Recording-2025-02-24T19:05:54.446Z

Nutrients and Cell Membranes

  • Cell membranes are crucial for concentrating nutrients and retaining them for:

    • Energy production

    • Building cellular molecules

  • All cells must synthesize proteins, facilitated by ribosomes.

  • Ribosome presence:

    • Varies by cell type (1 to thousands)

    • Essential for protein synthesis.

Cytoplasm

  • Definition: Jelly-like substance inside cells (fluid-filled).

  • Functions:

    • Surrounds all cellular structures not clearly visible.

    • Similar to the interstitial fluid in organisms.

    • Concentrates molecules from the environment for cellular needs.

Overview of Cellular Organelles

  • Introduction to organelles: Tour through various organelles begins.

Nucleus

  • Control center of the cell:

    • Contains DNA

    • Has a double membrane (nuclear envelope):

      • Composed of an inner and outer membrane with space in-between.

  • Function of double membrane:

    • Slows diffusion to protect DNA and nuclear contents.

    • Pores in the membrane permit selective transport in/out.

    • Special pores can close if DNA approaches, protecting it from cytoplasmic enzymes.

  • Importance of nucleus in cellular processes:

    • Prevents destruction of DNA from enzymes targeting rogue DNA (potential viruses).

  • RNA can exit the nucleus through pores (different from DNA's restricted movement).

Nucleolus

  • Nucleolus structure:

    • Region within the nucleus where DNA is concentrated.

    • Contains chromatin made from DNA wrapped around proteins for organization.

  • Chromatin vs. chromosomes:

    • Chromatin: Loosely organized DNA during non-dividing periods.

    • Chromosomes: Tightly wound, visible during cell division (mitosis).

  • Involvement in ribosome production:

    • Nucleolus synthesizes ribosomal RNA (rRNA) that forms ribosomes.

Ribosomes

  • Composition:

    • Made of ribosomal RNA and proteins.

    • Consist of two subunits (small and large).

  • Ribosome sizes in different cell types:

    • Prokaryotes:

      • Small subunit: 30S

      • Large subunit: 50S

      • Total functional ribosome: 70S

    • Eukaryotes:

      • Small subunit: 40S

      • Large subunit: 60S

      • Total functional ribosome: 80S

  • Significance of difference in ribosome structure:

    • Allows antibiotic targeting (e.g., macrolide antibiotics target bacterial ribosomes without affecting eukaryotic ribosomes).

Protein Synthesis

  • Importance for certain cells:

    • Cells like those in the pancreas producing insulin have many ribosomes (thousands) due to constant protein production.

    • Muscle fibers also contain numerous ribosomes for repairing proteins damaged by movement.

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