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Questions and Answers
Which statement accurately describes the function of the nuclear envelope?
Which statement accurately describes the function of the nuclear envelope?
Who is credited with the discovery of the nucleus in plant cells?
Who is credited with the discovery of the nucleus in plant cells?
What role does the nucleolus play within the nucleus?
What role does the nucleolus play within the nucleus?
Which of the following statements about chromatin is correct?
Which of the following statements about chromatin is correct?
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What is the primary importance of the nucleus in a cell?
What is the primary importance of the nucleus in a cell?
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What role does the nuclear envelope play during mitosis?
What role does the nuclear envelope play during mitosis?
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What characterizes the nuclear pore complex (NPC) in mammalian cells?
What characterizes the nuclear pore complex (NPC) in mammalian cells?
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How does transport between the nucleus and cytosol primarily occur?
How does transport between the nucleus and cytosol primarily occur?
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What is the current understanding of the nuclear pores in eukaryotic cells?
What is the current understanding of the nuclear pores in eukaryotic cells?
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Which statement is true regarding the posttranscriptional processing of mRNA?
Which statement is true regarding the posttranscriptional processing of mRNA?
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Study Notes
Nucleus Structure and Function
- Nucleus: Membrane-bound organelle found in eukaryotic cells (except red blood cells), containing DNA organized into chromosomes.
Discovery of the Nucleus
- Anton van Leeuwenhoek: Possibly first to observe nuclei in bird and amphibian blood cells.
- Francesco Fontana: Discovered nuclei in eel epidermal cells.
- Robert Brown: Observed nuclei in plant cells and coined the term "nucleus."
Nucleus Features
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Nuclear Envelope: Double membrane (inner and outer) surrounding the nucleus, separating it from the cytoplasm.
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Inner membrane: Contains proteins that anchor chromatin (DNA + protein complex).
- Nuclear lamina: Sheetlike network of nuclear lamins (intermediate filament proteins) providing structural support to the nuclear envelope, and regulating transcription. Anchored to inner membrane, and interact with chromatin.
- Outer membrane: Continuous with the endoplasmic reticulum (ER), studded with ribosomes.
- Nuclear pores: Perforations in the nuclear envelope that control the movement of molecules between the nucleus and cytoplasm. Regulate selective transport of RNA (out) and proteins (in).
- Perinuclear space: Space between the inner and outer membranes, continuous with the lumen of the ER.
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Inner membrane: Contains proteins that anchor chromatin (DNA + protein complex).
- Nucleolus: Contains ribosomal RNA (rRNA) and site of ribosome assembly. Present in cells requiring high protein synthesis.
Importance of the Nucleus
- Separates fragile chromosomes from the cytoplasm for proper function.
- Site of DNA replication, transcription, and RNA processing.
- Isolates RNA transcription from cytoplasmic translation machinery.
Regulation of Gene Expression by the Nuclear Envelope
- Post-transcriptional processing of mRNA occurs in the nucleus before transport to cytoplasm.
- Site of transcription, and involved in the transport of transcription factors from cytoplasm to nucleus. This allows regulation of gene expression.
Nucleus During Mitosis
- Nucleus temporarily disassembles during mitosis.
- Nuclear lamina depolymerizes.
- Nuclear pores disperse.
- Nuclear envelope membrane proteins disperse into ER membrane.
- Reassembly of the nuclear envelope occurs at the end of mitosis, near chromosomes.
Transport Between Nucleus and Cytoplasm
- Small molecules freely cross the nuclear envelope, but protein transport is regulated.
- Occurs via nuclear pore complexes (NPCs), which act as selective barriers.
- NPC basket collects materials for transport.
Nuclear Pores and Nuclear Pore Complex (NPC)
- NPC: ~30 nucleoporins arranged in an 8-fold rotational symmetry. Forms a large channel (~40nm diameter) allowing bidirectional transport of ~1000 macromolecules per second.
- Nucleoporins: Appear related to vesicle coat proteins, implying an ancestral membrane protein origin.
- NPC structure includes FG-nucleoporins forming a gel that restricts diffusion of larger molecules.
- Allows free passage of small molecules.
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Description
Explore the fascinating structure and function of the nucleus, the membrane-bound organelle found in eukaryotic cells. Delve into the history of its discovery by notable scientists like Anton van Leeuwenhoek and Robert Brown, and learn about the key features of the nuclear envelope, chromatin, and more.
