بصراحة انا مشفتش السؤال دا
بس حاسس انه سؤال اختيارات
و لو دي اختياراته
لا يمثل شفرة
لأن تحت وحدتي الريبوسوم تنفصلا قبل الوصول له بفعل عامل الاطلاق
دا يبئا اسمه غبااااااااااااااااء ,,,, لانه الاجابتين صح جداً
بس ,,,, انا حاسس ان اجابة الاستاذة بتاعتك اصح
Untranslated regions (UTRs) are sections of the mRNA before the start codon and
after the stop codon that are not translated, termed the
five prime untranslated region (5' UTR) and
three prime untranslated region (3' UTR), respectively. These regions are transcribed with the coding region and thus are
exonic as they are present in the mature mRNA. Several roles in gene expression have been attributed to the untranslated regions, including mRNA stability, mRNA localization, and
translational efficiency. The ability of a UTR to perform these functions depends on the sequence of the UTR and can differ between mRNAs.
The stability of mRNAs may be controlled by the 5' UTR and/or 3' UTR due to varying affinity for RNA degrading enzymes called
ribonucleases and for ancillary proteins that can promote or inhibit RNA degradation.
Translational efficiency, including sometimes the complete inhibition of translation, can be controlled by UTRs. Proteins that bind to either the 3' or 5' UTR may affect translation by influencing the ribosome's ability to bind to the mRNA.
MicroRNAs bound to the
3' UTR also may affect translational efficiency or mRNA stability.
Cytoplasmic localization of mRNA is thought to be a function of the 3' UTR. Proteins that are needed in a particular region of the cell can actually be translated there; in such a case, the 3' UTR may contain sequences that allow the transcript to be localized to this region for translation.
Some of the elements contained in untranslated regions form a characteristic
secondary structure when transcribed into RNA. These structural mRNA elements are involved in regulating the mRNA. Some, such as the
SECIS element, are targets for proteins to bind. One class of mRNA element, the
riboswitches, directly bind small molecules, changing their fold to modify levels of transcription or translation. In these cases, the mRNA regulates itself.
دا اللي في الموسوعة الحرة غن الاجزاء غير المترجمة ,, بص بئا ع ذيل العديد
Poly(A) tail
Main article:
Polyadenylation
The 3' poly(A) tail is a long sequence of
adenine nucleotides (often several hundred) added to the
3' end of the pre-mRNA. This tail promotes export from the nucleus and translation, and protects the mRNA from degradation.
و دي صفحة العديد ع الويكيبديا برضة