What is the average diameter of nuclear pores?
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80 nm.
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What is the average diameter of nuclear pores?
80 nm.
What is nuclear protoplasm?
A viscous matrix containing chromosomes and nucleoli.
What is the cytoplasmic ring?
A structure located around the cytoplasmic margin of the nuclear pore.
Which structure is NOT a clump of nucleoprotein near the nucleus?
Nuclear pore complex.
Which histone is associated with linker DNA between nucleosomes?
Histone H1.
What are nucleocytoplasmic shuttling signals?
Transport signals recognized by transporter proteins.
What is the total number of homologous pairs in the human genome?
23 homologous pairs, or 46 chromosomes.
What do exportins recognize to facilitate transport?
Nuclear export sequences.
What protein is contained in the pars granulosa?
Nucleostemin.
What is the function of the nucleolus?
It is the site of rRNA synthesis and contains transcriptionally active DNA for ribosomes.
Which option describes the functional significance of the dark-stained chromatin observed in the kidney biopsy?
Organization of inactive chromatin.
What happens to one female X chromosome in relation to lincRNAs?
It is transcribed to form lincRNAs that coat that X chromosome and prevent the transcription of its genes.
What are nuclear pores?
Openings in the nuclear envelope that connect the nucleus with the cytoplasm.
What does telomerase do?
Adds repeated nucleotide sequences to the telomere ends.
What does nurim bind to?
Lamin A and Lamin B.
What is ribosomal RNA biosynthesis?
It is the process of synthesizing rRNA, which is essential for ribosome formation.
What are the sizes of rRNA formed from pre-rRNA processing?
28S, 18S, and 5.8S.
What are exons?
Regions of DNA that code for specific RNAs.
From where do siRNAs frequently arise?
From the genome of RNA viruses that infect a cell.
What is heterochromatin?
A tightly packed form of DNA that is generally not active in transcription.
Can siRNAs be transcribed from the cell's own genome?
Yes, some siRNAs are transcribed from the cell’s own genome.
What is the function of the outer nuclear membrane?
It serves as a barrier and is involved in transport but not in transcription.
What regulates calcium signals in the nucleus?
Receptors for inositol 1,4,5-triphosphate.
What functions does nucleostemin have?
It regulates the cell cycle and cell differentiation.
What is the role of rRNA in ribosome formation?
It associates with many different proteins to form ribosomes.
What characteristic does the lumen of the nuclear pore have?
It may be a gated channel that impedes passive diffusion.
How is the perinuclear space related to the rough endoplasmic reticulum (rER)?
It is continuous with the rER cisterna.
When were miRNAs first discovered?
In the 1990s in roundworms.
What are the proteins that compose the nuclear pore complex called?
Nucleoporins.
What is the primary function of mRNA?
Carries the genetic code to the cytoplasm to direct protein synthesis.
What is the role of the transmembrane proteins in the nuclear pore?
They project into the lumen of the nuclear pore, anchoring the complex into the pore rim.
What type of movement does the nuclear envelope permit?
Passive movement via a 9- to 11-nm open channel for simple diffusion.
How many membranes make up the nuclear envelope?
Two membranes.
Which nuclear protein's reactivation may help cancer cells escape cellular senescence?
Telomerase.
What do the protein subunits surrounding the nuclear pore represent?
They represent the structural components of the nuclear pore complex.
What is the role of the nuclear lamina?
It provides structural support to the nucleus.
What surrounds the nuclear material?
The nuclear envelope.
What is the primary function of miRNAs?
To regulate gene expression.
What does the nuclear envelope direct the formation of?
Nuclear pore complexes (NPCs).
What structure does DNA form?
A double helix consisting of two complementary strands.
Where is the nucleoplasmic ring located?
Around the nucleoplasmic margin of the nuclear pore.
What is observed in chromosomes during mitosis after staining with Giemsa?
G-banding.
What results in the reassembly of lamins?
Dephosphorylation of lamins.
