This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Nucleus – Structure and Function”.
1. Nucleoporins are __________
a) Nuclear pores
b) Ribosomes on nuclear membranes
c) rRNAs in the nucleolus
d) None of the mentioned
Explanation: The nuclear membrane is a double-layered membrane that is interrupted in places by the nuclear pores. The nuclear pores provide channels for the transport of molecules such as water, proteins, RNAs etc. The nuclear pores are collectively known as Nucleoporins.
2. The transport factors that help in the transport of molecules through the nuclear pores are known as ___________
Explanation: Proteins, ribosomal subunits, and some DNAs are transported through the pore complexes mediated by a family of transport factors known as karyopherins. Karyopherins are of two types- those that mediate movement of molecules into the nucleus are called importins and those that mediate movement out of the nucleus are called exportins.
3. Lamin proteins that bind to the intra-nuclear chromatin are _____________
d) Cannot be said
Explanation: The nuclear lamina is mostly composed of lamin proteins. The cytosolic lamin proteins which face the cytoplasm, such as Emerin and Nesprin binds to the cytoskeleton to provide structural rigidity. Lamins such as LEM3 are found inside nucleus and form the nucleoplasmic veil and bind to the intra-nuclear chromatin.
4. Nuclear Organizer Regions (NOR) is found in ________
a) Nuclear matrix
c) Nuclear lamina
Explanation: The nucleolus is a dense granular region present inside the nucleus. It is concerned with the production of rRNA and consists of tandems of rDNAs, DNA that codes for rRNA. These rDNA rich regions of nucleolus is called Nuclear Organizer Regions (NOR).
5. Cajal bodies mainly consist of the protein _________
Explanation: Cajal bodies re sub-nuclear compact structures with diameter between 0.2-2.0 micrometers, depending on the species. Under electron microscope, the appear as small tangles threads with a dense dictricution of the Coilin protein. They are bound to the nucleolus by coilin proteins.
6. Which of the following is not a function of Cajal bodies?
a) snRNP biogenesis
b) histone mRNA processing
c) telomere assembly
d) tRNA processing
Explanation: Cajal bodies re sub-nuclear compact structures with diameter between 0.2-2.0 micrometers, depending on the species. They are mainly related to RNA synthesis and helps in RNA-related metabolic processes such as snRNPs biogenesis, maturation and recycling, histone mRNA processing and telomere maintenance.
7. Which of the following is also known as Kremer bodies?
a) Cajal bodies
b) PML bodies
c) Nuclear speckles
Explanation: Promyelocytic leukaemia bodies (PML bodies) are spherical bodies that are found scattered throughout the nucleoplasm and are around 0.1–1.0 µm. They are also known by a number of different names such as nuclear domain 10 (ND10), Kremer bodies, PML oncogenic domains and also nuclear dots.
8. Which of the following plays a role in oncogenic function?
a) Kremer bodies
b) Cajal bodies
c) Splicing speckles
d) None of the mentioned
Explanation: Kremer bodies, also known as Promyelocytic leukaemia bodies (PML bodies) are spherical matrix-associated nuclear bodies. Their specific role in not yet known though their role in ongenesis and viral infection is unavoidable. They may be a site for RNA transcription, storage of rRNAs of other transcriptional activity.
9. Nuclear speckles ______________
a) perform splicing of snRNPs
b) perform splicing of rRNAs
c) act as a transcription site for rRNAs
d) act as a storage site for snRNPs
Explanation: Nuclear speckles, also called as splicing speckles are subnuclear structures that are enriched in pre-messenger RNA splicing factors and are located in the interchromatin regions of the nucleoplasm. The splicing factors help in the splicing of snRNPs and other splicing proteins that are necessary for pre-mRNA processing.
10. Which of the following is not true?
a) Paraspeckles are irregular shaped sub-nuclear compartments
b) Paraspeckles disappear in absence of RNA polemerase II transcription
c) They are transcription dependent
d) They are present during interphase and absent during mitosis.
Explanation: Paraspeckles are irregular shaped sub-nuclear compartments which are transcription dependent. Paraspeckles disappear in absence of RNA polemerase II transcription and all of its associated protein components form a crescent shaped perinucleolar cap in the nucleolus. However, paraspeckles are present during the interphase and all the stages of mitosis except the telophase.
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