Prokaryotic transcription
Learning objective:
1. What is transcription
2. What are the stages of transcription
3. What are the functions of RNA polymerase
4. Promotor recognition
5. Transcriptional termination
6. Regulation of initiation, elongation and termination
The central dogma describes information flow
Francis and crick came up with the central dogma of biology
DNA to RNA to Protein is unidirectional
Viruses or retroviruses with RNA genome convert RNA to DNA
Retroviruses are a group of RNA viruses, which insert a DNA copy of their genome into the host cell in order
to replicate
- e.g. HIV
Viruses are not living organisms as lack properties that scientist associate with living organisms, such as
reproduce without the aid of a host.
Introns
- segments of DNA or RNA molecule which does not code for proteins and interrupts gene sequence
Exons
- segments of DNA or RNA molecule containing information coding for a protein or peptide sequence
Eukaryotes have introns and exons
Prokaryotes only have Extron
Prokaryotes do not have an intron because are more simple organism compared to the complexity of
eukaryotes
Difference between nucleotide and nucleoside
nucleotide Nucleoside
Phosphate group-pentose sugar- base Phosphate group- pentose sugar
LO1. WHAT IS TRANSCRIPTION?
Introduction
Transcription is 5’ to 3’ on a template that is 3’ to 5’
Coding ( non-template strand)- the DNA strand that has the same sequence as the MRNA (except U
replaces T) and is related by the genetic code to the protein sequence
RNA polymerase – an enzyme that synthesised RNA using DNA template (formally described as a DNA-
dependent RNA polymerase)
, DNA is a double helix with 1 non-template strand and the other as a template strand
Transcription is a process that requires a single strand of DNA template and produces a complementary
RNA copy, which means only one of the DNA strand can act as a template
Template strands (lagging) run from 3’ to 5’ direction due to the chemistry of transcription
RNA can only be produced from a 5’ to 3’ end therefore the template strand is the strand that runs from 3’
to 5’
In text books always see non-template strand (5’-3’)(leading)
Transcription unit
Promotor
- a region of DNA where RNA polymerase bind to initiate transcription
- Promoters promote genes encoding proteins but also genes that do not encode proteins
Start point- the position on DNA corresponding to the first base incorporated into RNA (begins at +1 )
Terminator- a sequence of DNA that cause RNA polymerase to terminate transcription
Transcription unit (gene) - the sequence between sites of initiation and termination by RNA polymerase.
May include more than 1 gene.
Everything upstream the transcription unit is designated -10,-20,-30 bp…
Sequence upstream are called regulators as they control transcription from the start point sign and mostly
called promotors as promotor transcription
Nucleotides downstream of +1 are the coding sequence (gene)
Transcription unit has a stop sign
There is a gap between the transcription start sign and coding sequence
The coding sequence ends up in the protein
Many MRNA have untranslated region, which is the start of the MRNA molecule and does not end up in the
protein instead it is the place where ribosomes start.
Prokaryotic vs Eukaryotic transcription
, In prokaryotes, transcription and translation occur at the same time as there is no nuclei so both processes
occur in the cytoplasm
In eukaryotes, transcription occurs in the nucleus and translation occurs in the cytoplasm by ribosomes
Structure of RNA polymerase is similar in archaea, prokaryotes and eukaryotes
As found in eukaryotes, prokaryotic RNA molecule can also be polyadenylated
Nucleocytoplasmic = relationship between the nucleus and cytoplasm of a cell
Transcription occurs by base pairing in a ‘’bubble’’ of unpaired DNA
RNA polymerase separates the 2 strands of DNA in a transient bubble.
