A Tour of the Cell

2 Types of Cells

  • Prokaryotes: Domain Bacteria & Archaea   * No nucleus   * DNA in a nucleoid   * Cytosol   * No organelles other than ribosomes   * Small size   * Primitive   * i.e. Bacteria & Archaea
  • Eukaryotes (Domain Eukarya): Protists, Fungi, Plants, Animals   * Has nucleus and nuclear envelope   * Cytosol   * Membrane-bound organelles with specialized structure/function   * Much larger in size   * More complex   * i.e. plant/animal cell

Cell Size and Scale

  • Cells must be small to maintain a large surface area to volume ratio
  • Large surface area allows increased rates of chemical exchange between cell and environment
  • The diffusion rate increases as the area to volume ratio increases.   * The two are directly proportional.

Nucleus

  • Nucleus Function: control center of cell
  • Contains DNA
  • Surrounded by double membrane (nuclear envelope)   * Continuous with the rough ER
  • Nuclear pores: control what enters/leaves nucleus
  • Chromatin: complex of DNA + proteins; makes up chromosomes
  • Nucleolus: region where ribosomal subunits are formed

Ribosomes

  • Ribosomes Function: protein synthesis
  • Composed of rRNA + protein
  • Large subunit + small subunit
  • Types:

     1. Free ribosomes: float in cytosol, produce proteins used within cell   2. Bound ribosomes: attached to ER, make proteins for export from cell

Endoplasmic Reticulum

  • Endoplasmic Reticulum: network of membranes and sacs
  • Types:

     1. Rough ER: ribosomes on surface      * Rough ER Function: package proteins for secretion, send transport vesicles to Golgi, make replacement membrane   2. Smooth ER: no ribosomes on surface      * Smooth ER Function: synthesize lipids, metabolize carbs, detox drugs & poisons, store Ca2+

Golgi Apparatus

  • Golgi Apparatus Function: synthesis & packaging of materials (small molecules) for transport (in vesicles); produce lysosomes
  • Series of flattened membrane sacs (cisternae)   * Cis face: receives vesicles   * Trans face: ships vesicles

Lysosomes

  • Lysosomes Function: intracellular digestion; recycle cell’s materials; programmed cell death (apoptosis)
  • Contains hydrolytic enzymes

Vacuoles

  • Vacuoles Function: storage of materials (food, water, minerals, pigments, poisons)
  • Membrane-bound vesicles
  • Eg. food vacuoles, contractile vacuoles
  • Plants: large central vacuole -- stores water, ions

Mitochondria

  • Mitochondria Function: site of cellular respiration
  • Double membrane: outer and inner membrane
  • Cristae: folds of inner membrane; contains enzymes for ATP production; increased surface area to ↑ ATP made
  • Matrix: fluid-filled inner compartment

Chloroplasts

  • Chloroplasts Function: site of photosynthesis
  • Double membrane
  • Thylakoid disks in stacks (grana); stroma (fluid)
  • Contains chlorophylls (pigments) for capturing sunlight energy

Endosymbiont Theory

  • Mitochondria & chloroplasts share similar origin
  • Prokaryotic cells engulfed by ancestors of eukaryotic cells
  • Evidence:    * Double-membrane structure   * Have own ribosomes & DNA   * Reproduce independently within cell

Peroxisomes

  • Peroxisomes Functions: break down fatty acids; detox alcohol
  • Involves production of hydrogen peroxide (H2O2)

Cytoskeleton

  • Cytoskeleton: network of protein fibers
  • Cytoskeleton Function: support, motility, regulate biochemical activities

Intracellular Junctions

  • Tight junctions: 2 cells are fused to form watertight seal
  • Desmosomes: “rivets” that fasten cells into strong sheets
  • Gap junctions: channels through which ions, sugar, small molecules can pass

Plant Cells

  • Cell wall: protect plant, maintain shape   * Composed of cellulose
  • Plasmodesmata: channels between cells to allow passage of molecules

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