Development of the cell theory:

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Chapter 4 Cellular Form and Function

• Development of the cell theory
• Hooke in 1663, observed cork (plant) named the
  cell
• Schwann in 1800s states all animals are made
  of cells
• Pasteurs work with bacteria 1860 disproved
  idea of spontaneous generation (living things
  from nonliving)
• Modern cell theory emerged by 1900

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Modern Cell Theory

• All organisms composed of cells and cell
  products.
• A cell is the simplest structural and functional
  unit of life. There are no smaller subdivisions
  of a cell or organism that, in themselves, are
  alive.
• An organisms structure and all of its functions
  are ultimately due to the activities of its
  cells.
• Cells come only from preexisting cells, not from
  nonliving matter. All life, therefore, traces its
  ancestry to the same original cells.
• Because of this common ancestry, the cells of all
  species have many fundamental similarities in
  their chemical composition and metabolic
  mechanisms.

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Cell Shapes

• thin, flat, angular contours

• round to oval

• irregular angular shapes, gt 4 sides

• disc shaped

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Cell Shapes 2

• squarish

• thick middle, tapered ends

• taller than wide

• long, slender

• Stellate
• nerve cells have extensions, look starlike

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Epithelial Cell Surfaces

• Epithelial cells line organ surfaces
• Basal surface
• cell rests on this lower surface
• Lateral surface
• the sides of the cell
• Apical surface
• exposed upper surface

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Cell Size

• Human cell size
• most range from 10 - 15 µm
• egg cells (very large)100 µm diameter, visible to
  naked eye
• nerve cell over 1 meter, muscle cell up to 30 cm,
  (too slender to be seen)
• Limitations on cell size
• as cell enlarges, volume increases faster than
  surface area so the need for increased nutrients
  and waste removal exceeds ability of membrane
  surface to exchange

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Cell Surface Area and Volume
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Evolving Perspective on Cells

• Early study with light microscope revealed
• surface membrane, nucleus and cytoplasm
• Electron microscopes have much higher resolution
  and revealed much greater details, such as the
  cell ultrastructure of the cytoplasm
• fibers, passageways and compartments, and
  organelles surrounded by cytosol (a clear
  gelatinous component also called intracellular
  fluid)

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Cell Structure
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Cell Structure 2
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Plasma Membrane

• Defines cell boundaries
• Controls interactions with other cells
• Controls passage of materials in and out of cell
• Appears as pair of dark parallel lines around
  cell (viewed with the electron microscope)
• intracellular face - side faces cytoplasm
• extracellular face - side faces outwards
• Structure described by fluid-mosaic theory
• arrangement of mobile globular proteins embedded
  in an oily film of phospholipids

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Plasma Membrane Preview
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Membrane Lipids

• Lipids constitute
• 90 to 99 of the plasma membrane
• Glycolipids
• 5 of the lipids, found only on extracellular
  face, contribute to glycocalyx

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Membrane Lipids 2

• Cholesterol
• 20 of the lipids, affects membrane fluidity (low
  conc.. more rigid, high conc.. more fluid)
• Phospholipid bilayer
• 75 of the lipids, with hydrophilic heads
  (phosphate) on each side and hydrophobic tails in
  the center
• motion of these molecules creates membrane
  fluidity, an important quality that allows self
  repair

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Membrane Proteins

• Proteins constitute
• only 1 to 10 of the plasma membrane, but they
  are larger and account for half its weight
• Integral (transmembrane) proteins
• pass through membrane, have hydrophobic regions
  embedded in phospholipid bilayer and hydrophilic
  regions extending into intra- and extracellular
  fluids
• most are glycoproteins, conjugated with
  oligosaccharides on the extracellular side of
  membrane

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Membrane Proteins 2

• Integral proteins (cont.)
• may cross the plasma membrane once or multiple
  times
• Peripheral proteins
• adhere to intracellular surface of membrane
• anchors integral proteins to cytoskeleton

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Membrane Protein Functions

• Receptors
• Second messenger systems
• Enzymes
• Channel proteins
• Carriers and pumps
• Motor molecules
• Cell-identity markers
• Cell-adhesion molecules

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Protein Functions - Receptors

