Due to their high transcription rate, active ribosomal RNA (rRNA) genes can be easily distinguished in electron micrographs of chromatin spreads. They have a characteristic "Christmas tree" appearance, where the DNA template is the "trunk" of the tree and the nascent RNA transcripts form closely packed "branches." At the base of each branch is an RNA polymerase extending that branch, while RNA processing complexes at the tip of the branch form terminal "ornaments." The top of the tree represents the ... of the rRNA gene, and the "ornaments" are at the ... end of the nascent rRNA molecules.
A) end; 3'
B) end; 5'
C) beginning; either 3' or 5'
D) beginning; 3'
E) beginning; 5'

Question

Quizplus · Accepted Answer

The shortest rRNA "branches" at the "top" of the tree emanate from the beginning of the gene since their transcription has just started. All branches extend at their 3′ end at their base while their 5′ end starts to associate with RNA processing complexes.

Due to Their High Transcription Rate, Active Ribosomal RNA (RRNA)