Lecture 16- Gene Regulation

Question 1

What are constitutive genes?

Answer 1

Genes that are always needed and constantly transcribed

Question 2

What is an operon?

Answer 2

Cluster of functionally-related genes that are controlled by a shared operator

Question 3

True or False: Operons are found in both eukaryotic and prokaryotic cells

Answer 3

False; operons are only found in prokaryotes

Question 4

How does histone methylation differ from histone acetylation?

Answer 4

Histone methylation reduces transcription whereas histone acetylation promotes transcription

Question 5

What are the three genes for lactose metabolism in E. coli?

Answer 5

Lac Z / Lac Y / Lac A

Question 6

True or false: In the absence of lactose, the Lac Operon will continue to transcribe Lac genes

Answer 6

False; the Lac Operon will not transcribe in the absence of lactose

Question 7

What is the function of the repressor in the Lac Operon?

Answer 7

Prevents transcription

Question 8

Inducer

Answer 8

On/off switch (where RNA polymerase has to pass through)

Question 9

How does the repressor become activated?

Answer 9

Inducer activates repressor

Question 10

What is an inducible gene?

Answer 10

Gene that is usually off (transcription needs to be turned on → inducer inactivates repressor)

Question 11

What is the inducer in the Lac Operon?

Answer 11

Allolactose (isomer of lactose)

Question 12

How does the inducer function in the Lac Operon?

Answer 12

Allolactose (inducer) binds to repressor and changes its shape → allows RNA polymerase to bind to promoter and transcribe gene

Question 13

True or false: Prokaryotes can regulate gene expression through various different mechanisms

Answer 13

False; prokaryotes can only regulate gene expression at transcription via operons

Question 14

True or false: The Lac Operon is considered a repressible operon

Answer 14

False; the Lac Operon is an inducible operon

Question 15

True or false: In the presence of lactose and absence of glucose, the repressor is tightly bound to the operator

Answer 15

False; in the presence of lactose and absence of glucose, the inducer (allolactose) will bind to the repressor, causing it to dissociate from the operator

Question 16

How are glucose and cAMP related?

Answer 16

Glucose and cAMP are inversely proportional. The presence of glucose inhibits the production of cAMP & the absence of glucose facilitates cAMP production (low glucose → high cAMP / high glucose → low cAMP)

Question 17

What is the function of cAMP in the Lac Operon?

Answer 17

cAMP activates CAP

Question 18

What is the function of CAP in the Lac Operon?

Answer 18

CAP binds to promoter and facilitates RNA polymerase in binding to DNA template

Question 19

How can eukaryotic cells regulate gene expression at the level of chromatin?

Answer 19

Formation of heterochromatin (tightly coiled chromatin) → inactive/inaccessible genes even during interphase (barr body for example)

Question 20

How can eukaryotic cells regulate gene expression at the level of transcription?

Answer 20

Aid or inhibit the attachment of RNA polymerase and/or transcription factors

Question 21

How can eukaryotic cells regulate gene expression at the level of the nucleosome?

Answer 21

Histone methylation to reduce transcription or histone acetylation to promote transcription

Question 22

How can eukaryotic cells regulate gene expression post-transcription?

Answer 22

Alternative splicing (introns/exons/5 G cap/3 poly-A tail)

Question 23

What is the difference between euchromatin and heterochromatin?

Answer 23

Heterochromatin is tightly coiled and therefore does not allow for transcription whereas euchromatin is loosely packed and allows for transcription

Question 24

By which process can a single individual gene be rendered inactive?

Answer 24

DNA methylation (methyl group added to cytosine → makes DNA hydrophobic → inhibits gene expression)

Question 25

How can eukaryotic cells regulate gene reexpression post-translation?

Answer 25

Cessation of protein folding