Tour of Cell

• All organisms are made of cells
• Cell


  The simplest collection of matter that can live
• Cell structure is correlated to cellular function
• All cells are related by their descent from earlier cells
• Microscopy


  Scientists use microscopes to visualize cells too small to see with the naked eye
• Light microscope (LM)


  Visible light passes through a specimen and then through glass lenses, which magnify the image
• Quality of an image

  • Magnification
  • Resolution
  • Contrast
• Size scale


  • Atoms
  • Small molecules
  • Lipids
  • Proteins
  • Ribosomes
  • Viruses
  • Smallest bacteria
  • Mitochondrion
  • Nucleus
  • Most bacteria
  • Most plant and animal cells
  • Frog egg
  • Chicken egg
  • Length of some nerve and muscle cells
  • Human height
• LMs can magnify effectively to about 1,000 times the size of the actual specimen
• Most subcellular structures, including organelles (membrane-enclosed compartments), are too small to be resolved by an LM
• Scanning electron microscopes (SEMs)

  Focus a beam of electrons onto the surface of a specimen, providing images that look 3-D
• Transmission electron microscopes (TEMs)

  Focus a beam of electrons through a specimen, used mainly to study the internal structure of cells
• Cell fractionation


  Takes cells apart and separates the major organelles from one another
• Cell fractionation


  1. Homogenization

  2. Differential centrifugation
• Cell fractionation enables scientists to determine the functions of organelles
• Biochemistry and cytology help correlate cell function with structure
• Prokaryotic cells


  Cells of the domains Bacteria and Archaea
• Eukaryotic cells


  Cells of protists, fungi, animals, and plants
• Basic features of all cells

  • Plasma membrane
  • Semifluid substance called cytosol
  • Chromosomes (carry genes)
  • Ribosomes (make proteins)
• Prokaryotic cells


  • No nucleus
  • DNA in an unbound region called the nucleoid
  • No membrane-bound organelles
  • Cytoplasm bound by the plasma membrane
• Eukaryotic cells


  • DNA in a nucleus that is bounded by a membranous nuclear envelope
  • Membrane-bound organelles
  • Cytoplasm in the region between the plasma membrane and nucleus
  • Generally much larger than prokaryotic cells
• Plasma membrane


  A selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell
• Biological membrane


  A double layer of phospholipids
• As the surface area increases


  The volume increases
• Small cells


  Have a greater surface area relative to volume
• Organelles in a eukaryotic cell

  • Endoplasmic reticulum
  • Golgi apparatus
  • Lysosomes
  • Vacuoles
  • Plasma membrane
  • Nucleus
  • Ribosomes
  • Mitochondrion
  • Chloroplast
  • Cytoskeleton
• Nucleus


  Contains most of the cell's genes and is usually the most conspicuous organelle
• Nuclear envelope


  Encloses the nucleus, separating it from the cytoplasm
• Chromatin


  DNA and proteins that form the genetic material
• Nucleolus


  Located within the nucleus and is the site of ribosomal RNA (rRNA) synthesis
• Ribosomes


  Particles made of ribosomal RNA and protein that carry out protein synthesis
• Endomembrane system


  Components: nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, plasma membrane
• Endoplasmic reticulum (ER)


  Accounts for more than half of the total membrane in many eukaryotic cells, with two distinct regions: smooth ER and rough ER
• Functions of smooth ER

  • Synthesizes lipids
  • Metabolizes carbohydrates
  • Detoxifies poison
  • Stores calcium
• Functions of rough ER


  • Has bound ribosomes that secrete glycoproteins
  • Distributes transport vesicles
  • Is a membrane factory for the cell
• Golgi apparatus


  Consists of flattened membranous sacs called cisternae, functions to modify products of the ER, manufacture certain macromolecules, and sort and package materials into transport vesicles
• Lysosome


  A membranous sac of hydrolytic enzymes that can digest macromolecules
• Phagocytosis


  A cell engulfs another cell, forming a food vacuole, which then fuses with a lysosome to digest the molecules
• Lysosomes also use enzymes to recycle the cell's own components
• Golgi apparatus


  Membrane factory for the cell, distributes transport vesicles, proteins surrounded by membranes