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Transcript
TRANSCRIPTION OF DNA
AND
TRANSLATION OF RNA
Student researchers:
Lolita MONNIER ;
Christine LAM ;
Thibault MARTIN-LAGARDETTE
School address : Lycée Romain Rolland
17, rue Lucien Nadaire
94200 Ivry / Seine
Grade : 2nde (section européenne)
Teachers : Martine PERNODET ; Nathalie OCTO
1°) Statement of purpose and hypothesis
We learned that the DNA (deoxyribonucleic acid) carries the genetic message of an
individual. So the DNA is the support of the genetic information. It is located in the nucleus
of eukaryote cells and in the cytoplasm of the prokaryote cells. DNA is a double helix
composed of two chains of nucleotides rolled up one around the other one. These chains
contain a deoxyribose and a phosphate associated to a nitrogenous base (adenine, guanine,
cytosine and thymine). Hydrogen bands situated between the nitrogenous bases connect both
chains. The proteins carry out information. So we want to explain the link between DNA and
the proteins, consequently, the link between DNA and the features of the organism. So, we
want to know what the link between DNA and the features of organism are; that is to say how
DNA encodes information.
We suppose that RNA is this link between DNA and proteins.
2) Methodology
To test our hypothesis, we were in quest of information about transcription of DNA
and about the translation of the RNA. That’s why we read few scientific articles on Internet
(www.mit.edu:8001/esgbio/dogma; www.brooklyn.cuny.edu/bc/ahp/BioInfo
www.blc.arizona.edu/Molecular_Graphics/DNA_Structure/DNA_Tutorial.HTML ).
After that, we worked on a biology school-book (sciences et vie de la Terre 1re S R.
TAVERNIER et C. LIZEAUX). As a result we made a model of the transcription of a DNA
sequence. Moreover, we realized the translation of our RNA molecule thanks to an
informatics program.
3) Analysis of data
The genes are located in the nucleus while their expression takes place in the
cytoplasm. That is the reason why they need an intermediary or a messenger. A copy of the
gene (DNA) in the form of RNA is thus necessary, it is realized during the transcription
process. The zone of synthesis moves along a DNA. strand. First of all, an enzyme called the
polymerase RNA unwinds DNA’s helix and breaks the bands between the bases pairs. Then, a
copy of DNA’s message is created: messenger the RNA is synthesized. The nucleotides of
thymine (T) are replaced by uracile (U) in the RNA molecule and it will allow the transfer of
the genetic information through the nucleus membrane towards the cytoplasm.
The RNA is very similar to a DNA stand: it is composed of a chain of nucleotides
containing a ribose (instead of a deoxyribose in DNA and a base [adenine guanine, cytosine,
and uracile instead thymine in DNA ] ).
The second stage of gene expression is the translation. In a bacteria, DNA, mRNA and
ribosomes are the same cellular compartment. In eukariotic cells, RNA goes in the cytoplasm
in order to be translated by the ribosome. A ribosome is an organelle, which allows the
synthesis of proteins. The genetic translation of the information begins with the association
between the mRNA and a ribosome at an initiating triplet (the three nucleotides AUG) of the
mRNA molecule. Each ribosome covers two triplet of mRNA and set up two molecules of
transfer RNA (tRNA) with their respective amino acid. During the progression oh the
ribosomes, amino acids are added to the peptide chain. This operation is repeated at each new
triplet of the mRNA. Finally, the polypeptide chain is released after the ribosome has met a
stop triplet.
4) Summary and conclusion
During the process of the transcription are involved in the translation, the genetic
information is transformed to produce proteins. This DNA’s translation allows the genetic
information to be amplified. For each gene, a lot of copies of mRNA are produced. Each
mRNA is translated many times, some a huge member of the protein is produced. Thus, DNA
is protected in the nucleus.
5)Vocabulary
Amino acid : Basic unity of proteins. There are 20 kind of amino acid in the nature
Cytoplasm: The substance contained within the plasma membrane of the cell. The
region in which translation takes place.
Gene: An inherited set of instructions for making proteins.
mRNA: (Messenger RNA). A type of RNA, which transports the information about
the sequence of the amino acids in the protein to be manufactured, from the nucleus to the
ribosomes.
Ribosome: A cellular component composed of proteins and another class of RNA
(rRNA).
tRNA: (Transfer RNA). tRNA binds to a specific amino acid and has an anticodon on
one end. The anticodon bears a set of three bases, which are complementary to the mRNA
cordon for that particular amino acid. It carries its amino acid to a ribosome during protein
synthesis.