1. Unit 4 Cell Membrane Structure & Cell Transport

2. The Structure and Function of the Cell Membrane
Question: What feature does the cell membrane, nucleus, mitochondria, and chloroplast have in common? All have a membrane.
The Cell Membrane:
1. The cell membrane is selectively permeable. This means that the cell membrane controls what materials can and can not enter the cell.

3. 2. The cell membrane is made of primarily phospholipids and proteins.
Phospholipids: Hydrophilic (Water-Loving) Heads and Hydrophobic (Water-Fearing) Tails

4. Some proteins are attached to the surfaces of the cell membrane and so are called peripheral proteins.
Some proteins are embedded in the lipid bilayer and are called integral proteins.
What is the purpose of these integral proteins? To allow molecules to be transported into the cell.

5. 6. With the use of the Scanning Electron Microscope (SEM), scientists now know that the membrane is constantly changing, proteins are moving laterally within the cell membrane and are not stationary. Because of this fluidity and the fact that the cell membrane is composed of many substances, scientists use the “Fluid Mosaic Model” to describe the cell’s membrane.

6. Cellular Physiology: Membrane Transport
Membrane Transport – movement of substance into and out of the cell
Transport is by two basic methods
Passive transport
No energy is required
Active transport
The cell must provide metabolic energy
Slide 3.20
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7. Selective Permeability
The plasma membrane allows some materials to pass while excluding others
This permeability includes movement into and out of the cell
Slide 3.22
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8. Passive Transport Processes
Diffusion
Particles tend to distribute themselves evenly within a solution
Movement is from high concentration to low concentration, or down a concentration gradient
Figure 3.8
Slide 3.23
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9. Passive Transport Processes
Types of diffusion
Simple diffusion
Unassisted process
Solutes are lipid-soluble materials or small enough to pass through membrane pores
Osmosis – simple diffusion of water
Highly polar water easily crosses the plasma membrane
Facilitated diffusion
Substances require a protein carrier for passive transport
Slide 3.24a
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10. Diffusion through the Plasma Membrane
Figure 3.9
Slide 3.25
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11. Active Transport Processes
Active Transport helps move substances into and out of the cell that are unable to pass by diffusion
They may be too large
They may not be able to dissolve in the fat core of the membrane
They may have to move against a concentration gradient
Two common forms of active transport
Solute pumping
Bulk transport
Slide 3.27
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12. Active Transport Processes
Solute pumping
Amino acids, some sugars and ions are transported by solute pumps
ATP energizes protein carriers, and in most cases, moves substances against concentration gradients
Slide 3.28a
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13. Active Transport Processes
Figure 3.10
Slide 3.28b
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14. Active Transport Processes
Bulk transport
Exocytosis
Moves materials out of the cell
Material is carried in a membranous vesicle
Vesicle migrates to plasma membrane
Vesicle combines with plasma membrane
Material is emptied to the outside
Slide 3.29a
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15. Active Transport Processes
Figure 3.11
Slide 3.29b
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16. Active Transport Processes
Bulk transport
Endocytosis
Extracellular substances are engulfed by being enclosed in a membranous vescicle
Types of endocytosis:
Phagocytosis – cell eating
Pinocytosis – cell drinking
Slide 3.30a
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17. Active Transport Processes
Figure 3.12
Slide 3.30b
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