This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “Nuclear Export”.
1. The proteins that are imported have a _______________
c) FG rich domain
d) Have to be less than 45KDa
Explanation: The importins are mainly needed for proteins that are greater than 45KDa so that they can’t diffuse randomly. They must have a nuclear localization signal which is a repeat of lysine rich sequences.
2. The basket like structure of filaments in NPC has _________ filaments and is located in ____________ side of the nuclear membrane.
a) 6, nuclear
b) 8, nuclear
c) 6, cytosolic
d) 8, cytosolic
Explanation: 8 filaments about 100nm in length come out from the nuclear side of the NPC and they are joined to the ring at the end forming a nuclear basket.
3. The central plug is a mesh of FG rich nucleoporins.
Explanation: There are some nucleoporins lining the nuclear pore which have long hydrophobic regains separated by FG domains. They are the FG rich proteins. They are not only present in the central plug but also attached to nuclear basket.
4. Choose the correct one seen in nuclear end of the NPC.
c) Ran. GTP
Explanation: Only Ran. GTP of the Four can be seen in the nuclear side of the membrane while the rest can be seen in the cytosolic end of the NPC.
5. The interaction of importin with Ran.GTP _____________________ its affinity for NLS.
c) Remains same
d) They never interact
Explanation: In the nuclear side of the cytoplasm the interaction of the importing with the Ran.GTP complex decreases its affinity for NLS which releases the cargo.
6. Nuclear export sequence is _______________ rich.
Explanation: The NES or Nuclear Export sequence that is recognized in the cargo to be exported is leucine rich. This marks it for export.
7. CRM1 is necessary for the export of mRNA.
Explanation: LMB or leptomycin B treatment prevents the export by CRM1 as it binds to the NES binding site. However, it doesn’t affect export of mRNA which shows that is via some other mechanism.
8. Which one of the following is wrong about TAP?
a) TAP can interact with the FG repeats
b) TAP directly passes the mRNA through the
c) siRNA against TAP will result in cytosolic accumulation of proteins with NLS
d) TAP directly interacts with Aly/REF
Explanation: TAP is the exportin that exports the mRNA out of the nucleus. It can bind to the poly A+ region of the mRNA and with help of Aly/REF protein it helps in export.
9. Which of the following proteins will have a higher cytosolic concentration?
Explanation: NTF2 helps RAN to return to the nuclear side of the membrane, and then it diffuses back to the cytosol. All other options here have a greater concentration in the nuclear half.
10. Which of these interactions are weak?
Explanation: The hydrolysis of the GTP reduces the interaction of Ran with the importin bound to cargo. This results in the release of the cargo into the cytosol.
11. Which of the following will be exported via CRM1?
Explanation: The exportin CRM1 is necessary for the export of the 5S rRNA. It is seen that it doesn’t export the mRNA. Exp-T exports tRNA and DNA is not usually exported.
12. Aly/REF is attached to the mRNA_______________
a) During poly adenylation
b) During G cap binding
c) During splicing
d) During editing
Explanation: The study of improperly spliced mRNA shows that Aly/REF is added to proteins during splicing by the SR proteins that mark the exon / intron junction.
Sanfoundry Global Education & Learning Series – Cytogenetics.
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