Seminari 7 - Regulació de l'expressió gènica (2017)

Ejercicio Catalán
Universidad Universidad Rovira y Virgili (URV)
Grado Bioquímica y Biología Molecular - 2º curso
Asignatura Expressió i replicació gèniques
Año del apunte 2017
Páginas 3
Fecha de subida 14/06/2017
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Seminari 7 – Regulació de l’expressió gènica E. R. gèniques Solucions al qüestionari corresponent al curs 2016/17. Les respostes correctes són les marcades en color vermell.
1. You are studying a bacterium that utilizes a sugar called athelose. This sugar can be used as an energy source when necessary. Metabolism of athelose is controlled by the ath operon. The genes of the ath operon code for the enzymes necessary to use athelose as an energy source. You have found the following: - The genes of the ath operon are expressed only when the concentration of athelose in the bacterium is high.
- When glucose is absent, the bacterium needs to metabolize athelose as an energy source as much as possible.
- The same catabolite activator protein (CAP) involved with the lac operon interacts with the ath operon.
Based on this information, how is the ath operon most likely controlled? Match the following elements with a possible regulation mechanism.
inactive activator cAMP active activator active repressor athelose inactive repressor Pàgina 1 2. Fill the gaps: - An operon is a stretch of DNA consisting of an operator, a promoter, and genes for a related set of proteins, usually making up an entire metabolic pathway.
- The genes of an operon is/are arranged sequentially after the promoter.
- A(n) promoter is a specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place.
- A(n) regulatory gene codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes.
- Regulatory proteins bind to the operator to control the expression of the operon.
- A(n) repressor is a protein that inhibits gene transcription. In prokaryotes, this protein binds to the DNA in or near the promoter.
- A(n) inducer is a specific small molecule that binds to a bacterial regulatory protein and changes its shape so that it cannot bind to an operator, thus switching an operon on.
En Pere de sa Somera Seminari 7 – Regulació de l’expressió gènica E. R. gèniques 3.
Match each term with its definition: - It is a product of dsRNA, produced by the cleavage of the Dicer enzyme.
Usually form an exactly complementary duplex with a mRNA causing its destruction: siRNA.
- It is the biological process in which RNA molecules inhibit gene expression by the formation of dsRNA molecules: RNAi - It is derived from ssRNA encoded in the genome. It forms a hairpin and it is processed by Drosha and Dicer enzymes to produce 20-30 nucleotide ssRNA. Usually form a partially complementary duplex with a mRNA causing its silence usually using a non-destructive inhibition of translation: miRNA - It is a small (50-200 nucleotides) ssRNA produced by bacteria. Some of them function as imperfect (meaning that only small regions within the sRNA are complementary to the target) antisense RNAs causing the activation or repression of certain genes: sRNA 4. Explain the possible consequences on its expression, if a gene is duplicated but reversing its orientation with respect to its promoter.
a. This results in transcription of an antisense RNA that is complementary to the mRNA of the original gene, so that they can base-pair and suppress the mRNA’s translation or affect its stability.
b. The antisense RNA generated will not have any function because it lacks a proper start codon.
c. The expression of the gene will increase because now there are two copies of the gene.
d. The promoter of the new copy will not function as a promoter because it has been reversed.
lacI promoter: non select lacI: select Promoter: select Operator: non select lacZ: select lacY: select lacA: non select En Pere de sa Somera Pàgina - 2 5. Which regions of the lac operon do you think could be mutated to produce cells that cannot use lactose as a source of energy? Seminari 7 – Regulació de l’expressió gènica E. R. gèniques Pàgina 3 6. Which regions of the lac operon do you think could be mutated to produce cells that express the lac operon even if lactose was not present in the medium? Think only in the negative inducible mechanism.
- lacI promoter: select - lacI: select - Promoter: non select - Operator: select - lacZ: non select - lacY: non select - lacA: non select En Pere de sa Somera ...

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