Transcript Lecture 16: Expression of genetic information

Expression of genetic
information
(Part I)
Objectives:
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To outline the flow of genetic information from
DNA to protein synthesis.
To identify the different types of RNA
To compare, the structure of DNA & RNA.
To outline the general characteristics of genetic
code & transcription process.
To explain the importance of tRNA, mRNA &
rRNA.
To diagram the process of protein synthesis.
To compare Eukaryotic & prokaryotic mRNA
• Gene
DNA
d. h.
Informational unit is required to
carry out one or more cellular
function.
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Number: 70,000 – 100, 000.
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A sequence of bases (A –T – C – G).
Has specific location on DNA d.h.
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The 4 bases A, T, C and G, form the
4 letters alphabet of the gene
(genetic) language.
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The word of the gene is called the
genetic code.
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The code is formed of 3 letters from
the alphabet of gene language. So
the genetic code is called triple
code
DNA strand
Letters of
alphabet of
genetic language
Triple code
(genetic word)
ATCGCCGGATT
Gene = Sequence of bases
& has specific location
• Genetic information flow
from nucleus into
cytoplasm
1- Triple code (3 successive
bases in DNA) determines the
complementary bases of mRNA
codon (during transcription).
2- Each codon determines the
anticodon of tRNA (during
translation).
3- Each tRNA carry specific
amino acid, so the codons in
mRNA determines the amino
acids of polypeptide chain
(protein).
Triple code
Transcription
mRNA codon
Translation by
Ribosomes
Amino acid of
polypeptide chain
Expression of genetic
information
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Definition:
a complex process in which the genetic information in DNA is decoded and
used to specify the manufacture of specific protein in the cell.
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Includes 2 steps:
2) Translation
1) Transcription or Copying
• Conversion of genetic language
in mRNA molecule (codons) into
amino acid language of protein
• mRNA molecules are synthesized
as complementary copies of DNA
template
Leads to
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RNA - molecules
Types : - mRNA (messenger
RNA)
- tRNA (transfer RNA)
- rRNA (ribosome)
Polynucleotides like DNA
It has some differences:
1- Single strand, but folded,
form short double stranded
segment.
2- Pentose sugar is ribose
3- The base Uracil substitutes
for thymine
Adenine
One
Base
Ph.
5’
4’
Sugar 1’
Guanine
Cytosine
Uracil
2’
3’
OH
One
Base
Ph.
Sugar
OH
OH
Overview of transcription and translation
Transcription
process
Structure of Gene in DNA strand:
2 strands
form DNA d. h.
Transcribed region
DNA strand
Promoter
region
Upstream
leader sequence
down stream
trailing region
Protein coding sequence
mRNA
termination signal
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Promoter: - specific sequence at beginning of the gene
- the binding site of RNA –polymerase
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Transcribed region:
– upstream leader sequence
– protein coding sequence
(translated region)
– down stream trailing sequence
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mRNA termination region:
- specific sequence at the end of the gene
- signal the RNA polymerase to stop the transcription
- release mRNA
Transcribed region
Steps of Transcription:
1- Binding of RNA –polymerase
to the promoter
2- Unwinding of DNA d.h.
3- RNA-polymerase remove 2
phosphates from each
complementary nucleoside
Down
str.
polymerase trailing
3’
3’
Rewinding
mRNA
termination
signal
-Sense or active strand
- DNA template
5’
5’
Unwinding
promoter
4- It covalently links the
remaining phosphate to 3’
end of the nucleotides of the
growing mRNA chain.
Transcript
mRNA
5- addition of nucleotides
continues in 5’
3’
direction.
6- At RNA- termination region,
RNA- polymerase receive
signal to stop transcription
and release mRNA
-Non-sense strand
- Inactive strand
RNA
Upst.
leader
Start
codon
Stop
codon
5’
3’
-OH
P-P-PUpst.
Leader
sq.
Protein coding sequence
(translated region)
Transcript mRNA
Down
str.
Trailing
sq.
Synthesis of mRNA
Transcription
• Characters of transcription
1- Proceed in 5’
3’ direction.
2- Active template DNA –strand
called sense strand.
3- Inactive DNA-strand called nonsense strand.
4- The sense strand of 2 different
genes is not always the same
strand.
5- RNA –polymerase uses nucleoside
as a source of energy, in building
mRNA.
6- The 1st nucleotide at 5’ –end of
mRNA retain its 3 phosphates.
7- Not need to RNA-primer.
8- Transcribed region are:
- Upstream leader region.
- Protein coding sequence.
- Down stream trailing region.
9- Non-transcribed regions:
- Promoter.
- Termination sequence.
10- Kinds of transcript RNA:
- mRNA
- tRNA
- rRNA