chap8 Flashcards
In addition to the promoter, the vast majority of genes include _ that are used to switch the gene on or off.
regulatory DNA sequences
Regulatory DNA sequences do not work by themselves. To have any effect, these sequences must be recognized by proteins called _.
transcription regulators
When tryptophan is plentiful, the bacterium doesn’t need to make more, so the production of these enzymes is turned off. This happens because a protein called the tryptophan _ binds to a specific DNA sequence (the operator) near the genes, blocking RNA polymerase from transcribing the _.
repressor
operon
A _ turns off genes by blocking RNA polymerase from starting transcription.
An _ does the opposite—it turns on genes by helping RNA polymerase bind to the DNA and start transcription, especially when the _ is weak.
repressor
activator
promoter
_ means that groups of transcription regulators (activators and repressors) work together to control the expression of a single gene.
Combinatorial control
_ cells, which can become different types of cells, similar to natural stem cells.
induced pluripotent stem (iPS)
induced pluripotent stem (iPS) cells, which can become _, similar to natural _
different types of cells
stem cells.
_:
A master transcription regulator activates its own gene, ensuring its continued production in both daughter cells after division.
This keeps the gene expression pattern stable across generations of cells.
Positive Feedback Loop
Positive Feedback Loop:
A _ activates its own gene, ensuring its continued _ in both daughter cells after division.
This keeps the gene expression pattern stable across generations of cells.
master transcription regulator
production
_:
Certain genes are turned off by adding methyl groups to DNA (on cytosine bases). This prevents gene expression.
Methylation patterns are copied to the daughter DNA during replication, keeping the same genes turned off.
DNA Methylation
DNA Methylation:
Certain genes are turned off by adding _ (on cytosine bases). This prevents gene _.
Methylation patterns are copied to the _ during replication, keeping the same genes turned off.
methyl groups to DNA
expression
daughter DNA
How Cells Maintain Their Identity (Cell Memory):
All of these mechanisms transmit gene expression patterns without changing the DNA sequence itself, a process known as epigenetic inheritance.
Positive Feedback Loop
DNA Methylation
Histone Modification
Organisms like plants and animals also produce many regulatory RNAs that control gene expression. These include:
_
microRNAs (miRNAs),
small interfering RNAs (siRNAs), and
long noncoding RNAs (lncRNAs).
Organisms like plants and animals also produce many _ that control gene expression. These include:
microRNAs (miRNAs),
small interfering RNAs (siRNAs), and
long noncoding RNAs (lncRNAs).
regulatory RNAs
_ are small RNA molecules that regulate gene expression by binding to specific mRNAs and either destroying them or blocking their translation into proteins.
MicroRNAs (miRNAs)
_ play a key role in defending cells against infections, particularly from viruses and harmful genetic elements.
Small interfering RNAs (siRNAs)
_ are RNA molecules longer than 200 nucleotides. There are about 5000 of these in human and mouse genomes, but their roles are mostly unclear.
Long noncoding RNAs (lncRNAs)
One well-understood lncRNA is _, which helps inactivate one X chromosome in female mammals. _ coats the X chromosome and attracts proteins that turn it into _, silencing it.
Xist
Xist
heterochromatin
A typical eukaryotic cell expresses _ of its genes, and the distinct types of cells in multicellular organisms arise because _.
only a fraction
_
different sets of genes are expressed as cells differentiate
In principle, gene expression can be controlled at any of the steps between_. For the majority of genes, however, the _ is the most important point of control.
a gene and its ultimate functional product
initiation of transcription
The transcription of individual genes is switched on and off in cells by _, proteins that bind to short stretches of DNA called _
transcription regulators
regulatory DNA sequences.
In bacteria, transcription regulators usually bind to regulatory DNA sequences close to where _. This binding can either _ transcription of the gene. In eukaryotes, regulatory DNA sequences are often _ by many thousands of nucleotide pairs.
RNA polymerase binds
activate or repress
separated from the promoter
Eukaryotic transcription regulators act in two main ways: (1) they can _, and (2) they can _.
directly affect the assembly process that requires RNA polymerase and the general transcription factors at the promoter
_
locally modify the chromatin structure of promoter regions
In eukaryotes, the expression of a gene is generally controlled by a _.
combination of different transcription regulators
In multicellular plants and animals, the production of different transcription regulators in different cell types ensures the expression of only those _.
genes appropriate to the particular type of cell
A master transcription regulator, if expressed in the appropriate precursor cell, can trigger the _ or _
formation of a specialized cell type
even an entire organ.
One differentiated cell type can be converted to another by _. A differentiated cell can also be reprogrammed into a stem cell by artificially expressing a different, specific set of such regulators.
artificially expressing an appropriate set of transcription regulators
Cells in multicellular organisms have mechanisms that enable their progeny to “_” what type of cell they should be. A prominent mechanism for propagating cell memory relies on transcription regulators that perpetuate transcription of their own gene—a form of _.
remember
positive feedback
There is also evidence for a form of epigenetic inheritance based on_.
transmitted chromatin structures
Cells can regulate gene expression by controlling events that occur _. Many of these post-transcriptional mechanisms rely on RNA molecules that can _
after transcription has begun
_
influence their own stability or translation.
MicroRNAs (miRNAs) control gene expression by base-pairing with specific _ and inhibiting their _.
mRNAs
stability and translation
Cells have a defense mechanism for destroying “foreign” double- stranded RNAs, many of which are produced by viruses. It makes use of small interfering RNAs (siRNAs) that are produced from the foreign RNAs in a process called _.
RNA interference (RNAi)
The Lac operon is controlled
by two transcription regulators, the
_ and _.
Lac repressor
CAP
For the LAC operon to be transcribed, _ must be absent (allowing the _ to bind) and _ must be present
glucose
CAP activator
lactose
An activator protein bound to a distant _ attracts RNA polymerase and
the _.
Looping of the intervening DNA permits contact between the _ and the _ bound to the _. A large protein complex called _ serves as a go-between. The TATA box is a _ for the first general transcription factor that binds to the promoter (see Figure 7–12). Some eukaryotic activator proteins bind to DNA as dimers, but others bind DNA as monomers, as shown.
enhancer
general transcription factors to the promoter
activator
transcription initiation complex
promoter
Mediator
DNA recognition sequence
Whereas the general transcription factors that assemble at the promoter
are the _ genes transcribed by RNA polymerase (see Figure 7–12), the transcription regulators and the locations of their DNA binding sites relative to the promoters are different for _ genes.
same for all
different
These regulators, along with chromatin- modifying proteins, are assembled at the _ by the _. The effects
of multiple transcription regulators combine to determine the final _ of transcription _.
promoter
Mediator
rate
initiation
A single transcription
regulator can coordinate the expression of _.
many different genes
Each _ miRNA transcript is processed to form a _, which is further processed to form a _.
This miRNA assembles with a _ into a complex called _, which then searches for mRNAs that have a nucleotide sequence complementary
to _.
Depending on how extensive the region of complementarity is, the target mRNA is either _ by a _ within the _ (shown on the left) or _ to an area of the cytoplasm where other _ destroy it (shown on the right).
precursor
double-stranded intermediate
mature, single-stranded miRNA
set of proteins
RISC
its bound miRNA
rapidly degraded
nuclease
RISC
transferred
nucleases
