Membrane Structure and Function

1
Chapter 7 Membrane Structure and Function
2
Fig. 7-2
Membranes
WATER
Hydrophilic head
Hydrophobic tail
WATER
3
Fig. 7-7
Fluid-Mosaic Model
4
Fig. 7-5a
Lateral movement (?107 times per second)
Flip-flop (? once per month)
(a) Movement of phospholipids
5
Fig. 7-5b
Fluid
Viscous
Unsaturated hydrocarbon tails with kinks
Saturated hydro- carbon tails
(b) Membrane fluidity
6
Fig. 7-5c
Cholesterol
(c) Cholesterol within the animal cell membrane

7
Two Categories of Membrane Proteins

• Integral Membrane Proteins penetrate the core
  of the lipid bilayer
• Peripheral Membrane Proteins loosely bound to
  the surface of the membrane

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Fig. 7-8
Integral Membrane Protein
9
Peripheral Membrane Protein
Peripheral Membrane Protein
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Functions of Membrane Proteins

• Transport
• Enzymatic Activity
• Signal Transduction
• Cell-cell recognition
• Intercellular joining
• Attachment to ECM

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Fig. 7-9
Signaling molecule
Enzymes
Receptor
ATP
Signal transduction
(a) Transport
(b) Enzymatic activity
(c) Signal transduction
Glyco- protein
(d) Cell-cell recognition
(e) Intercellular joining
(f) Attachment to the cytoskeleton and
extracellular matrix (ECM)
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Fig. 7-10
ER
1
Transmembrane glycoproteins
Secretory protein
Glycolipid
2
Golgi apparatus
Vesicle
3
Plasma membrane
Cytoplasmic face
4
Extracellular face
Transmembrane glycoprotein
Secreted protein
Membrane glycolipid
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Membrane Transport

• Passive Transport no energy
• Diffusion
• Osmosis
• Facilitated Diffusion
• Active Transport requires energy

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Fig. 7-11a
Diffusion
Molecules of dye
Membrane (cross section)
WATER
Equilibrium
Net diffusion
Net diffusion
(a) Diffusion of one solute
15
Fig. 7-11b
Diffusion (cont.)
Equilibrium
Net diffusion
Net diffusion
Net diffusion
Net diffusion
Equilibrium
(b) Diffusion of two solutes
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Fig. 7-12
Higher concentration of sugar
Lower concentration of solute (sugar)
Same concentration of sugar
H2O
Selectively permeable membrane
Osmosis
Osmosis
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Tonicity

• There are three types of environments a cell can
  be in.
• Isotonic solute concentration is the same
  outside the cell as inside
• Hypotonic solute concentration is lower outside
  the cell than inside
• Hypertonic solute concentration is higher
  outside the cell than inside

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Fig. 7-13
Tonicity
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Fig. 7-14
50 µm
Filling vacuole
(a) A contractile vacuole fills with fluid that
enters from a system of canals radiating
throughout the cytoplasm.
Contracting vacuole
(b) When full, the vacuole and canals contract,
expelling fluid from the cell.
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Fig. 7-15
EXTRACELLULAR FLUID
Channel protein
Solute
CYTOPLASM
(a) A channel protein
Facilitated Diffusion
Solute
Carrier protein
(b) A carrier protein
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Fig. 7-16-7
EXTRACELLULAR FLUID
Na
Na high
Na
K low
Na
Na
Na
Na
Na
Na
ATP
Na low
P
Na
P
K high
CYTOPLASM
ADP
2
3
1
K
K
K
K
K
P
K
P
6
5
4
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Fig. 7-17
Passive transport
Active transport
ATP
Diffusion
Facilitated diffusion
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Fig. 7-18
Active Transport
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Fig. 7-19
Cotransport
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Exocytosis
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Endocytosis

• There are three types of endocytosis
• Phagocytosis cellular eating
• Pinocytosis cellular drinking
• Receptor-mediated endocytosis

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Fig. 7-20a
Phagocytosis
PHAGOCYTOSIS
CYTOPLASM
EXTRACELLULAR FLUID
1 µm
Pseudopodium
Pseudopodium of amoeba
Food or other particle
Bacterium
Food vacuole
Food vacuole
An amoeba engulfing a bacterium via phagocytosis
(TEM)
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Fig. 7-20b
Pinocytosis
PINOCYTOSIS
0.5 µm
Plasma membrane
Pinocytosis vesicles forming (arrows) in a cell
lining a small blood vessel (TEM)
Vesicle
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Fig. 7-20c
RECEPTOR-MEDIATED ENDOCYTOSIS
Coat protein
Receptor
Coated vesicle
Coated pit
Receptor-Mediated Endocytosis
Ligand
A coated pit and a coated vesicle
formed during receptor- mediated endocytosis (TEMs
)
Coat protein
Plasma membrane
0.25 µm
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