The first step in protein synthesis is transcription. During this process, the DNA molecule serves as a template to synthesize messenger RNA (mRNA). Here's how it works:
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Unwinding of DNA: The DNA double helix unwinds and separates at the region of the gene that is to be expressed.
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Complementary base pairing: An enzyme called RNA polymerase binds to the promoter region of the gene and begins to synthesize a single strand of mRNA by incorporating complementary RNA nucleotides that pair with the exposed DNA template strand. For example, where there is an adenine (A) on the DNA, there will be a uracil (U) in the RNA.
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Elongation of mRNA: As RNA polymerase moves along the DNA, it continues to add RNA nucleotides, elongating the mRNA strand.
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Termination: This process continues until RNA polymerase reaches a termination signal in the DNA sequence, at which point the synthesis of mRNA is complete.
The resulting mRNA strand then undergoes processing (including splicing, capping, and polyadenylation) before it is transported out of the nucleus and into the cytoplasm, where it serves as a template for translation, the next step in protein synthesis.