07c: Control Of Gene Expression Flashcards
Lac operon is present in (bacteria/mammals)
Bacteria
Lac operon is suppressed when:
Enough glucose in cell so it doesn’t need to use other sugars
The lac operon genes are (mono/poly)cistronic, which means:
Polycistronic; the genes for all proteins are right next to each other
List the order in which the genes in lack operon are present.
- Regulatory gene (i)
- Promoter (CRP then O)
- Z then Y then A genes
Which genes in lac operon fall under the general “operon”?
All except regulatory gene (i)
What’s the regulatory gene in lac operon? What’s its function?
The i gene (repressor)
The Z gene in lac operon codes for (X) which has what function?
X = beta galactosidase
Breaks down lactose to glucose and galactose
And converts lactose to allolactose
The Y gene in lac operon codes for (X) which has what function?
X = galactoside permease
Allows lactose to enter cell
The A gene in lac operon codes for (X) which has what function?
X = thiogalactoside transacetylase
Unknown function..
If a significant amount of glucose present in cell, what happens in terms of lac operon?
Repressor expressed and binds operator (RNA pol binding and transcription of lac operon blocked)
(X) is an isomer of lactose. What’s its role in the lac operon?
X = allolactose
Binds repressor, changing conformation and preventing it from binding operator
High glucose levels means (low/high) cAMP levels.
Low
How do cAMP levels come into play for the lac operon?
At very low glucose level, cAMP high and binds CRP. This complex binds promoter region of operon to stimulate high level transcription
Almost all transcription factors bind (X) to the (Y) groove of DNA.
X = alpha helix Y = major
T/F: all transcription factors act as dimers.
False - many do, but not all
T/F: the helix-turn-helix motif is found in both bacteria and euk.
True
CRP, aka (X), has which transcription factor(s)?
X = cAMP binding protein
Helix-turn-helix
Describe interaction of CRP with DNA, in terms of its motif.
Helix-turn-helix motif;
Recognition helix (3) interacts with major groove of DNA and is connected via turn to stabilization helix (2)
When CRP interacts with DNA, it acts as (monomer/dimer/multimer).
Dimer
T/F: very few transcription factors have beta sheet motifs.
True
Motifs like helix-turn-helix have (strong/moderate/weak) interaction with DNA due to which bond(s)?
Strong interaction due to many weak hydrogen bonds
How many molecules of Zn are used in the Zn finger motif?
1 or more
What are the key residues found in Zn finger motif?
Repetitive motif of:
2 cys and 2 hys
OR 4 cys
With 12 AA bunch right in middle (forms finger)
When Zn finger interacts with DNA, it acts as (monomer/dimer/multimer).
Multimer (can’t be dimer)
Describe primary structure of leucine zipper.
35 AA stretch with leucine sticking out every 7 AA (interact to form coiled coil/zipper alpha helix
Bottom has basic region alpha helices that bind DNA
What’s bZIP?
Same motif as leucine zipper, but Arg or His replace leucine
The basic Helix-loop-helix is most similar to which other motif?
Leucine zipper, but there’s a non-helical loop in the zipper helix
List steps that take place to allow estrogen to affect transcription.
- Estrogen enter cell
- Estrogen receptor (ER) released from HSP and bind estrogen
- ER-Estrogen complex enters nucleus and dimerizes with a second complex
- Binding of dimer to ERE (estrogen response element) on DNA
Promoters of housekeeping genes are likely (hypo/hyper)-methylated.
Hypo methylated
How do (methylated/unmethylated) CpG islands in the (X) region of the gene block expression?
Methylated;
X = promoter
- Physically preclude transcription factor recruitment
- MeCP2 protein binds methyl groups and prevents transcription by recruiting chromatin remodeling factors
What’s MeCP2 and what’s its function?
Methyl CpG binding protein 2; binds methylated CpG islands in promoter and recruits chromatin remodeling factors (blocking gene transcription)
T/F: methylated CpG islands in promoter always inhibit gene expression.
False - not always
Igf2, aka (X), is a unique gene in that:
X = insulin-like growth factor 2
Imprinted gene that paternal gene (methylated) is expressed and maternal gene (unmethylated) is not
Why is the (paternal/maternal), (methylated/unmethylated) Igf2 gene expressed?
Paternal; methylated
Prevents binding of a repressor
What are methods that can impact nucleosome structure and thus gene expression?
- Positive super helical tension
- ATP-driven chromatin remodeling
- Covalent modification of Histone tails
T/F: Chromatin remodeling requires ATP.
True
Chromatin remodeling factors interact with (X) terminal of (Y) and use (Z) to (open up/close) nucleosome.
X = C Y = RNA Pol II Z = ATP
Open up
Covalent modification of Histone tails includes which three processes?
- Methylation
- Phosphorylation
- Acetylation
Which residues can be methylated on Histone tails?
Lys or Arg
Which residues can be phosphorylated on Histone tails?
Ser
Which residues can be acetylated on Histone tails?
Lys
Which enzyme is responsible for methylation of Histone tails?
Histone lysine methyltransferase
Or protein Arg methyltransferase
Covalent modification of Histone tails involves which terminus?
N-terminus
Which enzyme is responsible for acetylation of Histone tails?
HAT (Histone acetyl transferase)
Which enzyme is responsible for deacetylation of Histone tails?
HDAC (Histone deacetylase)
Acetylation in general affects the charge on the Histone tail in which way?
Makes it less positively charged
Binding of thyroid hormone to its receptor has what effect on transcription?
Changes HDAC domain to HAT domain, leading to acetylation and activation of transcription
List the one Histone tail modification that represses transcription.
Methylation of lysine
