Term
| What step(s) in transcription is/are regulated in prokaryotes? |
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Definition
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Term
| What step(s) in transcription is/are regulated in eukaryotes? |
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Definition
| Chromatin modifier and RNA polymerase |
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Term
| What does a typical bacteria protein-coding gene contain? |
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Definition
| A promoter regulatory region (with binding sites for RNA polymerase) and a transcribed region (which encodes a protein) |
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Term
| Where does RNA polymerase bind to DNA in bacteria? |
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Definition
| RNA polymerase binds DNA sequence-specifically to an ~60 base pair core promoter element within the promoter-regulatory region |
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Term
| Where, in terms of the core promoter element, does mRNA synthesis start? |
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Definition
| A fixed distance downstream of the core promoter element and a variable distance upstream of the ATG translational initiator codon |
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Term
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Definition
| Untranslated regions of mRNA |
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Term
| In bacteria, what three broad processes happen to mRNA simultaneously? |
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Definition
| Synthesis, translation, and degradation |
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Term
| Describe the protein subunits of bacterial RNA polymerase |
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Definition
Bacterial RNA polymerase is
composed of 6 protein subunits
referred to as the α, β, β’, ω and σ
subunits. One RNA polymerase
includes 2 α subunits and 1 each of
the β, β’, ω and σ subunits. |
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Term
| What is the purpose of a sigma (σ) factor? |
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Definition
| To allow for initiation of a specific DNA gene segment, then to fall off once initiation begins |
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Term
| What are the five examples of bacteiral transcriptional regulation? |
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Definition
1. Use of alternative σ factors
2. Induction
3. Catabolite repression
4. Transcriptional repression
5. Transcriptional attenuation |
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Term
| Define transcriptional induction |
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Definition
The ability of bacteria to turn on synthesis of mRNA encoding certain enzymes only when their substrates are present.
Example: Lactose (lac) operon. |
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Term
| Define catabolite repression |
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Definition
Decreased transcription of the genes required for catabolism of lactose and other sugars in the presence of glucose, even if lactose is present
Example: lac operon. |
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Term
| Define transcriptional repression |
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Definition
The ability of bacteria to turn off synthesis of mRNA encoding certain enzymes when their products are present.
Example: Tryptophan (trp) operon. |
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Term
| Define transcriptional attenuation |
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Definition
The ability of bacteria to fine-tune the rate of transcription of certain genes according to the concentration of their products.
Example: trp operon. |
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Term
| How does a σ factor contribute to specific DNA binding? |
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Definition
1. It decreases the affinity of RNA polymerase for general regions of DNA
2: It enables RNA polymerase to
recognize promoter sites. |
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Term
| What is the function of σ70? |
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Definition
Recognizes core promoters containing –35 and –10 elements for housekeeping proteins
(78% of σ factors) |
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Term
| What is the function of σ32? |
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Definition
Transcription by RNA polymerase of heat shock genes
Only expressed in heat or cold |
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Term
| What determines the availability of σ factors? |
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Definition
1. Regulated rates of synthesis and degradation of σ subunits
2. Post-synthetic modifications that switch σ subunits between active and
inactive forms
3. Various anti-proteins, each sequestering a particular σ subunit |
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Term
| What three genes are responsible for bacteria lactose metabolism, and what is the basic function of each? |
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Definition
1. lac Y: transports lactose in cell (via galactoside permease)
2. lac Z: modifies and splits lactose (via β-galactosidase)
3: lac A: detoxifies some lactose products (via thiogalactoside transacetylase) |
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Term
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Definition
| The lac operon is composed of 4 protein-coding genes: the lac I gene, which is transcribed by RNA polymerase from its own promoter-regulatory region, and the lac Z, lac Y, and lac A genes, which are all transcribed together into a single mRNA |
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Term
| What is in the lac I gene? |
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Definition
A repressor protein that is present in
cells in the absence of lactose and turns off transcription by RNA polymerase of the lac Z, lac Y, and lac A genes |
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Term
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Definition
A molecule that promotes certain RNA synthesis.
For example, when bacterial cells are grown in the presence of lactose, the inducer, synthesis by RNA polymerase of the mRNA encoding lac Z, lac Y, and lac A genes is turned on. |
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Term
| How does lactose turn on transcription of the lac Z, lac Y, and lac A genes by RNA polymerase? |
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Definition
| The inducer binds specifically to the lac repressor and converts it into an inactive form that cannot bind to the operator |
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Term
| Describe negative regulation |
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Definition
| A bound repressor inhibits transcription, an inducer removes it before mRNA synthesis can proceed |
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Term
| What steps bring about catabolite repression? |
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Definition
1. Addition of glucose
2. Reduction in cAMP levels
3. Inactivation of a cAMP-dependent
transcriptional activator protein, CRP
4. Lac operon is deactivated |
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Term
| What is the only sugar condition for when lac operon will be expressed? |
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Definition
Low glucose, high lactose
(CRP protein is active AND lac repressor is inactivated) |
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Term
| Give an example of transcriptional repression |
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Definition
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Term
| Under what conditions will a trp repressor bind the operator? |
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Definition
The trp repressor is only capable of binding to the trp operator in the presence of abundant tryptophan
Therefore, it is a corepressor |
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Term
| How does the trp repressor cause attenuation? |
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Definition
| When the corepressor is bound, the ribosome blocks sequence 2, allowing sequence 3 and 4 to attenuate |
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Term
| When tryptophan levels are low, what prevents attenuation? |
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Definition
| The ribosome pauses after sequence 1, allowing a 2:3 structure to form that does NOT inhibit transcription |
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Term
What happens when tryptophan levels are
A) Very high
B) High
C) Low |
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Definition
A) If very high, corepression
B) If high, attenuation (transcription weak)
C) If low, neither repression nor attenuation, transcription strong |
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