Chapter 4 A Tour of the Cell

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Chapter 4 A Tour of the Cell
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Cytology science/study of cells

• Light microscopy
• resolving power measure of clarity
• Electron microscopy
• TEM electron beam to study cell
  ultrastructure SEM electron beam to study
  cell surfaces
• Cell fractionation cell separation organelle
  study
• Ultracentrifuges cell fractionation 130,000
  rpm

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Cell Types Prokaryotic

• Nucleoid DNA concentration
• No organelles with membranes
• Ribosomes protein synthesis
• Plasma membrane (all cells) semi-permeable
• Cytoplasm/cytosol (all cells)

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Cell Size

• As cell size increases, the surface area to
  volume ratio decreases
• Rates of chemical exchange may then be inadequate
  for cell size
• Cell size, therefore, remains small

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Range of Cell Size
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Cell Fractionation
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Nucleus

• Genetic material... chromatin chromosomes nu
  cleolus rRNA ribosome synthesis
• Double membrane envelope with pores
• Protein synthesis (mRNA)

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Ribosomes

• Protein manufacture
• Free - cytosol, proteins function in cell
• Bound - endoplasmic reticulum, membranes,
  organelles, and export

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Compartmentalization

• Increases internal surface area
• Sometimes enzymes are incorporated into the
  membrane.
• Provide localized environmental areas.
• Sequester reactions (hydrolytic enzymes in
  lysosomes)

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The Endomembrane System

• Membranes may be interrelated directly or
  indirectly via vesicles.
• Membranes are dynamic structures.
• Nuclear Envelope
• Endoplasmic Reticulum
• Golgi Apparatus
• Lysosomes
• Vacuoles
• Plasma membrane (not actually a member of the
  system, but related to it).

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1. Endoplasmic Reticulum (ER)

• Continuous with nuclear envelope
• Smooth ER no ribosomes
  synthesis of lipids
• metabolism of carbohydrates detoxification of
  drugs and
• poisons
• Stores Ca2 ions
• Rough ER
• with ribosomes
• synthesis of secretory proteins
  (glycoproteins), membrane production

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Rough ER Ribosomes

• 1. Rough ER ribosomes synthesize secretory
  proteins
• 2. Growing polypeptide is threaded through the
  ER membrane into the lumen or cisternal space
• 3. Protein folds into its native conformation
• 4. Local enzymes catalyze covalent
  bonding-modifications
• 5. Protein departs in a transport vesicle

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2. Golgi Apparatus

• ER products are modified, stored, and then
  shipped
• Cisternae flattened membranous sacs
• trans face (shipping) cis face (receiving)
• Transport vesicles

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3. Lysosomes

• Sac of hydrolytic enzymes digestion of
  macromolecules
• Phagocytosis
• Autophagy recycle cells own organic material
• Tay-Sachs disease - lipid-digestion disorder
• Apoptosis

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• 4.Vacuoles
• Membrane-bound sacs (larger than vesicles)
• Food vacuole
• (phagocytosis)
• Contractile (pump
• excess water)
• Central vacuole (storage in plants)
• Tonoplast (membrane)

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Relationships Among Endomembranes
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Other Membranous Organelles

• Not part of endomembrane system
• Peroxisomes
• Mitochondria
• Chloroplasts

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Peroxisomes

• Single membrane
• Produce hydrogen peroxide in cells
• Metabolism of fatty acids detoxification of
  alcohol (liver)
• Hydrogen peroxide produced, then converted to
  water action of catalase.

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Mitochondria

• quantity in cell correlated
• with metabolic activity
• cellular respiration
• double membranous (phospholipid)
• cristae/matrix
• intermembrane space
• contain own DNA
• bacterial origin

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Chloroplasts

• type of plastid double membranous
  
• thylakoids (flattened disks) grana
  (stacked thylakoids)
• stroma own DNA

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The Cytoskeleton

• Fibrous network in cytoplasm
• Support, cell motility, biochemical regulation
• Microtubules thickest
• tubulin protein shape,
  support, transport, chromosome separation
• Microfilaments
• thinnest
• actin protein filaments
  motility, cell division, shape
• Intermediate filaments
• middle diameter keratin
  shape, nucleus anchorage

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Tubulin in endothelial cell
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Motor Molecules and the Cytoskeleton

• motor molecules on one microtubule grab and
  slide past another microtubule.
• b. motor molecules attach to receptors on
  organelles such as vesicles, enabling them to
  walk along the microtubule

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Centrosomes/centrioles

• Centrosome region near nucleus
• Centrioles 9 sets of triplet microtubules in a
  ring used in cell replication only in animal
  cells

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Cilia/flagella

• Locomotive appendages
• Ultrastructure 92
• 9 doublets of microtubules in a ring
• 2 single microtubules in center
• connected by radial spokes
• anchored by basal body
• dynein protein

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• ls. cilium
• cs cilium, showing 92 arrangement
• cs basal body, anchors the cilium to the cell
  third
• microtubule incorporated (centriole) central
  2 lost

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How Dynein walking Moves Cilia and Flagella
The dynein arms of one doublet grip the adjacent
doublet. Powered by ATP
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Microfilaments and Motility
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Cell Surfaces Junctions

• Cell wall
• not in animal cells
• protection, shape, regulation
• Plant cell
• primary cell wall produced first
• middle lamella of pectin (polysaccharide)
• holds cells together
• Some plants
• a secondary cell wall
• strong durable matrix
• wood (between plasma membrane and primary wall)

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Extracellular Matrix (ECM)

• Glycoproteins
• proteins covalently bonded to carbohydrate
• Collagen (50 of protein in human body)
• embedded in proteoglycan (another
  glycoprotein-95 carbohydrate)
• Fibronectins
• bind to receptor proteins in plasma membrane
  called integrins (cell communication?)

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Intracellular Junctions

• PLANTS
• Plasmodesmata cell wall perforations
• water and solute passage in plants
• ANIMALS
• Tight junctions fusion of neighboring cells
  prevents leakage between cells
• Desmosomes riveted, anchoring junction strong
  sheets of cells
• Gap junctions cytoplasmic channels allows
  passage of materials or current between cells

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Plamodesmata in a thin plant section
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Intercellular Junctions in Animals
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The Lives of a CellHarvard Animation

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Narrated version
Assignment
http//www.bu.edu/histology/m/t_electr.htm
Choose 4 images to draw and label