Ch 18 (3)
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Only __ of the human genome codes for proteins.
Of the remainder, a very small fraction consists of genes for small RNAs, such as rRNA and tRNA.
True or False: Before, the general idea was that since it didn’t code for proteins or the few known types of RNA, such DNA didn’t contain meaningful genetic info. Evidence contradicts this idea.
__account for some transcribed, nontranslated RNA, but only a small fraction of the total. A significant amount of the genome may be transcribed into non-protein-coding RNAs (__). noncoding RNAs. __are the most important RNAs functioning in the cell
- noncoding RNAs
Regulation by noncoding RNAs is known to occur at two points in the pathway of gene expression:
· __ and __
- mRNA translation
- Chromatin configuration
__ are small single-stranded RNA molecules capable of binding to complementary sequences in mRNA molecules.
The __ are formed from longer RNA precursors that fold back on themselves, forming one or more short double-stranded hairpin structures, held by __ bonds.
After each hairpin is cut away from the precursor, it is trimmed by an enzyme (__) into a short double-stranded fragment of about __ nucleotide pairs.
- MicroRNAs (miRNAs) x2
One of the two strands is degraded, while the other (__) forms a complex with one or more proteins: the __allows the complex to bind to any mRNA molecule with the complementary sequence.
The __then either degrades the target mRNA or blocks its translation.
It’s been estimated that expression of up to __ of all human genes may be regulated by miRNAs.
- miRNA x2
- miRNA-protein complex
Injecting double-stranded RNA molecules into a cell somehow turned off expression of a gene with the same sequence as the RNA, called __.
This is due to __, which are similar in size and function to miRNAs.
- RNA interference (RNAi)
- small interfering RNAs (siRNAs)
True or False
The same cellular machinery generates miRNAs and siRNAs and that both can associate with the same proteins, producing similar results.
What is the distinction between miRNAs and siRNAs?
- is based on the nature of the precursor molecule for each
- o An mRNA is usually formed from a single hairpin in a precursor RNA
- o siRNAs are formed from much longer double-stranded RNA molecules, each of which gives rise to many siRNAs.
Because the cellular __ pathway can lead to the destruction of RNAs with sequences complementary to those found in __ RNAs, this pathway may have evolved as a natural defense against infection by such viruses.
· However, the fact that the __ pathway can also affect the expression of nonviral cellular genes may reflect a different evolutionary origin for the __ pathway.
- RNAi x2
True or False:
In addition to affecting mRNAs, small RNAs can cause remodeling of chromatin structure.
Role of __in heterochromatin formation (such as in yeast cells): an RNA transcript produced from DNA in the centromeric region of the chromosome is copied into double RNA by a yeast enzyme and then processed into __. These __associate with a complex of proteins and act as a __, targeting the complex back to the centromeric sequences of DNA. Once there, proteins in the complex recruit enzymes that modify the chromatin, turning it into the highly condensed __found at the centromeres.
- siRNAs x3
- horning device
__may play a role in __formation in other species besides yeast. In experiments where __is inactivated, heterochromatin fails to form at centromeres.
__ RNAs can regulate gene expression at multiple steps.
- Regulator RNAs
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