Recording-2025-02-26T17:39:45.727Z.m4a

Ribosome Production and Nucleoli

• Ribosomes are partially formed in the nucleus and transported to the cytoplasm.

• Increased nucleoli activity correlates with higher ribosome production due to cellular activity demands.

Chromosome Organization in the Nucleus

• Chromosomal Localization: Chromosomes are positioned strategically within the nucleus to facilitate gene expression control.

  • Fluorescent dyes can highlight different chromosomes in mammalian nuclei and identify chromosome pairs (e.g., red, green, blue).

  • Chromosomes reside in distinct subdomains rather than being randomly distributed in nucleoplasm.

• Chromosomal Subdomains:

  • Active Genes: Decondensed genes at the periphery interact with enhancer/promoter elements across adjacent chromosomes.

  • Interchromosomal Channels: Spaces between chromosomes that restrict interaction, permitting controlled gene expression.

Transcription Factors and Gene Expression

• Transcription Regions: Regions where active transcription occurs (transcription factors) are located in interchromosomal channels.

  • Genes with nearby enhancer/promoter elements can interact for synchronized transcription.

• Kissing Chromosomes: Interaction between elements from different chromosomes is facilitated through spatial organization.

Nuclear Speckles as Subdomains

• Definition: Nuclear speckles are subdomains where splicing factors relevant for mRNA processing are found.

• Dynamics: Speckles can grow and change size based on transcriptional activity, adapting to cellular needs.

Nuclear Matrix

• Function: A structural scaffold within the nucleus that maintains shape and organization, connecting chromosomes and speckles.

• Unique Composition: Composed of specific proteins different from cytoplasmic cytoskeleton elements (actin, microtubules).

  • The dynamic nature of this structure allows for the spatial positioning of chromosomal regions.

Nuclear Envelope Structure

• Components: The nuclear envelope consists of three primary parts:

  1. Nuclear Membranes: Two membranes that enclose the nucleus and are continuous with the endoplasmic reticulum (ER).

  2. Lamina: A network providing mechanical support to the inner nuclear membrane, made up of lamin proteins.

  3. Nuclear Pore Complexes (NPCs): Structures facilitating transport between the nucleus and cytoplasm.

• Lamina Functions: The lamina anchors chromatin and provides structural stability to the nuclear envelope.

  • Mutations in lamin genes can lead to disorders such as progeria, affecting nuclear structure and function.

Nuclear Pore Complexes (NPCs)

• Role: NPCs are essential doorways for transport of RNA, proteins, and small molecules in and out of the nucleus.

• Characteristics:

  • Composed of around 40-50 proteins (nucleoporins) with an eightfold symmetry.

  • Central channel dimensions allow for selective transport based on size; molecules above 40 kilodaltons cannot pass.

• Central Scaffold and Structure:

  • The central scaffold is embedded in the nuclear envelope and connects to both cytoplasmic and nucleoplasmic rings.

  • FG Nucleoporins: Create a mesh-like structure within the pore, permitting selective passage and regulation of materials.

Pathway for Protein Recognition and Transport

• Cytoplasmic Filaments and Nuclear Basket:

  • Cytoplasmic filaments interact with incoming proteins to facilitate transport into the nucleus.

  • The nuclear basket serves as a final checkpoint where proteins can be accepted or rejected before entering the nucleoplasm.

• Transport Dynamics: NPCs organize in groups influenced by associated chromatin regions, enhancing efficiency based on cellular activity levels.