNA is usually defined as number of nucleotides or a pair of
nucleotide referred to as base pairs (bp) present in it. This also is the
characteristic of an organism.


For e.g.,

Organisms	Genetic material	Number of nucleotides or bp
Fhai-X174 Bacteriophage	ssDNA, circular	5386 bases
Lamda Phage	dsDNA, Linear	48502 bp
Escherichia coli	dsDNA, circular	4.6 x 106 bp
Haploid Human Genome	dsDNA, Linear	3.3 x 109 bp

Occurrence of DNA
It is an acidic substance first isolated from nucleus of pus cells.
In eukaryotes, DNA occurs inside nucleus and two types of semi-autonomous cell organelle, mitochondria and plastids (e.g., chloroplasts).

Name of the DNA	Location inside the cells	Feature
Nuclear DNA	Inside the Nucleus	Nuclear DNA is associated with histone protiens to form chromatin fibres.
Organelle DNA	Inside semi-autonomous cell organelle	Organelle DNA is without Histone protiens (naked DNA).
Chromosomal DNA	Naked DNA embedded in prokaryotic cytoplasm.	DNA may be folded with the help of RNA and polyamines.
Plasmids	Prokaryotic cytoplasm.	Extranuclear or extra-chromosomal small circular DNA.

Check out more types of DNA here : DNA types.
Check out next post for :-
~ What are Nucleotides?
~ What are base pairs (bp)?

Introduction to Molecular Biology

"Factors/Genes" were first detected and analyzed by Mendel and subsequently many other scientists, by following transmission form generation to generation. These studies, while greatly elucidating the nature of inheritance in living organisms, provided no insight into the structure or molecular composition of "factors". In 1926, the quest to to determine the mechanism for genetic inheritance reached the molecular level and the nature of the putative genetic material was investigated culminating in the realisation that DNA-deoxyribonucliec acid is the genetic material at least for majority of organisms. This is the substance which controls the inheritance of traits from one generation to the next and it is also able to express its effect through the formation and functioning of traits.
Nucliec acid is of two types in all living organisms i.e., deoxyribonucliec acid (DNA) and ribonucliec acid (RNA). DNA is genetic material in all organisms except some viruses. RNA is genetic material in Riboviruses. In others, RNA functions as a messenger carrying genetic information,
adapter for picking up amino acids, structural and catalytic
molecule in some cases.

The DNA

So in this website, we are going to discuss many topics including:-
1. The structure of DNA.
2. Replication of DNA.
3. The process of making RNA from DNA (transcription).
4. Genetic code that determines the sequence of amino acids in proteins.
5. Protein Synthesis- Translation.
6. Elementary Basis of their regulation.

DNA Maps

 And a great insight to many topics.