Generally the function of a gene is to encode a single polypeptide
(report a gene-a polypeptide), there are genes that code for RNA or DNA sequences that control other. has been shown by Beadle and Tatum with the model organism Neurospora exposed to X-rays that alter the structure of DNA and protein production.
The transmission of genetic information flows to the protein through two stages: transcription and translation
by the 
RNA that differs from DNA for a) single-stranded nucleotide b) ribose c) uracil instead of thymine. The information flow is unidirectional from DNA to RNA to protein (the central dogma of genetics) except for retrovirus
operating a reverse transcription of RNA to DNA. In the transcript ' mRNA (messenger RNA ) is created by transcribing (copying) the information contained in DNA.
In translating the mRNA is in contact with an adapter molecule that translates the information into polypeptide nucleotide, this molecule is the ' tRNA (transfer RNA ).
for transcription are required: a) a DNA template sequence, b) ribonucleoside triphosphate c) enzyme RNA polymerase. In gene during transcription is a single-stranded DNA template, the other is not used. The RNA polymerase recognizes specific bases in DNA, and there binds instead of creating a double-stranded helix. Here is a short sequence is denatured and then can create the pairing with the ribonucleotides of RNA. Transcription takes place in three stages: beginning
, elongation, termination .
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RNA polymerase promoter is looking for a
: a sequence that indicates the beginning of the gene to be transcribed as transcribed strand and in which direction to proceed. Elongation RNA polymerase carries out the filament in the direction of 3'-5 ', the primer is not necessary and there is no error control.
Termination
As there exist sequences starting terminator sequences that specify whether the RNA created comes off or if they have to act before other proteins. At this point we have not mRNA, but pre-mRNA that is longer and has run into major changes prior to mRNA.
each mRNA sequence of three nucleotides called codon and is equivalent to a
except for the amino acid codon
(which also corresponds to methionine) and the stop codon
. Note that amino acids are 20, while the possible combinations of four nucleotides in a sequence of 3 (4 ^ 3) is 64. There are different codons that relate to the same amino acid, so it is said that the genetic code is redundant. The genetic code is nearly universal and is transcribed in the same way in all species on the planet.
As the RNA is translated into proteins? For each amino acid there is a tRNA that carries out the functions of a) transport, b) bind to the mRNA molecule, c) interaction with ribosomes. The tRNA is composed of an acid binding site and a nucleotide sequence defined anticodon. Considering that the number of possible codons exceeds the number of codons for certain amino acids (eg, GCA, GCC, GCU corresponding all'alanina) to have a single tRNA, this phenomenon is called oscillation .
acid RNA loading is triggered by enzymes called aminoacyl-tRNA synthetase . The
ribosome is the workbench for the translation. Each ribosome is composed of two subunits, a greater and lesser composed of rRNA and protein.
The large subunit has three tRNA binding sites:
- site A (amino acid)
the anticodon of the tRNA is joined to the mRNA codon Allien amino acid in the correct position with the following link.
- site P (peptide) amino acid joins with the following - site E (exit)
tRNA exits and returns to the cytoplasm. The minor subunit of the ribosome
valid base pairing: If the H bonds are formed is not right and moves the tRNA from the ribosome. As for the translation and transcription takes place in stages: beginning
, elongation, termination
.
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The minor subunit rRNA of the ribosome binds to a sequence (Shine-Dalgarno sequence
) with the mRNA before the start codon UGA . When the tRNA with methionine binds to the subunit mRNA occurs. Methionine is not always the amino acid N-terminus of all proteins so some enzymes could take away the end. Elongation
tRNA with anticodon binds to the complementary subunit ribosomal higher at site A and that catalyzes two reactions: a) breaking the link between the P site tRNA and its amino acid, b) catalyzes the formation of a bond peptide between the amino acid in P and that in A. Finally, the E site tRNA is transferred and released. Since it is a major subunit to create links peptdici is said to accomplish a task
peptidyl transferase.
termination codons UAA, UAG or UGA attract a protein called releasing factor and allows the hydrolysis of the bond between the polypeptide chain and tRNA in the ribosomal P site and let them pass.
The signal sequence of the polypeptide indicates the destination of the protein.
To speed up the protein production often occurs in polysomes (multiple ribosomes) that are involved in translation.
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