1.7 Cellular level of organisation

Cells and Tissues

The Cell

Cytoskeleton

  • Support Function: Provides structural support and helps maintain cell shape.

  • Cell Motion: Plays a vital role in cell movement.

Components of the Cytoskeleton

  • Microtubules: Tubular structures of protein; found in cytoplasm, centrioles, cilia, and flagella.

  • Intermediate Filaments: Intertwined protein fibers; provide support and strength.

  • Actin Filaments: Twisted protein fibers; responsible for cell movement.

Organelles

  1. Nucleus

    • Command Center: Houses genetic material and regulates gene expression.

    • Nucleolus: Site for ribosome production.

    • Nuclear Envelope: Double membrane with nuclear pores for regulating substance passage.

  2. Ribosomes: Sites for protein synthesis, can be free or attached to the rough endoplasmic reticulum.

  3. Mitochondria: Organelles for energy extraction through oxidative metabolism.

  4. Lysosomes: Contain enzymes for breaking down macromolecules; function optimally in acidic conditions.

  5. Golgi Complex: Packages and distributes molecules synthesized in the cell.

  6. Peroxisomes: Contain enzymes for detoxification of harmful substances.

Nucleus

Structure

  • Nuclear Envelope:

    • Double membrane with openings called nuclear pores

    • connects with rough ER.

    • most cells have on necleus

    • few cells types have multiple nuclei

      • E.G. skeletal muscle cells

  • Chromatin: Complex of DNA and proteins; condenses into chromosomes during cell division.

    • A complex of DNA and proteins found in the nucleus of eukaryotic cells. It condenses into chromosomes during cell division and plays a key role in regulating gene expression by activating or suppressing genes.

  • Nucleolus

    • essential to make ribosomes

    • site of rRNA synthesis and initial ribosome assemble

    • Amembraneous

      • structures that play a critical role in cellular function, the nucleolus is not only involved in ribosome production but also in regulating cellular stress responses.

Function

  • Regulates gene expression by activating or suppressing genes.

  • Synthesises ribosomal subunits and exports them to the cytoplasm.

  • Houses the DNA

    • about 20 000 genes are present in the human genome, each playing a crucial role in the development and functioning of the organism.

Relationship to Disease

  • Mutations can affect gene regulation leading to diseases.

Cytosool

  • Intracellular liquid

  • surrounds organelles

  • 55% of total cell volume

Ribosomes

  • formed in the nuclus

  • contains high RNA

  • consist of 2 subunits

  • produces protein

  • attached to endoplasmic reticulum

    • Rough ER

      • Synthesis of proteins that are either secreted from the cell, incorporated into the cell's plasma membrane, or sent to an organelle.

      • Studded with ribosomes on its cytoplasmic surface, which are responsible for translating mRNA into protein, making it rough in appearance.

    • Free ribsomes

      • make proteins that t=are required inside the cell

Endoplasmic reticulum

  • Smooth Endoplasmic Reticulum:

    • Lacks ribosomes and is involved in lipid synthesis and detoxification processes.

  • Rough Endoplasmic Reticulum:

    • continuous with nuclear envelope

    • studded with ribosomes

    • structural modifications of proteins

Golgi Complex

  • Function:

    • Modifies, sorts, and packages proteins. Like a post office , the Golgi Complex ensures that proteins are delivered to their correct destinations, whether they are secreted outside the cell, sent to the cell membrane, or directed to lysosomes.

  • Structure: Composed of cisternae (flattened membrane sacs); two sides (cis and trans) for entry and exit.

  • Golgi Dysfunction: Linked to various diseases including pulmonary hypertension, neurodegenerative diseases, and hormone related conditions.

Lysosomal Diseases

  1. Gaucher Disease: Blood and bone-related symptoms.

  2. Fabry Disease: Eye movement and skin issues.

  3. Pompe Disease: Muscle weakness and loss of motor skills.

  4. Tay-Sachs Disease: Devastating neurological disease evident in infants.

Vesicle/Vacuoles

  • Vesicles:

    • Small membrane-bound sacs within the cell, involved in transport and storage of substances.

  • Function:

    • They can transport materials to various parts of the cell or even out of the cell, engulf other materials for digestion, or store substances for later use (like hormones or enzymes).

  • Vacuoles:

    • Larger membrane-bound sacs, often found in plant cells, that store various substances and help maintain turgor pressure for structural support.

  • Function:

    • They play roles in storage, waste disposal, and maintaining the integrity of the cell structure by keeping it turgid (swollen) with fluid, which is essential for plant cell rigidity and overall health.: Larger membrane-bound sacs, often found in plant cells, that store various substances and help maintain turgor pressure for structural support.
      Mitochondria

  • ATP Production: Main energy source for the cell; 100s to 1000s per cell.

  • Self Replication: Contains its own DNA.

  • Site of Cellular Respiration: Energetic processes occur within its inner membrane (cristae).

Cytoskeleton

  • Structure: Provides strength, shape, support, and flexibility.

  • Filament Types: Microtubules, intermediate filaments, and actin filaments.

  • Centrosome: Key for cell division and implicated in cancer and other diseases.

Cell Projections

  • Microvilli: Increase cell surface area.

  • Cilia: Hair-like structures to move fluid.

  • Flagella: Longer than cilia, used for cell movement.

Plasma Membrane

Function

  • Protection: Maintains structural integrity of cells and regulates substance entry and exit.

  • Communication: Participates in cellular signaling and maintains the chemical composition of cytoplasm and extracellular fluid.

Phospholipid Bilayer

  • Composed of hydrophilic heads and hydrophobic tails; crucial for membrane fluidity and integrity.

RNA Transcription

  1. Initiation: RNA polymerase begins transcription.

  2. Elongation: Synthesizes RNA from DNA template.

  3. Termination: Concludes transcription at terminator sequence.

Conclusions

  • Understanding cell and tissue structures is essential for relating cell biology to health and disease.