Cell Physiology: Structure and Function

Cell Physiology: Structure and Function

• Cells are the fundamental units of life, performing essential functions like reproduction, metabolism, and response.
• There are two main types of cells: prokaryotic and eukaryotic.
  • Prokaryotic cells lack a nucleus, found in bacteria, while eukaryotic cells are more complex, containing a nucleus, and found in plants, animals, and fungi.
• Cells are organized into levels: chemical, cellular, tissue, organ, system, and organismal.

Cell Structure

• Cell Membrane (Plasma Membrane):

  • Forms a barrier separating the cell's interior from its surroundings.
  • Controls the movement of substances in and out of the cell, maintaining homeostasis.
  • Composed of a phospholipid bilayer with hydrophilic heads facing outward (water-loving) and hydrophobic tails facing inward (water-fearing).
  • Contains embedded proteins with various functions, including transport, receptors, and structural support.

• Transport Across the Cell Membrane:

  • Passive Transport:
    • Requires no energy.
    • Moves substances down a concentration gradient (high to low concentration).
    • Includes simple diffusion (movement of molecules from higher to lower concentration), and facilitated diffusion (movement of molecules through channels or carrier proteins).
  • Active Transport:
    • Requires energy (ATP).
    • Moves substances against a concentration gradient (low to high concentration).
    • Includes ion pumps like Na+/K+.

• Vesicular Transport:

  • Substances moved into or out of the cell using vesicles or vacuoles.
  • Endocytosis:
    • Takes material into the cell.
    • Includes phagocytosis(cell eating) and pinocytosis (cell drinking).
  • Exocytosis:
    • Releases material from the cell.

Cell Organelles

• Nucleus:

  • Control center of the cell, containing DNA, controlling gene expression, and containing ribosomes necessary for protein synthesis.

• Mitochondria:

  • Powerhouses of the cell, producing energy in the form of ATP (adenosine triphosphate) through cellular respiration.

• Endoplasmic Reticulum (ER):

  • Network of membranes involved in protein and lipid synthesis, folding, and transport.
  • Rough ER has ribosomes, primarily for protein synthesis; smooth ER for lipid metabolism and detoxification.

• Golgi Apparatus:

  • Modifies, sorts, and packages proteins and lipids for secretion or use within the cell.

• Lysosomes:

  • Contain digestive enzymes that break down cellular waste products and foreign materials.

• Vacuoles:

  • Storage compartments for water, ions, nutrients, and waste products.

• Peroxisomes:

  • Break down fatty acids and other harmful substances.

• Ribosomes:

  • Involved in protein synthesis.

• Centrioles:

  • Important for cell division.

• Cilia and flagella:

  • Hair-like structures involved in movement and other cellular functions.

• Microvilli:

  • Increase surface area for absorption and secretion.

• Osmosis: Diffusion of water across a selectively permeable membrane. Important for maintaining water balance.