• Cells communicate with chemical signals that
  cannot enter target cells
• Receptors bind these messengers (hormones,
  neurotransmitters)
• Each receptor is usually specific for one
  messenger

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Second Messenger System

• A messenger (epinephrine) binds to a receptor 1
• Receptor releases a G protein 2
• G protein binds to an enzyme, adenylate cyclase,
  which converts ATP to cAMP, the 2nd messenger 3
• cAMP activates a kinase 4
• Kinases add Pi, activates or inactivates other
  enzymes

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Enzymes in Plasma Membrane

• Break down chemical messengers to stop their
  effects
• Final stages of starch and protein digestion in
  small intestine
• Involved in producing second messengers (cAMP)

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Protein Functions - Channel Proteins

• Formed by integral proteins
• Channels are constantly open, allow water and
  hydrophilic solutes in and out

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Protein Functions - Channel Proteins 2

• Gates open to three type of stimulants
• ligand-regulated gates bind to chemical
  messenger
• voltage-regulated gates potential changes across
  plasma membrane
• mechanically regulated gatesphysical stress such
  as stretch and pressure
• Gates control passage of electrolytes so are
  important in nerve signals and muscle contraction
  

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Protein Functions - Motor Molecules

• A filamentous protein that arises deep in the
  cytoplasm and pulls on membrane proteins causing
  movement
• within a cell (organelles)
• of a cell (WBCs)
• shape of cell (cell division, phagocytosis)

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Protein Functions - Carriers

• Integral proteins that bind to solutes and
  transfer them across membrane
• Carriers that consume ATP are called pumps

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Protein Functions - Cell-identity Markers

• Glycoproteins contribute to the glycocalyx, a
  surface coating that acts as a cells identity tag

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Protein Functions - Cell-adhesion Molecules

• Membrane proteins that adhere cells together and
  to extracellular material

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Glycocalyx

• Surface of animal cells
• CHO moieties of membrane glycoproteins and
  glycolipids that retains a film of water

• Functions
• immune response to infection and cancer
• basis of tissue transplant compatibility
• cellular uptake of water, dissolved solutes
• assists in cell adhesion, fertilization and
  embryonic development

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Microvilli

• Structure
• extensions of plasma membrane (1-2?m) that
  increase surface area for absorptive cells (by
  15- 40x in intestine, kidney)
• Brush border
• on some cells, they are very dense and appear as
  a fringe on apical cell surface
• Milking action
• protein filaments (actin) attach from the tip of
  microvillus to its base, anchors to a protein
  mesh in the cytoplasm called the terminal web and
  can shorten pushing absorbed contents into cell

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Cross Section of a Microvillus
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Cilia

• Hairlike processes 7-10?m long, 50-200 on cell
  surface move mucus, egg cells
• Covered by saline layer created by chloride pumps
• Cilia beat in waves, sequential power strokes
  followed by recovery strokes

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Cross Section of a Cilium
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Cilia 2

• Axoneme has a 92 structure of microtubules
• 2 central microtubules stop at cell surface
• 9 pairs of peripheral microtubules continue into
  cell as a basal body that acts as an anchor
• dynein (motor protein) arms on one pair of
  peripheral microtubules crawls up adjacent pair
  bending cilia
• Sensory cells
• some cilia lose motility and are involved in
  vision, smell, hearing and balance

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Cilium At Cell Surface
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Flagella

• Long whiplike structure that has an axoneme
  identical to that of a cilium
• Only functional flagellum in humans is the tail
  of the sperm

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Nucleus

• Largest organelle
• Nuclear envelope surrounds nucleus with two unit
  membranes
• Contains DNA, the genetic program for a cells
  structure and function

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Cell Structure
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Endoplasmic Reticulum

• Rough ER
• extensive sheets of parallel unit membranes with
  cisternae between them and covered with
  ribosomes, continuous with nuclear envelope
• function in protein synthesis and production of
  cell membranes
• Smooth ER
• lack ribosomes, cisternae more tubular and branch
  more extensively, continuous with rough ER
• function in lipid synthesis, detoxification,
  calcium storage

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Endoplasmic Reticulum Diagram
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Ribosomes

• Small dark granules of protein and RNA free in
  cytosol or on surface of rough ER
• Interpret the genetic code and synthesize
  polypeptides

