Where are a small fraction of the cell's genes located?
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In the mitochondria.
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Where are a small fraction of the cell's genes located?
In the mitochondria.
Are the contents of the nucleus uniform?
No, the interior of the nucleus contains subnuclear bodies made up of unique proteins, RNA molecules, and parts of chromosomes.
What provides mechanical support to the nucleus in animal cells?
Two networks of intermediate filaments, including the nuclear lamina.
Where is the nuclear lamina located?
On the internal face of the nuclear envelope.
Is the nucleolus surrounded by a membrane?
No, it is not surrounded by a membrane.
What extends into the nucleoplasm from the nuclear pore ring?
A structure called the nuclear basket.
How are nuclear chromosomes packaged in eukaryotes?
By proteins into a condensed structure called chromatin.
Why is nuclear transport crucial to cell function?
It is required for both gene expression and chromosomal maintenance.
What is the first step in ribosomal assembly?
Transcription of rDNA by RNA polymerase I, forming a large pre-rRNA precursor.
What is the structure that surrounds the eukaryotic cell nucleus?
The nuclear envelope.
What happens to chromatin during cell division?
It forms well-defined chromosomes that can be seen in a karyotype.
What is the molecular weight of nuclear pores?
About 125 million daltons.
What is a chromatid?
One of the two identical parts of a chromosome after the S phase.
What are chromosomes made of?
Multiple linear DNA molecules organized into structures.
What shape is the structure found at each nuclear pore?
Donut-shaped, eightfold-symmetric ring.
How is the movement of larger molecules like proteins regulated?
It requires active transport regulated by carrier proteins.
Where are nuclear pores located?
On the surface of the nuclear envelope.
What is the nuclear envelope also known as?
Nuclear membrane.
How many nuclear pores does a typical mammalian cell nucleus have?
About 3000 to 4000 pores.
What is the composition of the nuclear lamina?
Mostly composed of lamin proteins.
What does the nuclear envelope enclose?
The nucleus.
What is the structure that allows transport in and out of the nucleus?
Nuclear pores.
What are the two arms of a chromosome called?
Short arm and long arm.
What is the nucleolus?
A discrete densely stained structure found in the nucleus.
What is the distance between the inner and outer membranes of the nuclear envelope?
10 to 50 nanometers (nm).
What does a chromosome contain?
Many genes, regulatory elements, and other nucleotide sequences.
What are the two types of chromatin?
Euchromatin and heterochromatin.
What does the cell nucleus contain?
The majority of the cell's genetic material in the form of chromosomes.
What are the two membranes that make up the nuclear envelope?
An inner membrane and an outer membrane.
What is a chromosome?
An organized structure of DNA and protein found in cells.
What aids the processing and assembly of rRNA in the nucleolus?
Small nucleolar RNA (snoRNA) molecules.
What is the DNA in the nucleus complexed as?
Chromatin.
What are nucleolar organizer regions (NOR)?
Regions of DNA coding for ribosomal RNA (rRNA).
What allows long DNA molecules to fit into the cell nucleus?
The packaging of chromosomes into chromatin.
What is the function of the centromere?
It is the point where the two chromatids touch and where the microtubules attach.
What are the subunits that the pre-rRNA precursor is cleaved into?
5.8S, 18S, and 28S rRNA.
Where does the transcription and assembly of rRNA occur?
In the nucleolus.
What are the membranes of the nuclear envelope studded with?
Ribosomes.
How are lamins synthesized?
They are synthesized in the cytoplasm and then transported into the nucleus.
What do the filamentous extensions of the nuclear pore reach into?
The cytoplasm.
What is the total diameter of nuclear pores?
100 nm.
What are the components labeled in a cross section of a nuclear pore?
Outer ring, spokes, basket, and filaments.
During which phase of the cell cycle do chromatids become visible?
During metaphase.
What is chromatin?
A DNA-protein complex that organizes chromosomes during most of the cell cycle.
What are nuclear pores composed of?
Multiple proteins collectively referred to as nucleoporins.
What forms around tandem repeats of rDNA in the nucleolus?
Ribosomal RNA (rRNA).
What is the function of the nuclear envelope?
To separate the cell's genetic material from the surrounding cytoplasm and prevent macromolecules from diffusing freely.
What is significant about the assembled ribosomal subunits?
They are the largest structures passed through the nuclear pores.
How does ribosomal assembly affect the nucleolus?
It results in the transient association of nucleolar components, facilitating further ribosomal assembly.
What characterizes unduplicated chromosomes?
They are single linear strands.
What type of molecules can diffuse through the cell membrane and bind to nuclear receptor proteins?
Steroid hormones and small lipid-soluble molecules.
What is the nuclear genome?
