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What is the name given to proteins that are common to all cells of a multicellular organism?
What is the name given to proteins that are common to all cells of a multicellular organism?
Housekeeping proteins
What are the two main processes involved in the production of proteins?
What are the two main processes involved in the production of proteins?
The promoters of bacterial and eukaryotic genes have a transcription initiation site, where RNA synthesis begins.
The promoters of bacterial and eukaryotic genes have a transcription initiation site, where RNA synthesis begins.
True
What is the role of the general transcription factors in eukaryotes?
What is the role of the general transcription factors in eukaryotes?
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What is the name given to the short DNA sequence that is recognized by the tryptophan repressor protein in the tryptophan operon?
What is the name given to the short DNA sequence that is recognized by the tryptophan repressor protein in the tryptophan operon?
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What is the name of the protein that binds to the operator sequence in the tryptophan operon and regulates the expression of the operon's genes?
What is the name of the protein that binds to the operator sequence in the tryptophan operon and regulates the expression of the operon's genes?
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What is the consequence of the tryptophan repressor protein binding to the operator sequence in the tryptophan operon?
What is the consequence of the tryptophan repressor protein binding to the operator sequence in the tryptophan operon?
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What happens to the tryptophan repressor protein when the concentration of tryptophan is low?
What happens to the tryptophan repressor protein when the concentration of tryptophan is low?
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What is the name of the protein that helps to initiate transcription in the LAC operon?
What is the name of the protein that helps to initiate transcription in the LAC operon?
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What is the name of the protein that binds to the LAC operator and shuts off expression of the LAC operon?
What is the name of the protein that binds to the LAC operator and shuts off expression of the LAC operon?
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What is the enzyme encoded by the LACz gene in the LAC operon?
What is the enzyme encoded by the LACz gene in the LAC operon?
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Under what condition(s) will the LAC operon be transcribed and produce proteins that break down lactose?
Under what condition(s) will the LAC operon be transcribed and produce proteins that break down lactose?
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What is the name given to the DNA sites where eukaryotic gene activators bind?
What is the name given to the DNA sites where eukaryotic gene activators bind?
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What is the name of the large protein complex that helps link distantly bound transcription regulators to proteins at the promoter in eukaryotes?
What is the name of the large protein complex that helps link distantly bound transcription regulators to proteins at the promoter in eukaryotes?
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Eukaryotic repressor proteins promote transcription by assembling the same protein complex as activator proteins.
Eukaryotic repressor proteins promote transcription by assembling the same protein complex as activator proteins.
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What is one of the ways in which eukaryotic transcription regulators can contribute to gene expression?
What is one of the ways in which eukaryotic transcription regulators can contribute to gene expression?
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What are the structures responsible for packaging eukaryotic DNA?
What are the structures responsible for packaging eukaryotic DNA?
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What is one of the ways in which nucleosomes can inhibit the initiation of transcription?
What is one of the ways in which nucleosomes can inhibit the initiation of transcription?
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What type of enzymes can modify histone proteins and affect chromatin structure and gene expression?
What type of enzymes can modify histone proteins and affect chromatin structure and gene expression?
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Histone acetyltransferases promote the attachment of acetyl groups to lysines in histone tails, leading to a more closed chromatin conformation and reduced gene expression.
Histone acetyltransferases promote the attachment of acetyl groups to lysines in histone tails, leading to a more closed chromatin conformation and reduced gene expression.
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What is the name of the transcription regulator that can convert fibroblasts into muscle-like cells?
What is the name of the transcription regulator that can convert fibroblasts into muscle-like cells?
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The ability of transcription regulators to control gene expression plays a crucial role in the development of different cell types during embryonic development.
The ability of transcription regulators to control gene expression plays a crucial role in the development of different cell types during embryonic development.
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What is the name given to the process by which cells divide to produce identical daughter cells that maintain their parental cell type?
What is the name given to the process by which cells divide to produce identical daughter cells that maintain their parental cell type?
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What is the name of a type of feedback loop that occurs when a master transcription regulator activates transcription of its own gene?
What is the name of a type of feedback loop that occurs when a master transcription regulator activates transcription of its own gene?
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Pluripotent embryonic stem cells are capable of generating all the specialized cell types in a human body.
Pluripotent embryonic stem cells are capable of generating all the specialized cell types in a human body.
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What is the name given to cells that are generated from differentiated cells by introducing specific transcription regulators and can develop into pluripotent stem cells?
What is the name given to cells that are generated from differentiated cells by introducing specific transcription regulators and can develop into pluripotent stem cells?
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Gene silencing is a promising strategy for treating Huntington's disease, which aims to reduce the production of the toxic huntingtin protein.
Gene silencing is a promising strategy for treating Huntington's disease, which aims to reduce the production of the toxic huntingtin protein.
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What is one of the challenges in using gene silencing to treat Huntington's disease?
What is one of the challenges in using gene silencing to treat Huntington's disease?
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What is the name given to non-coding RNAs that are longer than 200 nucleotides and may regulate mammalian gene activity?