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Golgi Complex

• Synthesizes CHOs, processes proteins from RER
  and packages them into golgi vesicles
• Golgi vesicles
• irregular sacs near golgi complex that bud off
  cisternae
• some become lysosomes, some fuse with plasma
  membrane and some become secretory vesicles
• Secretory vesicles
• store a cell product for later release

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Lysosomes

• Package of enzymes in a single unit membrane,
  variable in shape
• Functions
• intracellular digestion - hydrolyze proteins,
  nucleic acids, complex carbohydrates,
  phospholipids and other substrates
• autophagy - the digestion of worn out organelles
  and mitochondrion
• autolysis - programmed cell death
• glucose mobilization - lysosomes in liver cells
  break down glycogen

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Peroxisomes

• Appear similar to lysosomes, lighter in color
• Abundant in liver and kidney
• Function
• neutralize free radicals
• produce H2O2 in process of alcohol detoxification
  and killing bacteria
• break down excess H2O2 with the enzyme catalase
• break down fatty acids into acetyl groups

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Mitochondrion

• Double unit membrane
• Inner membrane contains folds called cristae
• ATP synthesized by enzymes on cristae from energy
  extracted from organic compounds
• Space between cristae called the matrix
• contains ribosomes and small, circular DNA
  (mitochondrial DNA)
• Reproduce independently of cell and live for 10
  days

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Mitochondrion, Electron Micrograph
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Centrioles

• Short cylindrical assembly of microtubules,
  arranged in nine groups of three microtubules
  each
• Two centrioles, perpendicular to each other, lie
  near the nucleus in an area called the centrosome
• these play a role in cell division
• Other single centrioles migrate to plasma
  membrane forming basal bodies of cilia or
  flagella
• two microtubules of each triplet elongate to form
  the nine pairs of peripheral microtubules of the
  axoneme

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Perpendicular Centrioles Diagram
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Cytoskeleton

• Microfilaments
• made of protein actin, form network on
  cytoplasmic side of plasma membrane called the
  membrane skeleton
• supports phospholipids of p.m., supports
  microvilli and produces cell movement, and with
  myosin causes muscle contraction
• Intermediate fibers
• in junctions that hold epithelial cells together
  and resist stresses on a cell
• Microtubules

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Microtubules

• Cylinder of 13 parallel strands called
  protofilaments
• (a long chain of globular protein called tubulin)
• Hold organelles in place and maintain cell shape
• Form tracks to guide organelles and molecules to
  specific destinations in a cell
• Form axonemes of cilia and flagella, centrioles,
  basal bodies and mitotic spindle
• Not all are permanent structures and can be
  disassembled and reassembled where needed

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Microtubule Diagram
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Cytoskeleton Diagram
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Inclusions

• Highly variable appearance, no unit membrane
• Stored cellular products
• glycogen granules, pigments and fat droplets
• Foreign bodies
• dust particles, viruses and intracellular bacteria

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Membrane Transport Selective Permeability

• Plasma membrane allows passage of some things
  between cytoplasm and ECF but not others
• Passive transport requires no ATP, movement of
  particles across selectively permeable membrane,
  down concentration gradient
• filtration and simple diffusion
• Active transport requires ATP, transports
  particles up concentration gradient
• carrier mediated (facilitated diffusion and
  active transport) and bulk transport

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Membrane Transport Filtration

• Movement of particles through a selectively
  permeable membrane by hydrostatic pressure
• Hydrostatic pressure - the force exerted on the
  membrane by water
• In capillaries, blood pressure forces water,
  salts, nutrients and solutes into tissue fluid,
  while larger particles like blood cells and
  protein are held back

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Simple Diffusion

• Simple diffusion is the movement of particles as
  a result of their constant, random motion
• Net diffusion is the movement of particles from
  an area of high concentration to an area of low
  concentration (down or with the concentration
  gradient)

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Diffusion Rates

• Factors that affect rate of diffusion through a
  membrane
• Temperature - ? temp., ? motion of particles
• Molecular weight - larger molecules move slower
• Steepness of conc.gradient - ?difference, ? rate
• Membrane surface area - ? area, ? rate
• Membrane permeability - ? permeability, ? rate

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Osmosis

• Net diffusion of water through a selectively
  permeable membrane from an area of more water,
  side B (less dissolved solute) to an area of less
  water, side A (more dissolved solute)