The genes within the chromosomes of the nucleus.
What role does the nuclear lamina play in relation to chromosomes?
It provides anchoring sites for chromosomes.
What is the relationship between the outer nuclear membrane and the rough endoplasmic reticulum?
The outer nuclear membrane is continuous with the membrane of the rough endoplasmic reticulum (RER).
What is heterochromatin?
The more compact DNA form that contains DNA that is infrequently transcribed.
How do most karyopherins interact with their cargo?
Directly, although some use adaptor proteins.
What are chromosome territories?
Discrete individual patches that chromatin organizes into during interphase.
What is one of the primary functions of the nucleus?
To maintain the integrity of genes and regulate gene expression.
What are some sources of small nucleolar RNA (snoRNA)?
Derived from spliced introns from messenger RNAs encoding genes related to ribosomal function.
What is the viscous liquid found within the cell nucleus?
Nucleoplasm.
What are the main roles of the nucleolus?
To synthesize rRNA and assemble ribosomes.
What are the two forms in which chromosomes may exist?
Duplicated or unduplicated.
What is the largest cellular organelle in animals?
The nucleus.
What is constitutive heterochromatin?
Heterochromatin that consists of chromosome structural components such as telomeres and centromeres.
What role do nuclear receptor proteins serve when bound to their ligand?
They act as transcription factors.
How many proteins do nuclear pores consist of in yeast and vertebrates?
Around 50 in yeast and 100 in vertebrates.
What is the main function of the nucleolus?
Involved in the assembly of ribosomes.
What additional support does the nuclear envelope receive?
Less organized support on the cytosolic face of the envelope.
What is the space between the inner and outer membranes called?
Perinuclear space.
What is facultative heterochromatin?
Heterochromatin that consists of genes organized as such only in certain cell types or stages of development.
What must happen for larger molecules, such as nucleic acids and larger proteins, to enter or exit the nucleus?
They must be actively transported.
What is the viscous liquid within the nucleus called?
Nucleoplasm.
What is euchromatin?
The less compact DNA form that contains genes frequently expressed by the cell.
What are karyopherins that mediate movement into the nucleus called?
Importins.
What types of molecules are transported through nuclear pore complexes?
Most proteins, ribosomal subunits, and some RNAs.
What type of molecules can freely pass through nuclear pores?
Small water-soluble molecules.
What characterizes duplicated chromosomes?
They contain two copies joined by a centromere.
Where are active genes generally located in relation to chromosome territories?
Towards the chromosome's territory boundary, typically found in the euchromatic region.
What is the role of the nuclear basket and filamentous extensions?
To mediate binding to nuclear transport proteins.
What is the width of the gap through which molecules freely diffuse in nuclear pores?
About 9 nm.
What is the function of the nucleolus within the nucleus?
It is involved in ribosome assembly.
What is the average diameter of the nucleus in mammalian cells?
Approximately 6 micrometers (μm).
What results from the compaction of duplicated chromosomes during mitosis and meiosis?
The classic four-arm structure.
How is nucleoplasm similar to cytoplasm?
It is similar in consistency and function, found inside the nucleus compared to outside.
What are karyopherins that mediate movement out of the nucleus called?
Exportins.
What family of transport factors mediates the transport through nuclear pores?
Karyopherins.
How does the nucleus appear in terms of shape?
As a dense, roughly spherical organelle.
Where are ribosomes exported after being produced?
To the cytoplasm, where they translate mRNA.
What happens to lamins after they are transported into the nucleus?
They are assembled before being incorporated into the existing network of nuclear lamina.
How is the perinuclear space related to the rough endoplasmic reticulum?
It is continuous with the RER lumen.
What percentage of the total cell volume does the nucleus occupy?
About 10%.
How does nucleoplasm compare to cytosol?
It is similar in composition to the cytosol found outside the nucleus.
What happens to many nuclear receptors in the absence of ligand?
They function as histone deacetylases that repress gene expression.
What does the nucleus contain that is crucial for genetic information?
Most of the cell's genetic material organized as DNA molecules.
What are chromosomes made of?
Long linear DNA molecules complexed with proteins like histones.
What is the main function of the nuclear envelope?
To enclose the nucleus and separate its contents from the cellular cytoplasm.
What is the nuclear lamina and its role?
It provides mechanical support within the nucleus, similar to how the cytoskeleton supports the cell.
Why are nuclear pores necessary?
Because the nuclear membrane is impermeable to most molecules, allowing movement across the envelope.
What type of cells contain a nucleus?
Eukaryotic cells.
What do nuclear pores allow for?
Free movement of small molecules and ions.
What is the nucleus often referred to as in cell biology?
The 'control center' of the cell.
