TR

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
    1. 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