9. • Main enzyme of this process is RNA polymerase
• RNA polymerase enzyme is a holo enzyme which is consist
of two units:- core enzyme and sigma factor
• Core enzyme is also consist of four sub units 2α, 1β, 1β’
• Sigma factor is activator of this process.
• Transcription unit is a part of DNA which is involved in
Transcription have three region Promoter, Structural
genes and Terminator
Transcription
11. Steps of transcription
1. Activation of Nucleotides
2. Attachment of RNA polymerase on DNA
3. Synthesis of RNA
4. Termination of Transcription
12. LE 17-7
Elongation
Non-template
strand of DNA
RNA
polymerase
RNA nucleotides
3 end
3
5
5
Newly made
RNA
Template
strand of DNA
Direction of transcription
(“downstream”)
13. Synthesis of an RNA Transcript
• The three stages of transcription:
– Initiation
– Elongation
– Termination
14.
15. RNA processing in eukaryotes
1. Addition of methylated cap to 5’ end of
messenger RNA (mRNA)-> increases stability and
translation of mRNA
2. Addition of poly(A) tail to 3’ end (polyadenylation) ->
increases stability and translation of mRNA
3. Splicing
removal of introns and joining together of exons
All processing events occur in nucleus
before transport to cytoplasm
16. • RNA splicing:
carried out by spliceosomes
• Spliceosomes
complex of proteins and several small nuclear
ribonucleoproteins (snRNPs)
Recognize splice sites (specific RNA sequences)
cleave out introns and splice together exons (coding
region)
17.
18. LE 17-11
Exon 1
5
Intron Exon 2
Other proteins
Protein
snRNA
snRNPs
RNA transcript (pre-mRNA)
Spliceosome
5
Spliceosome
components
Cut-out
intron
mRNA
Exon 1 Exon 2
5
19. TRANSLATION
• Translation- synthesis of polypeptide in
association with ribosome and directed by an
mRNA molucule with the help of tRNA and
several highly specific protein factor.
• or
• Translation is the process of decoding the
mRNA into a polypeptide chain
20. Translation process requires the
following major components
• 1. mRNA
• 2. tRNA
• 3. Ribosome (containing rRNA
• 4. Many other factors
21. MESSENGER RNA (mRNA)
• Carries the information for a specific protein
• Made up of 500 to 1000 nucleotides long
• Sequence of 3 bases called codon
• AUG – methionine or start codon
• UAA, UAG, or UGA – stop codons
22. TRANSFER RNA (tRNA)
• Clover-leaf shape
• Single stranded molecule with attachment site
at one end for an amino acid
• Opposite end has three nucleotide bases
called the anticodon
27. Steps of translation
1. Activation of amino acids
2. Transfer of amino acid to t-RNA
3. Chain initiation
4. Elongation of polypeptide chain
5. Termination of polypeptide chain
6. Modification of released polypeptide
28. CHARGING OF tRNA
Amino acid reacts with ATP to form “Amino acyl
AMP enzyme complex”
This reaction catalyzed by a specific “Amino acyl
t-RNA snthetase” enzyme.
Amino acyl AMP-enzyme complex+t-RNA
=Amino acyl t-RNA complex +AMP +enzyme
Amino acyl t-RNA complex is called Charged t-
RNA
Now Amino acyl t-RNA moves to the ribosome
for protein synthesis.
29. THE TRANSLATION PROCESS
• The process of translation may be divided into
the following steps:
• 1. INITIATION
• 2.ELONGATION .
• 3.TERMINATION
30. STEP -1 INITIATION
• In this step 30 s and 50 s sub units of
ribosome ,GTP,mg+2 ,charged t-RNA ,m-
RNA and some initiation factor are
required.
• In prokaryotes there are three initiation
factor present –IF1,IF2,IF3
• In Eukaryotes ten initiation factors have
been identified in red blood cells-
• eIF1, eIF2,
eIF3,eIF4A,eIF4B,eIF4C,eIF4D,eIF4F,eI
F5,eIF6
31.
32. 32
INITIATION
mRNA
A U G C U A C U U C G
2-tRNA
G
aa2
A U
A
1-tRNA
U A C
aa1
anticodon
hydrogen
bonds codon
copyright cmassengale
33. ELONGATION
• New tRNA with new amino acid ia attach at ‘A’
site of ribosome.
• The link between amino acid of ‘P’ site of tRNA is
broken and t-RNA of P-site is discharged so -
COOH of P-site A.A. Becomes free.
• Now peptide bond takes place between –COOH
group of P-site amino acid and –NH2 group of A-
site amino site.
• Now t-RNA OF A- site is transferred to P-site and
A-site become empty.
34.
35. 35
mRNA
A U G C U A C U U C G
1-tRNA 2-tRNA
U A C G
aa1 aa2
A U
A
anticodon
hydrogen
bonds codon
peptide bond
3-tRNA
G A A
aa3
Elongation
copyright cmassengale
36. 36
mRNA
A U G C U A C U U C G
1-tRNA
2-tRNA
U A C
G
aa1
aa2
A U
A
peptide bond
3-tRNA
G A A
aa3
Ribosomes move over one codon
(leaves)
copyright cmassengale
37. 37
mRNA
A U G C U A C U U C G
2-tRNA
G
aa1
aa2
A U
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
copyright cmassengale
38. 38
mRNA
G C U A C U U C G
aa1
aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
copyright cmassengale
39. 39
mRNA
G C U A C U U C G
aa1
aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
Ribosomes move over one codoncopyright cmassengale
40. TERMINATION
• Due to slidind of ribosome over m-RNA when any
Nonsence codon (UUA,UAG,UGA)available at A-
site of ribosome ,then polypeptide chain
terminates.
• The linkage between the last t-RNA and the
polypeptide chain is broken by three release
factors called RF1, RF2, RF3 with the help of GTP.
• In eukaryotes only one release factor is known –
eRF1.
41.
42. 42
mRNA
A C A U G U
aa1
aa2
U
primary
structure
of a protein
aa3
200-tRNA
aa4
U A G
aa5
C U
aa200
aa199
terminator
or stop
codon
Termination
copyright cmassengale
43. 43
End Product –The Protein
• The end products of protein synthesis is
a primary structure of a protein
• A sequence of amino acid bonded
together by peptide bonds
aa1
aa2 aa3 aa4
aa5
aa200
aa199
copyright cmassengale
