THE STUDY OF CELLS - STRUCTURE CYTOLOGY THE STUDY OF CELLS - STRUCTURE

GENERAL Cell = Smallest Living Unit Produced by Cell Division or Fertilization Surrounded by Interstitial / Extracellular Fluid Components: Plasma (Cell) Membrane Cytoplasm Nucleus

THE PLASMA MEMBRANE Structure Phospholipid bilayer self-orienting, reseals hydrophilic heads (face outward) hydrophobic tails (face inward) Proteins (floating or anchored) Cholesterol (keeps it “fluid”) Heads are polar & therefore hydrophilic; tails are non-polar & therefore hydrophobic. Glycolipids are also present in outer phospholipid layer.

THE PLASMA MEMBRANE Functions: Physical Barrier (Selective!) Proteins: Fat-soluble do pass through Water-soluble don’t Proteins: Channels or Carriers (transport) Enzymes (chemical reactions) Receptor sites (“docking” of molecules) Anchors

THE PLASMA MEMBRANE Illustration of cell membrane structure as in Martini Fig 3-2 p.50 or Marieb Fig 3.2 p.63

CYTOPLASM Material Between Plasma Membrane & Nucleus Components Cytosol (fluid with solutes) Cytoplasmic Organelles Inclusions (stored materials) Site of chemical reactions

NUCLEUS Organelle Double Nuclear Membrane with Pores DNA – Instructions for making proteins Chromatin - loose; protein synthesis Chromosomes - dense, rod-like; cell division Nucleolus Assembly of ribosomes

STRUCTURE OF THE NUCLEUS Illustration of cell nucleus structure as in Tortora Fig 3.10 p.48 or Marieb Fig 3.21a p.83

CYTOPLASMIC ORGANELLES Mitochondria ATP synthesis (cellular energy) Self-replicating Contains DNA “Little Organs” with specialized functions Membranes isolate secretions, enzymes or toxins

CYTOPLASMIC ORGANELLES Ribosomes Site of Protein Synthesis Free or Attached Rough Endoplasmic Reticulum Membrane synthesis Proteins made for export

CYTOPLASMIC ORGANELLES Smooth ER Lipid synthesis & breakdown Detoxification No ribosomes, but Smooth ER does have unique enzymes making it functionally more diverse than Rough ER. Synthesizes fatty acids & steroids (e.g. estrogen & testosterone), In Liver, enzymes help release glucose from glycogen, & deactivate or detoxify lipid-soluble drugs , alcohol, pesticides & carcinogens. In muscles cells, special Smooth ER stores Ca+ ions , triggering muscle coontraction.

CYTOPLASMIC ORGANELLES Golgi Apparatus Prepares proteins for export Makes lysosomes Packages material to add to plasma membrane (Gol’ je)

CYTOPLASMIC ORGANELLES Lysosomes Digestion within the cell Defense Recycle worn-out cells Peroxisomes Detoxify Alcohol Formaldehyde Free Radicals Peroxisomes contain oxidases that oxidize (remove hydrogen atom) harmful substances like alcohol & H2O2 (catalase/H2O2). Free radicals contain un-paired electrons & are therefore highly reactive. Peroxisomes also self-replicate.

CYTOPLASMIC ORGANELLES Cytoskeleton Proteins Support & Shape Movement inside cell Centrioles Form Spindle Form base of cilia & flagella

CYTOPLASMIC ORGANELLES Cilia – short, numerous, move substances over free surfaces Flagella – long, singular, move cell Microvilli – thin folds of cell membrane, increase surface area to maximize absorption Both cilia & flagella are projections

Cytoplasmic Organelles Proteosomes Ring of stacked proteins around central core Break-up undesirable proteins Vaults Ribonucleoprotein (proteins + RNA) May be involved in transport between nucleus & cytoplasm? Proteasomes are sometimes described as giant “waste disposal” complexes of protein-digesting enzymes. They break up un-need, damaged or faulty proteins via proteases. Their activity is pronounced during periods of starvation when they degrade pre-existing proteins to provide the body with small peptides for synthesis of essential proteins. Proteins called ubiquitins attach to undesirable proteins, marking them for destruction. Vaults have been linked to multidrug resistant cancer cells. Vaults are being modified to act as a drug delivery system aimed at treating cancer & viral infections.