BIOL. 1406 Chapter 18 Regulation of Gene Expression

Question 1

How can two cells with the same set of genes function differently?

Answer 1

To be expressed, each gene requires a particular set of transcription factors.

Question 2

Differential Gene Expression

Answer 2

The expression of different genes, allowing cells to carry their specific function.

Question 3

Regulation of enzyme production by a cell

Answer 3

feedback inhibition and gene regulation

Question 4

Feedback Inhibition

Answer 4

The end product of metabolic pathway shuts down further synthesis of the product by inhibiting enzyme activity.

Question 5

Regulating Gene Expression

Answer 5

Adjusting production level of certain enzymes by a cell;
the control of enzyme production is thus at the level of transcription

Question 6

Operon

Answer 6

the entire stretch of DNA that includes the operator, the promoter, and the genes that they control

Question 7

Operator

Answer 7

A segment of DNA that acts as an on-off switch that can coordinate a cluster of functionally related genes

Question 8

Repressor

Answer 8

A protein that switches off the operon;
it prevents gene transcription by binding to the operator and blocking RNA polymerase;
can be in an active or inactive form, depending on the presence of other molecules.

Question 9

Regulatory Gene

Answer 9

A gene that is located some distance from the operon itself and produces the repressor protein

Question 10

Corepressor

Answer 10

A molecule that cooperates with a repressor protein to switch an operon off.

Question 11

Activator

Answer 11

A stimulatory protein that are used in positive control

Question 12

Eukaryotic Gene Expression Is Regulated At Many Stages

Answer 12

all organisms must regulate which genes are expressed at any given time;
genes are turned off and on in response to the internal and external environments;
in multicellular organisms, regulation of gene expression is essential for cell specialization

Question 13

Differential Gene Expression

Answer 13

Expression of different genes by cells with the same genome;
most of the time is equated with gene transcription

Question 14

Chromatin

Answer 14

makeup of chromosomes in organisms other than bacteria; it includes DNA, RNA, and protein.

Question 15

Expression Regulation by Chromatin Structure

Answer 15

The structural organization of chromatin helps regulate gene expression in several ways;
genes within highly packed heterochromatin are usually not expressed;
in euchromatin, gene transcription is affected by the location of nucleosomes;
chromatin structure and gene expression can be influenced by chemical modifications of the histone proteins on the nucleosome

Question 16

Euchromatin

Answer 16

A lightly packed form of chromatin that is enriched in genes, and is often under active transcription

Question 17

Nucleosome

Answer 17

a structural unit of a eukaryotic chromosome, consisting of a length of DNA coiled around a core of histones

Question 18

Histone Acetylation

Answer 18

Acetyl groups are attached to an amino acid in a histone tail.
This appears to open up chromatin structure, thus promoting the initiation of transcription.

Question 19

DNA Methylation

Answer 19

Addition of methyl groups to certain DNA bases;
associated with reduced transcription;
can cause long-term inactivation of genes in cellular differentiation;
Can change the activity of a DNA segment without changing the sequence

Question 20

Epigenetic Inheritance

Answer 20

inheritance of traits transmitted by mechanisms not directly involving the nucleoside sequence

Question 21

Control Elements

Answer 21

Segments of noncoding DNA that serve as binding sites for transcription factors that help regulate transcription

Question 22

Specific Transcription Factors

Answer 22

A different set of factors that high levels of transcription depend on for genes that are not expressed all the time

Question 23

Proximal Control Elements

Answer 23

Control elements that are located close to the promoter

Question 24

Enhancers

Answer 24

distal control elements, groupings that may be far away from the gene or even located in an intron;
each enhancer is associated with only one gene and no other

Question 25

Activator

Answer 25

a protein that binds to an enhancer and stimulates the transcription of a gene; has two domains: one binds to DNA and the other one that activates the transcription; bound activators facilitate a sequence of protein-protein interactions that result in enhanced transcription of a given gene

Question 26

Mediator proteins

Answer 26

A group of proteins that that interact with general transcription factors at the promoter; they come into contact with bound activators; this helps assembly and position the preinitiation complex.