How many transmembrane proteins are involved in the luminal spoke ring?
Eight transmembrane proteins.
What interrupts the perinuclear space?
Nuclear pores.
What is the length of miRNA molecules?
19 to 25 nucleotides.
What do the ribosomes on the outer nuclear membrane synthesize?
Proteins that enter the perinuclear cisterna.
What does karyotype refer to?
The number and morphology of chromosomes.
What do codons in mRNA correspond to?
They are complementary to the DNA codons from which it was transcribed.
What are clumps of nucleoprotein concentrated near the periphery of the nucleus called?
Heterochromatin.
Which nucleotide is present only in RNA?
Uracil.
What is chromatin composed of?
DNA complexed with histones and nonhistone proteins.
What is the basic packaging unit of chromatin?
A nucleosome.
What is one function of the nucleolus?
Synthesis of rRNA.
What structure is exhibited on the nucleoplasm side of the nuclear pore complex?
A nuclear basket.
What is a genome?
The complete set of hereditary information that an individual possesses.
Which option is NOT a nuclear protein related to cellular senescence?
Rb tumor suppressor protein.
What bridges the nuclear pore complex?
A unit membrane.
What type of DNA sequences does Giemsa specifically stain?
DNA sequences rich in adenine (A) and thymine (T).
What structure controls the movement of proteins in and out of the nucleus?
Nuclear pore complex.
What forms chromatin in the nucleus?
Nuclear DNA.
What are nuclear localization segments?
Clusters of certain amino acids that act as signals for transport.
What occurs during the preliminary assembly in the nucleolus?
Assembly of ribosome subunit precursors.
What is the nucleoplasmic ring also known as?
Nuclear ring.
What is the responsibility of the nuclear envelope during mitosis?
Disassembly and reassembly of the nuclear envelope.
What leads to the disassembly of lamins?
Phosphorylation of lamins.
What holds the two strands of the DNA double helix together?
Hydrogen bonds between the base pairs A – T and G – C.
What are nuclear pores associated with?
The nuclear pore complex (NPC).
What is micro-RNA (miRNA)?
A small non-coding RNA molecule that regulates gene expression.
What does the nuclear basket extend into?
The nucleoplasm.
What does lincRNA stand for?
Large/long intergenic noncoding RNA.
What is one function of lincRNAs?
They function in gene regulation.
What is a codon?
A sequence of three bases in the DNA that codes for a single amino acid.
Where is the distal ring attached?
To the distal end of the nuclear basket.
What is a luminal subunit?
A moiety of each transmembrane protein that projects into the perinuclear cistern.
In what forms does chromatin exist in the nucleus?
As heterochromatin and euchromatin.
What components make up a nucleosome?
Histones and nonhistone proteins.
What is a gene?
A segment of DNA that contains information for encoding a single mRNA molecule and regulatory sequences that control trait expression.
How do some miRNAs prevent transcription?
By methylating specific regions of DNA.
What structure is formed when DNA winds around an octamer?
A nucleosome.
What is the primary function of DNA?
Stores genetic information and acts as a template for the synthesis of RNA.
What are the names of the rings in the nuclear pore complex?
Cytoplasmic ring, luminal spoke ring, nuclear ring, distal ring.
What role do Ran proteins play in nucleocytoplasmic transport?
They regulate the functions of exportins and importins.
Where are anticodons located?
In tRNA.
What is the space between the inner and outer nuclear membranes called?
Perinuclear space.
With which structure is the outer nuclear membrane continuous at certain sites?
Rough endoplasmic reticulum.
What is found on the cytoplasmic surface of the outer nuclear membrane?
Ribosomes.
What can a gene be composed of in certain viruses?
RNA rather than DNA.
What is the structure of DNA?
A long double-stranded helical linear molecule of nucleotides.
What is characteristic of a karyotype?
It is characteristic for each species.
What is the primary function of tRNA?
Involved in protein synthesis.
What is the typical length of siRNAs?
19 to 25 nucleotides.
