MIMG 101 Midterm 2 Test Questions
and All Actual Answers 2026 Updated.
how does the Trp repressor work? what is it called when trp is around and not around? -
Answer No trp: it is an aporepressor- it does not bind to operon and transcription occurs
Yes trp: it is a holorepressor- trp binds to repressor and turns it into a holorepressor. the
holorepressor binds to operon and supresses transcription. NOTE! the holorepressor is a leaky
repressor, some transcription continues to occur- this is why there are more means to control
expression
what is transcriptional attenuation? - Answer -uses ribosomes to sensor amino acid level
-ability to translate mRNA determines whether transcription continues: usually it comes from
mRNA folding into alternative secondary structures
transcriptional attenuation in Trp
-leader sequence
-structures formed by what? - Answer trp gene has a leader sequence- no enzymatic
product!! this encodes a trp mRNA has 4 sequences (1,2,3,4). Just before sequence 1, there are
2 codons for trp there is a also a stop codon in between 2 and 3. The mRNA can form
1) anti-attenuator stem loop- btwn 2 and 3
2) attenuator stem loop - btwn 1-2 and 3-4
transcriptional attenuation- high amount of trp in cell - Answer when plenty of trp, ribosome
moves quickly through the mRNA and 1-2 and 3-4 stemloop forms: the attenuator stemloop.
this causes RNA pol to pause. the newly transcribed region is attached to DNA, but it has a lot of
Uracil= weak bonding.
The mRNA easily separates from DNA and RNA Pol falls off before reading trp gene
transcriptional attenuation- low amount of trp in cell - Answer when no trp, ribosome gets
stuck at the codons before sequence 1 that need trp. This allows for the 2-3 stemloop to form:
anti-attenuator stemloop.
RNA pol can continue transcribing the trp gene
types of regulatory RNAs - Answer sRNA
asRNA
sRNA - Answer small RNA
-post transcriptional control
,-bind to complementary sequences on target mRNA
- can stimulate/prevent translation or degradation
asRNA - Answer cis-antisence RNA
-transcribed from the non-template strand of DNA that lays opposite of mRNA encoding
template strand
-base pair with conjugate mRNA and control expression
what do some sRNA's require? - Answer RNA chaperone protein called: Hfq
-stabilizes sRNA
-hexameric ring protein with sRNA and mRNA binding faces
sRNA- inhibit translation - Answer sRNA will base pair with mRNA's ribosome binding site to
prevent ribosome from attaching, therefore inhibiting translation
sRNA- enhance translation - Answer sRNA will bind to part of long 5' cap upstream of RBS-->
prevents mRNA from folding in a way that hides the RBS. The RBS is exposed and ribosome can
bind and begin translation
RBS - Answer ribosome binding site
sRNA- promote degradation - Answer sRNA alters mRNA folding to expose RNase cleavage
sites
sRNA- prevent degradation - Answer sRNA binds to RNaseE-binding site and blocks it form
RNase
sRNA- mRNA processing - Answer sRNA can help separate monocistronic mRNA from
polycistronic mRNA by exposing RNase cleavage sites
what is the benefit of sRNA vs large regulatory protein for controlling gene expression? - Answer
sRNA:
-does not require protein synthesis
-can diffuse rapidly
-can act on preexisting messages
an economical way to inhibit gene expression
, what molecular structures can recognize and bind to low molecular weight structures? - Answer
proteins and ribozymes
what is a ribozyme - Answer ribozyme: catalytic RNA
with a 3D structure that had enzymatic functions
riboswitch- what is it, where is it found, what does it do? - Answer riboswitch:
-mRNA found at the 5' untranslated region upstream of coding sequence.
-it can take on 2 alternative stemloop structures, in response to a metabolite.
resembles activator/repressor protein bc it binds to a cell metabolite to control gene expression
riboswitch- affects translation - Answer excess ligand (amino acid or vitamin):
the ligan will bind to the riboswitch, which stabilizes it into a structure that hids the RBS,
preventing translation of mRNA
no ligand:
alternative riboswitch structure exposes RBS, translation occurs
what will you not have on an sRNA gene? - Answer ATG- methionine codon
riboswitch: affects transcription - Answer ligand binds to riboswitch prevents transcription
termination! coding region is expressed
northern blot - Answer RNA blot- study gene expression thru detection of mRNA
experiment to show that trp gene can be controlled by attenuation - Answer S1 nuclease
mapping:
create probe: radioactive antisense RNA that will base pair with gene of interest.
expose hybrids to S1 nuclease- which digests all
ss mRNA!
-if long mRNA, it has long probe so the non-digested pieces will be large and heavy.
-If short mRNA (product of attenuation- just leader sequence), the non-digested pieces will be
small and short.
Do this to cells with trp and without trp.
