Cell Biology Ch. 8 Word Scramble

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Question	Answer
Gene expression	process by which a gene makes a product that is useful to the cell or organism by directing the synthesis of a protein or an RNA molecule with a characteristic activity
differentiation	process by which a cell undergoes a progressive, coordinated change to a more specialized cell type
differentiation is brought about by long-term changes in what?	gene expression
different cell types of a multicellular organism contain the same what?	DNA
if different cell types of a multicellular organism contain the same DNA, how is it that they differ?	they differ not because they contain different genes, but because they express them differently
a cell can change the expression of its genes in response to _____________ ____________	external signals
Give an example of a cell changing the expression of its genes in response to external signals	when exposed to cortisol, a liver cell dramatically increases the production of several proteins
Gene expression can be ______________ at various steps from DNA to RNA to protein	regulated
gene expression can be controlled at any of the steps between a gene and its ultimate functional product. For the majority of genes, however, what is the most important point of control?	the initiation of transcription
the promoter region of a gene binds to the enzyme, ____ ____________, and correctly orients the enzyme to begin its task of making an RNA copy of the gene	RNA polymerase
the promoters of both bacterial and eukaryotic genes include a ________________ ______________ _______, where RNA synthesis begins	transcription initiation site
nearly all genes have ___________________ DNA sequences that are used to switch the gene on or off	regulatory DNA sequences
regulatory DNA sequence	DNA sequence to which a transcription regulator binds to determine when, where, and in what quantities a gene is to be transcribed into RNA
transcription of individual genes is switched on and off in cells by transcription regulator _____________, which bind to short stretches of regulatory DNA sequences	proteins
transcription regulators	protein that binds specifically to a regulatory DNA sequence and is involved in controlling whether a gene is switched on or off
many transcription regulators bind to the DNA helix as dimers. What does this dimerization do?	doubles the area of contact with the DNA, thereby greatly increasing the strength and specificity of the protein-DNA interaction
transcriptional repressor	binds to a regulatory sequence on the DNA and PREVENTS TRANSCRIPTION (switches gene off)
transcriptional activator	binds to regulatory DNA sequence to PERMIT TRANSCRIPTION (switch gene on)
activator proteins often have to do what to be able to bind DNA?	have to interact with a second molecule (like protein CAP having to bind cAMP before binding DNA)
In many cases, the activity of a single promoter is controlled by two different transcription regulators. What is a good example?	the activator and repressor control of the Lac operon in E. coli
What does the Lac operon encode?	proteins required to import and digest disaccharide lactose
What are the two transcription regulators that control the lac operon?	the Lac repressor and the CAP
Control of the Lac operon: what happens when lactose is absent?	Lac repressor binds to the Lac operator and shuts off expression of the operon
Control of the Lac operon: What results from the addition of lactose?	allolactose increases, which binds to Lac repressor, causing conformational changes that unbinds the protein from DNA
Control of the Lac operon: What happens when glucose is absent?	cAMP is produced, which activates CAP to bind to DNA. LacZ encodes enzyme beta-galactosidase which breaks down lactose to galactos and glucose
In bacteria, transcription regulators usually bind to regulatory DNA sequences close to where RNA polymerase binds. This binding can either activate or repress transcription of the gene. How do eukaryotes differ?	in eukaryotes, regulatory DNA sequences are often separated from the promoter by many thousands of nucleotide pairs
in eukaryotes, how can gene ACTIVATION occur at a distance?	an activator protein bound to a distant enhancer attract RNA polymerase and general transcription factors to the promoter.
