lecture

• The cell is the basic structural and functional unit of life
• Single-celled organisms have a short distance for substances to enter the cell, while multicellular organisms have a larger distance due to a higher surface area to volume ratio
• Plasma membrane:

  • Also known as cell membrane or plasmalemma
  • Thickness: 7.5 to 10 nm
  • Trilaminar appearance under TEM
  • Components include phospholipid bilayer, cholesterol, proteins, and oligosaccharide chains
• Phospholipid Bilayer:

  • Fat molecule with attached phosphate groups
  • Polar Heads, Nonpolar Tails (Hydrophilic head, hydrophobic tail)
  • Outer and inner layer lipids are different, making all membranes in the cell asymmetric
• Glycolipids:

  • Outer layer lipid with oligosaccharide chain extending outward
  • Contributes to a cell surface coating called glycocalyx
  • Important for cell recognition, cell-to-cell attachments, and as receptor or binding sites for different bloodborne hormones
• Cholesterol:

  • Stabilizes the cell membrane
  • Modulates fluidity of all membrane components
• Proteins:

  • Approximately 50% of the membrane is made of protein
  • Able to move laterally
  • Integral proteins within the bilayer (multipass proteins)
  • Peripheral proteins bound to one of the two membrane surfaces
  • Glycoproteins have carbohydrate moieties contributing to the glycocalyx
• Functions of the cell membrane:

  1. Physical Barrier

  2. Selective Permeability

  3. Electrochemical Gradients

  4. Communication
• Endocytosis:

  • Ingestion of extracellular material into the cell
  • Types include pinocytosis and phagocytosis
• Exocytosis:

  • Release of material from the cell
• Cytoplasm:

  • Material between the plasma membrane and the nucleus
  • Consists of fluid part (cytosol), organelles, cytoskeleton, and inclusions
• Ribosomes:

  • Two associated globular subunits of RNA and protein
  • Function as scaffold and catalyst for protein synthesis
• Endoplasmic Reticulum:

  • Convoluted network of membrane enclosing continuous spaces
  • Acts as a quality control center of the cell
  • Rough ER is the site of protein synthesis and folding
  • Smooth ER is the site of lipid synthesis, carbohydrate metabolism, and detoxification
• Golgi Apparatus:

  • Series of flattened, stacked cisternae
  • Functions in posttranslational modification and packaging of proteins
  • Forms secretory vesicles and lysosomes
• Lysosomes:

  • Spherical-shaped membrane-bound organelles
  • Contains hydrolytic enzymes for intracellular digestion and recycling
• Mitochondria:

  • Double-membrane bound organelles known as the "powerhouse of the cell"
  • Contains enzymes for ATP synthesis
  • Inner membrane releases cytochrome c triggering apoptosis in states of stress
• Peroxisomes:

  • Sacs with single outer membranes housing enzymes
  • Functions include breakdown of lipids, synthesis of bile acids, and detoxification
• Nucleus:

  • Largest organelle containing chromatin, nucleoli, nuclear matrix, and cellular DNA
  • Chromatin is the combination of DNA and histone proteins
  • Functions as the genetic material for directing protein synthesis
• Centrosomes:

  • Contains a pair of centrioles
  • Functions in organizing microtubules and mitotic spindle formation during cell division
• Cytoskeleton:

  • Organized network of protein filaments and hollow tubules
  • Provides structural support, assists with cell motility, and helps move organelles and materials throughout the cell
• Microfilaments:

  • Long, thin rods
  • Made up of actin monomers organized into two thin, intertwined protein filaments (actin filaments)
  • More common along the peripheral regions of the cell
  • Functions:
  • Shapes the cell, involved in cell movement and movement of cytoplasmic organelles
  • Enable cells to withstand stretching and compression (maintain cell shape)
  • Distributed throughout the cells and are used as anchors at cell junctions
• Intermediate filaments:

  • Thicker than microfilaments
  • Composed of different types of proteins in different cell types
  • Examples in specific cell types:
  • Epithelial cells: Keratin
  • Mesenchymal cells: Vimentin Filaments
  • Smooth and Striated muscles: Desmin Filaments
  • Nerve cells and their processes: Neurofilament Proteins
  • Astrocytic Glial Cells and the Nervous System: Glial Filaments
  • Inner layer of the nuclear membrane: Lamin Intermediate Filaments
  • Function: Stabilize the shape of the cell and attachments to adjacent cells
• Microtubules:

  • Hollow cylinders composed of tubulin proteins (⍺ and β tubulin)
  • Examples of structures:
  • Cilia
  • Motile Cilia (Movement) and Primary Cilia (Sensory Function)
  • Flagella
  • Centrosomes and Centrioles
  • Functions:
  • Motile Cilia: Generate coordinated movement to move the cell or propel substances along its surface
  • Primary Cilia: Serve as antennae to sense signals from outside cells and stimulate cells to move
  • Bardet-Biedl Syndrome: A disorder affecting cilia function, leading to various health issues
• Cell Division:

  • Process by which cells multiply
  • A parent cell divides into two daughter cells
  • Part of the cell cycle
  • Two main types: Meiosis and Mitosis
• Meiosis vs. Mitosis:

  • Meiosis produces genetically different daughter cells (e.g., gametes)
  • Daughter cells in meiosis are haploid
  • Mitosis produces genetically identical daughter cells
  • Daughter cells in mitosis are diploid
• The Cell Cycle:

  • Consists of two general phases: Interphase and M Phase
  • M Phase includes four stages: Prophase, Metaphase, Anaphase, Telophase
• Interphase:

  • Long period between mitoses
  • Three phases: Gap 1 (G1), S Phase or Synthesis, Gap 2 (G2)
  • Some cells do not exhibit division, while others only divide to replace damaged or lost cells
  • Cells that do not divide further enter an inactive G0 phase
• M Phase:

  • Partitions genetic material into two daughter cells
  • Includes four stages: Prophase, Metaphase, Anaphase, Telophase
  • Progression through the cell cycle is halted by adverse conditions like inadequate nutrition or DNA damage
• Mitosis:

  1. Prophase

  • Chromosomes condense, nuclear envelope disappears, centrosomes divide

  2. Metaphase

  • Chromosomes align in the center of the cell

  3. Anaphase

  • Chromatids separate and move towards opposite poles

  4. Telophase

  • Chromosomes migrate to opposite sides, nuclear envelope reforms, cleavage furrow appears for cell division
• Meiosis:

  • Specialized cell division in germ cells
  • Produces haploid ova and sperm with genetic recombination
  • Two meiotic divisions result in haploid cells
• Apoptosis:

  • Process of programmed cell death
  • Involves activation of caspases and endonucleases leading to cell and nuclear shrinkage
  • Cell membrane changes produce blebbing, and apoptotic bodies are phagocytosed
  • Rapid process with little inflammation
• Medications used in chemotherapy target specific steps in the cell division/cell cycle to hinder the growth of cancer cells
• Mitotic count is part of the grading system of some tumors in histopathology
• Medications like Granulocyte – Colony Stimulating Factor (G-CSF) and erythropoietin are used in treating patients
• Stem cell treatment is used in some forms of cancer
• Most organs can be divided into parenchyma and stroma
• Epithelial cells exhibit polarity with apical, lateral, and basal poles
• Functions of epithelium include covering, lining, protecting surfaces, absorption, and secretion
• Surface modifications of epithelium include microvilli, stereocilia, and cilia
• Basement Membrane is beneath epithelial cells and consists of Basal Lamina and Reticular Lamina