Question 27

Transcription Factors in Gene Expression

Answer 27

Some act as repressors, inhibiting expression of a particular gene in several ways; some repressors bind directly to control elements and block activator binding; others interfere with activators, so they cannot bind the DNA; some activators and repressors may indirectly affect transcription by altering chromatin structure.

Question 28

Combinatorial Control of Gene Activation

Answer 28

A particular combination of control elements can activate transcription only when the appropriate activator proteins are present; with only a dozen or so control elements, a large number of potential combinations is possible

Question 29

Coordinately Controlled Genes in Eukaryotes

Answer 29

Co-expressed eukaryotic genes are not organized in operons (with a few exceptions); these genes can be scattered over different chromosomes, but each has the same combination of control elements; activator proteins in the nucleus recognize specific control elements and promote simultaneous transcription of genes

Question 30

Mechanisms of Post-Transcriptional Regulation

Answer 30

Transcription alone does not constitute gene expression; regulatory mechanisms can operate at various stages after transcription; such mechanisms allow a cell to rapidly fine-tune gene expression in response to environmental changes

Question 31

Alternative Splicing

Answer 31

different RNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which introns; it significantly expands the repertoire of a eukaryotic genome; proposed explanation for the surprisingly low number of genes in the human genome; more than 90% of the human protein-coding genes undergo alternative splicing

Question 32

Initiation of translation

Answer 32

can be blocked by regulatory proteins that bind to sequences or structures of the mRNA; may be regulated simultaneously

Question 33

Protein Processing and Degradation

Answer 33

after translation, polypeptides undergo processing and chemical modifications; the length time each protein functions is regulated by selective degradation; cells mark proteins for degradation by attaching ubiquitin to them; the mark is recognized by proteasomes, which recognize and degrade proteins

Question 34

MicroRNAs (miRNAs)

Answer 34

small, single-stranded RNA molecules that can bind complementary sequences in mRNA; these molecules along with associated proteins cause degradation of the target mRNA or sometimes block its translation; at least one half of genes may be regulated by miRNAs

Question 35

Small Interfering RNAs (siRNAs)

Answer 35

similar to miRNAs in size and function; used in laboratory as means of disabling genes to investigate their function; used by bacteria as a defensive system, called CRISPR-Cas9 system, against viruses that infect them

Question 36

RNA Interference

Answer 36

blocking of gene expression by siRNAs

Question 37

Chromatin Remodeling and Effects on Transcription by ncRNAs

Answer 37

some ncRNA can cause remodeling of chromatin structure; in some yeasts, siRNAs reform heterochromatin at centromeres after chromosome replication; in most mammalian cells, siRNAs have not been found

Question 38

piwi-interacting RNAs (pRNAs)

Answer 38

small ncRNAs induce formation of heterochromatin, blocking the expression of parasitic DNA elements in the genome known as transposons; help reestablish appropriate methylation patterns during gamete formation in many animal species

Question 39

Long noncoding RNAs (lncRNAs)

Answer 39

range from 200 to hundreds of thousands nucleotides in length; one type is responsible for inactivation of the X chromosome; can act as a scaffold, bringing DNA, proteins, and other RNAs together into complexes, promoting gene expression

Question 40

A program of differential gene expression

Answer 40

orchestrates the developmental programs of animals; during embryonic development, a fertilized egg gives rise to many different types of cell; cells are organized successfully into tissues, organs, organ systems, and organisms

Question 41

Genetic Program for Embryonic Development

Answer 41

transformation from zygote to an adult results from cell division, cell differentiation, and morphogenesis

Question 42

Cell differentiation

Answer 42

the process by which cells become specialized in structure and function; a cell attains its determined fate

Question 43

Morphogenesis

Answer 43

the physical processes that give an organism its shape

Question 44

Cytoplasmic Determinants

Answer 44

maternal substances in the egg that influence early development; as cells divides by mitosis, cells contain different cytoplasmic determinants, which lead to different gene expression

