Lecture 17- Regulation of Gene Expression I

Question 1

differential gene expression theory

Answer 1

1. genome is constant in all somatic cells
2. only a small proportion of genome in any cell type is expressed
3. unused genes that are not transcribed are not mutated or destroyed, they retain potential to be expressed

Question 2

central dogma

Answer 2

DNA -> mRNA -> protein

Question 3

gene expression

Answer 3

process by which information encoded in a DNA sequence is translated into a product that has some effect on a cell or organism

Question 4

gene expression can be regulated at many levels

Answer 4

1. transcriptional control
2. RNA processing control
3. mRNA transport and localization control
4. mRNA degradation control
5. translation control
6. protein degradation control
7. protein activity control

(2-7 is posttranscriptional regulation)

Question 5

transcriptional control

Answer 5

• relatively slow acting
• most energy efficient
• most common control point for long term regulation

Question 6

protein activity control

Answer 6

• fast acting

- readily reversible

Question 7

elements of prokaryotic transcriptional regulation

Answer 7

promoter (upstream) and terminator (downstream)

Question 8

promoter

Answer 8

• contains sequences recognized and bound by RNA polymerase
• located upstream of transcription start site
• vary in their strength of binding to RNA polymerase
• activity is inhibited by transcriptional response
• activity is enhanced by transcriptional activators

Question 9

transcriptional regulators =

Answer 9

transcription factors= transcriptional activators or repressors

Question 10

process of prokaryotic transcriptional regulation

Answer 10

• RNA polymerase starts art start site where promoter is
• RNA synthesis begins
• sigma factor release, polymerase clamps down on DNA, synthesis continues
• termination and release of both polymerase and completed RNA transcript as it approaches terminator
• sigma factor rebinds to polymerase after it has detached from the gene/DNA

Question 11

transcriptional regulators (activators and repressors) are proteins that have DNA binding domains

Answer 11

• DNA binding domain of a transcription factor binds a stretch of unique DNA sequences
• different DNA binding domains can bind to different DNA sequences, allowing for specificity
• activators and repressors can act in concert to provide highly sensitive transcriptional regulation

Question 12

cluster of bacterial genes can be transcribed from a single promoter- an operon

Answer 12

expression of operon is controlled by regulator sequence called the operator

Question 13

an activator and repressor control the Lac operon

Answer 13

• e. coli use glucose as energy source
• if there is no glucose available, they break down lactose (disaccharide of glucose and galactose)
• genes of Lac operon allow e. coli to utilize lactose

Question 14

genes in Lac operon are expressed only when

Answer 14

glucose is not available AND lactose is in the medium

Question 15

Lac repressor inhibits transcription when lactose is not present

Answer 15

removing repressor is not sufficient to allow transcription because the promoter is weak

Question 16

CAP activates transcription when glucose is not present

Answer 16

cAMP levels go up

Question 17

how does activator and repressor work together to regulate Lac operon?

Answer 17

• (+glucose + lactose) both CAP and repressor inactive, so operator OFF
• (+glucose -lactose) CAP inactive, repressor active, operator OFF
• (-glucose -lactose) CAP and repressor active, operon OFF
• (-glucose +lactose) CAP active, repressor inactive, operon ON and polymerase can transcribe

Question 18

eukaryotic transcription is more complex than prokaryotic transcription

Answer 18

• eukaryotic cells contain three distinct RNA polymerases: I, II, III
• specific transcription activators or repressors bind DNA sequences located far from the promoter that they regulate

Question 19

function of the eukaryotic polymerases I, II, III

Answer 19

I: rRNA
II: mRNA (protein encoding genes)
III: tRNA

course focuses on RNA Pol II as it transcribes all mRNAs

Question 20

eukaryotic regulatory proteins act at a distance

Answer 20

• enhancer (binding site for activator protein)
• promoter / TATA box
• DNA looping (see slide)

Question 21

enhancers

Answer 21

• regulatory DNA sequences bound by transcriptional regulators
• function to allow transcription of a given gene in specific cells or at specific developmental stages
• can be located far away from transcription start site

Question 22

transcriptional regulators work together as a “committee”

Answer 22

• enhancer can be bound by multiple transcriptional regulators
• combined actions of multiple transcriptional regulators (activators and repressors) ensure precise regulation of gene expression

Question 23

Shh (sonic hedgehog) regulates anterior-posterior patterning of limb by acting as a morphogen

Answer 23

expression of Shh in limb is controlled by limb specific enhancer

Question 24

ectopic expression of Shh causes extra digit formation

Answer 24

ectopic expression: expression of gene in place(s) or time(s) where/when the gene is not normally expressed

Question 25

a single base pair change that causes ectopic expression of Shh in limbs results in digit duplication in mouse

Answer 25

this G to A change is location 10^6 base pair away from Shh start codon (ATG)

Question 26

Shh limb enhancer is conserved in mouse, humans, and fish; but not limbless reptiles

Answer 26

ZRS enhancer=Shh limb enhancer

Question 27

what happens if mouse enhancer is substituted with the snake enhancer?

Answer 27

mouse does not develop limbs

Question 28

what happens when (in snake substitued mouse), the snake enhancer is made more like the human enhancer?

Answer 28

the mouse develops limbs similar to humans (arms grow straight out of sides, legs grow same direction as tail)

Question 29

loss of limb enhancer for Shh is associated with loss of limb in advanced snakes