What is the name given to non-coding RNAs that are longer than 200 nucleotides and may regulate mammalian gene activity?
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What is one of the ways long noncoding RNAs can regulate gene expression?
What is one of the ways long noncoding RNAs can regulate gene expression?
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Study Notes
Gene Regulation and Genetic Switches
- Gene expression can change inside cells depending on the cell type, differentiating housekeeping genes from cell-specific genes.
- Transcriptional switches (regulators) control the process, and diagrams (logo diagrams) visualize their function.
- Repressors and activators are proteins that control gene expression mechanisms, playing distinct roles in initiating or preventing transcription.
- Bacterial operons, like the Tryptophan and Lac operons, use specific mechanisms. E.g., tryptophan's abundance regulates enzyme production inside bacteria.
- Eukaryotes employ a complex transcription complex (Mediator) and chromatin mechanisms for gene expression control.
- Gene expression is regulated at multiple levels, from DNA to RNA to protein, involving different processes like transcription, mRNA processing, mRNA transport, and translation control.
Different Cell Types and the Same DNA
- Different cell types in multicellular organisms have the same DNA.
- Genes are not lost during cell differentiation; instead, the activation and deactivation of genes are controlled by mechanisms.
- Reprogramming experiments demonstrate this: a differentiated cell's genome can develop into a complete organism. For example, injecting a frog skin cell nucleus into an enucleated egg can produce a tadpole.
- This shows that genetic information persists throughout an organism.
Analyzing Gene Expression Differences
- Analyzing differences in gene expression between cell types involves examining the protein content and mRNA content of those cells.
- Housekeeping proteins are common to all cells. Specialized proteins, like hemoglobin in red blood cells, are cell-type specific.
- Profiling mRNA allows researchers to pinpoint which genes are active in certain cell types.
- Eukaryotes express a subset of their genome-coding genes (approx. 5000–15,000 genes).
Changes in Gene Expression due to External Signals
- External signals, such as steroid hormones like cortisol, can affect gene expression.
- Cortisol affects gene expression in different cell types.
- For example, liver cells increase the production of several proteins in response to cortisol, including enzymes related to glucose production. Fat cells reduce the expression of tyrosine aminotransferase.
Gene Expression Control Levels
- Gene expression can be controlled at multiple levels (transcription, RNA processing, RNA transport, mRNA degradation, translation).
- Each stage provides a point for fine-tuning, and the control mechanism is different.
Transcriptional Switches.
- Regulatory DNA sequences that control transcription aren't active alone.
- They act as binding sites that interact with regulatory proteins.
- Regulatory proteins, typically proteins called transcription regulators bind to specific, regulatory DNA sequences.
- In bacteria, regulators are short.
- In eukaryotes, regulators are longer and contain multiple regulatory sequences that bind to multiple regulators.
- Both bacterial and eukaryotic regulators use specific nucleotide sequences.
- These interactions use different mechanisms for transcriptional control.
The Lac Operon
- The Lac operon is a cluster of genes in bacteria used to metabolize lactose; it's activated when glucose is absent, and lactose is present.
- This operon has two main control elements: the repressor and CAP.
- The Lac repressor usually blocks transcription. Lactose triggers a conformational change in the repressor causing it to detach from the operator.
- CAP, with cyclic AMP, facilitates attachment of RNA polymerase to the promoter which initiates transcription.
Eukaryotic Transcription Regulators
- Eukaryotic proteins regulate gene expression over long distances. Enhancers are DNA elements that can enhance the rate of transcription.
- Enhancers function despite the long distance due to looping or looping out of the DNA elements.
- Several models for this mechanism exist.
- Multiple proteins (ex: Mediator complex) help initiate transcription by physically linking enhancers and promoters.
Chromatin Structure and Gene Regulation
- Histone proteins form part of the nucleosome, which compacts DNA. Chromatin modification changes how easy it is to read the genes.
- Gene activators bring in chromatin-modifying proteins to loosen chromatin structure near promoters, increasing accessibility for transcription machinery.
- For example, histone acetyltransferases (HATs) add acetyl groups which loosen the DNA-histone complex. Histone deacetylases (HDACs) remove acetyl groups for silencing.
Specialized Cell Types and Transcription Factors
- Eukaryotic cells use combinations of transcription regulators to produce specialized cell types.
- These combinations lead to different gene sets being turned on or off, leading to cell specialization.
- Some transcription regulators can convert one specialized cell type to another.
- The addition of a transcription regulator such as MyoD can reprogram fibroblast cells into muscle cells.
Maintaining Cell Identity
- Transcription regulators maintain cell identity during cell division in eukaryotes.
- Master transcription regulators can continually produce their own proteins to keep the positive feedback loop active.
- Specialized cell types can be converted into pluripotent stem cells experimentally via transcription regulators (such as Oct4, Sox2, and Klf4).
Conclusion
- Transcription regulators generally regulate gene expression by promoting or hindering the transcription of specific genes.
- The vast majority of genes are controlled in this manner.
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