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Summary Chapter 16 - Gene Regulation in Eukaryotes II: Epigenetics
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Chapter 16 of Genetics by Brooker.
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Chapter 12 Gene transcription and RNA modification12.1 Overview of transcription
Gene expression is the overall process by which the information within a gene is used to
produce a functional product.
Transcription:
The site for beginning the transcription is called the promoter. The end of transcription is the
terminator. The DNA is transcribed from promoter to terminator. The base sequence of the
RNA is complementary to the template strand. The non-template strand is the coding strand
of the DNA.
The transcription factors control the rate of transcription. They bind directly to the promoter.
Others recognize the regulatory sequences or elements.
Translation:
In bacteria a short sequence within the mRNA, the ribosome binding site (Shine-Dalgarno
sequence) provides a location for the ribosome to bind and begin translation.
mRNA contains a series of codons, three nucleotides, which contain information for
polypeptide sequences. The first codon is the start codon (AUG). The translation stops with
the stop codon.
Three stages of transcription:
1. Initiation: recognition step
2. Elongation: the transcription
3. Termination: reaching the terminator
2.2 Transcription in Bacteria
A promoter is a short sequence of DNA that is necessary to initiate transcription. The
bases are numbered in relation to the transcriptional start site, which is denoted as +1. The
bases preceding this site are numbered in a negative direction.
Consensus sequence:
-35: 5'- TTGACA-3'
-10: 5'- TATAAT-3' → Pribnow box
+1: Transcription start site
Bacterial transcription is initiated when RNA polymerase holoenzyme binds at a
promoter. The sigma factor subunit of RNA polymerase holoenzyme recognizes the -35 and
-10 sequences of the promoter. The DNA unwinds at the -10 sequence to form an open
complex, and a short RNA is made. Then sigma factor dissociates from the holoenzyme,
and RNA polymerase core enzyme proceeds down the DNA, synthesizing RNA and forming
an open complex as it goes.
The RNA transcript is synthesized during the elongation stage. RNA polymerase slides
along the DNA, creating an open complex as it moves. The DNA strand known as the
template strand is used to make a complementary copy of RNA, resulting in an RNA-DNA
hybrid. RNA polymerase moves along the template strand in a 3' to 5' direction and RNA is
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