Recording-2025-01-22

Cellular Organelles

Lysosomes

• Structure: Sac-like organelles containing digestive enzymes.

• Function: Break down waste materials and cellular debris.

Peroxisomes

• Contain oxidative enzymes.

• Major sites of oxygen utilization.

• Detoxify harmful compounds and fatty acids.

• Use oxygen to remove hydrogen atoms, forming water as a byproduct, affecting pH.

• Synthesize special phospholipids for myelination of nerve cells, critical for insulating nerve fibers with myelin.

Mitochondria

• Known as the powerhouse of the cell.

• Responsible for cellular respiration and energy production.

• Function: Combination of oxygen and nutrients to produce adenosine triphosphate (ATP), the energy currency of the cell.

Cytosol

• The semi-liquid portion of the cytoplasm, making up over half of the cell's volume.

• Functions:

  • Sites for enzymatic biochemical reactions (intermediary metabolism).

  • Ribosome activity for protein synthesis.

  • Storage of wastes and nutrients.

Cytoskeleton

• Provides structural support to the cell.

• Facilitates movement of substances within the cell.

• Composed of microtubules that form a latticework for structural integrity and organelle support.

• Key role in protecting DNA.

Plasma Membrane

• The outer boundary of the cell.

• Functions:

  • Regulates entry and exit of substances via selective transport.

  • Provides cell-to-cell recognition through surface markers (antigens).

  • Cell mobility and shape maintenance.

Membrane Structure

Phospholipid Bilayer

• Composed of hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.

• Orientation: Hydrophobic tails face inward, hydrophilic heads face outward toward the aqueous environment.

Embedded Structures

• Include channels for material transport and receptor sites for enzyme release.

• Proteins within the bilayer serve numerous functions, including:

  • Transport of substances.

  • Acting as receptors for signaling molecules.

  • Serving as surface markers for cell identification.

  • Adhesion molecules for cell-to-cell attachment.

Cellular Communication

• Essential for maintaining homeostasis and coordinating cellular functions.

• Types of signaling include:

  • Paracrine signaling: Chemical messages sent to nearby cells.

  • Autocrine signaling: Cells stimulate themselves, often seen in cancer.

  • Hormonal signaling: Hormones released into the bloodstream targeting distant tissues.

  • Neurohormonal signaling: Nerves releasing substances into blood for systemic effects.

  • Neurotransmitter: Signals between nerve and muscle cells, facilitating contractions.

Cell Junctions and Adhesion

• Structures that bind cells together to form tissues.

• Extracellular matrix: Fibrous proteins that connect cells (e.g., collagen, elastin).

• Cell adhesion molecules: Integrins, cadherins, and selectins facilitate connections between cells.

• Several types of specialized junctions:

  • Desmosomes: Provide mechanical linkages between cells.

  • Hemidesmosomes: Attach cells to the basement membrane.

Cellular Metabolism

• Involves chemical reactions that maintain cellular function.

• Divided into:

  • Anabolism: Energy-utilizing processes for building molecules.

  • Catabolism: Energy-releasing processes for breaking down molecules.

• ATP is produced in mitochondria via respiratory processes combining carbohydrates, lipids, or proteins.

• Energy from food is processed through glycolysis and the Krebs cycle to produce ATP efficiently.