Northern blot
Cells with Trp: have small mRNA after s1 nuclease. meaning attenuation happened
and All Actual Answers 2026 Updated.
how does the Trp repressor work? what is it called when trp is around and not around? -
Answer No trp: it is an aporepressor- it does not bind to operon and transcription occurs
Yes trp: it is a holorepressor- trp binds to repressor and turns it into a holorepressor. the
holorepressor binds to operon and supresses transcription. NOTE! the holorepressor is a leaky
repressor, some transcription continues to occur- this is why there are more means to control
expression
what is transcriptional attenuation? - Answer -uses ribosomes to sensor amino acid level
-ability to translate mRNA determines whether transcription continues: usually it comes from
mRNA folding into alternative secondary structures
transcriptional attenuation in Trp
-leader sequence
-structures formed by what? - Answer trp gene has a leader sequence- no enzymatic
product!! this encodes a trp mRNA has 4 sequences (1,2,3,4). Just before sequence 1, there are
2 codons for trp there is a also a stop codon in between 2 and 3. The mRNA can form
1) anti-attenuator stem loop- btwn 2 and 3
2) attenuator stem loop - btwn 1-2 and 3-4
transcriptional attenuation- high amount of trp in cell - Answer when plenty of trp, ribosome
moves quickly through the mRNA and 1-2 and 3-4 stemloop forms: the attenuator stemloop.
this causes RNA pol to pause. the newly transcribed region is attached to DNA, but it has a lot of
Uracil= weak bonding.
The mRNA easily separates from DNA and RNA Pol falls off before reading trp gene
transcriptional attenuation- low amount of trp in cell - Answer when no trp, ribosome gets
stuck at the codons before sequence 1 that need trp. This allows for the 2-3 stemloop to form:
anti-attenuator stemloop.
RNA pol can continue transcribing the trp gene
types of regulatory RNAs - Answer sRNA
asRNA
sRNA - Answer small RNA
-post transcriptional control
,-bind to complementary sequences on target mRNA
- can stimulate/prevent translation or degradation
asRNA - Answer cis-antisence RNA
-transcribed from the non-template strand of DNA that lays opposite of mRNA encoding
template strand
-base pair with conjugate mRNA and control expression
what do some sRNA's require? - Answer RNA chaperone protein called: Hfq
-stabilizes sRNA
-hexameric ring protein with sRNA and mRNA binding faces
sRNA- inhibit translation - Answer sRNA will base pair with mRNA's ribosome binding site to
prevent ribosome from attaching, therefore inhibiting translation
sRNA- enhance translation - Answer sRNA will bind to part of long 5' cap upstream of RBS-->
prevents mRNA from folding in a way that hides the RBS. The RBS is exposed and ribosome can
bind and begin translation
RBS - Answer ribosome binding site
sRNA- promote degradation - Answer sRNA alters mRNA folding to expose RNase cleavage
sites
sRNA- prevent degradation - Answer sRNA binds to RNaseE-binding site and blocks it form
RNase
sRNA- mRNA processing - Answer sRNA can help separate monocistronic mRNA from
polycistronic mRNA by exposing RNase cleavage sites
what is the benefit of sRNA vs large regulatory protein for controlling gene expression? - Answer
sRNA:
-does not require protein synthesis
-can diffuse rapidly
-can act on preexisting messages
an economical way to inhibit gene expression
, what molecular structures can recognize and bind to low molecular weight structures? - Answer
proteins and ribozymes
what is a ribozyme - Answer ribozyme: catalytic RNA
with a 3D structure that had enzymatic functions
riboswitch- what is it, where is it found, what does it do? - Answer riboswitch:
-mRNA found at the 5' untranslated region upstream of coding sequence.
-it can take on 2 alternative stemloop structures, in response to a metabolite.
resembles activator/repressor protein bc it binds to a cell metabolite to control gene expression
riboswitch- affects translation - Answer excess ligand (amino acid or vitamin):
the ligan will bind to the riboswitch, which stabilizes it into a structure that hids the RBS,
preventing translation of mRNA
no ligand:
alternative riboswitch structure exposes RBS, translation occurs
what will you not have on an sRNA gene? - Answer ATG- methionine codon
riboswitch: affects transcription - Answer ligand binds to riboswitch prevents transcription
termination! coding region is expressed
northern blot - Answer RNA blot- study gene expression thru detection of mRNA
experiment to show that trp gene can be controlled by attenuation - Answer S1 nuclease
mapping:
create probe: radioactive antisense RNA that will base pair with gene of interest.
expose hybrids to S1 nuclease- which digests all
ss mRNA!
-if long mRNA, it has long probe so the non-digested pieces will be large and heavy.
-If short mRNA (product of attenuation- just leader sequence), the non-digested pieces will be
small and short.
Do this to cells with trp and without trp.
Northern blot
Cells with Trp: have small mRNA after s1 nuclease. meaning attenuation happened
