A Tour of the Cell

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A Tour of the Cell

• Chapter 7

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Plasma Membrane (PM)

• phospholipid bilayer with proteins (integral,
  peripheral)
• fluid mosaic model (iceberg)

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Nucleus

• 5-10?m diameter
• directs cellular activities (DNA)
• enclosed by nuclear membrane/envelope with pores
  (100 nm diameter)
• nuclear envelope double membrane
• contains chromatin (DNA chromosomes protein
  histones) humans possess 46
• nucleolus composed of RNA protein synthesizes
  ribosomal subunits (10,000/min)
• DNA ? mRNA ? mRNA leaves nucleus thru pores ?
  ribosome ? protein synthesized

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Ribosomes

• 20-30 ?m fully assembled (made of large small
  subunits) not membrane bound
• required (with mRNA) to synthesize proteins in
  cytoplasm
• certain drugs can paralyze prokaryotic ribosomes
  without inhibiting eukaryotic ribosomes that make
  proteins (eg tetracycline, streptomycin)
• free ribosomes float in cytosol synthesize
  proteins that remain in cytosol
• bound ribosomes are attached to rough ER
• both are structurally identical interchangeable

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Endoplasmic Reticulum

• network of tubes sacs (cisternae)
• continuous with nuclear envelope
• ? rough ER ribosome-studded ER, produces
  membrane secretory proteins
• growing protein threads way into cisternal
  space into ER, marker attaches and complex folds

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ER

• ? smooth ER no ribosomes
• lipid (hormone) synthesis
• carb metabolism (in liver) carbs stored as
  glycogen, hydrolysis leads to glucose
  phosphate, sER removes phosphate allowing
  glucose to be released from liver cells
  regulates blood sugar concentration
• detox of drugs poisons (in liver) adds
  hydroxyl groups making drugs more soluble

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Golgi Apparatus/Complex

• 1 ?m
• modifies, stores, secretes ER products
• flattened membrane stacks (dictyosome) resembles
  pita stacks
• two sides
• cis face receiving side, closely associated
  with smooth ER, by fusion of vesicles
• trans face shipping side, produces vesicles
  by pinching, to travel
• elsewhere
• Golgi products have markers added to them for
  eventual destination (act as docking sites)
• Products include lysosomes

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Lysosome

• 0.25-0.5 ?m
• vesicle filled with hydrolytic enzymes to digest
  macromolecules, other substances
• enzymes work best at pH5 (pumps H ions from
  cytosol) made by rER ? Golgi (trans)
• two fates
• phagocytosis engulf food particles
• autophagy recycle cells organic material
• selectively destroys own cells (tadpole ? frog,
  human paw ? digits)
• rare genetic disorder can result from missing
  lysosomal enzyme (accumulates impairs organs)
  Pompes (liver) and Tay-Sachs (brain) diseases

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Lysosome in Action

• Lysosome digesting mitochondrion

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Food Vacuole

• Membrane bound organelles, larger than vesicles
• Food vacuole food particle encased in vesicle
  from phagocytosis fuses with lysosome (digestion)

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Contractile Vacuole

• Protists pump out excess water to maintain
  specific pressure

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Central Vacuole

• Plant, large central vacuole for maintaining
  water pressure

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Mitochondrion

• 2-10 ?m
• site of cellular respiration generates ATP by
  extracting energy from molecules (with the help
  of oxygen)
• bounded by double membrane proteins
• its membrane proteins are made by free ribosomes
  and ribosomes in it
• contains small amount of DNA that controls the
  synthesis of these proteins
• smooth outer membrane
• folded inner membrane cristae (intermembrane
  space)
• large surface area enhances productivity of cell
  respiration

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Mitochondria

• Mitochondria ER ?
• Intestinal mitochondrion ?

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Chloroplast Anatomy
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Chloroplast

• 5 ?m X 0.5-1 ?m
• convert light energy to chemical energy
• bounded by double membrane proteins
• its membrane proteins are made by free ribosomes
  and ribosomes in it
• contains small amount of DNA that controls the
  synthesis of these proteins
• a kind of plastid
• amyloplast (leucoplast) colorless, store
  starch, root tubers
• chromoplast pigmented, give color to fruits,
  flowers, leaves
• chloroplast contain green pigment enzymes
  for photosynthesis
• develop from protoplastids in unspecialized cells
• contains
• thylakoids flattened structures (poker chips)
• grana stacks of flattened structures
• stroma fluid

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Peroxisome

• Single membrane-bound organelle containing
  enzymes
• Enzymes transfer hydrogen ions to oxygen (forming
  hydrogen peroxide, H2O2), breaks down fatty
  acids, detoxifies alcohol other harmful
  substances

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Cytoskeleton

• Fibrous network within cytosol, made of protein
• Mechanical support, keeps organelles in place,
  changes cell shape, movement, transport
• Microtubules
• Microfilaments
• Intermediate Filaments

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Microtubules

• 25 nm (diam), 0.0024 µm 25 µm length
• Composed of thin, hollow tubes act as
  monorails
• Grow out from area called centrosome, where a
  pair of centrioles are located (help organize
  microtubule assembly
• Basal body attachment site of cilia or flagellum
  (structurally similar to centriole)
• Dyenin motor molecule between the 92
  microtubule arrangement

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Centrioles

• 150 nm
• Arise from MOC (microtubule-organizing center)
• Role in cell division
• Present in animal cells

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Microtubules Cellular Division

• Specialized microtubules involved in cell
  division (kinetochores)

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Cilia

• Hairlike projections that produce a current for
  movement, direction of food particles (toward
  mouth)

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Flagella

• Tail-like projection whose rhythmic whip-like
  movements (energy supplied by ATP and
  mitochondria) provide movement

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Microfilaments

• 7 nm diameter
• Composed of threads of protein called actin and
  myosin
• Examples include components of muscles and those
  responsible for cell movement
• Assist in pseudopodia (cellular extensions) in
  ameba, cytoplasmic streaming

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Intermediate Filaments

• 8-10 nm
• More permanent that MT or MF
• Especially important in reinforcing shape and
  fixing positions of organelles strengthens
  neurons

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Cell surfaces and junctions

• Cell wall protects, supports, controls water
  uptake thicker than PM
• Primary thin, flexible first wall secretes
  by young plant
• Middle lamella glues cells together (sticky
  polysacc called pectins used in thickening
  jellies/jams)
• Secondary between PM and primary wall
  strong, durable, storage

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Extracellular matrix (ECM)

• Glycoproteins collagen (animal cells) forms
  fibers outside cell (accounts for ½ of all
  protein in human body)
• Proteoglycans collagen embedded in this network
  rich in carbs (up to 95)
• Fibronectin bind to receptor proteins
  (integrins) built into PM
• Integrins transmit changes in ECM to
  cytoskeleton ( vice versa), involved in
  communication with a cell, influence activity of
  genes in nucleus

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Intercellular junctions

• Allows cells to adhere, interact, communicate
  with other cells
• Plants plasmodesmata (channels in walls) living
  contents of adjacent cells are connected

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Tight Junctions

• Animals tight junctions (cells fused here),
  desmosomes (anchoring sites), gap junctions
  (communication)

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Desmosomes, Gap Junctions