CH4

• Cells

  1. Discovered in 1665 by Robert Hooke

  2. Schleiden and Schwann proposed the Cell Theory in the 1830s
• Cell Theory
• 2. Cells are the smallest living things, the basic unit of organization.
• 3. Cells arise only from pre-existing cells, copying their DNA and dividing into two
• 1. All organisms are composed of one or more cells.
• Cell Size
• Cells are small, limited by diffusion
• Volume increases ~10x faster than surface area
• Key microscope parameters:
• Surface area to volume ratio
• Microscopes are required to visualize most cells
• 1. Magnification – enlarging an object
• Electron microscopes are capable of higher magnification and resolution, very specialized and expensive, can't be used with living organisms
• 2. Resolution – distinguishing adjacent structures as separate
• Transmission electron microscopes (TEM) can show detail within cells
• All cells contain:
• Components of all cells

  • Genetic material – DNA in nucleus or nucleoid region
  • Cytoplasm – gel-like, semi-fluid
  • Plasma (cell) membrane – separates the inside from the outside of the cell
  • Ribosomes – for protein synthesis
• Scanning electron microscopes (SEM) provide 3-D exterior views
• Prokaryotic Cell

  1. Cytoplasm

  2. (aka plasma membrane)
• Prokaryotic shapes

  • Coccus = Spherical
  • Bacillus = Rod-shaped
  • Spirillum = Helical
• Prokaryotes are typically single-celled, less than 10 µm in diameter, have a single circular chromosome, have no membrane-bounded organelles, are surrounded by a cell wall and sometimes a capsule, and may have external structures
• Cell Structure

  • Cell theory
  • Cell size & Microscopes
  • Prokaryotic cells
  • Eukaryotic cells
  • Extracellular structures
  • Cell-to-cell interactions
• Ribosomes

  For protein synthesis
• TEM showing internal structures

  1. Nucleoid region

  2. Ribosomes

  3. Invaginated membranes - For respiration or photosynthesis
• Prokaryotic Cell Walls

  1. Protect the cell and maintain cell shape

  2. May be composed of peptidoglycan - Chains of sugars crosslinked by short peptides

  3. May be Gram positive or Gram negative
• Eukaryotic Cell parts

  • Plasma membrane
  • Microvilli
  • Cytoplasm
  • Nucleus
  • Smooth ER
  • Rough ER
  • Golgi apparatus
  • Lysosome
  • Mitochondrion
  • Ribosomes
  • Centrioles
  • Cytoskeleton
  • Peroxisome
• The Bacterial Cell Wall in Gram-positive cells is thick single-layered peptidoglycan wall and stains purple. In Gram-negative cells, it is multi-layered with a thin peptidoglycan layer and stains pink
• Eukaryotic Cells are more complex and typically larger than prokaryotic cells, have a membrane-bound nucleus, membrane-bound organelles and the endomembrane system, and a cytoskeleton
• Cytoplasm consists of organelles suspended in gel-like cytosol plus the cytoskeleton, and is 70-80% water but has a semi-solid consistency due to proteins within it
• The Nucleus typically stores the genetic material in chromosomes, DNA is organized with proteins to form chromatin, often has a nucleolus, and is surrounded by a nuclear membrane
• Nuclear envelope

  • Double membrane
  • Contains nuclear pores which regulate flow of molecules into and out of the nucleus
• Chromatin


  • Complex of DNA with proteins, especially histone proteins
  • Forms nucleosomes
• Nuclear Pores


  • Regulate flow of molecules into and out of the nucleus
• Nucleus

  • Typically the largest organelle
  • Stores the genetic material in chromosomes
  • DNA is organized with proteins to form chromatin
  • Often has nucleolus
  • Surrounded by a nuclear envelope
• Cytosol


  • Contains the cytoskeleton
  • 70-80% water but has semi-solid consistency due to proteins within it
• Nuclear lamina

  • Meshwork of proteins just inside the nucleus
• Nucleolus


  • Region inside the nucleus where ribosomes are assembled from RNA & proteins
• Two states of DNA

  • Highly condensed during cell division forming linear chromosomes
  • Relaxed during interphase, thread-like and non-distinct = chromatin
• Endomembrane System


  • A series of membranes throughout the cytoplasm dividing the cell into compartments where different cellular functions occur
  • Includes Endoplasmic Reticulum, Golgi apparatus, Secretory vesicles, Lysosomes, Endosomes
• Learning Objectives include explaining the structures, functions, and locations of the parts of animal and plant cells, describing protein transport through the endomembrane system, explaining the model and support for the theory of endosymbiosis, describing the cytoskeleton composition and functions, describing extracellular structures, and differentiating between different types of cell junctions