What are the stop codons that terminate protein synthesis?
UAA, UAG, or UGA.
What are the components of a nucleotide?
A base (purine or pyrimidine), deoxyribose sugar, and a phosphate group.
What happens to telomeres with each cell division?
They shorten.
What type of calcium is found within the nucleus?
Nuclear calcium.
What are nuclear lamins?
A specialized type of nuclear intermediate filament (type V) consisting of lamins A, B1, B2, and C.
How do siRNAs resemble miRNAs?
They resemble miRNAs in their mode of action.
What does the outer nuclear membrane face?
The cytoplasm.
What surrounds the cytoplasmic aspect of the outer nuclear membrane?
A loosely arranged mesh of intermediate filaments (vimentin).
What is the role of the nuclear envelope in the cell?
It organizes nuclear envelope and chromatin.
What are the openings called where the membranes of the nuclear envelope fuse?
Nuclear pores.
What role does nucleostemin play in the cell cycle?
Cell cycle checkpoint signaling.
How many nuclear pores can be found in a cell?
From dozens to thousands, depending on metabolic activity.
Which component is associated with the nuclear pore complex?
It facilitates transport but is not the site of transcriptional activity.
What percentage of the genome is composed of protein-coding genes?
About 2%.
What are the ends of the chromosomes called?
Telomeres.
How do proteins pass through the nuclear pore complex?
Via receptor-mediated transport.
What are introns?
Regions of DNA that do not code for RNAs but serve important regulatory functions.
What is the nucleolus primarily involved in?
Ribosome biogenesis.
What is located at the terminal end of tRNA?
Adenylic acid (where amino acids attach).
What do importins recognize for transporting molecules into the nucleus?
Nuclear localization sequences.
Which inclusion is not bounded by a membrane and is observable only during interphase?
Nucleolus.
What separates the nuclear material from the nuclear lamina?
The nuclear envelope.
How do most proteins pass through the nuclear envelope?
By receptor-mediated transport, regardless of size.
What is the focus of the talk at the national meeting on regenerative medicine?
Cellular senescence and cancer.
What is processed in the nucleolus related to micro RNAs?
Primary processing of micro RNAs.
What is the function of the nuclear pore complex?
It permits free communication between the nucleus and the cytoplasm.
What is the site of transcriptional activity?
Euchromatin.
What is the term used to describe a series of nucleosomes?
Beads on a string.
How long would the complete nucleotide of a cell measure if stretched out?
Almost 6 feet in length.
How many pairs of sex chromosomes are in the human genome?
1 pair (either XX or XY).
What are lincRNAs?
Long intergenic non-coding RNAs that are more than 200 nucleotides in length.
What structure do nucleosomes help package into?
A solenoid-like structure, which is a thick 30-nm fiber.
What are interchromatin granules?
Clusters of particles containing RNP and various enzymes.
What does the dark-stained ring of marginal chromatin in the nucleus of an endothelial cell indicate?
Organization of inactive chromatin.
What is the function of the luminal spoke ring in the nuclear pore complex?
It interposes between the cytoplasmic and nucleoplasmic rings.
How does the euchromatin/heterochromatin ratio in malignant cells compare to normal cells?
It is higher in malignant cells than in normal cells.
How many copies of histones H2A, H2B, H3, and H4 are in a histone octamer?
Two copies each.
What is the space between the two membranes of the nuclear envelope called?
Perinuclear cisterna.
What is the role of telomerase in cancer cells?
It enables cancer cells to continue to proliferate and maintain genomic stability.
What do other miRNAs do to mRNA strands?
They insert into a matching portion, preventing translation.
What are the two main types of transporter proteins involved in nucleocytoplasmic transport?
Exportins and importins.
How many pairs of autosomes are in the human genome?
22 pairs of autosomes.
How many subunits compose the nucleoplasmic ring?
Eight subunits.
What is the role of the nucleolus?
It is involved in ribosome production, not directly in transcriptional activity.
