Unfertilized eggs of several animal species contain many mrnas that should not be translated until fertilization occurs. describe a molecular strategy employed by the egg to ensure timely activity of the proteins encoded by such mrna.

Unfertilized eggs are arrested in pachytene of prophase I in meiosis. This arrest must be relieved before fertilization to enable the mitotic divisions. Exposure to some hormones and/or other proteins outcomes in breakdown of nuclear envelope enabling the meiosis to continue from prophase I. Furthermore, those proteins activate some posttranscriptional modifications of mRNA, such as polyadenylation, permitting the translation of the mRNA.

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.