in eukaryotes, activation can occur at a distance when an activator protein bound to a distant enhancer attracts RNA polymerase and general transcription factors to the promoter. What does the looping of the intervening DNA permit?	contact between the activator and the transcription initiation complex bound to the promoter
Often times, additional proteins serve to link the distantly bound transcription regulators to these proteins at the promoter. What is the most important of these regulators?	a large complex known as mediator
eukaryotic repressor proteins do the opposite:	they decrease transcription by preventing the assembly of the same protein complex
Eukaryotic transcription regulators have an additional mechanism of action:	they can help initiate transcription by recruiting chromatin-modifying proteins
in eukaryotic cells, activator and repressor proteins exploit chromatin structure to do what?	help turn genes on and off
chromatin structure can be altered by ___________-____________ complexes and by enzymes that covalently modify histone proteins that form the core of the nucleosome	chromatin-remodeling complexes
many gene activators recruit chromatin-modifying proteins to promoters. What can this modification do?	alters chromatin structure, allowing greater accessibility to the underlying DNA to help initiate gene transcription
gene repressor proteins can modify chromatin in ways that do what?	reduce the efficiency of transcription initiation
eukaryotic genes are controlled by combinations of ________________ ____________________	transcription regulators
combinatorial control	describes the way in which groups of transcription regulators work together to regulate the expression of a single gene
the expression of different genes can be coordinated by a single ____________	protein
In addition to day-to-day regulation of cell function, what can combinatorial control generate?	different cell types
How can combinatorial control generate different cell types? for example, the development of muscle cells	A set of regulators activate the transcription of genes that code for muscle-specific proteins by binding to specific DNA sequences present in their regulatory regions
Some transcription regulators can even convert one specialized cell type to another. how?	by artificially expressing an appropriate set of transcription regulators
transcription regulators can also coax various differentiated cells to de-differentiate into pluripotent stem cells. What are pluripotent stem cells?	cell capable of giving rise to any of the specialized cell types in the body
induced pluripotent stem cells (iPS cells)	somatic cells that have been reprogrammed to resemble and behave like a pluripotent embryonic stem cell through the artificial introduction of a set of genes encoding particular transcription regulators
What can human iPS cells be used for?	they can be directed to generate a population of differentiated cells for use in the study or treatment of disease
the formation of an entire organ can be trigger by a single transcription factor. how? (generally)	the action of a single transcription factor can produce a cascade of regulators that work in combination, leading to the formation of an organized group of many different types of cells
Once a cell has become differentiated into a particular cell type, it will generally remain differentiated, and all its progeny will remain that same cell type. For a proliferating cell to maintain its identity it must have cell memory, which is what?	the ability of differentiated cells and their descendants to maintain their identity
cells in multicellular organisms have mechanisms that enable their progeny to "remember" what type of cell they should be. A prominent mechanism for propagating cell memory relies on what?	transcription regulators that perpetuate transcription of their own gene- a form of positive feedback
positive feedback loop	form of regulation in which the end product of a reaction or pathway stimulated continued activity (controls gene expression)
DNA methylation is used to reinforce cell identity.. how?	the pattern of DNA methylation can be transmitted from one cell generation to the next, producing a form of epigenetic inheritance that helps a cell remember the state of gene expression in its parent cell
epigenetic inheritance	the transmission of a heritable pattern of gene expression from one cell to its progeny that does not involve altering the nucleotide sequence of the DNA
cells can regulate gene expression by controlling events that occur after transcription has begun. Many of these post-transcriptional mechanisms rely on RNA molecules that can do what?	influence their own stability or translation
each mRNA controls its own __________________ and _______________	degradation and translation
Whether bacterial or eukaryotic, an mRNA's lifetime is dictated by specific ______________ _____________ within the untranslated regions that lie upstream and downstream of the protein-coding sequence.	nucleotide sequences
These nucleotide sequences often harbor binding sites for proteins that are involved in what?	RNA degradation
each mRNA possesses a sequence that help control how often or how efficiently it will be translated into protein. These sequences control ______________ _______________	translation initiation
how do bacterial mRNAs control translation initiation?	by blocking or exposing the ribosome-binding sequence, the bacterium can inhibit or promote the translation of mRNA
how do eukaryotic mRNAs control translation initiation?	they possesses a 5' cap that guide the ribosome to the start codon. repressors can inhibit translation initiation by binding to 5' untranslated region on mRNA, preventing the ribosome from finding the start codon
______________ RNAs control the expression of thousands of genes	regulatory RNAs
Regulatory RNA	RNA molecule that plays a role in controlling gene expression (noncoding RNA)
What are the three major types of regulatory RNAs?	microRNAs, small interfering RNAs, and long noncoding RNAs
microRNA (miRNA) are tiny RNA molecules that control gene expression how?	by base-pairing with specific mRNAs and inhibiting their stability and translation
two features of miRNAs make them useful regulators of gene expression. (1) a single miRNA is capable of what?	inhibiting the transcription of a whole set of mRNAs (as long as all the mRNAs carry a common sequence)
two features of miRNAs make them useful regulators of gene expression. (2) a gene that encodes an miRNA occupies relatively little _______ in the genome compared with one that encodes a transcription regulator.	space
cells have a defense mechanism for destroying "foreign" double-stranded RNAs, many of which are produced by viruses. It makes use of what?	small interfering RNAs (siRNA)
What are siRNAs produced from?	the foreign RNAs in a process called RNA interference (RNAi)
RNA interference (RNAi)	cellular mechanism activated by double-stranded RNA molecules that results in the destruction of RNAs containing a similiar mucleotide sequence
What is RNA interference widely exploited for?	an experimental tool for preventing the expression of selected genes (gene silencing)
RNAi (1) the double-stranded, foreign RNAs are what?	cut into short fragments by a protein dicer to make siRNAs
RNAi (2) the siRNAs are then taken up by RISCs, which discard one strand of foreign siRNA duplex and use the other strand to what?	to locate and destroy foreign RNAs with a complementary sequence
the recent discovery of thousands of long noncoding RNAs in mammals has what?	opened a new window to the roles of RNAs in gene regulation

Created by: cmccartney2