What are the three types of posttranscriptional processing, and what are the consequences of preventing each of these modifications in terms of gene expression?
What will be an ideal response?
(a) 5? capping: the addition of a modified nucleotide to the 5? end of mRNA. The 5? cap has several functions, including (1 ) protecting mRNA from rapid degradation, (2 ) facilitating mRNA transport across the nuclear membrane, (3 ) facilitating subsequent intron splicing, and (4 ) enhancing translation efficiency by orienting the ribosome on mRNA.
(b) 3? polyadenylation: cleavage at the 3? end of mRNA and addition of a tail of multiple adenines to form the poly-A tail. The 3? poly-A tail has several functions, including (1 ) facilitating transport of mature mRNA across the nuclear membrane, (2 ) protecting mRNA from degradation, and (3 ) enhancing translation by enabling ribosomal recognition of messenger RNA.
(c) intron splicing: RNA splicing to remove introns and ligate exons. Intron splicing requires exquisite precision to remove all intron nucleotides accurately without intruding on the exons and without leaving behind additional nucleotides, so that the mRNA sequence encoded by the ligated exons will completely and faithfully direct synthesis of the correct polypeptide.
Disrupting any one of the transcriptional processes would ultimately disrupt normal gene expression by resulting in mRNA degradation, reduced translation, or improper splicing and, thus, production of the wrong gene product.
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What will be an ideal response?
Organic molecules that end in the suffix "-ase" often function as ________ molecules
A) structural B) enzymatic C) transport D) storage
Which pathogens require a host cell because they aren't able to make proteins on their own?
A) blue-green algae B) bacteria C) protozoans D) viruses
Figure 12.5
The accompanying figure illustrates ____.
A. anaphase I B. metaphase I C. metaphase II D. crossing over E. migration