Objectives:

1
Expression of genetic
information (Part I)

• Objectives
• 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

2

• Gene

DNA d. h.

• Informational unit is required to carry out
  one or more cellular function.
• Number 70,000 100, 000.
• A sequence of bases (A T C G).
• Has specific location on DNA d.h.
• The 4 bases A, T, C and G, form the 4 letters
  alphabet of the gene (genetic) language.
• The word of the gene is called the genetic code.
• The code is formed of 3 letters from the
  alphabet of gene language. So the genetic code is
  called triple code

DNA strand
Triple code (genetic word)
Letters of alphabet of genetic language
ATCGCCGGATT
Gene Sequence of bases has specific location
3

• Genetic information flow from nucleus into
  cytoplasm

Triple code
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).
Transcription
mRNA codon
Translation by Ribosomes
Amino acid of polypeptide chain
4
Expression of genetic information

• 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.
• Includes 2 steps

• 1) Transcription or Copying
• mRNA molecules are synthesized as complementary
  copies of DNA template

• 2) Translation
• Conversion of genetic language in mRNA molecule
  (codons) into amino acid language of protein

Leads to
5

• RNA - molecules

Adenine Guanine Cytosine Uracil

• 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

Ph.
One Base
5
1
4
Sugar
2
3
OH
Ph.
One Base
Sugar
OH OH
6

• Overview of transcription and translation

7
Transcriptionprocess

• Structure of Gene in DNA strand

2 strands form DNA d. h.
Transcribed region
DNA strand
Promoter Upstream
down stream mRNA region
leader sequence
trailing region termination signal
Protein coding sequence
8

• Promoter - specific sequence at beginning of
  the gene
• - the binding site of
  RNA polymerase
• Transcribed region
• upstream leader
  sequence
• protein coding
  sequence
• (translated region)
• down stream trailing
  sequence
• mRNA termination region
• - specific sequence at
  the end of the gene
• - signal the RNA
  polymerase to stop the transcription
• - release mRNA

9
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 4- It covalently
links the remaining phosphate to 3 end of the
nucleotides of the growing mRNA chain. 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
Down str. trailing
Upst. leader
RNA polymerase
5
3
3
Rewinding
Unwinding
promoter
mRNA termination signal
-Sense or active strand - DNA template
5
Transcript mRNA
Start codon
Stop codon
3
5
-OH
P-P-P-
Upst. Leader sq.
Down str. Trailing sq.
Protein coding sequence (translated
region) Transcript mRNA
10

• Synthesis of mRNA

11

• Transcription

12

• Characters of transcription

• 1- Proceed in 5 3 direction.
• 2- Active template DNA strand called sense
  strand.
• 3- Inactive DNA-strand called non-sense 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