1. Chapter 4 Cell Membrane Structure and Function
Copyright © 2005 Pearson Prentice Hall, Inc.

2. Figure: 4-CO
Title:
Cell Membrane Structure and Function
Caption:
A rattlesnake prepares to strike.

3. How Is the Structure of a Membrane Related to Its Function?
The Plasma Membrane Isolates the Cell While Allowing Communication with Its Surroundings
Membranes Are “Fluid Mosaics” in Which Proteins Move Within Layers of Lipids
Phospholipid (p. 58)
Phospholipid Bilayer (p. 58)
The plasma membrane is a fluid mosaic (p. 59)
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4. tails (hydrophobic) head (hydrophilic) CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH3N
CH2
CH2 O P O
CH2 O CH
CH3 O HC O C
CH2
CH2
CH2
CH2
CH2
CH2
CH2 CH O
Figure: 4-UN1
Title:
Phospholipid
H2C O C
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH3
tails
(hydrophobic)
head
(hydrophilic)

5. extracellular fluid (watery environment) phospholipid hydrophilic
heads
hydrophobic
tails
bilayer
Figure: 4-UN2
Title:
Phospholipid Bilayer
hydrophilic
heads
cytoplasm
(watery environment)

6. extracellular fluid (outside) glycoprotein
binding site
phospholipid bilayer
carbohydrate
cholesterol
phospholipid
Figure :4-1
Title:
The plasma membrane is a fluid mosaic
Caption:
The plasma membrane is a bilayer of phospholipids in which various proteins are embedded. Many proteins have carbohydrates attached to them, forming glycoproteins.
receptor protein
transport protein
protein filaments
recognition protein
cytoplasm (inside)

7. 4.1 How Is the Structure of a Membrane Related to Its Function?
The Phospholipid Bilayer Is the Fluid Portion of the Membrane
A Mosaic of Proteins Is Embedded in the Membrane
Held in place by hydrophobic bonds to phospholipids Kinemage C13MEMBR.KIN mage 3 view 2 ar s.c.
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8. Cell Surface Specializations
Various Specialized Junctions Allow Cells to Connect & Communicate
Desmosome
Tight junction
urinary bladder
Cell
Attachment
Structures
(F4.10 p. 68)
small intestine
Tight
Junction:
Prevents
Leakage
Between
Cells
cells lining small
intestine
cells lining
bladder
plasma
membranes
(edge view)
Desmosomes:
Attach Cells
Together
protein
filaments in
cytoplasm
Desmosome
Tight Junction
Copyright © 2005 Pearson Prentice Hall, Inc.

9. Cell Surface Specializations
Cell Communication Structures (F4.11 p. 69)
Gap Junctions & Plasmodesmata
Allow
Communication
Between Cells
Plasmodesmata
Gap Junctions
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10. How Do Substances Move Across Membranes?
Molecules in Fluids Move in Response to Gradients
Gradient: an upward or downward slope
Diffusion of a dye in water CHAOS (F4.2 p. 61)
Copyright © 2005 Pearson Prentice Hall, Inc.

11. drop of dye water molecule Figure :4-2 Title:
Diffusion of a dye in water
Caption:

12. How Do Substances Move Across Membranes?
Movement Across Membranes Occurs by Both Passive and Active Transport
Transport Across Membranes (T4.1 p. 62)
Copyright © 2005 Pearson Prentice Hall, Inc.

13. Figure :4-T1
Title:
Transport Across Membranes
Caption:

14. How Do Substances Move Across Membranes?
Passive Transport Includes Simple Diffusion, Facilitated Diffusion, and Osmosis
Plasma Membranes Are Selectively Permeable to Diffusion of Molecules
Some Molecules Move Across Membranes by Simple Diffusion
Diffusion through the plasma membrane (F4.3 p. 63)
Copyright © 2005 Pearson Prentice Hall, Inc.

15. ions channel protein amino acids, sugars, small proteins carrier
Simple diffusion
Facilitated diffusion through a channel
(extracellular fluid)
lipid-soluble molecules
(O2, CO2, H2O)
ions
channel
protein
(cytoplasm)
Facilitated diffusion through a carrier
(extracellular fluid)
amino acids,
sugars,
small proteins
Figure :4-3
Title:
Diffusion through the plasma membrane
Caption:
(a) Simple diffusion: gases such as oxygen and carbon dioxide and lipid-soluble molecules can diffuse directly through the phospholipids. (b) Facilitated diffusion through a channel: protein channels (pores) allow passage of some water-soluble molecules, principally ions, that cannot diffuse directly through the bilayer. (c) Facilitated diffusion through a carrier. Exercise Imagine an experiment that measures the initial rate of diffusion into cells placed in sucrose solutions of various different concentrations. Sketch a graph (initial diffusion rate versus solution concentration) that shows the result expected if diffusion is simple, and a graph that shows the result expected for facilitated diffusion.
carrier
protein
(cytoplasm)

16. How Do Substances Move Across Membranes?
Other Molecules Cross the Membrane by Facilitated Diffusion, with the Help of Membrane Transport Proteins
Osmosis Is the Diffusion of Water Across Membranes (F4.4 p. 64)
Effects of Osmosis: Plays an Important Role in the Lives of Cells (F4.5 p. 65)
Copyright © 2005 Pearson Prentice Hall, Inc.