What is the function of the nuclear pore complex?
It regulates the transport of molecules between the nucleus and the cytoplasm.
Which rRNA subunits are assembled in the pars granulosa?
18S rRNA and 28S rRNA subunits.
What feature of the nuclear pore complex faces the cytoplasm?
A luminal ring.
What does telomere length indicate?
The lifespan of the cell.
What is heterochromatin?
A tightly packed form of DNA that is transcriptionally inactive.
What must be maintained for a cell to survive indefinitely?
Telomere length.
What is euchromatin?
A loosely packed form of DNA that is transcriptionally active.
How do lincRNAs interact with mRNAs?
They compete with certain mRNAs for miRNAs.
What determines the specific amino acid molecule in the growing polypeptide chain?
Anticodon recognition.
What types of DNA are found in the Pars fibrosa?
Transcriptionally active DNA and ribosomal genes.
Why is negatively supercoiled DNA important?
It is required for most biological reactions.
Which enzymes are involved in DNA supercoiling?
Topoisomerases.
What type of RNA is mostly found in the nucleolus?
rRNA (ribosomal RNA).
What sugar does RNA contain?
Ribose instead of deoxyribose.
What extends into the cytoplasm from the cytoplasm side of the nuclear pore complex?
Cytoplasmic filaments.
How many rings does the nuclear pore complex have?
Four rings.
How are genes classified?
Into protein coding genes and noncoding segments of DNA.
Which structure is continuous with the Rough Endoplasmic Reticulum (RER)?
Outer nuclear membrane.
What shape is tRNA folded into?
Cloverleaf shape.
What are the main components of the nucleus?
Chromatin, nucleolus, nuclear envelope, nuclear pores, and nucleoplasm.
What do the subunits of the cytoplasmic ring possess?
A cytoplasmic filament.
What are the purines found in DNA?
Adenine (A) and Guanine (G).
What is the final structure formed after further condensation of chromatin?
A chromosome.
What are chromosomes composed of?
Two chromatids joined together at the centromere.
How do lincRNAs affect transcription on different chromosomes?
They prevent the transcription of various genes on different chromosomes.
What is G-banding used for?
To identify chromosomes and chromosomal anomalies.
What is the role of the kinetochore complex?
It is involved in chromosome segregation during cell division.
What is a supercoiled structure?
A helix twisted around itself in three-dimensional space.
What does the Pars fibrosa (F) surround in the nucleolus?
The fibrillar centers.
What are small nuclear RNPs (snRNPs)?
Complexes of proteins and small RNAs involved in hnRNP splicing or in cleavage reactions.
What is euchromatin?
Transcriptionally active chromatin.
How does euchromatin appear in a transmission electron microscope (TEM)?
As electron-lucent regions.
What phase is a cell in when it exits the cell cycle and remains as a reserve stem cell?
G0 phase.
What type of molecule is RNA?
Single stranded linear molecule.
What are ribozymes?
RNAs that can act as enzymes, catalyzing the formation of peptide bonds during protein synthesis.
What is the start codon for initiating protein synthesis?
AUG.
Where is the nuclear pore complex located?
Only at specific nuclear pore sites.
What is the composition of the pars granulosa?
It is composed of maturing ribosomal precursor particles.
What is the function of the nucleolus?
It is involved in ribosome production, but it is not a clump of nucleoprotein near the periphery.
What is the difference between euchromatin and heterochromatin?
Euchromatin is transcriptionally active DNA, while heterochromatin is more condensed and less active.
What is the outer nuclear membrane?
It is a membrane surrounding the nucleus, not a clump of nucleoprotein.
What are the pyrimidines found in DNA?
Cytosine (C) and Thymine (T).
What type of structure do mitochondrial DNA and most prokaryotic DNA have?
Closed circular structures.
What is the small point where two chromatids are joined called?
The centromere.
What percentage of total chromatin does heterochromatin comprise?
Approximately 90%.
How is heterochromatin formed?
