MBIO 3401 TTU Exam 2 Fall 2025| Questions and Verified Answers/Accurate Solutions|
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Regulatory proteins help a cell sense internal changes and alter its gene expression to
match.
There are 2 forms of regulatory proteins: - Repressors (negative control)
- Activators (positive control)
Repressors bind to regulatory sequences in the DNA and prevent transcription of target
genes.
- some must first bind a small ligand.
Activators bind to regulatory sequences in the DNA and stimulate transcription of target
genes.
- most must first bind a small ligand.
Microbes control gene expressions at several levels - Alterations of DNA sequence
- Control of transcription
- Control of mRNA stability
- Translational control
- Post-translational control
,Paradigm of the Lactose Operon Scientist Jacques Monod and Francois Jacob - genes could
be regulated.
E. coli, enzymes used to metabolize lactose were inducible, glucose were constitutive.
- 1965 nobel prize for his study of phage nysogeny.
LacZYA operna E. coli was 1st gene regulatory system described.
Organization of LacZYA Opepn
If lactose is absent then LacI binds as a tetramer to operator region.
- represses the lac operon by preventing open complex formation by RNA ploymerase.
If lactose is present then B-galactosidase (LacZ) at low levels, cleaves and rearranges lactose
to make inducer allolactose.
- Allolactose binds to LacI, reducing affinity to operator allowing induction of operon.
cAMP and cAMP receptor protein (CRP) are required for the maximum expression of the lac
operon.
Catabolite repression operon enabling catabolism of one nutrient is repressed by the
presence of a more favorable nutrient.
Diauxic growth the biphasic curve if a culture growing in 2 carbon soruces.
,Inducer exclusion glucose transport by phosphotransferase system causing catabolite
repression by inhibiting the LacY permease activity.
- if lactose can't enter the cell, lacZYA operon can't be induced.
Major regulator AraC can repress or activate gene expression.
AraC forms a ___ that can assume one of two conformations depending on whether arabinose
is available? dimer
When arabinose is absent, AraC shape is rigid and elongated.
- represses the expression of the genes that break down arabinose.
When arabinose is present, AraC shape is more compact.
- stimulates binding of RNA pol = transcribes genes.
Genes encoding biosynthetic enzymes are regulated by Inactive aporepressors.
Corepressor bind end product of pathway.
Tryptophan Operon - Repression
- Attenuation
, trp Operon - Repression internal trp level exceeds cellular needs - excess trp (corepressor)
bind to inactive aporepressors, TrpR.
- holorepressor binds to operator DNA sequence upstream of trp operon.
- represses expression of the structural genes by blocking RNA polymerase.
- repression lowers expression about 100-fold.
trp Operon - Attenuation regulatory mechanism in which translation of leader peptide
affects transcription of downstream structural gene.
- attenuator region of trp operon has 2 trp codons and is capable of forming stem-loop
structures.
RNA polymerae a complex enzyme that carries out transcription by making RNA copies
(transcripts) of DNA template strand.
In bacteria, RNA polymerase holoenzyme is composed of - core polymerase, α2, β, β' -
required for elongation.
- sigma factor, σ - required for initiation.
Sigma factors help core enzyme detect ___________, signals beginning of the fene.
promoter
In E. coli, ___________ is the "housekeeping cell". Sigma-70
Regulon set of genes and operon scattered around chromosomes with related functions.
Already Graded A+
Regulatory proteins help a cell sense internal changes and alter its gene expression to
match.
There are 2 forms of regulatory proteins: - Repressors (negative control)
- Activators (positive control)
Repressors bind to regulatory sequences in the DNA and prevent transcription of target
genes.
- some must first bind a small ligand.
Activators bind to regulatory sequences in the DNA and stimulate transcription of target
genes.
- most must first bind a small ligand.
Microbes control gene expressions at several levels - Alterations of DNA sequence
- Control of transcription
- Control of mRNA stability
- Translational control
- Post-translational control
,Paradigm of the Lactose Operon Scientist Jacques Monod and Francois Jacob - genes could
be regulated.
E. coli, enzymes used to metabolize lactose were inducible, glucose were constitutive.
- 1965 nobel prize for his study of phage nysogeny.
LacZYA operna E. coli was 1st gene regulatory system described.
Organization of LacZYA Opepn
If lactose is absent then LacI binds as a tetramer to operator region.
- represses the lac operon by preventing open complex formation by RNA ploymerase.
If lactose is present then B-galactosidase (LacZ) at low levels, cleaves and rearranges lactose
to make inducer allolactose.
- Allolactose binds to LacI, reducing affinity to operator allowing induction of operon.
cAMP and cAMP receptor protein (CRP) are required for the maximum expression of the lac
operon.
Catabolite repression operon enabling catabolism of one nutrient is repressed by the
presence of a more favorable nutrient.
Diauxic growth the biphasic curve if a culture growing in 2 carbon soruces.
,Inducer exclusion glucose transport by phosphotransferase system causing catabolite
repression by inhibiting the LacY permease activity.
- if lactose can't enter the cell, lacZYA operon can't be induced.
Major regulator AraC can repress or activate gene expression.
AraC forms a ___ that can assume one of two conformations depending on whether arabinose
is available? dimer
When arabinose is absent, AraC shape is rigid and elongated.
- represses the expression of the genes that break down arabinose.
When arabinose is present, AraC shape is more compact.
- stimulates binding of RNA pol = transcribes genes.
Genes encoding biosynthetic enzymes are regulated by Inactive aporepressors.
Corepressor bind end product of pathway.
Tryptophan Operon - Repression
- Attenuation
, trp Operon - Repression internal trp level exceeds cellular needs - excess trp (corepressor)
bind to inactive aporepressors, TrpR.
- holorepressor binds to operator DNA sequence upstream of trp operon.
- represses expression of the structural genes by blocking RNA polymerase.
- repression lowers expression about 100-fold.
trp Operon - Attenuation regulatory mechanism in which translation of leader peptide
affects transcription of downstream structural gene.
- attenuator region of trp operon has 2 trp codons and is capable of forming stem-loop
structures.
RNA polymerae a complex enzyme that carries out transcription by making RNA copies
(transcripts) of DNA template strand.
In bacteria, RNA polymerase holoenzyme is composed of - core polymerase, α2, β, β' -
required for elongation.
- sigma factor, σ - required for initiation.
Sigma factors help core enzyme detect ___________, signals beginning of the fene.
promoter
In E. coli, ___________ is the "housekeeping cell". Sigma-70
Regulon set of genes and operon scattered around chromosomes with related functions.
