RNA has several important functions in the cell. It exists in multiple forms including messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). mRNA carries genetic information from DNA in the nucleus to the cytoplasm where it is used to produce proteins. rRNA makes up the major component of ribosomes, the sites of protein synthesis, and helps translate mRNA. tRNA transfers amino acids to the ribosome during protein production. Together, these RNA molecules play key roles in copying and expressing genetic material as well as building proteins from mRNA instructions.

1. Shri Shankaracharya Mahavidyalaya, Junwani , Bhilai
Structure & Function of RNA
Dr. Sonia Bajaj, (Head of Department)

2. Introduction
RNA is polymer of ribo nucleotides.
RNA is a single-stranded helix.
The strand has a 5′end (with a phosphate group) and a 3′end (with a hydroxyl
group).
The ribo nucleotides are linked together by 3′ –> 5′ phosphodiester bonds.
A ribo nucleotides in the RNA chain contains ribose pentose sugar one, four
nitrogenous bases (A, U, G, and C), and a phosphate group.
RNA do not follow Chargaff's rule.
RNA found in Reo-virus is double stranded.

3. Types of RNA
1. Genetic RNA or Genomic RNA- eg- Reo-virus, TMV
2. Non -Genetic RNA – a. m-RNA (messenger)
b. r-RNA (ribosomal)
C. t-RNA (transfer)
Messenger RNA (mRNA)
The m-RNA is 1- 5% of the total RNA in the cell.
Discovered by Jacob and Monad.
The m- RNA is produced by genetic DNA in the nucleus. The process Known as transcription.
It is least stable RNA.
It carries the genetic code copied from the DNA during transcription in the form of triplets of nucleotides called
codons.
As part of post-transcriptional processing in eukaryotes, the 5’ end of m-RNA is capped with a guanosine
triphosphate nucleotide, which helps in mRNA recognition during translation or protein synthesis.
Similarly, the 3’ end of an m-RNA has a poly A tail or multiple adenylate residues added to it, which prevent
enzymatic degradation of m-RNA. Both 5’ and 3’ end of an mRNA imparts stability to the m-RNA.
Function
m-RNA transcribes the genetic code from DNA into a form that can be read and used to make proteins. m-RNA
carries genetic information from the nucleus to the cytoplasm of a cell.

4. Ribosomal RNA (r-RNA)
 This RNA is 80% of the total RNA present in the cell.
 r-RNA was discovered by Kuntze.
 It is found in ribosome and it is produced in nucleolus.
 It is most stable from of RNA.
 Ribosomes consist of two major components: the small ribosomal subunits, which read the RNA, and the
large subunits, which join amino acids to form a polypeptide chain.
 There are present 80s type of ribosome in Eukaryotic cells. Their subunits are 60sand 40s .In 60s sub unit of
ribosome three types of r-RNA are found -5s, 5.8s, 28s.
 40s sub unit of ribosome has only one type of r-RNA i.e. 18s.
 So 80s ribosome has total 4 types of r-RNA.
 Prokaryotic cells have 70s type of ribosome and its subunit are 50s and 30s.
 50s sub unit of ribosome contain 2types of r-RNA i.e.5s and 23s.
 30s sub unit of ribosome has 16s type of r-RNA.
 So 70s RNA has total 3 types of r-RNA.
• r-RNA 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.
Function
 r-RNA directs the translation of mRNA into proteins.

5. Transfer RNA (t-RNA)
 It is 10-15% of total RNA.
 It is synthesized in the nucleus by DNA.
 It is also known as soluble RNA (sRNA).
 It is known as Adapter RNA.
 It is the smallest RNA. (4s).
 t-RNAs are an essential component of translation, where their main function is the transfer of amino acids
during protein synthesis. Therefore they are called transfer RNAs.
Structure of t-RNA
 Holley presented clover leaf Model of its structure.
 Three structural loops are formed via hydrogen bonding.
 The 3′ end serves as the amino acid attachment site.
 3′ end is known as Acceptor arm.
 The center loop encompasses the anticodon.
 The anticodon is a three-base nucleotide sequence that binds to the mRNA codon.
 Loops- Attachment loop, Anticodon loop, DHU (Dihydrouridine) loop.
Function
Transfer RNA (t-RNA) carries amino acids to the ribosome where they are joined to form proteins.

7. FUNCTIONS OF RNA
 RNA is a nucleic acid messenger between DNA and ribosomes.
 It serves as the genetic material in some organisms (viruses).
 Some RNA molecules play an active role within cells by catalyzing biological reactions, controlling gene
expression, or sensing and communicating responses to cellular signals.
 Messenger RNA (m-RNA) copies DNA in the nucleus and carries the info to the ribosomes (in
cytoplasm).
 Ribosomal RNA (r-RNA) makes up a large part of the ribosome; reads and decodes mRNA.