CHAPTER 7 A TOUR OF THE CELL

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CHAPTER 7A 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
• Ultracentrifuge cell fractionation 130,000rpm

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A cell is a living unit greater than the sum of
its parts

• While the cell has many structures that have
  specific functions, they must work together.

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Cell Types Prokaryotic

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

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Cell types Eukaryotic

• Nucleusmembrane enclosed organelle containing
  chromosomes
• Membrane bound organelles of specialized form and
  function
• Generally larger than prokaryotic 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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Nucleus

• Genetic material
• chromatin
• Chromosomes
• Nucleolus rRNA
• ribosome synthesis
• Double membrane
• with pores
• mRNA protein synthesis

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Ribosomes

• Protein manufacture
• Types a) free cytosolprotein function in cell
• b) bound endoplasmic reticulum
  membranes, organelles and export

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The Endomembrane System

• Endoplasmic reticulum(ER)
• Continuous with nuclear envelope
• Smooth ER
• no ribosomes
• Synthesis of lipids
• Metabolism of carbohydrates
• Detoxification of drugs poisons
• Rough ER
• With ribosomes
• Synthesis of secretory proteins
• (glycoproteins)
• Membrane production

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The 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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Lysosomes

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

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Vacuoles

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

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Other Membranous Organelles

• Mitochondria and chloroplasts are the main energy
  transformers of cells
• Both organelles have small quantities
  of DNA that direct the synthesis of the
  polypeptides produced by these internal
  ribosomes.
• Mitochondria and chloroplasts grow and reproduce
  as semiautonomous organelles.
• 2. Peroxisomes generate and degrade H2O2 in
  performing various metabolic functions

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Mitochondria

• Site of cellular respiration
• have a smooth outer membrane
• and a highly folded inner membrane, the cristae
• inner membrane encloses the mitochondrial matrix,
  
• a fluid-filled space with DNA, ribosomes, and
  enzymes.

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chloroplasts

• found in plants and eukaryotic algae
• site of photosynthesis.
• Inside the innermost membrane is a fluid-filled
  space, the stroma, in which float membranous
  sacs, the thylakoids.

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Peroxisomes

• generate and degrade H2O2 in performing various
  metabolic functions
• bounded by a single membrane.
• They form not from the endomembrane system, but
  by incorporation of proteins and lipids from the
  cytosol.

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The Cytoskeleton

• Providing structural support to the cell, the
  cytoskeleton also functions in cell motility and
  regulation

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There are three main types of fibers in the
cytoskeleton microtubules, microfilaments, and
intermediate filaments.
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Microtubules

• the thickest fibers, are hollow rods about 25
  microns in diameter.
• They move chromosomes during cell division.
• Another function is as tracks that guide motor
  proteins carrying organelles to their
  destination.

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cilia and flagella.

• Microtubules are the central structural support
• Cilia usually occur in large numbers on the cell
  surface.
• There are usually just one or a few flagella per
  cell

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cilia and flagella.

• A flagellum has an undulatory movement

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cilia and flagella.

• Cilia move more like oars with alternating power
  and recovery strokes.

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cilia and flagella

• have the same ultrastructure.

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Microfilaments

• the thinnest class of the
• cytoskeletal fibers,
• are solid rods of the globular protein
• actin.
• designed to resist tension

• form a three-dimensional
• network just inside
• the plasma membrane.

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Microfilaments

• In muscle cells, thousands of actin filaments are
  arranged parallel to one another.
• Thicker filaments, composed of a motor protein,
  myosin, interdigitate with the thinner actin
  fibers

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Microfilaments

• In other cells, these actin-myosin aggregates are
  less organized but still cause localized
  contraction

• Pseudopodia, cellular extensions, extend and
  contract through the reversible assembly and
  contraction of actin subunits into microfilaments.

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Microfilaments

• In plant cells (and others), actin-myosin
  interactions and sol-gel transformations drive
  cytoplasmic streaming.

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Intermediate filaments,

• more permanent fixtures
• of the cytoskeleton than
• are the other two classes
• reinforce cell shape
• and fix organelle location.

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Cell Surfaces and Junctions

• 1. Plant cells are encased by cell walls
• 2. The extracellular matrix (ECM) of animal
  cells functions in support, adhesion, movement,
  and regulation
• 3. Intercellular junctions help integrate cells
  into higher levels of structure and function
• 4. The cell is a living unit greater than the
  sum of its parts

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Plant cells are encased by cell walls

• The cell wall, found in prokaryotes, fungi, and
  some protists, has multiple functions.
• In plants, the cell wall protects the cell,
  maintains its shape, and prevents excessive
  uptake of water.
• It also supports the plant against the force of
  gravity.

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A mature cell wall consists of a primary cell
wall, a middle lamella with sticky
polysaccharides that holds cell together, and
layers of secondary cell wall.
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The extracellular matrix (ECM) of animal cells
functions in support, adhesion, movement, and
regulation

• In many cells, fibronectins in the ECM connect to
  integrins, intrinsic membrane proteins.

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. Intracellular junctions help integrate cells
into higher levels of structure and function

• Plant cells are perforated with plasmodesmata,
  channels allowing cysotol to pass between cells.

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Animal have 3 main types of intercellular links
tight junctions, desmosomes, and gap junctions

• In tight junctions, membranes of adjacent cells
  are fused, forming continuous belts around cells.
• This prevents leakage of extracellular fluid.

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Desmosomes (or anchoring junctions) fasten cells
together into strong sheets, much like rivets.

• Gap junctions (or communicating junctions)
  provide cytoplasmic channels between adjacent
  cells.

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Microtubules

• In many cells, microtubules grow out from a
  centrosome near the nucleus.
• In animal cells, the centrosome has a pair of
  centrioles, each with nine triplets of
  microtubules arranged in a ring.
• During cell division the centrioles replicate.