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Membrane Structure and Function

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Title: Membrane Structure and Function


1
Membrane Structure and Function
Topic 3
2
Plasma Membrane Functions
Maintain a high concentration of materials in the
cell.
Keep harmful materials out.
Control the movement of materials into and out of
the cell.
Let the cell sense its environment.
3
Membrane Structure
  • Phospholipid bilayer
  • Amphipathic
  • liquid-crystal properties/behavior allow for
    constant movement of HC tails

4
The Plasma Membrane is Semipermeable
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Davson-Danielli vs. Fluid Mosaic
8
Membrane Characteristics
  • self-sealing
  • Flexible
  • Tend to form vesicles
  • (ENDOCYTOSIS)
  • Tend to fuse w/ other bilayers
  • (EXOCYTOSIS)

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LIPID MOBILITY
11
http//www.d.umn.edu/sdowning/Membranes/phospholi
pidlateralmovanim.html
http//www.d.umn.edu/sdowning/Membranes/phospholi
pidrotationalanim.html
12
Relationships w/ other intracellular membranes
  • Nuclear Rough
  • Memb. ER
  • vesicles
  • Golgi Bodies
  • lysosomes vesicles
    cell memb
  • vacuoles

13
MEMBRANE PROTEINS
  • Integral Proteins
  • Anchored into membrane
  • Transmembrane proteins

14
  • Peripheral Proteins
  • no anchoring to membrane
  • often bound to exposed regions of integral
    proteins

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PROTEIN MOBILITY
http//www.d.umn.edu/sdowning/Membranes/proteinmo
bilityanim.html
19
Proteins Are Critical to Membrane Function
20
Membrane Protein Functions
  • Cell Adhesion
  • Communication Channels
  • Transport Channels
  • Signal Receptors btwn. Ext/Int cell
  • Attachment Sites
  • Pumps
  • Enzymes
  • Peripheral
  • Integral
  • Integral
  • Integral
  • Peripheral
  • Integral
  • Both

21
Protein Signaling
http//www.d.umn.edu/sdowning/Membranes/signaling
anim.html
22
Membrane Components
Phospholipids
Proteins (peripheral and integral)
Cholesterol
Carbohydrates
23
The Plasma Membrane Gateway to the Cell
24
MOVEMENT ACROSS THE CELL MEMBRANE
25
Transport Processes - Diffusion
Solutes move down a concentration gradient until
they are evenly distributed. This is diffusion.
Another way of saying this is that solutes move
from a region of higher concentration to a region
of lower concentration until there is no
difference in concentration.
26
Methods of Movement
  • PASSIVE TRANSPORT
  • DIFFUSION
  • SIMPLE DIFFUSION
  • OSMOSIS
  • FACILITATED DIFFUSION

27
Three Forms of Transport Across the Membrane
28
  • ACTIVE TRANSPORT
  • PUMPS
  • EXOCYTOSIS
  • ENDOCYTOSIS
  • PHAGOCYTOSIS
  • PINOCYTOSIS
  • RECEPTOR-MEDIATED

29
DIFFUSION
  • Cell obtains / releases substances by taking
    advantage of natural properties of movement
    (kinetic E)!

30
Diffusion is
  • NET movement of mcls from
  • Down the gradient . NO Energy required.

31
Rate of Diffusion influenced by
  • Size / shape of molecules moving
  • Electrical charges across membrane
  • Temperature ( movement,
  • . Diffusion )

32
  • Substances diffuse down their own gradient
  • NOT affected by gradient of other
    substances !!

33
Diffusion continues until
  • Dynamic
  • Equilibrium
  • is
  • reached!

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OSMOSIS
  • Diffusion of water across the semi-permeable
    plasma membrane.
  • Water moves down its own gradient.
  • Zones of Hydration

36
Spheres of Hydration
37
Osmotic Pressure
  • tendency of water to move into a solution by
    osmosis.
  • High solute low water
  • High Osmotic Pressure

38
Comparing Solutions
  • HYPOTONIC
  • refers to the less concentrated
  • (more dilute) of two solutions.

39
  • HYPERTONIC
  • refers to the more concentrated
  • (less dilute) of two solutions.

40
  • If a cell is placed in a hypotonic solution, the
    cell will.
  • S W E L L and
  • B U R S T !!
  • Turgidity issues

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  • If a cell is placed in a hypertonic
  • solution, the cell will
  • S H R I N K !
  • (CRENATION)

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  • ISOTONIC
  • refers to two solutions where there is no net
    movement of water between the two.

47
  • a cell is placed in an isotonic solution, there
    will be.
  • no net movement of water
  • into / out of the cell.

48
The Problem of Osmotic Pressure
  • Whats the risk?
  • How can osmotic pressure be minimized?

49
  • Live in an isotonic enviroment
  • Contractile vacuoles
  • plasmolysis
  • Marine invertebrates
  • Human RBCs
  • Unicellular protists
  • Plant cells

50
Contractile Vacuoles
51
Plasmolysis Cell Wall Action
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Transport Problems ?
  • CYSTIC FIBROSIS
  • LIDDLES SYNDROME
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