Control of Gene expression 2 (lecture 9)

Question 1

Alternative splicing produces _________ form the same genes

Answer 1

different forms of proteins

Question 2

Explain alternative splicing

Answer 2

splicing of RNA transcripts differently (there can be optional exons or introns)

Question 3

___% of genes in humans undergo alternative RNA processing

Answer 3

75%

Question 4

RNA splicing can be regulated negatively by ____ that prevents splicing machinery access to splice site

Answer 4

Repressor molecule

Question 5

RNA splicing can be regulated positively by ____ that recruits and helps direct splicing machinery

Answer 5

activating molecule

Question 6

mRNAs travel to destination using _____ motors

Answer 6

cytoskeletal

Question 7

Several mechanisms for mRNA localization have been discovered all of which require

Answer 7

specific signals in the mRNA itself (note that these signals are usually concentrated in the 3’ untranslated region (UTR), the region of RNA that extends from the stop codon that terminates protein synthesis to the start of the poly-A tail

Question 8

After mRNAs leave the nucleus through pores what are their three modes of localization

Answer 8

• directed transport on cytoskeletal motors
• Random diffusion and trapping
• Generalized degradation in combination with local protection by trapping
• Note that cytoskeletal motors and trapping hold mRNAs with anchor proteins which protect them from degradation
• note that each mode is marked by specific signals in the mRNA itself (these signals are usually concentrated in the 3’ untranslated region (UTR))

Question 9

what is the half life of most mRNAs

Answer 9

30 minutes

Question 10

what is the half life of globin mRNA

Answer 10

10 hours

Question 11

The shortening of the poly-A tail acts as a timer. Once reduced to ____ nucleotides two pathways converge (decaying followed by rapid 5’to3’ degradation and rapid 3’-to-5’ degradation to degrade mRNA)

Answer 11

25

Question 12

The poly-A tail is gradually shortened by an

Answer 12

exonuclease

Question 13

Changes in mRNA stability can _____ Gene expression

Answer 13

regulate

Question 14

Two general mechanisms exist for eventually destroying the mRNA that is made by the cell. Bothe begin with

Answer 14

the gradual shortening of the poly-A-Tail by an exonuclease, a process that starts as soon as the mRNA reaches the cytosol.

Question 15

what are the two pathways for mRNA degradation

Answer 15

• Decapping: exposed mRNA degraded form 5’ end (The 5’ cap serves to protect RNA form RNA degrading enzymes)
• mRNA degraded from 3’ end through poly-A trial and into coding region

Question 16

Control of RNAs involved in iron metabolism

Answer 16

• when iron is absent the binding of aconite to the 5’UTR of the ferritin receptor mRNA blocks translation initiation; its binding to the 3’UTR of the transferrin receptor mRNA blocks an endonuclease cleave site and thereby stabilizes the mRNA thus transferrin receptor is made. In response to an increase in iron concentration in the cytosol, a cell increases its synthesis of ferritin in order to bind the extra iron and decreases its synthesis of transferrin receptors in order to import less iron across the plasma membrane

Question 17

erythroid precursors in bone marrow have _____TfR (transferrin-receptor) molecules per cell

Answer 17

800,000

Question 18

a ___ pH leads to release of transferrin

Answer 18

neutral