MBIO 3401 EXAM 2 QUESTIONS AND ANSWERS 2026
Regulatory proteins - Answers - help a cell sense internal changes and alter its gene
expression to match.
There are 2 forms of regulatory proteins: - Answers - - Repressors (negative control)
- Activators (positive control)
Repressors - Answers - bind to regulatory sequences in the DNA and prevent
transcription of target genes.
- some must first bind a small ligand.
Activators - Answers - 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 - Answers - - Alterations of DNA
sequence
- Control of transcription
- Control of mRNA stability
- Translational control
- Post-translational control
Paradigm of the Lactose Operon - Answers - 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 - Answers - E. coli was 1st gene regulatory system described.
Organization of LacZYA Opepn - Answers -
If lactose is absent then - Answers - 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 - Answers - 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) - Answers - are required for the maximum
expression of the lac operon.
Catabolite repression - Answers - operon enabling catabolism of one nutrient is
repressed by the presence of a more favorable nutrient.
Diauxic growth - Answers - the biphasic curve if a culture growing in 2 carbon soruces.
Inducer exclusion - Answers - 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 - Answers - can repress or activate gene expression.
AraC forms a ___ that can assume one of two conformations depending on whether
arabinose is available? - Answers - dimer
When arabinose is absent, - Answers - AraC shape is rigid and elongated.
- represses the expression of the genes that break down arabinose.
When arabinose is present, - Answers - AraC shape is more compact.
- stimulates binding of RNA pol = transcribes genes.
Genes encoding biosynthetic enzymes are regulated by - Answers - Inactive
aporepressors.
Corepressor - Answers - bind end product of pathway.
Tryptophan Operon - Answers - - Repression
- Attenuation
trp Operon - Repression - Answers - 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 - Answers - 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 - Answers - a complex enzyme that carries out transcription by making
RNA copies (transcripts) of DNA template strand.
In bacteria, RNA polymerase holoenzyme is composed of - Answers - - 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. -
Answers - promoter
In E. coli, ___________ is the "housekeeping cell". - Answers - Sigma-70
Regulon - Answers - set of genes and operon scattered around chromosomes with
related functions.
- coordinately controlled by single repressor or activator protein.
Heat shock response of E. coli - Answers - secondary structure at 5' end of mRNA
obscure access to ribosome-binding sites.
- heat melts secondary structure and increases translation of the alternate sigma factor.
- heat draws chaperones away from alternate sigma factor - accumulation.
Sporulation relies on hierarchical activation of series of different sigma factors. -
Answers - temporary asymmetrical distribution of chromosome between forespore and
mother cell results in differential activation of compartment-specific alternative sigma
factors.
Sigma F - Answers - forespore-specific sigma factor regulated by anti-sigma and anti-
anti-sigma factors.
Regulatory Rnas - Answers - - Small RNA (sRNA) molecules, which are encoded by
intergenic regions (between genes).
- cis-antisense RNA (asRNA) molecules, which are transcribed from DNA strand
opposite the mRNA-encoding template strand.
Regulatory proteins - Answers - help a cell sense internal changes and alter its gene
expression to match.
There are 2 forms of regulatory proteins: - Answers - - Repressors (negative control)
- Activators (positive control)
Repressors - Answers - bind to regulatory sequences in the DNA and prevent
transcription of target genes.
- some must first bind a small ligand.
Activators - Answers - 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 - Answers - - Alterations of DNA
sequence
- Control of transcription
- Control of mRNA stability
- Translational control
- Post-translational control
Paradigm of the Lactose Operon - Answers - 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 - Answers - E. coli was 1st gene regulatory system described.
Organization of LacZYA Opepn - Answers -
If lactose is absent then - Answers - 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 - Answers - 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) - Answers - are required for the maximum
expression of the lac operon.
Catabolite repression - Answers - operon enabling catabolism of one nutrient is
repressed by the presence of a more favorable nutrient.
Diauxic growth - Answers - the biphasic curve if a culture growing in 2 carbon soruces.
Inducer exclusion - Answers - 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 - Answers - can repress or activate gene expression.
AraC forms a ___ that can assume one of two conformations depending on whether
arabinose is available? - Answers - dimer
When arabinose is absent, - Answers - AraC shape is rigid and elongated.
- represses the expression of the genes that break down arabinose.
When arabinose is present, - Answers - AraC shape is more compact.
- stimulates binding of RNA pol = transcribes genes.
Genes encoding biosynthetic enzymes are regulated by - Answers - Inactive
aporepressors.
Corepressor - Answers - bind end product of pathway.
Tryptophan Operon - Answers - - Repression
- Attenuation
trp Operon - Repression - Answers - 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 - Answers - 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 - Answers - a complex enzyme that carries out transcription by making
RNA copies (transcripts) of DNA template strand.
In bacteria, RNA polymerase holoenzyme is composed of - Answers - - 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. -
Answers - promoter
In E. coli, ___________ is the "housekeeping cell". - Answers - Sigma-70
Regulon - Answers - set of genes and operon scattered around chromosomes with
related functions.
- coordinately controlled by single repressor or activator protein.
Heat shock response of E. coli - Answers - secondary structure at 5' end of mRNA
obscure access to ribosome-binding sites.
- heat melts secondary structure and increases translation of the alternate sigma factor.
- heat draws chaperones away from alternate sigma factor - accumulation.
Sporulation relies on hierarchical activation of series of different sigma factors. -
Answers - temporary asymmetrical distribution of chromosome between forespore and
mother cell results in differential activation of compartment-specific alternative sigma
factors.
Sigma F - Answers - forespore-specific sigma factor regulated by anti-sigma and anti-
anti-sigma factors.
Regulatory Rnas - Answers - - Small RNA (sRNA) molecules, which are encoded by
intergenic regions (between genes).
- cis-antisense RNA (asRNA) molecules, which are transcribed from DNA strand
opposite the mRNA-encoding template strand.
