Types of RIbonucleaic Acid-Types of RNA.ppt

Transcription and regulation of gene expression.ppt

1. TYPES OF RNA
Messenger RNA
•Messenger RNA (mRNA) is synthesized from a
gene segment of DNA which ultimately contains
the information on the primary sequence of
amino acids in a protein to be synthesized. The
genetic code as translated is for m-RNA not
DNA. The messenger RNA carries the code
into the cytoplasm where protein synthesis
occurs.

2. mRNA and tRNA are widely used in the cell
during protein synthesis.
When mRNA is formed, it is caped from 5’
side . This cap is due to presence of
7methyl guanosine triphosphate. mRNA is
not stable structure. Endonucleases and
exonucleases enzymes degrade mRNA
molecule, so protect from nucleases
particularly from 5’ exonucleases, the 5’
side is caped.

3. It is also protected from 3’ end due to
presence of 20 to 250 adenylate
nucleotides and this structure is known as
poly-A tail.
7 methyl guanosine
triphosphate
Poly-A tail
5’
3’
mRNA
A UCCG AAG UA

4. Ribosomal RNA:
•In the cytoplasm, ribsomal RNA (rRNA)
and protein combine to form a
nucleoprotein called a ribosome. The
ribosome serves as the site and carries
the enzymes necessary for protein
synthesis.

5. Transfer RNA:
•Transfer RNA (tRNA) contains about 75 nucleotides,
three of which are called anticodons, and one amino acid.
The tRNA reads the code and carries the amino acid
to be incorporated into the developing protein.
•There are at least 20 different tRNA's - one for each
amino acid. The basic structure of a tRNA is shown in the
figure. Part of the tRNA doubles back upon itself to form
several double helical sections. On one end, the amino
acid, phenylalanine, is attached. On the opposite end, a
specific base triplet, called the anticodon, is used to
actually "read" the codons on the mRNA.
•The tRNA "reads" the mRNA codon by using its own
anticodon. The actual "reading" is done by matching the
base pairs through hydrogen bonding following the base
pairing principle. Each codon is "read" by various tRNA's
until the appropriate match of the anticodon with the
codon occurs.

6. •Codon: A triplet of nitrogen bases on the
messenger RNA is known as codon.
•Anticodon: A triplet of bases which are
complimentary to the codon of mRNA.
•D-Loop: D-loop is important for proper
recognition of amino acyle tRNA synthatase. It
attracts the appropriate amino acid.
•T-Loop: T-loop is involved in binding of
aminoacyl tRNA to the ribosomal surface at the
site of protein synthesis.
•Extra Loop: On the basis of this small extra
loop, different types of tRNA have been
classified.

8. •GENETIC CODE
•The genetic code is the set of rules by which
information encoded within genetic material (
DNA or mRNA sequences) is translated into
proteins by living cells.
•How can a polymeric nucleotide with only four
different heterocyclic amines specify the
sequence of 20 or more different amino acids? If
each nucleotide coded for a single amino acid,
then obviously only 4 of the 20 amino acids
could be accommodated. If the nucleotides were
used in groups of two, there are 16 different
combinations possible which is still inadequate.

9. It has been determined that the genetic code is
actually based upon triplets of nucleotides
which provide 64 different codes using the 4
nucleotides. During the 1960's, a tremendous
effort was devoted to proving that the code was
read as triplets, and also to solving the genetic
code. The genetic code was originally translated
for the bacteria E. Coli, but its universality has
since been established. The genetic code is
"read" from a type of RNA called messenger
RNA (mRNA). Each nucleotide triplet, called a
codon, can be "read" and translated into an
amino acid to be incorporated into a protein
being synthesized. The genetic code is shown
below.

10. Standard genetic code
1st
base
2nd base
3rd
base
U C A G
U
UUU
(Phe/F)
Phenylalanine
UCU
(Ser/S) Serine
UAU
(Tyr/Y) Tyrosine
UGU
(Cys/C) Cysteine
U
UUC UCC UAC UGC C
UUA
(Leu/L)
Leucine
UCA UAA Stop (Ochre) UGA Stop (Opal) A
UUG UCG UAG Stop (Amber) UGG
(Trp/W)
Tryptophan 
   
G
C
CUU CCU
(Pro/P) Proline
CAU
(His/H) Histidine
CGU
(Arg/R) Arginine
U
CUC CCC CAC CGC C
CUA CCA CAA
(Gln/Q) Glutamine
CGA A
CUG CCG CAG CGG G
A
AUU
(Ile/I)
Isoleucine
ACU
(Thr/T)
Threonine 
       
AAU
(Asn/N) Asparagine
AGU
(Ser/S) Serine
U
AUC ACC AAC AGC C
AUA ACA AAA
(Lys/K) Lysine
AGA
(Arg/R) Arginine
A
AUG
[A]
(Met/M)
Methionine
ACG AAG AGG G
G
GUU
(Val/V)
Valine
GCU
(Ala/A) Alanine
GAU
(Asp/D)
Aspartic acid
GGU
(Gly/G) Glycine
U
GUC GCC GAC GGC C
GUA GCA GAA
(Glu/E) Glutamic
acid
GGA A
GUG GCG GAG GGG G