RNA is a single strand therefore RNA polymerase needs to access a single strand of DNA in the double helix
It uses one strand as a template to direct synthesis of a complementary sequence of RNA
The length of the transcription bubble is approx. 12-14 bp
The length of the RNA-DNA hybrid within the RNA-DNA hybrid is approx. 8-9 bp
The RNA strand comes out of the RNA Polymerase
Learning objective:
1. What is transcription
2. What are the stages of transcription
3. What are the functions of RNA polymerase
4. Promotor recognition
5. Transcriptional termination
6. Regulation of initiation, elongation and termination
The central dogma describes information flow
Francis and crick came up with the central dogma of biology
DNA to RNA to Protein is unidirectional
Viruses or retroviruses with RNA genome convert RNA to DNA
Retroviruses are a group of RNA viruses, which insert a DNA copy of their genome into the host cell in order
to replicate
- e.g. HIV
Viruses are not living organisms as lack properties that scientist associate with living organisms, such as
reproduce without the aid of a host.
Introns
- segments of DNA or RNA molecule which does not code for proteins and interrupts gene sequence
Exons
- segments of DNA or RNA molecule containing information coding for a protein or peptide sequence
Eukaryotes have introns and exons
Prokaryotes only have Extron
Prokaryotes do not have an intron because are more simple organism compared to the complexity of
eukaryotes
Difference between nucleotide and nucleoside
nucleotide Nucleoside
Phosphate group-pentose sugar- base Phosphate group- pentose sugar
LO1. WHAT IS TRANSCRIPTION?
Introduction
Transcription is 5’ to 3’ on a template that is 3’ to 5’
Coding ( non-template strand)- the DNA strand that has the same sequence as the MRNA (except U
replaces T) and is related by the genetic code to the protein sequence
RNA polymerase – an enzyme that synthesised RNA using DNA template (formally described as a DNA-
dependent RNA polymerase)
, DNA is a double helix with 1 non-template strand and the other as a template strand
Transcription is a process that requires a single strand of DNA template and produces a complementary
RNA copy, which means only one of the DNA strand can act as a template
Template strands (lagging) run from 3’ to 5’ direction due to the chemistry of transcription
RNA can only be produced from a 5’ to 3’ end therefore the template strand is the strand that runs from 3’
to 5’
In text books always see non-template strand (5’-3’)(leading)
Transcription unit
Promotor
- a region of DNA where RNA polymerase bind to initiate transcription
- Promoters promote genes encoding proteins but also genes that do not encode proteins
Start point- the position on DNA corresponding to the first base incorporated into RNA (begins at +1 )
Terminator- a sequence of DNA that cause RNA polymerase to terminate transcription
Transcription unit (gene) - the sequence between sites of initiation and termination by RNA polymerase.
May include more than 1 gene.
Everything upstream the transcription unit is designated -10,-20,-30 bp…
Sequence upstream are called regulators as they control transcription from the start point sign and mostly
called promotors as promotor transcription
Nucleotides downstream of +1 are the coding sequence (gene)
Transcription unit has a stop sign
There is a gap between the transcription start sign and coding sequence
The coding sequence ends up in the protein
Many MRNA have untranslated region, which is the start of the MRNA molecule and does not end up in the
protein instead it is the place where ribosomes start.
Prokaryotic vs Eukaryotic transcription
, In prokaryotes, transcription and translation occur at the same time as there is no nuclei so both processes
occur in the cytoplasm
In eukaryotes, transcription occurs in the nucleus and translation occurs in the cytoplasm by ribosomes
Structure of RNA polymerase is similar in archaea, prokaryotes and eukaryotes
As found in eukaryotes, prokaryotic RNA molecule can also be polyadenylated
Nucleocytoplasmic = relationship between the nucleus and cytoplasm of a cell
Transcription occurs by base pairing in a ‘’bubble’’ of unpaired DNA
RNA polymerase separates the 2 strands of DNA in a transient bubble.
RNA is a single strand therefore RNA polymerase needs to access a single strand of DNA in the double helix
It uses one strand as a template to direct synthesis of a complementary sequence of RNA
The length of the transcription bubble is approx. 12-14 bp
The length of the RNA-DNA hybrid within the RNA-DNA hybrid is approx. 8-9 bp
The RNA strand comes out of the RNA Polymerase
