Answer:A set of five nitrogenous bases is used in the construction of nucleotides, which in turn build up the nucleic acids like DNA and RNA. These bases are crucially important because the sequencing of them in DNA and RNA is the way information is stored.
The outer layer of a cell that acts as a gatekeeper to a cell is the plasma membrane.
The plasma membrane's job is to selectively permit or restrict substances from entering or leaving the cell.
The top level of the pyramid
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When a hairpin loop forms in the nascent mRNA: The hairpin will destabilize the interaction and possibly lead to transcriptional termination.
Transcription in prokaryotes like E. coli is terminated either by a rho-dependent process or a rho-independent process. Intrinsic termination is controlled by the specific sequences of RNA .
When the termination process starts, the transcribed mRNA forms a stable secondary structural hairpin loop, also known as a stem-loop. Several uracil nucleotides follow this RNA hairpin. The uracil and adenine connections are exceedingly weak. NusA, a protein attached to RNA polymerase, attaches to the stem-loop structure so firmly that it momentarily stalls the polymerase.
The polymerase is pausing at the same time that the poly-uracil sequence is being transcribed. The RNA-DNA duplex can unwind and separate from the RNA polymerase because the weak adenine-uracil interactions reduce the energy of destabilization for the RNA-DNA duplex. Overall, transcription is terminated by the modified RNA structure.
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