biochemistery

1. 4

2. TRANSCRIPTION
By
Dr.Elrasheed Eltaher Osman

3. DNA VS. RNA
 DNA
 Double Helix
 Deoxyribose sugar
 Adenine pairs with
Thymine (A-T)
 Stays in nucleus
RNA
 Single strand
 Ribose sugar
 Uracil replaces
Thymine!
 Leaves nucleus to do
the work

4. THREE TYPES OF RNA:
 mRNA
 “messenger” RNA
 Carries code for
proteins from DNA
 Carries “codon”
 tRNA
 “transfer” RNA
 Attaches specific
Amino Acids to the
protein chain by
matching the mRNA
codon with the
anticodon.

5. RIBOSOMAL RNA
RRNA
 Where Protein
synthesis
occurs

6. TRANSCRIPTION
Definition
Location
Requirements
Characteristics
Steps
Posttranscriptionl modification

7. DEFINITION OF TRANSCRIPTION
Is the synthesis of RNA from
DNA
It is the process of making an
RNA copy of a single gene.
Genes are specific regions of the
DNA of a chromosome.

8. LOCATION
Occur in nucleus
In every nucleated cell

9. REQUIREMENTS OF TRANSCRIPTION
Building blocks
Energy
Enzymes
Accessories

10. BUILDING BLOCKS
Are ribonucleotides of adenine.
Guanine, cytosine and uracil
ATP, GTP, CTP and UTP
They are the source of energy as
well as building blocks
Synthesized by de novo or
salvage pathway

11. ENZYMES
 Called RNA polymerases
DNA-dependent polymerase
Not need a primer
Three types
1- RNA polymerase I ( rRNA)
2- RNA polymerase II (mRNA)
3- RNA polymerase III (tRNA)

12. ACCESSORIES
Include
DNA template
Transcriptional unit
Transcriptional factors

13. PROMOTOR
Place where RNA polymerase
bound
 has specific sequence
Contain many consensus
sequences e.g TATAAT box
Found just 5` upstream to
structural gene

14. DNA TEMPLATE
A part of DNA is transcribed
called the gene
Usually one strand is transcribed
this strand called template
strand
The other strand in called coding
strand has sequences similar to
the new RNA except U replace T

15. THE GENE
DNA sequences that encode RNA
(polypeptide) found in template
strand
Consists of two part
1- Structural gene
2- Regulatory gene

16. STRUCTURAL GENE
Is the DNA sequences that give
rise to RNA
In nuclear genome have
1- Exons the coding sequences
2- Introns intervening sequence
Mitochondrial and prokaryote
genome lack intron

17. REGULATORY GENE
DNA sequences found 5`
upstream to structural gene
Consist of many areas
1- Promotor
2- Hormone response
elements
3- Others

18. A GENE IS A TRANSCRIPTION UNIT
DNA
mRNA 5
Promoter & Regulatory
sequences
Terminator
Ribosome binding site
Transcription
Start
codon
Stop
codon
Open
reading
frame
3
Coding sequences

19. TRANSCRIPTIONAL FACTORS
 These are proteins that regulation
the different steps of transcription
 Include
1- Rho (σ)and sigma (ξ) protein in
prokaryote
2- Transcriptional factors TFII A, B,
C, D, E. F and H
May encode in same template cis
acting or in the other strand trans

20. CHARACTERISTICS OF TRANSCRIPTION
Occur to a part of DNA (gene)
Occur so many times to the gene
Has 5`->3` direction
Produces heterogeneous length
of RNA
Need further processing

22. STEPS OF TRANSCRIPTION
Three steps
1- Initiation
2- Elongation
3- Termination

23. INITIATION
Involve
Binding of TFIID (sigma)
Binding of TBP
Binding of RNA polymerase
Local unwinding and
formation of the first base

24. BINDING OF TFIID (SIGMA)
This complex protein binds the
promotor
They marked the starting of
transcriptiom
Resemble sigma protein in
prokaryotes
Its binding facilitated by TBP
binding

25. BINDING OF RNA POLYMERASE
Involve
Interaction of other TFII A,B,C,E,F
and H
Some recognize TFIID other bind
DNA while some binds RNA
polymerase
In prokaryote binding of RNA
polymerase facilitated by sigma

26. LOCAL UNWINDING
Binding of RNA polymerase
and by aids of some TFII local
unwinding occur
Then the polymerase start to
synthesize RNA
The first nucleotide usually
that enter is a purine

27. STEP 1:
 RNA polymerase attaches to DNA.

28. ELONGATION
As bases enter according to base
pair phenomena RNA
polymerase continues to
synthesize the RNA
The newly synthesized RNA is
complementary to the template
strand and having the same
sequences as coding strand (U

29. STEP 2:
 DNA splits at site of RNA polymerase.
 RNA polymerase attaches matching bases to
form new RNA strand from DNA template.

