Theme 2: Transcrip/on
• 3.3.2 In transcrip.on, DNA is used as a template to
make a complementary RNA.
• As a region of the DNA duplex unwinds, one strand is used as a
template, for the synthesis of an RNA transcript that is
complementary in sequence to the template according to the
base-pairing rules
a. BUT, U (uracil) replaces T (thymine)
• RNA Polymerase: The transcript is produced by polymerizaHon of
ribonucleoside triphosphates, which is what this enzyme carries
out; Acts by adding successive nucleoHdes to the 3ʹ end of the
growing transcript
a. Only the template strand of DNA is transcribed
i. Its partner, called the non-template strand, is not
transcribed
b. Note: RNA polymerase begins synthesis upstream at the
promoter region
c. RNA polymerase will move along in a 3' to 5' direcHon unHl
it reaches the terminator (which is the end of that specific
gene) on the template strand
• All nucleic acids are synthesized by addiHon of nucleoHdes to the
3ʹ end (i.e. They grow in a 5ʹ-to-3ʹ direcHon; From the 5'
phosphate on a nucleoHde to the 3' OH group of a nucleoHde)
• Because of the anHparallel nature of the DNA–RNA duplex, the
DNA template that is being transcribed runs in the opposite
direcHon, from 3ʹ to 5ʹ
a. Such that RNA polymerase moves along the template strand
in the 3ʹ-to-5ʹ direcHon
3.3.3 TranscripHon starts at a promoter and ends at a
terminator.
, • Promoters: Regions of usually a few hundred base pairs where
RNA polymerase and associated proteins bind to the DNA duplex
b. Many eukaryoHc and archaeal promoters contain a TATA box
(5ʹ-TATAAA-3ʹ) (which is an example of a consensus
sequence which represents the nucleoHde sequence in the
DNA that is found at this site rather than the only variaHon
and is derived by comparing that parHcular region of a
sequence in many different promoters and finding common
elements or nucleoHdes)
i. The first nucleoHde to be transcribed is usually
posiHoned about 10-25 base pairs downstream from
the TATA box
• Consensus Sequences- Enhance the rate of transcripHon
a. ProkaryoHc genes have addiHonal consensus sequences like
the TTGCCA sequence
• Transcripts from a DNA duplex may be produced from either
strand, depending on the orientaHon of the promoter
• Housekeeping Genes- Their products are needed at all Hmes in all
cells so, transcripHon occurs conHnuously
a. Examples- Genes important for structural proteins, RNA and
DNA polymerases and genes that are coding for ribosomal
proteins
• Most genes though, are transcribed at certain Hmes, under certain
condiHons and/or in certain cell types
a. Example: Genes that encode proteins needed to uHlize
lactose are transcribed only when lactose is present in the
environment
b. So, regulaHon of transcripHon depends on whether the RNA
polymerase and associated proteins can bind with the
promoter
• In bacteria, promoter recogniHon is mediated by a protein known
as sigma factor which associates with RNA polymerase (to form a
holoenzyme)and facilitates its binding to specific promoters (one
primary sigma factor is used for transcripHon of housekeeping
genes and many others; but, there are others for genes whose
expression is needed under special condiHons)
• 3.3.2 In transcrip.on, DNA is used as a template to
make a complementary RNA.
• As a region of the DNA duplex unwinds, one strand is used as a
template, for the synthesis of an RNA transcript that is
complementary in sequence to the template according to the
base-pairing rules
a. BUT, U (uracil) replaces T (thymine)
• RNA Polymerase: The transcript is produced by polymerizaHon of
ribonucleoside triphosphates, which is what this enzyme carries
out; Acts by adding successive nucleoHdes to the 3ʹ end of the
growing transcript
a. Only the template strand of DNA is transcribed
i. Its partner, called the non-template strand, is not
transcribed
b. Note: RNA polymerase begins synthesis upstream at the
promoter region
c. RNA polymerase will move along in a 3' to 5' direcHon unHl
it reaches the terminator (which is the end of that specific
gene) on the template strand
• All nucleic acids are synthesized by addiHon of nucleoHdes to the
3ʹ end (i.e. They grow in a 5ʹ-to-3ʹ direcHon; From the 5'
phosphate on a nucleoHde to the 3' OH group of a nucleoHde)
• Because of the anHparallel nature of the DNA–RNA duplex, the
DNA template that is being transcribed runs in the opposite
direcHon, from 3ʹ to 5ʹ
a. Such that RNA polymerase moves along the template strand
in the 3ʹ-to-5ʹ direcHon
3.3.3 TranscripHon starts at a promoter and ends at a
terminator.
, • Promoters: Regions of usually a few hundred base pairs where
RNA polymerase and associated proteins bind to the DNA duplex
b. Many eukaryoHc and archaeal promoters contain a TATA box
(5ʹ-TATAAA-3ʹ) (which is an example of a consensus
sequence which represents the nucleoHde sequence in the
DNA that is found at this site rather than the only variaHon
and is derived by comparing that parHcular region of a
sequence in many different promoters and finding common
elements or nucleoHdes)
i. The first nucleoHde to be transcribed is usually
posiHoned about 10-25 base pairs downstream from
the TATA box
• Consensus Sequences- Enhance the rate of transcripHon
a. ProkaryoHc genes have addiHonal consensus sequences like
the TTGCCA sequence
• Transcripts from a DNA duplex may be produced from either
strand, depending on the orientaHon of the promoter
• Housekeeping Genes- Their products are needed at all Hmes in all
cells so, transcripHon occurs conHnuously
a. Examples- Genes important for structural proteins, RNA and
DNA polymerases and genes that are coding for ribosomal
proteins
• Most genes though, are transcribed at certain Hmes, under certain
condiHons and/or in certain cell types
a. Example: Genes that encode proteins needed to uHlize
lactose are transcribed only when lactose is present in the
environment
b. So, regulaHon of transcripHon depends on whether the RNA
polymerase and associated proteins can bind with the
promoter
• In bacteria, promoter recogniHon is mediated by a protein known
as sigma factor which associates with RNA polymerase (to form a
holoenzyme)and facilitates its binding to specific promoters (one
primary sigma factor is used for transcripHon of housekeeping
genes and many others; but, there are others for genes whose
expression is needed under special condiHons)
