Molecular Genetics of Prokaryotes Problem Set

Problem 11: Features of hnRNA

Help to answer the question

Which of the following features would you NOT expect to find in heterogeneous nuclear RNA (hnRNA)?
A. intron
B. polycistronic coding
C. polyadenylation at 3'-end
D. 5-' cap structure
E. U nucleotides


Heterogeneous nuclear RNA (hnRNA)
The primary precursor mRNA transcript made in the eukaryotic nucleus are called "hnRNA," an abbreviation for "heterogeneous nuclear RNA." What are the features of hnRNA?

Since many eukaryotic nuclear genes are interrupted by introns, RNA transcripts of intron-containing genes have intronic RNA sequences.

Poly A tails at the 3'-end:
Poly A tails added to the 3'-end of most, but not all hnRNAs during nuclear RNA processing. These tails are retained in the processed mRNA.

5'-Cap structure:
A modified GTP is covalently attached to the 5'-end of most precursors to mRNA. This cap structure is also retained in the processed mRNA.

Base Composition and relation to template strand:
RNA is synthesized from a DNA template. The sequence of the RNA is complementary to the DNA template strand, and opposite in polarity. C and T in the DNA template are transcribed by RNA polymerase as G and A in the hnRNA, respectively. A and G in the DNA template are transcribed as U and C in hnRNA. Thus hnRNA and mRNA are sequences of A, G, C and U's.

The Biology Project
University of Arizona
Tuesday, November 4, 1997
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