WEEK 2: Cell Structures & Functions

• Cell Structures


  Specialized structures in cells that perform specific functions
• Organelles


  • Nucleus, mitochondria, ribosomes
• Cytoplasm


  Jelly-like substance that holds organelles
• Cell membrane


  Also termed the plasma membrane, a structure that encloses the cytoplasm

  
• Functions of the cell


  • Smallest units of life
  • Cell metabolism and energy use
  • Synthesis of molecules
  • Communication
  • Reproduction and inheritance
• Robert Hooke looked at a piece of cork under a microscope and called the chambers he saw as cells


  1665
• Anton van Leeuwenhoek studied organisms found in pond water and called them animalcules


  1665-75
• Schleiden and Schwann summarized the findings of many scientists and concluded that all living organisms are made of cells, forming the basis of the Cell Theory


  1830
• Cell Theory


  • All organisms are composed of cells
  • The cell is the structural unit of life
  • Cells arise by division of pre-existing cells
  • Cells can be cultured to produce more cells
• Cell membrane


  The outer most component of a cell, forms a boundary between material inside and outside the cell

  
• Intracellular


  Materials inside the cell
• Extracellular


  Materials outside the cell
• Cell membrane acts as

  A selective barrier
• Fluid-mosaic model


  The model used to describe the cell membrane structure

  
• Components of the cell membrane

  • Phospholipids
  • Cholesterol
  • Proteins
  • Carbohydrates
• Phospholipid bilayer


  The structure of the cell membrane

  
• Phospholipid structure


  Polar head region (hydrophilic) and nonpolar tail region (hydrophobic)
• Nucleus


  A large organelle usually located near the center of the cell, bounded by a nuclear envelope
• Nuclear envelope


  Consists of outer and inner membranes with a narrow space between them
• Nuclear pores


  Allow materials to pass into or out of the nucleus
• Chromosomes


  23 pairs in human cells, consist of DNA and proteins
• Chromatin


  Loosely coiled chromosomes during most of a cell's life
• Nucleoli


  Diffuse bodies within the nucleus where ribosomal subunits are formed
• Ribosomes


  Organelles where proteins are produced, may be attached to other organelles or free in the cytoplasm
• Endoplasmic reticulum (ER)


  A series of membranes forming sacs and tubules, rough ER involved in protein synthesis, smooth ER involved in lipid synthesis and calcium ion storage

  
• Golgi apparatus


  Collects, modifies, packages, and distributes proteins and lipids manufactured by the ER

  
• Lysosomes


  Membrane-bound vesicles formed from the Golgi apparatus, contain enzymes that function as intracellular digestive systems
• Peroxisomes


  Small, membrane-bound vesicles containing enzymes that break down fatty acids, amino acids, and hydrogen peroxide
• Mitochondria


  Organelles responsible for producing ATP by aerobic metabolism, have inner and outer membranes
• Cytoskeleton


  Protein structures that support the cell, hold organelles in place, and enable the cell to change shape
• Microtubules


  Hollow structures formed from protein subunits, perform various roles including supporting the cytoplasm, assisting in cell division, and forming components of cilia and flagella
• Microfilaments


  Small fibrils formed from protein subunits that structurally support the cytoplasm and are involved in cell movement
• Intermediate filaments


  Fibrils formed from protein subunits that provide mechanical support to the cell, including keratin in skin cells
• Centrosome


  Specialized area of cytoplasm close to the nucleus where microtubule formation occurs, contains two centrioles
• Centrioles


  Small, cylindrical organelles composed of microtubules, involved in mitosis
• Cilia


  Cylindrical structures that extend from the cell surface and are composed of microtubules, responsible for the movement of materials over the cell surface
• Flagella


  Similar structure to cilia but much longer, usually one per cell, propel sperm cells
• Microvilli


  Specialized extensions of the cell membrane supported by microfilaments, increase the surface area of cells
• The cell cycle


  1. G1 - first gap

  2. S - DNA synthesis

  3. G2 - second gap

  4. M - mitosis
• Centriole


  • Cilia project from the surface of certain cells
  • They are responsible for the movement of materials over the top of cells, such as mucus
  • Cilia are cylindrical structures that extend from the cell and are composed of microtubules