pp 19

Question 1

What is the difference between gene expression in bacterias vs eukaryotes?

Answer 1

Bacteria: no need to export transcript to another location
Eukaryotes: several export mechanisms, posttranscriptional regulation

Question 2

How is the post-transcription regulated in bacteria?

Answer 2

regulating expression post-transcriptionally like Riboswitch

Question 3

What is a riboswitch?

Answer 3

RNA structure that binds a ligand and while doing so will change conformation altering the expression, affecting either transcription and or translation

Question 4

How does a riboswitch regulate?

Answer 4

found on untranslated regions of mRNA and can influence translation as well as transcription. In mRNA, they can trigger self-cleaving ribozyme and mRNA degradation

Question 5

How do Riboswitches control expression?

Answer 5

highly specific binding of the small-molecule-binding element to target ligand, which triggers confomational change in the regulatory region altering the structure of the RNA

Question 6

How do riboswitches inhibit transaltion?

Answer 6

Translation riboswitch binding of ligand results in a change in RNA conformation that blocks RBS

Question 7

How do riboswitches activate translation?

Answer 7

Translation riboswitche binding of the ligand results in a change in RNA conformation that activates RBS

Question 8

What is TPP riboswitch?

Answer 8

Thiamine pyrophosphate riboswitch

Question 9

What does TPP riboswitch do?

Answer 9

controls post-transcriptional regulation of thiamine biosynthesis genes, without TPP ligand, the RNA can be digested by RNase, so it would be degraded.

Question 10

What does the glmS gene code for?

Answer 10

an enzyme involved in sugar metabolism, generating glucosamine 6-phosphate

Question 11

How does the glmS riboswitch trigger mRNA cleavage?

Answer 11

5’ untranslated of glmS gene included a riboswitch that binds to GlcN6P, resulting in a change in conformation triggering RNA slef-cleavage (ribozyme activity) once cleaved. promoting degradation

Question 12

What is required for the initiation of translation in eukaryotes?

Answer 12

several eukaryotic initiation factors (eLFs)

Question 13

What regulatory mechanisms occur after transcription in eukaryotes?

Answer 13

1. transcripts are routinely proceed and not immediately translated
2. mRNA’s can be stored and translated later (allowing more rapid response to cellular needs or signals)

Question 14

What are the steps of initiation with the eLFs

Answer 14

1. GTP bound eLF2 delivers initiator methionyl-tRNA to the P site of 40S ribosomal subunit with hydrolysis of GTP
2. Recycling of GDP-eLF2 to GTP-eLF2 involves eLF2B but is prevented by phosphorylation
3. Translation of proteins can be regulated by phosphorylation of eLF2 through signal transduction

Question 15

What is required for translation initiation?

Answer 15

Recruitment of eukaryotic initiation factors elF4E and eLF4G at the 5’ UTR

Question 16

What is required to recruit elF4G?

Answer 16

coordinated interaction with elF4E at 5’ UTR and poly(A) binding protein (PABP) at the 3’ poly (A) tail

Question 17

What does the binding of elF4E and PABP form?

Answer 17

loop or circularized mRNA structure that facilitates recruitment of other translational regulators and ribosomal subunits for translation initiation

Question 18

What is a common form of post-transcriptional control of gene expression?

Answer 18

involving a seuqence of elements in 5’ or 3’ UTR that binds proteins affecting mRNA stability and translatability

Question 19

What is transferrin?

Answer 19

Iron binding protein used to carry iron from outside cell into cell

Question 20

What is transferrin receptor (TfR)

Answer 20

Transfers iron-bound transferrin into the cell. mRNA relatively high with low iron levels (mRNA degraded) and mRNA relatively low with high iron levels.W

Question 21

What is ferritin?

Answer 21

Iron binding protein used to sequester iron within the cell

Question 22

What is the iron response in elements?

Answer 22

Binding of a protein to a sequence called an iron response element in the 5’ or 3’ UTR can either enhance the stability or an mRNA (protecting from cleavage) or block translation. The stability of TfR mRNA is enhanced by protein binding to the 3’ IRE. Translation of ferritin is blocked by binding to the 5’ IRE

Question 23

What do iron response elements at the 5’ UTR of ferritin mRNA and 3’ UTR of TfR mRNA contain?

Answer 23

Stem loops with conserved sequences

Question 24

How do the electrophoretic mobility shift assay shpw cell proteins binding IRE?

Answer 24

unlabeled RNA as competitor for protein binding Lane 1: No competitor. Lane 2: unlabeled ferritin mRNA. Lane 3: unlabelled TfR mRNA. Lane 4: unlabeled B-globin mRNA

Question 25

What are the proteins binding IREs?

Answer 25

Iron regulatory proteins (IRP)

Question 26

What are IRPS

Answer 26

proteins that bid to iron response elements (IREs) when iron is low

Question 27

What does binding or IRPS to IREs result in when referring to mammals?

Answer 27

Blocks production of proteins that use and store iron (ferritin) while promoting production for proteins for iron uptake (transferrin receptor)