From euchromatin that is folded into 30-nm thick filaments.
What role do lincRNAs play in relation to miRNAs?
They act as decoys that protect mRNAs from the inhibitory actions of miRNAs.
Which enzyme catalyzes the synthesis of rRNA?
RNA polymerase I.
What additional histone is found in condensed chromatin?
H1.
What forms the large (60S) subunit of the ribosome?
The RNP containing 28S and 5.8S rRNA combines with 5S rRNA.
Name a protein found in the nucleolus.
Nucleostemin.
How is RNA synthesized?
By transcription of DNA.
What are the main components of nuclear protoplasm?
Macromolecules, ions, transcriptional processing apparatus, and nucleoplasmic reticulum.
How many subunits compose the cytoplasmic ring?
Eight subunits.
What is the relationship between the nucleoplasmic reticulum and the nuclear envelope?
The nucleoplasmic reticulum is continuous with the nuclear envelope and endoplasmic reticulum.
How many nucleotides does tRNA contain approximately?
Approximately 80 nucleotides.
What do nuclear pores permit?
Passage of certain molecules in either direction.
What is the composition of the filament in the cytoplasmic ring?
Made of a Ran-binding protein (GTP-binding protein).
What is characteristic for each species in terms of chromosomes?
G-banding patterns.
What is the potential function of the filaments in the cytoplasmic ring?
They may serve as a staging area prior to protein transport.
What is the structure of the nuclear envelope?
It consists of a double membrane with an inner and outer membrane separated by a perinuclear cisternal space.
How does Lamin B interact with the nuclear structure?
It attaches the lattice to the inner nuclear membrane via lamin receptors.
What is the role of the nucleolar matrix?
It is a fiber network involved in the organization of the nucleolus.
What causes supercoiling in DNA?
Strain on the molecule caused by under- or overwinding the double helix.
How does heterochromatin appear in a transmission electron microscope (TEM)?
As electron-dense regions.
During which phase of the cell cycle does DNA synthesis occur?
S phase.
What is it called when there are malfunctions at the G1, S, and G2 checkpoints?
Mitotic catastrophe.
What type of chromatin is metabolically active with dispersed DNA?
Euchromatin.
How are nuclear pores formed?
By the fusion of the inner and outer nuclear membranes.
What does banding in chromosomes represent?
Highly folded DNA loops.
What is the function of the distal ring?
Assists in the export of RNA into the cytoplasm.
What are the four distinct regions of the nucleolus?
Fibrillar centers (FC), Pars fibrosa (F), and others.
What are perichromatin granules?
Single dense granules surrounded by a less dense halo, located at the periphery of heterochromatin.
What structure do lamins A and C form?
An orthogonal lattice/meshwork.
What are the two forms in which mitochondrial DNA can exist?
Relaxed circles or supercoiled structures.
What does one end of the folded tRNA molecule possess?
An anticodon.
What is nucleoplasm?
The nuclear content other than the chromatin and nucleolus.
What happens to chromatin during mitosis and meiosis?
It condenses, making chromosomes visible.
What is the state of chromatin when it is not visible by light microscopy?
It is extended.
What does histone H1 do in condensed chromatin?
It wraps around groups of nucleosomes.
What is the structural unit of a chromosome?
The 30-nm diameter filaments of helical coils.
What are nucleolar organizer regions (NORs)?
Portions of chromosomes where rRNA genes are located.
What does RNA polymerase III synthesize?
tRNA.
What is the function of small interfering RNAs (siRNAs)?
They play a role in RNA interference and gene silencing.
What is heterochromatin?
Condensed chromatin that is not being transcribed.
How do miRNAs regulate gene expression?
By binding to complementary sequences on target mRNAs, leading to their degradation or inhibition.
What enzyme do malignant cells overexpress?
Telomerase.
When are chromosomes visible with light microscopy?
Only during mitosis and meiosis.
Where does rRNA synthesis take place?
In the nucleolus.
What is the outcome of lincRNAs protecting mRNAs?
