Tissues and Stem Cells Flashcards
(19 cards)
Transplanting the nucleus of an epithelial cell into an egg cell lacking genetic information leads to the formation of
a normally developing embryo.
Nuclear transplantation experiments took different types of adult body cells and placed them in egg cells without any DNA and these cells developed into normal embryos and then into a normal animal. This showed that differentiated cells contain all the genetic information for making any other type of cell.
A housekeeping gene is a gene whose cellular function is
important for processes found in all cell types.
Housekeeping genes encode proteins that play critical roles in basic cellular processes that are found in all cell types. They include the genes that encode the enzymes of glycolysis, gene expression, metabolism, and basic cell structure.
What is the main point of control for regulating gene expression levels?
transcription
While the expression of gene products can be regulated at many different steps as the information moves from DNA to RNA to protein, the main point of control is the level of transcription. Inhibiting the transcription of genes that are not currently needed help keep unnecessary intermediates from being synthesized.
Mutations in what element would abrogate RNA polymerase’s ability to activate gene expression?
promoter
RNA polymerase binds to the promoter, a specialized sequence that orients the enzyme in the direction of transcription. Transcription will then start further downstream of the promoter at the transcription initiation site.
Excess amounts of the amino acid tryptophan result in downregulation of the expression of the enzymes required for its synthesis due to
the repressor binding to the operator.
When excess tryptophan is present, the amino acid will bind to its repressor protein, activating it and enabling it to bind to the operator sequence near the promoter. The binding of the repressor in the proximity of the promoter inhibits the binding of RNA polymerase, and thus the expression of the trp genes is blocked.
Generally, bacterial promoters that are regulated by transcriptional activators bind ___________ to RNA polymerase on their own, but promoters that are regulated with transcriptional repressors bind ___________ to RNA polymerase.
weakly; strongly
Transcriptional activators in bacteria bind to an activator binding site to help the RNA polymerase bind to the promoter. Without this aid, the binding of the polymerase to the promoter is weak and does not activate transcription at high frequency. Genes controlled by transcriptional repressors have promoters that strongly bind polymerase, and this binding can be blocked by the binding of the repressor in the region.
If lactose and glucose are both available to a bacterial cell, which carbon source(s) will be used?
glucose
Bacteria prefer to use glucose whenever it is present. When glucose is present, it will be the only sugar used and expression of the Lac operon genes will be reduced. When only lactose is present, the production of lactose-breakdown enzymes will increase to enable the usage of this alternative carbon source.
Eukaryotic repressor proteins can decrease transcription using which of the following mechanisms?
preventing the assembly of the transcription initiation complex
Eukaryotic repressor proteins can act to reduce transcription by inhibiting assembly of the transcriptional initiation complex, or they can recruit histone-modifying complexes like deacetylases, which remove the activating acetyl groups from nearby histones.
What mechanism describes how eukaryotic activator proteins can regulate chromatin packaging to enhance transcription?
recruiting chromatin-remodeling complexes to eject or slide nearby nucleosomes
Activator proteins in eukaryotes can act to enhance transcription in a variety of ways, but the regulation transcription through chromatin is typically via (1) attraction of histone-modifying complexes that place activating marks (like acetyl groups) on histones, or (2) the recruitment of chromatin-remodeling complexes.
In the cell, enhancer sequence functions are limited in their range of action by the formation of ___________ that hold specific genes and enhancers in close proximity.
loops
Enhancers act at a distance from their target gene, so they are prevented from inappropriately activating the transcription of other nearby genes by the formation of chromosome loops that restrict the engagement of the enhancers to just the genes within the same loop.
Many transcriptional regulators function together to decide the expression level of a particular gene. This describes the concept of
combinatorial control.
Transcriptional regulators work as a committee to determine the level of expression of a gene; this is called combinatorial control. Operons, on the other hand, are a set of genes under the control of a specific transcriptional regulator, a typical control mechanism in prokaryotes.
In eukaryotes, multiple genes can be expressed simultaneously by
the binding of a specific transcriptional regulator to several genes.
In eukaryotes, gene expression is often decided by a committee of transcriptional regulators. A single transcriptional regulator can act as the final voice in the committee to turn on expression by coordinated binding to several genes at once.
A reporter gene is an experimentally engineered regulatory DNA sequence from a gene of interest that has been fused to a gene that encodes a protein that is easily observed experimentally. Why is this approach useful?
It provides information into where and when a gene is expressed.
Reporter genes make it easy to view the location and timing of a gene’s expression because the regulatory sequences drive the expression of a gene product that is easily monitored.
A transcriptional regulator that activates expression of additional transcriptional regulators that induce production of a particular cell type or organ is called a
master regulator.
Master transcription regulators drive the development of a particular cell type and even whole organs by turning on specific genes. The master regulator turns on the expression of other regulators that regulate other genes in a cascade of expression, coordinating the formation of an organized group of cells.
The control of a gene product’s levels or activity after transcription has taken place is called
post-transcriptional control.
The level of expression of a gene can be regulated by changing the level at which the transcript is produced, but the levels can be altered after the point of transcription. There are many processes that alter the levels or activity of a gene product, but collectively these are called post-transcriptional control.
Noncoding RNAs include all of the following
rRNA, tRNA, regulatory RNA
MicroRNAs block the expression of a specific gene product by binding to the ___________ and inhibiting ___________.
mRNA; translation
MicroRNAs form a complex with RISC proteins and once the miRNA forms a complementary base-paired duplex with target RNA, it either targets the mRNA for destruction or reduces the efficiency of translation.
Which protein complex mediates the RNAi silencing process by inhibiting RNA polymerase via histone methylation and heterochromatin formation?
RITS
Small interfering RNAs (siRNAs) can form a complex with different protein complexes to lead to different effects on gene expression. siRNAs that form a complex with RITS (RNA-induced transcriptional silencing) will bind to the RNA coming from RNA polymerase and will lead to the formation of repressive chromatin structures at that gene region.
Long noncoding RNA (lncRNA) can function as a(n)
protein scaffold.
