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Ch. 13 - Regulation of Gene Expression in Eukaryotes
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
Chapter 13, Problem 23

Microbiologists describe the processes of transcription and translation as 'coupled' in bacteria. This term indicates that a bacterial mRNA can be undergoing transcription at the same moment it is also undergoing translation. Is coupling of transcription and translation possible in single-celled eukaryotes such as yeast? Why or why not?

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1
Understand the concept of 'coupling' in bacteria: In bacteria, transcription and translation are coupled, meaning that translation of mRNA can begin while the mRNA is still being synthesized by RNA polymerase.
Consider the cellular structure of bacteria: Bacteria are prokaryotes, which lack a nucleus, allowing ribosomes to access mRNA as it is being transcribed.
Examine the cellular structure of eukaryotes: Eukaryotes, including single-celled organisms like yeast, have a nucleus that separates transcription (in the nucleus) from translation (in the cytoplasm).
Analyze the implications of the nuclear membrane: The presence of a nuclear membrane in eukaryotes means that mRNA must be fully transcribed and processed before it can be transported to the cytoplasm for translation.
Conclude based on cellular differences: Due to the separation of transcription and translation by the nuclear membrane in eukaryotes, coupling of these processes, as seen in bacteria, is not possible in single-celled eukaryotes like yeast.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Transcription

Transcription is the process by which the genetic information encoded in DNA is copied into messenger RNA (mRNA). In prokaryotes, this occurs in the cytoplasm, allowing for immediate access to ribosomes for translation. The enzyme RNA polymerase plays a crucial role in synthesizing the mRNA strand complementary to the DNA template.
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Eukaryotic Transcription

Translation

Translation is the process by which ribosomes synthesize proteins using the mRNA as a template. This occurs in the cytoplasm, where ribosomes read the mRNA sequence in codons and assemble the corresponding amino acids into a polypeptide chain. In bacteria, translation can begin even before transcription is complete, leading to the coupling of these processes.
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Eukaryotic Cell Structure

Eukaryotic cells, such as those in yeast, have compartmentalized structures, including a nucleus where transcription occurs. This spatial separation means that mRNA must be processed and transported out of the nucleus before translation can begin in the cytoplasm. Consequently, the coupling of transcription and translation, as seen in bacteria, is not possible in single-celled eukaryotes due to this additional layer of complexity.
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Related Practice
Textbook Question

Using the components in the accompanying diagram, design regulatory modules (i.e., enhancer/silencer modules) required for 'your' gene to be expressed only in differentiating (early) and differentiated (late) liver cells. Answer the three questions presented below by describing the roles that activators, enhancers, repressors, silencers, pioneer factors, insulators, chromatin remodeling complexes, and chromatin readers, writers, and erasers will play in the regulation of expression of your gene, that is, what factors will bind and be active in each case? Specify which transcription factors need to be pioneer factors. How will its expression be maintained?

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Textbook Question

Using the components in the accompanying diagram, design regulatory modules (i.e., enhancer/silencer modules) required for 'your' gene to be expressed only in differentiating (early) and differentiated (late) liver cells. Answer the three questions presented below by describing the roles that activators, enhancers, repressors, silencers, pioneer factors, insulators, chromatin remodeling complexes, and chromatin readers, writers, and erasers will play in the regulation of expression of your gene, that is, what factors will bind and be active in each case? Specify which transcription factors need to be pioneer factors. How will expression be prevented in other cell types?

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Textbook Question

The majority of this chapter focused on gene regulation at the transcriptional level, but the quantity of functional protein product in a cell can be regulated in many other ways as well. Discuss possible reasons why transcriptional regulation or posttranscriptional regulation may have evolved for different types of genes.

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Textbook Question
The Drosophila even-skipped (eve) gene is expressed in seven stripes in the segmentation pattern of the embryo. A sequence segment of 8 kb 5' to the transcription start site (shown as in the accompanying figure) is required to drive expression of a reporter gene (lacZ) in the same pattern as the endogenous eve gene. Remarkably, expression of most of the seven stripes appears to be specified independently, with stripe 2 expression directed by regulatory sequences in the region 1.7 kb 5' to the transcription start site. To further examine stripe 2 regulatory sequences, you create a series of constructs, each containing different fragments of the 1.7-kb region of the 5' sequence. In the lower part of the figure, the bars at left represent the sequences of DNA included in your reporter gene constructs, and the + and − signs at right indicate whether the corresponding eve-lacZ reporter gene directs stripe 2 expression in Drosophila embryos transformed through P element mediation. How would you interpret the results—that is, where do the regulatory sequences responsible for stripe 2 expression reside?
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