Clear and orderly summary of Chapter 12 of the book "Genetics: Analysis and Principles, 6th Edition by Robert Brooker". Together with all my other summaries of Genetics I got an 8,5 for this course.
Genetic summary Chapter 12 – Gene transcription and RNA modification
Function of genetic material, DNA, is to store information necessary to create a living
organism. Information is contained within units (genes).
Gene is a segment of DNA that contains information to make a function product,
either RNA or a polypeptide.
Protein-encoding genes (structural genes), are genes that produce mRNA and
encode polypeptides
Central dogma of genetics; the idea that the usual flow is DNA-RNA-proteins
(polypeptide). In addition, DNA replication serves to copy the information so it can be
transmitted from cell to cell and from parent to offspring.
12.1 Overview of transcription
Promotor; a sequence within a gene that initiates (beginnen) transcription
Terminator; a sequence within a gene that signals the end of transcription
The base sequence in the RNA transcript is complementary to the template strand/
non-coding strand/ antisense strand of DNA. The opposite strand of DNA is
nontemplate strand/coding strand/sense strand and can’t be used for mRNA
synthesis because it has the same sequence as the transcribed mRNA, except the T
and U.
Transcription factors; proteins that influence the ability of RNA polymerase to
transcribe DNA into RNA.
- Some transcription factors bind to
the promotor and facilitate
(vergemakkelijken) transcription.
- Other transcription factors
recognize regulatory sequences
(regulatory elements). Some
increase and other inhibit the
transcription.
Ribosome-binding site (shine-Dalgarno sequence); a sequence in bacterial
(prokaryote) mRNA that is needed to bind a ribosome and initiate (beginnen)
translation
In mRNA there is a series of codons (sequence of 3 nucleotides).
- Start codon; AUG, encondes methionine
- Stop codon; UAA, UAG, UGA
Let op; the start and stop codon don’t affect the transcription. It affects the
translation!
3 stages of transcription
1. Initiation; this is the recognition (herkenning) step. The sequence of bases
within the promotor is recognized by one or more transcription factors.
The specific binding of transcription factors to the promotor identifies the
starting site for transcription.
, Transcription factors makes it
possible that RNA polymerase
bind to the promotor, when DNA
is in the form of a double helix.
After binding the DNA is
denatured (verlies van
ruimtelijke structuur) into an
open complex.
2. Elongation (synthesis of the
RNA transcript); RNA
polymerase slides along the
DNA in an open complex to
synthesize DNA
3. Termination; the terminator is reached (bereikt), the terminator causes that
RNa polymerase and the RNA transcript dissociate (weggaan) from the DNA
12.2 Transcription in bacteria (prokaryote)
1. Initiation
Promotor is located just ahead (upstream from) the site
where transcription begins.
Transcriptional start site; the site in a gene where
transcription begins.
+1, is the number of the base where the transcription
begins. The sequences in the promoter are numbered
negative, because they are for the number of the
beginning base. Let op; no base is numbered 0.
The two sequences located at approximately the -35 and -10 sites in the promotor
are important.
-35; 5’ – TTGACA – 3’
-10; 5’ – TATAAT – 3’, this sequence is called the
Pribnow box
Consensus sequence; the most occurring (voorkomende)
bases within a sequence element. Zie afbeelding
hiernaast.
Polymerase Holoenzyme binds at promotor
RNA polymerase, is the enzyme that catalyzes the synthesis of RNA.
Core enzyme, the subunits of an enzyme that are needed for catalytic activity.
The core enzyme is composed of five subunits.
The sixth subunit is sigma factor
RNA polymerase holoenzyme; the sixth subunit + the core enzyme. So, it is an
enzyme that contains all the subunits.
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