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Cell Membrane and Transport

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Basic unit of structure & function in body. Highly organized molecular factory ... crenated. 6-19. Regulation of Blood Osmolality ... – PowerPoint PPT presentation

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Title: Cell Membrane and Transport


1
Chapter 3 6
  • Cell Membrane and Transport

2
Chapter 3 Outline
  • Plasma Membrane
  • Extracellular Environment
  • Movement Across Plasma Membrane
  • Osmosis
  • Membrane Transport Systems

3
Cell
  • Basic unit of structure function in body
  • Highly organized molecular factory
  • Has 3 main components plasma membrane, cytoplasm
    organelles

Fig 3.1
4
Plasma Membrane
  • Surrounds gives cell form selectively
    permeable
  • Formed by a double layer of phospholipids
  • restricts passage of polar compounds

Fig 3.2
5
Plasma Membrane continued
  • Proteins customize membranes
  • Provide structural support
  • Serve as transporters, enzymes, receptors
    identity markers

Fig 3.2
6
Plasma Membrane continued
  • Carbohydrates in form of glycoproteins
    glycolipids are part of outer surface
  • Impart negative charge to surface

Fig 3.2
7
Bulk Transport
  • Move large molecules particles across plasma
    membrane
  • Some cells use phagocytosis to take in
    particulate matter
  • E.g. white blood cells macrophages

Fig 3.3
8
Bulk Transport
  • Some cells use endocytosis to take in large
    compounds
  • Membrane invaginates to take in a vesicle of
    extracellular substance
  • Pinocytosis is non-specific intake

9
Bulk Transport
  • Receptor-mediated endocytosis uses receptors to
    take in specific compounds
  • Including some viruses

1. plasma membrane pit forming
3.vesicle forming
2.membranepouching inward
4. vesicle inside cell
Fig 3.4
10
Bulk Transport
  • Cells use exocytosis to export products into the
    extracellular fluid
  • Via secretory vesicles

11
Surface Specializations
  • Some epithelial cells have cilia projecting from
    surface
  • Hair-like structures that beat in unison
  • E.g. cilia lining respiratory reproductive
    tracts

Fig 3.5
12
Surface Specializations
  • Some epithelial cells have microvilli on surface
    to increase surface area for absorption (Fig 3.6)
  • Fingerlike structures to expand surface area

13
Extracellular Environment
  • Includes all constituents of body outside cells
  • 67 of total body H20 is inside cells
    (intracellular compartment)
  • 33 is outside cells (extracellular
    compartment-ECF)
  • 20 of ECF is blood plasma
  • 80 of ECF is interstitial fluid contained in
    gel-like matrix

14
Transport Across Plasma Membrane
  • Plasma membrane is selectively permeable
  • Many important molecules have transporters
    channels
  • Carrier-mediated transport specific protein
    transporters
  • Non-carrier mediated transport occurs by
    diffusion

15
Transport Across Plasma Membrane continued
  • Passive transport moves compounds DOWN
    concentration gradient
  • requires no energy
  • Active transport moves compounds UP a
    concentration gradient
  • requires energy transporters

16
Diffusion
  • Random motion of molecules
  • Net movement is from region of high to low
    concentration

17
Diffusion
  • Non-polar compounds readily diffuse thru cell
    membrane
  • Also some small molecules (C02 H20)
  • Diffusion of H20 osmosis

18
Diffusion continued
  • Cell membrane is impermeable to charged most
    polar compounds
  • Must have an ion channel or transporter to move
    across membrane

19
Fig. 6.4
20
Diffusion continued
  • Rate of diffusion depends on
  • Magnitude of its concentration gradient
  • Permeability of membrane to it
  • Temperature
  • Surface area of membrane

21
Osmosis
  • Net diffusion of H20 across a selectively
    permeable membrane
  • H20 diffuses down its concentration gradient
  • H20 is less concentrated where there are more
    solutes
  • Solutes have to be osmotically active
  • i.e. cannot freely move across membrane

22
Osmosis continued
  • H20 diffuses down its concentration gradient
    until it reaches equilibrium.
  • Some cells have water channels (aquaporins) to
    facilitate osmosis

23
Osmotic Pressure
  • Force that would have to be exerted to stop
    osmosis
  • Indicates how strongly H20 wants to diffuse
  • Is proportional to solute concentration

24
Molarity Molality
  • 1 molar solution (1.0M) 1mole of solute
    dissolved in 1L of solution
  • Doesn't specify exact amount of H20
  • 1 molal solution (1.0m) 1 mole of solute
    dissolved in 1 kg H20
  • Osmolality (Osm) is total molality of a solution
  • E.g. 1.0m of NaCl yields a 2 Osm solution
  • Because NaCl dissociates into Na Cl-

25
Fig. 6.8a
26
Fig. 6.8b
27
Molarity Molality
  • Osmolality (Osm) is total molality of a solution
  • E.g. 1.0m of NaCl yields a 2 Osm solution
  • Because NaCl dissociates into Na Cl-

28
Tonicity
  • Effect of a solution on osmotic movement of H20
  • Isotonic same osmotic pressure
  • Hypertonic higher osmotic pressure are
    osmotically active
  • Hypotonic lower osmotic pressure
  • Isosmotic solutions same osmolality as plasma
  • Hypo-osmotic solutions lower osmotic pressure
    than plasma
  • hyperosmotic higher pressure than plasma

29
Effects of tonicity on RBCs
Fig 6.11
crenated
6-19
30
Regulation of Blood Osmolality
  • Blood osmolality maintained in narrow range
    around 300m Osm
  • If dehydrated, osmoreceptors in hypothalamus
    stimulate
  • ADH release
  • Which causes kidney to conserve H20
  • thirst

31
Carrier-Mediated Transport
  • Molecules too large polar need protein carriers
  • Protein carriers exhibit
  • Specificity for single molecule
  • Competition among substrates for transport
  • Saturation all carriers are occupied
  • Tm (transport maximum)

32
Facilitated Diffusion
  • Is passive transport down concentration gradient
    by carrier proteins

33
Active Transport
  • Transport of molecules against a concentration
    gradient
  • ATP required

Fig 6.16
34
Na/K Pump
  • Uses ATP to move 3 Na out 2 K in
  • Against their gradients

35
Secondary Active Transport
  • Uses energy from downhill transport of Na to
    drive uphill movement of another molecule
  • Also called coupled transport
  • ATP required to maintain Na gradient

36
Transport Across Epithelial Membranes
  • Absorption is transport of digestion products
    across intestinal epithelium into blood
  • Reabsorption transports compounds out of urinary
    filtrate back into blood

37
Transport Across Epithelial Membranes continued
  • Transcellular transport moves material from 1
    side to other of epithelial cells
  • Paracellular transport moves material through
    tiny spaces between epithelial cells

38
Fig. 6.20a
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