Protein Synthesis
Legend:
Process whereby DNA encodes for the production of amino acids and proteins.
This process can be divided into two parts:
1. Transcription
Before the synthesis of a protein begins, the corresponding RNA molecule
is produced by RNA transcription. One strand of the DNA double helix is
used as a template by the RNA polymerase to synthesize a messenger RNA (mRNA).
This mRNA migrates from the nucleus to the cytoplasm. During this step,
mRNA goes through different types of maturation including one called splicing
when the non-coding sequences are eliminated. The coding mRNA sequence can
be described as a unit of three nucleotides called a codon.
2. Translation
The ribosome binds to the mRNA at the start codon (AUG) that is recognized
only by the initiator tRNA. The ribosome proceeds to the elongation phase
of protein synthesis. During this stage, complexes, composed of an amino
acid linked to tRNA, sequentially bind to the appropriate codon in mRNA
by forming complementary base pairs with the tRNA anticodon. The
ribosome moves from codon to codon along the mRNA. Amino acids are added
one by one, translated into polypeptidic sequences dictated by DNA and represented
by mRNA. At the end, a release factor binds to the stop codon, terminating
translation and releasing the complete polypeptide from the ribosome.
One specific amino acid can correspond to more than one codon. The genetic
code is said to be degenerate.
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