BCH 100 Final Exam -Questions With
100% Verified Answers.
What happens when lactose is not available in E. coli? - ✔✔Lac repressor binds the
operator region and blocks the transcription of downstream structural genes including B-
galactosidase
*However, a 'basal transcriptional level' of B-galactosidase (very low) still exists*
What happens when only lactose is available in E. coli? - ✔✔Lactose is converted
to galactose and glucose as well as allolactose by the basal level galacosidase
Lac repressor binds to allolactose and undergoes a structural change that dissociates it from DNA
RNA polymerase then binds to the promoter and transcribes the structural genes of the operon
In E. coli, the concentration of cAMP increases when the concentraction of glucose ________. -
✔✔Decreases!
cAMP binds the CAP and the cAMP-CAP complex binds to DNA near the start site of the lac
operon to stimulate the activity of RNA polymerase
Enhancer sequences - ✔✔Cis-acting
elements Do not belong to core promoter
Operate in conjunction with specific enhancer-binding proteins (transcription factors/activators)
that may interact with the mediator complex
May be excised and inserted elsewhere in the chromosome, and still affect transcription of
nearby genes
Mediator complex - ✔✔Recruits polymerase II and the general transcription factors to
carry out transcription
Chromosomal translocations - ✔✔Can sometimes place a gene under the control of
a powerful enhancer
,Ex: Dysregulation of the gene myc, a transcription factor, resulting from the translocation of an
enhancer to a region near the myc gene plays a role in the development of Burkitt lymphoma
and B-cell leukemia
Combinatorial control - ✔✔A given regulatory factor can have different effects on
transcription depending upon the nature of the other compounds of the regulatory complex
Mediator - ✔✔A large complex of protein subunits
Acts as a bridge between transcription factors bearing activation domains and RNA polymerase
II
Help recruit and stabilize RNA polymerase II near specific genes that are then transcribed
Usually do not directly bind to DNA
Estradiol - ✔✔Controls the genes in the development of female secondary sex characteristics
Exerts its effects by forming a complex with a specific receptor protein called the
estrogen receptor (ER), a transcription factor
Nuclear hormone receptors - ✔✔Bind to specific regions of the DNA called
response elements
2 highly conserved domains:
1. DNA binding domain (zinc-finger domains)
2. Ligand binding domain (causes a structural change that enables the receptor to recruit other
proteins to regulate transcription
Agonists - ✔✔Progesterone
Estradiol
Retinoic Acid
*Activate a nuclear hormone receptor*
Antagonists - ✔✔Tamoxifen
, ICI
RU
*Inhibit nuclear hormone receptors*
What are the 2 ways that nuclear hormone receptors can alter transcription? - ✔✔1.
The complex of receptor and ligand can recruit proteins, called coactivators, that stimulate
transcription
2. In the unbound form, some receptors bind to corepressors and inhibit transcription. Upon
ligand binding, the repression is relieved and transcription occurs, the ligand-bound form of
the receptor may then bind to a coactivator
How can coactivators stimulate transcription? - ✔✔By loosening the interactions
between histones and DNA, making the DNA more accessible to the transcription
machinery
What does HAT do? - ✔✔It weakens the interaction of the histones with the DNA by
acetylation of the histones on specific lysine residues
*Acetylation changes the charge of histone tails and also provides docking sites for other
proteins*
HATs are components of coactivators or are recruited by coactivators
What are the 3 ways histones can be modified? - ✔✔1. Acetylation
2. Methylation
3. Phosphorylation
*All covalent modifications are reversible*
How does HDAC inhibit transcription? - ✔✔It catalyzes the removal of acetyl groups from
histones
*Reverse of acetylation*
Bromodomains - ✔✔Acetyllysine binding domains where components of the transcription
machinery bind to the acetylated histones
100% Verified Answers.
What happens when lactose is not available in E. coli? - ✔✔Lac repressor binds the
operator region and blocks the transcription of downstream structural genes including B-
galactosidase
*However, a 'basal transcriptional level' of B-galactosidase (very low) still exists*
What happens when only lactose is available in E. coli? - ✔✔Lactose is converted
to galactose and glucose as well as allolactose by the basal level galacosidase
Lac repressor binds to allolactose and undergoes a structural change that dissociates it from DNA
RNA polymerase then binds to the promoter and transcribes the structural genes of the operon
In E. coli, the concentration of cAMP increases when the concentraction of glucose ________. -
✔✔Decreases!
cAMP binds the CAP and the cAMP-CAP complex binds to DNA near the start site of the lac
operon to stimulate the activity of RNA polymerase
Enhancer sequences - ✔✔Cis-acting
elements Do not belong to core promoter
Operate in conjunction with specific enhancer-binding proteins (transcription factors/activators)
that may interact with the mediator complex
May be excised and inserted elsewhere in the chromosome, and still affect transcription of
nearby genes
Mediator complex - ✔✔Recruits polymerase II and the general transcription factors to
carry out transcription
Chromosomal translocations - ✔✔Can sometimes place a gene under the control of
a powerful enhancer
,Ex: Dysregulation of the gene myc, a transcription factor, resulting from the translocation of an
enhancer to a region near the myc gene plays a role in the development of Burkitt lymphoma
and B-cell leukemia
Combinatorial control - ✔✔A given regulatory factor can have different effects on
transcription depending upon the nature of the other compounds of the regulatory complex
Mediator - ✔✔A large complex of protein subunits
Acts as a bridge between transcription factors bearing activation domains and RNA polymerase
II
Help recruit and stabilize RNA polymerase II near specific genes that are then transcribed
Usually do not directly bind to DNA
Estradiol - ✔✔Controls the genes in the development of female secondary sex characteristics
Exerts its effects by forming a complex with a specific receptor protein called the
estrogen receptor (ER), a transcription factor
Nuclear hormone receptors - ✔✔Bind to specific regions of the DNA called
response elements
2 highly conserved domains:
1. DNA binding domain (zinc-finger domains)
2. Ligand binding domain (causes a structural change that enables the receptor to recruit other
proteins to regulate transcription
Agonists - ✔✔Progesterone
Estradiol
Retinoic Acid
*Activate a nuclear hormone receptor*
Antagonists - ✔✔Tamoxifen
, ICI
RU
*Inhibit nuclear hormone receptors*
What are the 2 ways that nuclear hormone receptors can alter transcription? - ✔✔1.
The complex of receptor and ligand can recruit proteins, called coactivators, that stimulate
transcription
2. In the unbound form, some receptors bind to corepressors and inhibit transcription. Upon
ligand binding, the repression is relieved and transcription occurs, the ligand-bound form of
the receptor may then bind to a coactivator
How can coactivators stimulate transcription? - ✔✔By loosening the interactions
between histones and DNA, making the DNA more accessible to the transcription
machinery
What does HAT do? - ✔✔It weakens the interaction of the histones with the DNA by
acetylation of the histones on specific lysine residues
*Acetylation changes the charge of histone tails and also provides docking sites for other
proteins*
HATs are components of coactivators or are recruited by coactivators
What are the 3 ways histones can be modified? - ✔✔1. Acetylation
2. Methylation
3. Phosphorylation
*All covalent modifications are reversible*
How does HDAC inhibit transcription? - ✔✔It catalyzes the removal of acetyl groups from
histones
*Reverse of acetylation*
Bromodomains - ✔✔Acetyllysine binding domains where components of the transcription
machinery bind to the acetylated histones
