Major Parts of the Cell – Quick Review

Plasma Membrane

• Primary barrier separating cytoplasm from external environment
• Built mainly from a phospholipid bilayer
  • Each phospholipid: hydrophilic phosphate head + 2 hydrophobic fatty-acid tails
  • Heads face cytoplasm & exterior; tails face inward
• Additional components: glycolipids, glycoproteins, cholesterol, membrane proteins
• Key property: selective permeability
  • Permits: lipids, alcohol, $O<em>2$, $N</em>2$, $H<em>2O$, $CO</em>2$
  • Blocks: polar molecules, glucose, proteins

Cytoskeleton

• Network of protein fibers providing internal framework & motility
• Three main elements
  • Microtubules
  • Helices of tubulin subunits
  • Thickest filament type
  • Functions: chromosome movement, organelle transport
  • Microfilaments (actin filaments)
  • Thin strands of actin
  • Functions: cell shape changes, cytoplasmic streaming, organelle movement
  • Intermediate Filaments
  • Rope-like fibers of varied proteins
  • Functions: maintain cell shape, anchor nucleus, reinforce plasma membrane

Cytoplasm

• Semi-fluid region between plasma membrane & nucleus
• Consists of cytosol (water + inorganic/organic molecules) plus suspended organelles

Cell Wall

• Rigid external structure surrounding plasma membrane (plants, bacteria, fungi)
• Functions: shape maintenance, protection, prevents osmotic bursting
• Composition
  • Plants: cellulose fibers
  • Bacteria: peptidoglycan
  • Fungi: chitin

Quick Facts

• Cell’s three main regions: plasma membrane, cytoplasm, nucleus (focus here: non-nuclear parts)
• Combined roles: barrier integrity, structural support, controlled transport, overall survival