Final Exam: Exam 5 Flashcards
Regulation of transcription
DNA binding proteins
DNA binding proteins
-homodimeric
-specific protein domains
homodimeric
2 protein subunits that are the same
specific protein domain
-helix turn helix
-zinc finger
-leucine zipper
helix turn helix
-2 alpha helix connected by small turn (about 3 AA)
-most commonly seen
first alpha helix
recognition helix, usually glycine
second alpha helix
stabilizing helix
zinc finger
alpha helix that binds zinc at the end
leucine zipper
regularly spaced leucine residues within alpha helix that allow them to fit together like a ziper
DNA proteins will bind to the
-major grooves and look for inverted repeats within the groove
-NO stem loop
how can DNA binding proteins act
As repressors or activators
repression can cause
repression or induction (both negative control)
repression
when end product is present then end product will repress synthesis of enzymes needed to make it
when is repression seen the is
synthesis of anabolic reactions
the repressor needs to
bind to the DNA and inhibit transcription
binding of the repressor is controlled by
co-repressor or effector protein
activation
an enzyme or enzymes will only be made if their substrate is present
the effector protein of the co-repressor is the
-end product
-relay message that DNA binding protein needs to binds
DNA binding proteins are
Allosteric, have two binding sites
upon binding a co-repressor
conformational change will occur within repressor which allows binding to the DNA at the operator
When argenine (enzyme) is absent
want RNA polymerase to make argenine
when arginine is present
arginine acts as co-repressor or effector molecule
corepressor binds to the
repressor which then binds to DNA and blocks the RNA polymerase from making more of the enzyme
Induction
-negative control
-type of repression where substrate becomes present so mechanisms needs to be turned on
induction is seen in ______ reactions
catabolic
induction in absence of lactose
repressor bound bc there isnt any lactose that needs broken down
induction in presence of lactose
need to remove repressor so lactose can be broken down
what is the effector in induction
-wahtever is being used (lactose)
in induction effector will bind to….
repressor then releases the DNA binding protein from DNA so RNA polymerase can continue
positive control
DNA binding protein is acting as an activator
activator
promotes initiation of transcription
activator binding site
where activator binds
activator binding site is located
upstream the promoter
in positive control of transcription the promoter site is
weak
since promoter is weak so
RNA polymerase needs helping determining where to bind
when activator protein binds in positive control then
modification of the DNA can occur or it can physically interact with RNA polymerase to allow binding
in presence of sugar
activator binds to activator binding site to pull in RNA polymerase, inducer (sugar) binds to allosteric site allowing for activator to bind and pull RNA poly in to make all genes needed to break down sugar
the promoters of positively controlled genes have
nucleotide sequences that bind RNA poly weakly and have poor consensus sequences
operon
cluster of genes where expression is under control of a single operon
regulon
more than one operon is under the control of a single regulatory protein