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Osmotic Pressure

• Osmosis opposed by filtration of water back
  across membrane due to ? hydrostatic pressure
• Amount of hydrostatic pressure required to stop
  osmosis is called osmotic pressure

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Osmolarity

• One osmole is 1 mole of dissolved particles
• 1M NaCl contains 1 mole Na ions and 1 mole Cl-
  ions/L, both affect osmosis, thus 1M NaCl 2
  osm/L
• Osmolarity osmoles/liter solution

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Tonicity

• Tonicity - ability of a solution to affect fluid
  volume and pressure within a cell
• depends on concentration and permeability of
  solute
• Hypotonic solution
• has low concentration of nonpermeating solutes
  (high water concentration)
• cells in this solution would absorb water, swell
  and may burst (lyse)
• Hypertonic solution
• has high concentration of nonpermeating solutes
  (low water concentration)
• cells in this solution would lose water shrivel
  (crenate)

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Membrane Transport Carrier Mediated Transport

• Proteins in cell membrane carry solutes through
  it
• Specificity
• solute binds to a receptor site on carrier
  protein that is specific for that solute
• Two types of carrier mediated transport are
  facilitated diffusion and active transport
• Exhibits saturation (see next slide)

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Carrier Saturation

• As concentration of solute ?, rate of transport ?
  up to the point when all carriers are occupied
  and rate of transport levels off at the transport
  maximum

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Membrane Transport Facilitated Diffusion

• Passive transport of solute down its
  concentration gradient, across membrane, with aid
  of a carrier
• Solute binds to carrier, carrier changes shape
  and releases solute on other side of membrane

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Active Transport

• Active transport of solute up its concentration
  gradient, across membrane, carrier requires ATP
• Carrier binds to ligand
• ATP phosphorylates carrier
• Carrier changes conformation
• Carrier releases ligand on other side
• Prominent example is the sodium-potassium pump

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Sodium-Potassium Pump

• 3Na bind to receptor, carrier phosphorylated,
  changes conformation, releases Na in ECF, binds
  2K, releases Pi, resumes conformation, releases
  K

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Functions of Sodium-Potassium Pump

• Regulation of cell volume
• cell swelling stimulates the Na- K pump ? ion
  concentration, ? osmolarity and cell swelling
• Heat production
• Maintenance of a membrane potential
• Na- K pump keeps inside of membrane negative,
  outside of membrane positive
• Secondary active transport
• transport of solute particles by carrier that
  does not need ATP, but depends on the
  concentration gradient provided by active
  transport pumps ...

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Secondary Active Transport

• Transport of glucose by facilitated diffusion,
  along with Na by SGLT carrier (no ATP), depends
  on Na- K pump (uses ATP)

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Cotransport

• When carrier transports 2 different solutes
  simultaneously, or within one transport cycle
• Symport - a carrier that transports both solutes
  in the same direction
• Antiport - a carrier that transports solutes in
  opposite directions

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Bulk Transport

• Transport of large particles and fluid droplets
  through membrane, using vacuoles or vesicles of
  plasma membrane, uses ATP
• Endocytosis - bulk transport into cell
• Exocytosis - bulk transport out of cell
• Endocytosis has three forms
• phagocytosis- engulfing large particles by
  pseudopods
• fluid phase pinocytosis
• receptor mediated endocytosis

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Phagocytosis
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Fluid-phase Pinocytosis

• Cell takes in droplets of ECF
• Plasma membrane dimples, then pinches off as
  pinocytotic vesicle
• Occurs in all human cells

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Receptor Mediated Endocytosis

• Receptors on membrane bind to specific molecules
  in ECF, cluster together, then sink in, become
  coated with a peripheral protein, clathrin, and
  pinch off into cell as clathrin-coated vesicle
• This occurs in the uptake of LDLs by endothelium
  of blood vessels
• Transcytosis uses this process to move a
  substance across a cell
• insulin absorbed into endothelial cell from blood
  by RME, then transported out into tissues

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Receptor Mediated Endocytosis
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Receptor Mediated Endocytosis EM
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Exocytosis

• Eliminating or secreting material from cell and
  replacement of plasma membrane

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Exocytosis EM