RNA comes in several types that serve different functions. Messenger RNA (mRNA) acts as a template for protein synthesis by carrying genetic code from DNA to the ribosomes. Transfer RNA (tRNA) transfers amino acids to the ribosome during protein synthesis. Ribosomal RNA (rRNA) is a core component of ribosomes and catalyzes peptide bond formation. Other non-coding RNAs include microRNAs (miRNAs) that regulate gene expression at the post-transcriptional level, and small nuclear RNAs (snRNAs) that are involved in splicing mRNA transcripts. RNAs play essential roles in coding, decoding, regulating, and expressing genes.

1. RNA- Ribonucleic acid
Dr. V.P.Acharya

2. Single stranded
Ribose Sugar
5 carbon sugar
Phosphate group
Adenine, Uracil, Cytosine, Guanine
Chargaff’s rule not followed

3. Types of RNA
 Messenger RNA (mRNA)
Protein coding RNA Non-Protein coding RNA
Large ribosomal RNA
(rRNA)
Long Noncoding RNAs
(lncRNA)
Small noncoding
transfer RNAs (tRNA)
Small nuclear RNA
(SnRNA)
Micro RNA (miRNA)
Silencing RNA (SiRNA)

5. Types of RNAs Primary Function(s)
mRNA - messenger translation (protein synthesis)
regulatory
rRNA - ribosomal translation (protein synthesis) <catalytic>
t-RNA - transfer translation (protein synthesis)
hnRNA - heterogeneous nuclear precursors & intermediates of mature mRNAs
& other RNAs
scRNA - small cytoplasmic signal recognition particle (SRP)
tRNA processing <catalytic>
snRNA - small nuclear
snoRNA - small nucleolar
mRNA processing, poly A addition <catalytic>
rRNA processing/maturation/ methylation
regulatory RNAs (siRNA,
miRNA, etc.)
regulation of transcription and translation,
other??
Sca RNA Small cajal RNAs , used to modify snoRNAs
and snRNAs

6. mRNA
 Messenger RNA
 5’ end capped by 7-methyl-guanosine triphosphate
 Cap helps in recognition of m-RNA
 Prevents attack by 5’-exonucleases
 3’ end- Poly (A) tail
 Tail- prevents attack by 3’-exonuclease
 mRNA- serves as template for protein synthesis
 DNA→ mRNA → Protein

7. tRNA
 Transfer RNA
 Synonym- s RNA (easily
soluble)
 Transfer the desired AA to
protein synthesis machinery
 At least 20 tRNA s
 73-93 nucleotides
 Secondary structure- Clover
leaf model

8.  4 arms, one extra
arm
 Acceptor arm
 D arm
 TΨ C arm
 Anticodon arm

9.  Acceptor arm -Accepts the AA--
Ends with CCA sequence at 3’
end
7 bp
 D arm- Presence of
Dihydrouridine base
3-4 bp
 Anticodon arm- pairs with the
codon on mRNA
 TΨ C arm- Ribothymidine &
pseudouridine
5 bp
Tertiary structure

10. r RNA
 In nucleolus rRNA is synthesised
 Found in cytoplasm
 Catalytic properties- Ribozymes
 Protein synthesis machinery
 Mammalian ribosome- 80 s unit- 60s & 40s
 60s- 23s, 5.8s, 5s RNA + 40 proteins
 40s- 18s RNA + 30 proteins

11. Ribozymes
 Ribonuclease P- catalyzes maturation of
tRNA
 Peptidyl transferase activity- protein
synthesis
 SnRNA - Molecular scissors; SNURPs

13. Other RNAs
 hn RNA (Heteronuclear mRNA)
- Primary transcript
- Mammals
- Editing of mRNA
 Sn RNA- Small nuclear RNA
- Molecular scissors/ Spliceosomes
- 90-300 nucleotides
- 1 million copies per cell
- U1, U2, U4, U5, U6 & U7

14.  Sno RNA- Small nucleolar RNA
- Involved in Pseudouridine synthesis
- Methylation activity
 Mi RNA- Micro RNA
- Regulatory
- Gene expression- base pair with
complementary sequences in target mRNAs and silence
them
- small ~ 22 nucleotides
- >1000 miRNAs
 Si RNA- RNA silencing
- dsRNA molecule 20-25bp long
-Triggers degradation of mRNAs complementary to either
strand of a dsDNA

15. mi-RNA
 Derived from large primary transcripts through specific
nucleolytic processing
 Transcribed by RNAP-II or III
↓
Long primary miRNA (pri-miRNA) with a cap and a poly-A tail
↓
short 70-nt stem-loop structures known as precursor miRNAs
(pre-miRNAs)
↓
miRNA duplex
↓
gets incorporated into RISC (RNA induced silencing
complex)
↓
Mature miRNA

17. Xist RNA- inactivation of the extra
copy of the x chromosome
 PIWI-interacting RNAs (piRNAs)
 endogenous small interfering RNAs (endo-
siRNAs or esiRNAs)
 promoter associate RNAs (pRNAs)

18. Biomedical significance
 Ab against U1 SnRNP- SLE (Systematic lupus
erythematosus)
 miRNAs are most studied ncRNAs- involved in
modulating 60% of all genes- regulation of
differentiation, proliferation, apoptosis and
development
 Dysregulation of miRNAs- Muscular dystrophy, cancer,
DM

19. Kind words can be short and easy but
their echoes are truly endless

20. For more ppt on Medical
Biochemistry please visit my
website www.vpacharya.com