文档介绍：Chapter 26 RNA Metabolism
1. How is RNA synthesized using DNA templates (transcription)?
2. How is newly synthesized primary RNA transcripts further processed to make functional RNA molecules?
3. How is RNA and DNA synthesized using RNA as template (reverse transcription);
is the evolutionary implication of the structural and plexity of RNA molecules?
1. RNA molecules have great structural and functional diversity
With parable to proteins plexity and uniqueness.
Function as messengers between DNA and polypeptides (mRNA), adapters (tRNA) to match a specific amino acid with its specific ic code carried on mRNA, and the structural and ponents of the protein-synthesizing ribosomes (rRNA).
Stores ic information in RNA viruses.
Catalyzes the processing of primary RNA transcripts.
Might have appeared before DNA during evolution.
2. DNA and RNA syntheses are similar in some aspects but different in others
Similar in fundamental chemical mechanism: both are guided by a template; both have the same polarity in strand extension (5` to 3`); both use triphosphate nucleotides (dNTP or NTP).
Different aspects: No primers are needed; only involves a short segment of a large DNA molecule; uses only one of the plementary DNA strands as the template strand; no proofreading; subject to great variation (when, where and how efficient to start).
3. The multimeric RNA polymerase in has multiple functions
The holoenzyme consists of five types of subunits (a2bb’ s)and its is used to synthesize all the RNA molecules in E. coli.
The multiple functions include:
searches for initiation sites on the DNA molecule and unwinds a short stretch of DNA (initiation);
selects the correct NTP and catalyzes the formation of phosphodiester bonds (elongation);
detects termination signals for RNA synthesis (termination).
The E. coli RNA polymerase holoenzyme consists of
six subunits: a2bb’ s.
Possible catalytic subunits
Promoter
specificity
Enzyme assembly,
promoter recognition,
ac