Gene Expression Overview
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Gene Expression
The Gene Structure
Protein Synthesis
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Gene Expression
Gene expression is the
process by which the
information contained in a
gene is converted into the
structures and functions of a
cell by producing a biologically
functional protein.
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Eukaryotic Cell
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Gene Structure

Eukaryotic gene structure:
Most eukaryotic genes in
contrast to typical
bacterial genes, the
coding sequence (exons)
are interrupted by
noncoding DNA (introns).
The gene must have
( Exon; start signals; stop
signals; regulatory control
elements).
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Protein Synthesis
Protein Synthesis is the

process in which cells
build proteins from
information in a DNA
gene in a two major
steps:
I-Transcription and
II-Translation

Transcription :
synthesis of an RNA
(mRNA) that is
complementary to one of
the strands of DNA.

Translation : ribosomes
read a messenger RNA
and make protein
according to its
instruction.
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Protein Synthesis
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Transcription
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http://biology.unm.edu/ccouncil/Biology_124/Images/transcription.gif
Transcription
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RNA polymerase copies both the exons and the introns.
The stretch of DNA that is transcribed into an RNA molecule
is called a transcription unit.
A transcription unit that is translated into protein contains
coding sequence that is translated into protein and
sequences that direct and regulate protein synthesis;
Transcription proceeds in the 5' → 3' direction.
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RNA Splicing
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Translation
http://www.nature.com/embor/journal/v4/n9/images/embor923-f3.jpg
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Translation
Translation is the process by which ribosomes read the
genetic message in the mRNA and produce a protein
product according to the message's instruction.
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Ribosomes are the site
of protein biosynthesis
using the mRNA as a
template, the ribosome
traverses each codon of
the mRNA, pairing it with
the appropriate amino
acid. This is done using
molecules of transfer
RNA (tRNA) containing a
complementary anticodon
on one end and the
appropriate amino acid
on the other.
http://www.molecularexpressions.com/cells/ribosomes/images/ribosomesfigure1.jpg
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Elongation
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Transfer of proper
aminoacyl-tRNA from
cytoplasm to A-site of
ribosome;

Peptide bond formation;
Peptidyl transferase
forms a peptide bonds
between the amino acid
in the P site and the
newly arrived aminoacyl
tRNA in the A site. This
lengthens the peptide by
one amino acids.
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Elongation

Translocation;
translocation of the new
peptidyl t-RNA with its
mRNA codon in the A site
into the free P site occurs
Now the A site is free for
another cycle of
aminoacyl t-RNA codon
recognition and
elongation. Each
translocation events
moves mRNA , one
codon length through the
ribosomes.
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Protein Synthesis
http://bioinfo.bact.wisc.edu/themicrobialworld/lysozyme.gif 
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Reading the instruction means
translating the code in the RNA
from bases
(building block of DNA and RNA)
to amino acids (building block of
Protein proteins).
Synthesis
www.bseinquiry.gov.uk/report/volume2/fig1_2.htm
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