cell structure

Overview of Cellular Biology

• Discussion focuses on eukaryotic cells and their various systems, particularly the endomembrane system and the fluid mosaic model.

Prokaryotic vs Eukaryotic Cells

Prokaryotic Cells

• Comprise two domains: bacteria and archaea.

• Characterized by smaller size and absence of membrane-bound compartments.

Eukaryotic Cells

• Larger than prokaryotes and contain a nucleus and membrane-bound organelles.

• Include kingdoms: animals, plants, fungi, often multicellular.

Viruses

• Not classified as living organisms; consist of a protein capsid and genetic material but cannot regulate transport or perform metabolic activities autonomously.

• Obligate intracellular parasites requiring host cells for replication and propagation.

  • Example: Bacteriophage uses host cell to replicate viral DNA/RNA.

  • Influenza virus injects viral RNA into host cells to replicate.

  • HIV integrates genetic material into host's genome, affecting immune cells.

Structure of Eukaryotic Cells

Nucleus

• Contains the genome of eukaryotic organisms, enclosed in a nuclear envelope.

  • Double phospholipid bilayer allows for transport via nuclear pores.

  • Inner lining is the nuclear lamina, providing structural support.

  • Nucleolus is where ribosomal RNA is synthesized.

Endomembrane System

• Essential for synthesis, modification, and transport of proteins and lipids.

• Main components:

  • Endoplasmic Reticulum (ER)

    • Rough ER: Studded with ribosomes; synthesizes proteins for export or membrane embedding.

    • Smooth ER: Responsible for lipid synthesis, detoxification, and calcium storage.

  • Golgi Apparatus

    • Processes, modifies, and sorts proteins synthesized in the ER; involved in glycosylation.

    • Package proteins into vesicles for delivery to plasma membrane (exocytosis) or lysosomes.

  • Lysosomes

    • Single-membrane organelles responsible for cellular digestion via processes such as phagocytosis, autophagy, and receptor-mediated endocytosis.

Movement of Materials in & out of Cells

Exocytosis and Endocytosis

• Exocytosis: Process of exporting materials out of the cell through vesicles.

• Endocytosis: Process by which cells uptake materials.

Fluid Mosaic Model of Cell Membrane

• Describes the cell membrane as a phospholipid bilayer with integrated proteins and other molecules that move fluidly.

• Mosaic refers to the diverse components of lipids, proteins, and carbohydrates embedded in the membrane.

Organelles Outside the Endomembrane System

Peroxisomes

• Responsible for oxidation reactions such as breaking down hydrogen peroxide.

• Involved in metabolism of fatty acids and other compounds.

Vacuoles

• Membrane-bound sacs, primarily found in plant and fungal cells, used for storing water and maintaining cell rigidity.

Mitochondria

• Known as the powerhouse of the cell, responsible for cellular respiration and ATP production.

  • Contains cristae and mitochondrial matrix for maximizing surface area for reactions.

  • Transform glucose into ATP, the cell’s energy currency.

Chloroplasts

• Site of photosynthesis in plant cells; converts solar energy into chemical energy in the form of glucose.

• Contains thylakoids for light reactions and stroma for Calvin cycle.

Evolutionary Theory of Organelles

• Evidence suggests that mitochondria and chloroplasts evolved from prokaryotic cells via endosymbiosis, characterized by their own circular DNA and double membranes.

Cell Wall vs Cell Membrane

• Cell membrane: All cells have it, made of phospholipids.

• Cell wall: Present in certain cells (plants, fungi, bacteria) for structure and support, made of materials such as cellulose, chitin, and peptidoglycan.

  • Cellulose: Found in plants.

  • Chitin: Found in fungi and arthropods.

  • Peptidoglycan: Found in bacterial cell walls.

Summary

• Understanding of eukaryotic cells is essential for studying complex organisms and their interactions with viruses and other cellular structures.