Question 45

Induction

Answer 45

a process, in which signal molecules from embryonic cells cause changes in the nearby target cells

Question 46

Determination

Answer 46

irreversibly commits a cells to become of particular type

Question 47

MyoD

Answer 47

a master regulatory gene that encodes a transcription factor that commits the cell to becoming skeletal muscle; some encode information for production of additional muscle-specific transcription factors

Question 48

Pattern Formation

Answer 48

development of spatial organization of tissues and organs; begins with the establishment of major axes

Question 49

Positional Information

Answer 49

molecular cues that control pattern formation, tells a cell its location relative to the body axes and neighboring cells

Question 50

Homeotic genes

Answer 50

genes that control pattern formation in the late embryo, larva, and adult stages in drosophila melanogaster

Question 51

Embryonic Lethals

Answer 51

mutations that cause death during embryogenesis

Question 52

Maternal Effect Genes

Answer 52

encode cytoplasmic determinants that initially establish the axes of the body of the drosophila

Question 53

Bicoid

Answer 53

one maternal effect gene that affects the front half of the body

Question 54

Morphogens

Answer 54

gradients of substances that establish an embryo's axes and other features of its form

Question 55

Oncogenes

Answer 55

Genes, resulted from mutations in proto-oncogenes; (proto-oncogenes code for proteins in regular cell growth and division); arises from a change that leads to an increase either in the amount of protein product or in the activity of protein molecule

Question 56

genetic changes that convert proto-oncogenes into oncogenes

Answer 56

1) epigenetic changes 2) translocation 3) gene amplification 4) point mutations

Question 57

Tumor-suppressor genes

Answer 57

normally inhibit cell division; mutations to these genes decrease protein products and contribute to cancer onset; normally repair damaged DNA, control cell adhesion, and act in cell-signaling pathways that inhibit the cell cycle

Question 58

Interference with Normal Cell-Signaling Pathways

Answer 58

Mutations in the ras proto-oncogene and p53 tumor-suppressor gene are common in human cancers

Question 59

Ras gene

Answer 59

mutations in it can produce hyperactive ras protein and increased cell division

Question 60

Ras protein

Answer 60

a G protein that relays a signal from a growth factor receptor on the cell surface

Question 61

p53 gene

Answer 61

mutations in it prevent suppression of the cell cycle; suppression of the cell cycle can be important in the case of damage to a cell's DNA; its normal version prevents a cell from passing on mutations; it activates expression of miRNAs that inhibit the cell cycle, and can turn on genes directly involved in DNA repair; it activates cell "suicide" genes; elephants have 20 copies of p53 gene compared to just 1 copy in humans and other mammals (elephants have very low cancer rates 3%)

Question 62

The Multi-Step of Cancer Development

Answer 62

multiple mutation are generally needed for full-fledge cancer; incidents increase with age; a DNA level, a cancerous cell is usually characterized by at least one oncogene and the mutation of several tumor-suppressor genes

Question 63

Inherited Predisposition and Environmental Factors Contributing to Cancer

Answer 63

Individuals can inherit oncogenes or mutant alleles of tumor-suppressor genes

Question 64

Adenomatous Polyposis Coli

Answer 64

tumor suppressor gene; inherited mutations of it are common in individuals with colorectal cancer

Question 65

Mutations in the BRCA1 and BRCA2 genes

Answer 65

mutations found in at least half of inherited breast cancers, and tests using DNA sequencing can detect these mutations

Question 66

The role of viruses in cancer

Answer 66

a number of tumor viruses can also cause cancer in humans and animals; viruses can interfere with normal gene regulation in several ways if they integrate into the DNA of a cell; viruses are powerful biological agents

Question 67

General Transcription Factors

Answer 67

Factors that are essential for transcription of all protein-coding genes; Their assistance is required by RNA Polymerase II to initiate transcription