Gene Expression II Test Two

Question 1

What is one way to produce different forms of protein from the same gene?

Answer 1

Alternative splicing. Splicing RNA transcripts differently

Question 2

Describe positive and negative control of alternative splicing?

Answer 2

Negative control through a repressor which prevents the splicing machines to access the splice sites. Positive control is through an activator which recruits and directs splicing machines.

Question 3

Explain what is meant by poly-A tail timer.

Answer 3

The tail is gradually shortened by exonucleases and once it hits a certain point, 25 nt, it signals for degradation.

Question 4

What are IRE’s and IRP’s? (Dr. Whites Ex ?)

Answer 4

Iron responsive elements are recognition sites on mRNA for binding. Iron responsive regulatory proteins are proteins tha bind to mRNA

Question 5

How do mRNA’s travel to cytoplasm?

Answer 5

They use cytoskeletal motors to travel through nuclear pores.

Question 6

What causes destruction of the 5’cap?

Answer 6

Degradation through the poly A tail into the coding region of the gene or decapping exposing the 5’ end.

Question 7

What does Ferritin mRNA do?

Answer 7

Helps with storage of iron. Binds thousands of Fe3+ molecules and is found in most cells

Question 8

What does TfR mRNA do?

Answer 8

helps with iron absorbance. Has erythroid precursors in bone marrow

Question 9

Describe what occurs during iron starvation.

Answer 9

Cells no longer need to store iron it needs to be circulated. There is a decrease in Ferritin through IRP binding IRE of ferritin mRNA and an increase in TfR mRNA through IRP binding IRE at 3’ end transferrin receptor.

Question 10

What happens when there is excess iron in the body?

Answer 10

Iron no longer needs to be circulated but stored. There is less TfR mRNA and more Ferritin mRNA produced so more storage occurs. The IRP binds to iron to inactivate it and ferritin is made with no suppression.

Question 11

How do IRP’s regulate iron storage and circulation?

Answer 11

They can bind to the IRE at the 5’ ferritin mRNA end to block translation-no ferritin made. They can also bind IRE at the 3’ transferrin receptor on mRNA- make receptor for transferrin stabilizing the mRNA

Question 12

What occurs if IRP does not bind to hte 5’ ferritin mRNA or the 3’ TfR mRNA?

Answer 12

If IRP isn’t bound at 5’ mRNA gets made and ferritin is made If doesn’t bind IRE at 3’ end no transferrin receptor is made.

Question 13

Iron Starvation:

Answer 13

IRP binds ferritin and TfR mRNA –> no ferritin, TfR is made

Question 14

Iron Excess:

Answer 14

IRP does NOT bind–> Ferritin is made, no TfR made

Question 15

What do miRNA’s do?

Answer 15

Degrade RNA or block translation. binds to the complementary sequences in the 3’ UTR of mRNA. RNA with hairpin loop. Each miRNA can repress humdreds of mRNA’s and can change expression in disease states

Question 16

Are changes in miRNA expression causative or responsive to disease?

Answer 16

Both. miRNA;s have mutations that likely CAUSED the disease. Increase in miRNA expression down regulates genes in RESPONSE to disease to limit severity.

Question 17

Describe miRNA involvement with Tourette’s syndrome.

Answer 17

Change in the recognition sequence on the target mRNA increased the miRNA binding it binds efficiently to decrese the expression of SLITRK1 gene leading to tourettes.

Question 18

What destroys proteins?

Answer 18

Proteasome

Question 19

What is a proteosome?

Answer 19

A hollow chamber that degrades proteins, it has six ATP dependent active sites. Recognizes Ubiquinated proteins

Question 20

What does Bortezomid do?

Answer 20

Interacts with one of the proteolytic sites on proteosomes it reversibly inhibits it. It can prevent apoptosis. It triggers apoptosis in neoplastic cancer cells, specifically myelomas.

Question 21

Describe genomic imprinting and how it can lead to disease. (Dr. Whites ex ?)

Answer 21

Genomic imprinting is when expression of a particular gene is only expressed from one set of parents even though both are present. If there is a deletion of one set of alleles there will be presence of disease because the other allele is silent due to methylation. Imprinting is a form of epigenetics.

Question 22

Describe the RNA control of ferritin mRNA and transferrin receptor mRNA under conditions of excess iron. (Dr. Whites ex ?)

Answer 22

If there is an excess of iron in the body the IRP will bind to the IRE at the 5’ end of the ferritin mRNA. This binding will allow ferritin to be translated. The IRP will not bind the IRE at the 3’ end because that would cause TfR mRNA to be produced which would circulate iron.

Question 23

Describe the RNA control of ferritin mRNA and transferrin receptor mRNA under conditions of iron starvation. (Dr. Whites ex ?)

Answer 23

More iron is needed in the body and less needs to be stored therefore IRP will bind to the 3’ end of the transferrin receptor mRNA increasing stability to translate the Transferrin receptor IRP will not bind to the IRE at the 5’ of ferritin mRNA as that will cause a blockage of translation and no ferritin will be made because storage is not needed.

Question 24

What are four types of gene expression controls?

Answer 24

1. Coordinated expression of genes 2. Decision for specialization 3. Methylation and genomic imprinting 4. X chromosome inactivation

Question 25

Where is excess iron stored?

Answer 25

Liver Lungs Pancreas

Question 26

How can RNA splicing be regulated negatively?

Answer 26

Through a repressor that prevents splicing machines to access the splice site

Question 27

What confers stability in an mRNA?

Answer 27

Poly A tail

Question 28

What is hemosiderin?

Answer 28

Granules of ferritin

Question 29

How many mRNA molecules can miRNA regualte?

Answer 29

They can regulate more than one, they could potentially repress hundreds of mRNA’s and they have widespread binding sites

Question 30

How are proteins modified Post translationally?

Answer 30

Protein kinases Glycosylation Bind to other protein subunits Modifying enzymes act for ex thrombin cutting fibrinogen to form fibrin in blood clotting

Question 31

Describe the ubiquitin complex?

Answer 31

E1 is the activating enzyme, it couples with E2 and E3 Ubiquitin Ligase to form the final complex which marks for destruction. E2/E3 is necessary protein The complex is added to lysine side chain on the protein each chain of ubiquitin is added to lysine

Question 32

How is ubiquitin ligase activated?

Answer 32

1. protein kinase 2.allosteric transition through ligand binding 3. allosteric transition caused by protein subunit addition

Question 33

How is the target protein degradation signal activated?

Answer 33

1.Protein kinase 2.Unmask by protein dissociation 3.Create destabilized N terminus