BIOLOGY 1A03 Lecture Notes - Lecture 6: Adenine, Polyadenylation, Endomembrane System
27 Jun 2018
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Termination of transcription
Prokaryotes have two types of terminator sequences.
1) Rho-independent terminator sequences consist of inverted nucleotide repeat sequences.
Inverted repeats are sequences of nucleotides that are usually followed downstream by a
specific reverse complement. Near the end of transcription, these Rho-independent terminator
sequences are transcribed and then fold back on themselves to form what is referred to as a G-
C rich hairpin loop along that same mRNA strand. This pauses the RNA polymerase and leads
to the release of the mRNA transcript.
2) Rho-dependent terminator sequences use a specific prokaryotic protein or Rho factor, which can
bind to and subsequently utilize ATP energy to move along the formed RNA transcript while
unwinding it from the DNA template. Therefore the Rho factor is able to destabilize the
interaction between RNA and the DNA template, leading to the release of the transcript and the
transcription complex.
Prokaryotes, transcription & translation
Process of translating mRNA into a polypeptide can begin even
before transcription is complete.
Two processes can be temporally and spatially coordinated due to
the fact that prokaryotic cells lack compartmentalization.
Specifically, prokaryotes have no nuclear envelope that separates
that process of transcription and translation.
Unit 3 – Transcription & mRNA processing in eukaryotes
Transcription in eukaryotes
A number of specific proteins called general transcription factors are required to mediate the
binding of RNA polymerase to a promoter and to initiate transcription
RNA polymerases I and III transcribe structural, non-coding RNAs.
RNA polymerase I transcribes the genes for the ribosomal RNAs (rRNAs)
RNA polymerase III transcribes the genes for the transfer RNAs (tRNAs), as well as other small
regulatory RNA molecules.
It is RNA polymerase II that transcribes the messenger RNAs, which serve as the templates for
production of protein molecules.
There are core promoter consensus sequences required to set up a transcription initiation
complex, specific for the particular RNA polymerase and gene being transcribed. But in
eukaryotes, termination of transcription occurs by many different processes, depending upon the
exact polymerase utilized.
A mRNA is a copy of the DNA that leaves the nucleus
transcription and translation are physically separated in the cell by the nuclear membrane.
During transcription, RNA polymerase reads a sequence of DNA and is able to produce a
complementary, antiparallel strand of RNA.
Upon the termination of transcription, the RNA is released from the RNA polymerase.
Primary mRNA transcript must now be modified in the nucleus to produce mature mRNA.
This is also true for the other noncoding RNA (such as tRNA and rRNA) but it is the messenger
RNA that we will focus on.
It is only once an RNA has been modified can it exit the nucleus.
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Document Summary
(cid:57) termination of transcription (cid:120) prokaryotes have two types of terminator sequences: rho-independent terminator sequences consist of inverted nucleotide repeat sequences. Inverted repeats are sequences of nucleotides that are usually followed downstream by a specific reverse complement. Near the end of transcription, these rho-independent terminator sequences are transcribed and then fold back on themselves to form what is referred to as a g- C rich hairpin loop along that same mrna strand. Rna polymerase iii transcribes the genes for the transfer rnas (trnas), as well as other small regulatory rna molecules. The sequences of the mrna that are necessary for coding (cid:120) the sequence of amino acids in the protein - exons. The spliceosome then catalyzes a reaction that allows for a specific hydroxyl group on a nucleotide in the branch site to effectively. Attack and form a new phosphodiester bond with a nucleotide at the donor site.
