chapter 36 Flashcards
what is the template strand also called
antisense (-)
what is the coding strand also called
sense (+)
the antisense strand is complementary to
the sequence of the RNA transcript
the sense strand of DNA has the same sequence as
the RNA transcript with T in place of U
the first nucleotide to be transcribed is denoted
as +1
the nucleotide immediately preceding the first nucleotide to be transcribed is denoted with
-1
what is the role of σ subunit
identify promoters
common promoters in E. coli are where
-10 sequence and -35 sequence, together called the core promoter
what initiates transcription
RNA polymerase binds to promoter sites on the DNA template
with is UP element
upstream promoter, located 40 to 60 nucleotides upstream from the start site
what must happen to the DNA for transcription to occur
the DNA must be unwound
how many base pairs need to be unwound
approx. 17 base pairs of DNA
what is an intermediate in RNA synthesis
a DNA-RNA hybrid helix approx. 8 nucleotides in length
transcription occurs at the rate of
50 nucleotides per second
DNA replication occurs at the rate of
800 nucleotides per second
elongation continues until
a termination signal (terminator) is detected
the simplest stop signal is
a palindromic GC-rich region, which forms a hairpin structure pausing the RNA polymerase, and followed by multiple U for easy dissociation
what does rho do
termination signal that binds to a particular sequence on the RNA product and uses the energy of ATP hydrolysis to chase down the polymerase in the transcription bubble
contact with rho causes the transcription bubble to dissociate
does RNA polymerase proofread its product
yes
constitutively expressed genes are
those that are transcribed all of the time
most gene regulation occurs at the level of
transcription
what’s the most common way of regulating gene expression
DNA sequences (usually upstream) in the vicinity of the gene
DNA-binding proteins bind to these sequences and enhance or repress gene expression
what regulatory system was one of the first to be elucidated
lac repressor system
in the absence of lactose…….
the gene for β-galactosidase, which metabolizes lactose, is minimally transcribed
in the presence of lactose…..
the genes for β-galactosidase as well as two other enzymes—a permease and thiogalactoside transacetylase—are expressed
what are the DNA components of an operon
regulator gene, an operator, a promoter, structural genes
in the lac operon, the regulatory gene encodes…..
a protein called the lac repressor that binds to the operator site in the absence of lactose and prevents promoter use and this transcription of the structural genes
when lactose is present….
the small amount of β-galactosidase in the cell converts it to
galactose and glucose
what is generated in a side reaction in the conversion of β-galactosidase to glucose
allolactose
what is the inducer of the lac operon
allolactose
upon binding allolactose, the lac repressor…….
undergoes a structural change that greatly reduces its affinity for DNA
what happens after allolactose binds to the lac operon and a structural change is undergone
RNA polymerase binds to the promoter and transcribes the structural genes of the operon