17. H2O selectively permeable membrane sugar pore selectively permeable
Figure :4-4
Title:
Osmosis
Caption:
(a) Membrane pores allow “free” water molecules to pass through, but sugar molecules are too large. “Bound” water molecules, attracted to the sugars by hydrogen bonds, are also prevented from passing through the pore. (b) A bag is made of a membrane selectively permeable to free water molecules (white dots) but not to larger molecules, such as sugar (yellow hexagons) or water molecules held to the sugars by hydrogen bonds. If the bag is filled with a sugar solution and suspended in pure water, free water molecules will diffuse down their concentration gradient from the high concentration of water outside the bag to the lower concentration of water inside the bag. The bag will swell and may burst as water enters. Question Imagine a container of glucose solution, divided into two compartments (A and B) by a membrane that is permeable to water and glucose but not to sucrose. If some sucrose is added to compartment A, how will the contents of compartment B change?
selectively
permeable
membrane
sugar
molecule
water
molecule

18. Isotonic solution Hypertonic solution Hypotonic solution
10 micrometers
Isotonic solution
Hypertonic solution
Hypotonic solution
Figure :4-5
Title:
The effects of osmosis
Caption:
(a) If red blood cells are immersed in an isotonic salt solution, which has the same concentration of dissolved substances as the blood cells do, there is no net movement of water across the plasma membrane. The red blood cells keep their characteristic dimpled disk shape. (b) A hypertonic solution, with too much salt, causes water to leave the cells, shriveling them up. (c) A hypotonic solution, with less salt than is in the cells, causes water to enter, and the cells swell. Question All freshwater fish swim in a solution that is hypotonic to the fluid inside their bodies. Why don't freshwater fish swell up and burst?

19. How Do Substances Move Across Membranes?
Active Transport Uses Energy to Move Molecules Against Their Concentration Gradients (F4.6 p. 66)
Copyright © 2005 Pearson Prentice Hall, Inc.

20. (extracellular fluid)
ATP
Ca2+
binding
site
recognition
The transport protein
binds both ATP and Ca2+. 1
(extracellular fluid)
(cytoplasm)
Energy from ATP changes
the shape of the transport
protein and moves the ion
across the membrane. 2 P
ADP
The protein releases
the ion and the remnants
of ATP (ADP and P) and
closes. 3
Figure :4-6
Title:
Active transport
Caption:
Active transport uses cellular energy to move molecules across the plasma membrane, often against a concentration gradient. A transport protein (blue) has an ATP binding site and a recognition site for the molecules to be transported, in this case calcium ions (Ca2+).

21. How Do Substances Move Across Membranes?
Cells Engulf Particles or Fluids by Endocytosis
Three types of endocytosis (F4.7 p. 67)
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22. (extracellular fluid) (extracellular fluid) food particle pseudopods
Pinocytosis
Phagocytosis
(extracellular fluid)
(extracellular fluid)
food particle
pseudopods 1 3 2 1
vesicle containing extracellular
fluid 2
food vacuole
(cytoplasm)
(cytoplasm) 3
A dimple forms in the plasma membrane, which deepens
and surrounds the extracellular fluid The membrane encloses the extracellular fluid, forming a vesicle. 1 2
The plasma membrane extends pseudopods toward an
extracellular particle (for example, food) The ends of
the pseudopods fuse, encircling the particle A vesicle called
a food vacuole is formed containing the engulfed particle. 1 3 2 3
Receptor-mediated endocytosis
(extracellular fluid)
nutrients
receptors
Figure :4-7
Title:
Three types of endocytosis
Caption:
Question Compare and contrast receptor-mediated endocytosis with active transport. 1
coated pit 2 3 4
(cytoplasm)
coated vesicle
Receptor proteins for specific molecules or complexes of
molecules are localized at coated pit sites The receptors bind
the molecules and the membrane dimples inward The coated
pit region of the membrane encloses the receptor-bound
molecules A vesicle ("coated vesicle") containing the bound
molecules is released into the cytoplasm. 1 1 2 3 4

23. 4.2 How Do Substances Move Across Membranes?
Pinocytosis Moves Liquids into the Cell
Receptor-Mediated Endocytosis Moves Specific Molecules into the Cell (F4.8 p. 67)
Copyright © 2005 Pearson Prentice Hall, Inc.

24. extracellular particles bound to receptors coated vesicle
(extracellular fluid)
(cyto-
plasm)
protein
coating
coated pit
0.1 micrometer
plasma membrane
Figure :4-8
Title:
Receptor-mediated endocytosis
Caption:
These electron micrographs illustrate the sequence of events in receptor-mediated endocytosis. (a) The shallow depression in the plasma membrane is coated on the inside with a protein (dark, fuzzy substance in the micrographs) and bears receptor proteins on the outside (not visible). (b, c) The pit deepens and (d) eventually pinches off as a coated vesicle. The protein coating is recycled back to the plasma membrane.

25. extracellular particles bound to receptors
(extracellular fluid)
(cyto-
plasm)
Figure :4-8 part a
Title:
Receptor-mediated endocytosis part a
Caption:
These electron micrographs illustrate the sequence of events in receptor-mediated endocytosis. (a) The shallow depression in the plasma membrane is coated on the inside with a protein (dark, fuzzy substance in the micrographs) and bears receptor proteins on the outside (not visible). (b, c) The pit deepens and (d) eventually pinches off as a coated vesicle. The protein coating is recycled back to the plasma membrane.
protein
coating
coated pit
plasma membrane

26. 4.2 How Do Substances Move Across Membranes?
Phagocytosis Moves Large Particles into the Cell
Exocytosis Moves Material Out of the Cell (F4.9 p. 68)
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27. (extracellular fluid)
secreted
material
plasma membrane
(extracellular fluid)
plasma membrane
vesicle
Figure :4-9
Title:
Exocytosis
Caption:
Exocytosis is functionally the reverse of endocytosis. Question How does exocytosis differ from diffusion of materials out of a cell?
(cytoplasm)
0.2 micrometer