chap8

Question 1

In addition to the promoter, the vast majority of genes include _ that are used to switch the gene on or off.

Answer 1

regulatory DNA sequences

Question 2

Regulatory DNA sequences do not work by themselves. To have any effect, these sequences must be recognized by proteins called _.

Answer 2

transcription regulators

Question 3

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 _.

Answer 3

repressor
operon

Question 4

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.

Answer 4

repressor
activator
promoter

Question 5

_ means that groups of transcription regulators (activators and repressors) work together to control the expression of a single gene.

Answer 5

Combinatorial control

Question 6

_ cells, which can become different types of cells, similar to natural stem cells.

Answer 6

induced pluripotent stem (iPS)

Question 7

induced pluripotent stem (iPS) cells, which can become _, similar to natural _

Answer 7

different types of cells
stem cells.

Question 8

_:

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.

Answer 8

Positive Feedback Loop

Question 9

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.

Answer 9

master transcription regulator
production

Question 10

_:

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.

Answer 10

DNA Methylation

Question 11

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.

Answer 11

methyl groups to DNA
expression
daughter DNA

Question 12

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.

Answer 12

Positive Feedback Loop

DNA Methylation

Histone Modification

Question 13

Organisms like plants and animals also produce many regulatory RNAs that control gene expression. These include:

_

Answer 13

microRNAs (miRNAs),
small interfering RNAs (siRNAs), and
long noncoding RNAs (lncRNAs).

Question 14

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).

Answer 14

regulatory RNAs

Question 15

_ are small RNA molecules that regulate gene expression by binding to specific mRNAs and either destroying them or blocking their translation into proteins.

Answer 15

MicroRNAs (miRNAs)

Question 16

_ play a key role in defending cells against infections, particularly from viruses and harmful genetic elements.

Answer 16

Small interfering RNAs (siRNAs)

Question 17

_ are RNA molecules longer than 200 nucleotides. There are about 5000 of these in human and mouse genomes, but their roles are mostly unclear.

Answer 17

Long noncoding RNAs (lncRNAs)

Question 18

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.

Answer 18

Xist
Xist
heterochromatin

Question 19

A typical eukaryotic cell expresses _ of its genes, and the distinct types of cells in multicellular organisms arise because _.

Answer 19

only a fraction
_
different sets of genes are expressed as cells differentiate

Question 20

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.

Answer 20

a gene and its ultimate functional product
initiation of transcription

Question 21

The transcription of individual genes is switched on and off in cells by _, proteins that bind to short stretches of DNA called _

Answer 21

transcription regulators
regulatory DNA sequences.

Question 22

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.

Answer 22

RNA polymerase binds
activate or repress
separated from the promoter

Question 23

Eukaryotic transcription regulators act in two main ways: (1) they can _, and (2) they can _.

Answer 23

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

Question 24

In eukaryotes, the expression of a gene is generally controlled by a _.

Answer 24

combination of different transcription regulators

Question 25

In multicellular plants and animals, the production of different transcription regulators in different cell types ensures the expression of only those _.

Answer 25

genes appropriate to the particular type of cell

Question 26

A master transcription regulator, if expressed in the appropriate precursor cell, can trigger the _ or _

Answer 26

formation of a specialized cell type
even an entire organ.

Question 27

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.

Answer 27

artificially expressing an appropriate set of transcription regulators

Question 28

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 _.

Answer 28

remember
positive feedback

Question 29

There is also evidence for a form of epigenetic inheritance based on_.

Answer 29

transmitted chromatin structures

Question 30

Cells can regulate gene expression by controlling events that occur _. Many of these post-transcriptional mechanisms rely on RNA molecules that can _

Answer 30

after transcription has begun
_
influence their own stability or translation.

Question 31

MicroRNAs (miRNAs) control gene expression by base-pairing with specific _ and inhibiting their _.

Answer 31

mRNAs
stability and translation

Question 32

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 _.

Answer 32

RNA interference (RNAi)

Question 33

The Lac operon is controlled
by two transcription regulators, the
_ and _.

Answer 33

Lac repressor
CAP

Question 34

For the LAC operon to be transcribed, _ must be absent (allowing the _ to bind) and _ must be present

Answer 34

glucose
CAP activator
lactose

Question 35

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.

Answer 35

enhancer
general transcription factors to the promoter
activator
transcription initiation complex
promoter
Mediator
DNA recognition sequence

Question 36

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.

Answer 36

same for all
different

Question 37

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 _.

Answer 37

promoter
Mediator
rate
initiation

Question 38

A single transcription
regulator can coordinate the expression of _.

Answer 38

many different genes

Question 39

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).

Answer 39

precursor
double-stranded intermediate
mature, single-stranded miRNA
set of proteins
RISC
its bound miRNA
rapidly degraded
nuclease
RISC
transferred
nucleases