Chapter 12

Question 1

What’s an operon

Answer 1

groups of functionally related structural genes and the sequences that control their transcription.

Question 2

Whats negative control

Answer 2

a repressor protein binds to DNA and inhibits transcription

Question 3

What’s positive control

Answer 3

an activator (regulatory protein) binds to DNA (usually at a site other than the operator) and stimulates transcription

Question 4

What’s an inducible operon

Answer 4

transcription is normally off and must be turned on

Question 5

What’s a repressible operon

Answer 5

repressible operons, transcription is normally on and must be turned off.

Question 6

What kind of operon is the lac operon of E.coli and why

Answer 6

The lac operon of E. coli is a negative inducible operon. In the absence of lactose, a repressor binds to the operator and prevents the transcription of genes that encode β-galactosidase, permease, and transacetylase. When lactose is present, some of it is converted into allolactose, which binds to the repressor and makes it inactive, allowing the structural genes to be transcribed.

Question 7

What kind of operon is the trp operon of E.coli

Answer 7

The trp operon of E. coli is a negative repressible operon that controls the biosynthesis of tryptophan.

Question 8

In what ways do eukaryotic cells differ from bacteria in gene regulation

Answer 8

the absence of operons
the presence of chromatin
presence of a nuclear membrane.

Question 9

How can chromatin structure be altered?

Answer 9

1) by chromatin-remodeling complexes that reposition nucleosomes
2) by modifications of histone proteins, including acetylation, phosphorylation, and methylation.

Question 10

What control(s) the initiation of eukaryotic transcription and how

Answer 10

1) general transcription factors that assemble into the basal transcription apparatus
2) by transcriptional regulator proteins that stimulate or repress normal levels of transcription by binding to regulatory promoters and enhancers.

Question 11

Enhancers affect the transcription of distant or proximal genes

Answer 11

distant genes

Question 12

What are regulatory elements

Answer 12

DNA sequences that are not transcribed but play a role in regulating other nucleotide sequences

Question 13

What are regulatory gene

Answer 13

encoding products that interact with other sequences and affect the transcription and translation of these sequences (DNA sequence–encoding products that affect the operon function but are not part of the operon)

Question 14

Gene regulation’s role in bacteria

Answer 14

gene regulation maintains internal flexibility, turning genes on and off in response to environmental changes.

Question 15

What’s a negative inducible operon

Answer 15

The control at the operator site is negative (repressor). Molecule is initially binding to the operator, inhibiting transcription. Such operons are usually off and need to be turned on, so the transcription is inducible.

Question 16

What’s a corespressor

Answer 16

a small molecule that binds to the repressor and makes it capable of binding to the operator to turn off transcription

Question 17

What’s a negative repressible operon

Answer 17

The control at the operator site is negative. But such transcription is usually on and needs to be turned off, so the transcription is repressible.

Question 18

What’s the inducer of the lac operon

Answer 18

allolactose

Question 19

T/F:repression of the lac operon

completely shuts down transcription

Answer 19

False: repression of the lac operon never

completely shuts down transcription.

Question 20

What’s the role of insulators

Answer 20

Insulators limit the action of enhancers by blocking their action in a position-dependent manner.

Question 21

T/F: Coordinately controlled genes in eukaryotic cells respond to the same factors because they have common response elements that are stimulated by the same transcriptional activator.

Answer 21

True

Question 22

Name 4 elements important in controlling the stability of eukaryotic mRNAs.

Answer 22

1) 5’ cap
2) the poly(A) tail
3) the 5’ UTR, the coding region
4) sequences in the 3’ UTR

Question 23

What do siRNA’s and miRNA’s do

Answer 23

These complexes cleave RNA, inhibit translation, affect RNA degradation, and silence transcription.

Question 24

What makes Arabidopsis thaliana a good model organism

Answer 24

small and easy to maintain in lab , short generation time

Question 25

What causes epigenetic changes

Answer 25

DNA methylation, histone modifications, RNA molecules, and alterations in chromatin structure.

Question 26

Can epigenetic changes be affected by environmental factors?

Answer 26

yes

Question 27

Are epigenetic changes unstable

Answer 27

no, they’re stable

Question 28

What external factors may cause epigenetic changes:

Answer 28

1) Early life experiences can produce epigenetic changes that have long-lasting effects on behavior.
2) Environmental chemicals may produce epigenetic effects that are passed to later generations.

Question 29

Phenotypic differences between genetically identical monozygotic twins may result from______?

Answer 29

epigenetic effects

Question 30

What does the lac operon regulate

Answer 30

lactose metabolism

Question 31

What’s catabolite repression

Answer 31

using glucose when available and repressing the metabolite of other sugars

Question 32

Is catabolite repression a positive or negative control mechanism and why

Answer 32

This is a positive control mechanism. The positive effect is activated by catabolite activator protein (CAP). cAMP binds to CAP; together CAP–cAMP complex binds to a site slightly upstream from the lac gene promoter. They help RNA polymerase do transcription

Question 33

What’s the relationship between cAMP and glucose

Answer 33

The concentration of cAMP is inversely proportional to

the level of available glucose.

Question 34

What does CAP do?

Answer 34

binds to the promoter of the lac operon and stimulates transcription.

Question 35

What does acetylation do to chromatin

Answer 35

The acetylation of histone proteins alters chromatin structure (opens it up) and permits some transcription factors to bind to DNA.

Question 36

Name 4 ways we can modify histones

Answer 36

1) Phosphates
2) Methyl groups
3) Acetyl groups
4) Ubiquitin

Question 37

Histone acetylation is catalyzed by ______

and is removed by _____.

Answer 37

1) acetyltransferases (HATs)

2) deacetylatases (HDACs)

Question 38

What kind of methylation causes gene repression

Answer 38

DNA methylation of cytosine to produce 5-methylcytosine

Question 39

What’s a structural gene

Answer 39

DNA sequence that encodes a protein that functions in metabolism or biosynthesis or that has a structural role in the cell.