They facilitate the translation of the mRNA to synthesize a particular protein.
What percentage of total chromatin does euchromatin comprise?
Approximately 10%.
In which phase does the initial appearance of the cleavage furrow occur during mitosis?
Anaphase.
What are the key regulatory protein complexes in regulating the cell cycle?
Cyclin B and Cyclin dependent kinase - 2.
What does RNA polymerase I synthesize?
rRNA.
What is euchromatin?
A less condensed form of chromatin that is actively involved in transcription, not concentrated near the periphery.
What do perichromatin granules contain?
4.7S RNA and two peptides similar to those found in heterogeneous nuclear RNPs (hnRNPs).
What is the role of RNA polymerase I in the nucleolus?
It is responsible for the transcription of rRNA.
What is the function of nucleosome assembly?
It helps in the packaging of DNA into chromatin.
What is the Barr body?
The condensed form of one of the two X chromosomes in female mammals.
What characterizes negatively supercoiled DNA?
DNA is wound more loosely than in Watson-Crick DNA.
Which proteins are associated with the nucleolus?
Fibrillarin and nucleolin.
What forms the small (40S) subunit of the ribosome?
The RNP containing 18S rRNA.
What is another protein associated with the nucleolus?
Nucleolin.
What catalyzes the transcription of RNA?
Three RNA polymerases.
What does each tRNA combine with?
A specific amino acid that has been activated by an enzyme.
What effect do siRNAs have on DNA?
They methylate specific regions of the DNA and interfere with transcription.
What are hnRNP particles?
Heterogeneous nuclear RNA (hnRNA) complexes of precursor mRNA (pre-mRNA) and proteins of variable densities.
What is the primary role of siRNAs?
To mediate the degradation of mRNA and prevent translation.
What is the purpose of a DNA replication center?
It is where DNA replication occurs during the cell cycle.
What significant quantity is found in the Pars fibrosa?
Substantial quantity of rRNA.
Where does ribosomal RNA (rRNA) synthesis and initial ribosomal assembly occur?
In the nucleolus.
What is primarily observed in interphase cells?
The structure of the nucleolus, which is actively synthesizing proteins.
Which human chromosomes contain nucleolar organizer regions?
Chromosomes 13, 14, 15, 21, and 22.
What types of RNA can be formed from noncoding segments of DNA?
tRNA, rRNA, and regulatory RNAs.
What composes the Fibrillar centers (FC) of the nucleolus?
Nucleolar organizer regions (NORs) and ribonucleoprotein (RNP) signal recognition particle.
In which types of cells are large quantities of nucleostemin present?
In cancer cells and stem cells.
During protein synthesis, rRNA associates with which molecules?
mRNA and tRNA.
What is the role of hnRNP particles?
Involved in pre-mRNA processing.
What is the function of Lamin B receptor (LBR)?
It binds Lamin B.
What is the initial precursor rRNA called?
45S precursor rRNA (pre-rRNA).
What is the diameter of the filaments formed by condensed chromatin?
30 nm.
What does a Barr body represent in a nucleus?
Facultative heterochromatin.
Which base does RNA contain instead of thymine?
Uracil (U).
What is the significance of lincRNAs?
They are involved in regulating gene expression and chromatin organization.
What is the role of emerin in relation to lamins?
Emerin binds both lamin A and B.
What type of chromatin is metabolically inactive and dark-stained?
Heterochromatin.
What is the role of telomerase in cells?
It is essential for cellular lifespan.
What characterizes positively supercoiled DNA?
DNA is wound more tightly than in Watson-Crick DNA.
How many nucleosomes are in each turn of the helical coils formed by condensed chromatin?
Six nucleosomes.
Which protein is involved in the nucleolus and is essential for rRNA processing?
Fibrillarin.
Where do microtubules attach to chromosomes?
At the kinetochore.
What small amount of genetic material is present in the nucleolus?
DNA.
What does RNA polymerase II synthesize?
mRNA.