30. STEP 3:
 RNA polymerase keeps adding bases
making the RNA strand grow…

32. TERMINATION
Terminal signal appear this
may be short DNA loop
Then by aid of termination
factor (Rho) nascent RNA
is released which is called
primary transcript

33. TRANSCRIPTION

35. ‫اا‬‫ا‬ ‫اات‬‫ا‬‫ك‬ ‫االد‬‫ا‬‫ك‬ ‫إذا‬
‫اال‬ ‫واناالد‬ ‫و‬ ‫اا‬ ‫ؤو‬
‫فااا‬ ‫ااال‬ ‫وم‬ ‫اااوو‬ ‫ف‬
‫اا‬ ‫وكساالى‬ ‫و‬ ‫تاا‬
‫و‬ ‫جسم‬‫ا‬ ‫أغ‬ ‫فأن‬
‫ان‬75%‫سانلد‬ ‫ان‬
‫لكم‬ ‫اك‬.

37. POSTTRANSCRIPTIONL MODIFICATION
This is after transcription
modification for the primary
transcript in order to produce
mature
1- mRNA
2- rRNA
3- tRNA

38. AFTER TRANSCRIPTION
In prokaryotes, the RNA copy of a
gene is messenger RNA, ready to
be translated into protein. In fact,
translation starts even before
transcription is finished.

39. AFTER TRANSCRIPTION
 In eukaryotes, the primary RNA
transcript of a gene needs further
processing before it can be
translated. This step is called “RNA
processing”. Also, it needs to be
transported out of the nucleus into
the cytoplasm.
 Steps in RNA processing:
1. Add a cap to the 5’ end
2. Add a poly-A tail to the 3’ end

40. CAPPING
 At the 5’ end, a
slightly
modified
guanine (7-
methyl G) is
attached
“backwards”,
by a 5’ to 5’
linkage, to the
triphosphates
of the first
transcribed

41. TAILING
At the 3’ end, of the primary
transcript RNA is cut at a
specific site and 100-200
adenine nucleotides are
attached: the poly-A tail.
Note that these A’s are not
coded in the DNA of the

42. INTRONS
 Introns are regions within a gene that
don’t code for protein and don’t
appear in the final mRNA molecule.
Protein-coding sections of a gene
(called exons) are interrupted by
introns.
 The function of introns remains
unclear. They may help is RNA
transport or in control of gene
expression in some cases, But , no
generally accepted reason for the
There are a few prokaryotic
examples, but most introns are
found in eukaryotes.
Some genes have many long
introns: the dystrophin gene
(mutants cause muscular
dystrophy) has more than 70
introns that make up more than
99% of the gene’s sequence.
However, not all eukaryotic
genes have introns: histone
genes, for example, lack introns.

43. INTRON SPLICING
Introns are
removed from the
primary RNA
transcript while it
is still in the
nucleus.
.
Introns are “spliced
out” by RNA/protein
hybrids called
“spliceosomes”. The
intron sequences are
removed, and the
remaining ends are re-
attached so the final
RNA consists of exons
only

44. RNA PROCESSING
 Introns are pulled out and exons
come together.
 End product is a mature RNA
molecule that leaves the nucleus
to the cytoplasm.
 Introns bad…… Exons good!

45. RNA PROCESSING
pre-RNA molecule
intron intronexon exon exon
exon exon exon
Mature RNA molecule
exon exon exon
intron intron
splicesome splicesome

46. TRANSFER RNA (tRNA)
amino acid
attachment site
U A C
anticodon

47. SUMMARY OF RNA PROCESSING
 In eukaryotes, RNA polymerase
produces a “primary transcript”, an
exact RNA copy of the gene.
 A cap is put on the 5’ end.
 The RNA is terminated and poly-A is
added to the 3’ end.
 All introns are spliced out.
 At this point, the RNA can be called
messenger RNA. It is then transported
out of the nucleus into the cytoplasm,
where it is translated.

48. TRANSCRIPTION
Click image to view movie
•Messenger RNA--Transcribing the message

49. THANK U