1. Membrane Structure and Function
Chapter 5

2. Membrane Structure and Function
5.1

3. Membrane Structure and Function
Plasma membrane- phospholipid bilayer. Creates separation between the cell and the external environment as well as compartments within the cell itself. .
Highly similar to each other, easy to fuse.

4. Fluid-Mosaic Model Flexible
Lipid content responsible for fluidity. Like Olive Oil
Cholesterol prevents it from becoming too fluid
Number and types of proteins may vary
Both side of the plasma membrane are not identical
Carbon chains on the outer surface

5. Glycoproteins and Glycolipids
Glycoproteins- attached to proteins
Glycolipids- attached to lipids
Both give the cell its “fingerprint”
Plays a role in cellular identification
Transplant rejection

6. Protein Functions
Channel Protein- move substance from one side to the other
Carrier Protein- receives substance, changes its shape thus moving substance across membrane
Cell Recognition Protein- glycoproteins that help cell recognize when its being invaded

7. a. b. c. d. e. f.

8. Protein Functions
Receptor Protein- allow only specific molecule to bind to it. No passing of a substance. Something binds and cell responds. “Message”
Enzymatic Protein- carry out metabolic reactions
Junction Protein- binds to cells together so signal molecule can be passed cell-to-cell

9. a. b. c. d. e. f.

10. Permeability Selectively permeable- only allows certain things
Hydrophobic substances can diffuse freely across because they can get through the middle.
Concentration gradient- area of concentration
Things that do NOT use energy go from high to low concentration or down their concentration gradient
Water should NOT be able to freely pass through because it is polar BUT cells have channel proteins (aquaporins) that make it go a little faster.

11. Bulk Transport
Exocytosis- exit cell through a vesicle Endocytosis- enter cell through a vesicle

12. Passive Transport
5.2

13. Diffusion
Movement across from high to low concentration or down its concentration gradient
Solution
Solvent (liquid)
Solute (Solid)
Example: Making sweet tea. Sugar diffuses through tea, going down its concentration gradient
**Gases freely diffuse because small and nonpolar
Oxygen/ carbon dioxide exchange

14. Osmosis
Diffusion of water across a selectively permeable membrane from high to low concentration
Isotonic-same, inside the cell and outside the cell content is equal
Hypotonic-cell swells, intake of water
Hypertonic- cell shrinks, water rushes out
Meat preservation, bacon, jerky

15. Osmosis in Animal and Plant Cells
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Animal
cells
plasma
membrane
nucleus
In an isotonic solution, there is no net
movement of water.
In a hypotonic solution, water
mainly enters the cell, which may
burst (lysis).
In a hypertonic solution, water
mainly leaves the cell, which
shrivels (crenation).
Plant
cells
cell
wall
nucleus
central
vacuole
plasma
membrane
chloroplast
In an isotonic solution, there is no
net movement of water.
In a hypotonic solution, vacuoles
fill with water, turgor pressure
develops, and chloroplasts are
seen next to the cell wall.
In a hypertonic solution, vacuoles
lose water, the cytoplasm shrinks
(plasmolysis), and chloroplasts
are seen in the center of the cell.

16. Facilitated Diffusion
Rapid transport by carrier protein
No energy needed
STILL diffusion
Usually uses carrier protein to help or facilitate across membrane

17. Active Transport
5.3

18. Active Transport Moves molecules against their concentration gradient.
Requires energy (ATP)
From low to high concentration
Carrier proteins also needed.
When used in active transport they are called PUMPS
Ex: iodine collects in cells of thyroid

19. Sodium-Potassium Pump
3 sodium (Na+) ions bind
A Phosphate from ATP is added to carrier protein
It changes shape moving 3 sodium ions outside the cell
Now, the protein can pick up 2 potassium ions
Phosphate from earlier leaves
Changes back to original shape moving potassium ions inside the cell

21. Exocytosis
A vesicle fuses with the plasma membrane a secretion occurs.
Hormones, neurotransmitters, and digestive enzymes are transported through exocytosis
The vesicle becomes part of the plasma membrane

22. Endocytosis
Cells take in substances by forming vesicles around the material
The membrane pinches off to form a vesicle inside the cell
3 types
Phagocytosis-large particles or another cell.
Pinocytosis- engulfs a liquid or tiny particles
Receptor-mediated Endocytosis-form of pinocytosis, uses receptors to recognize molecules and take them into the cell.
Called a coated pit

23. Three Methods of Endocytosis

24. Modification of Cell Surfaces
5.4

25. Modifications of Cell Surfaces
Cell Surfaces in Animals
Junctions Between Cells
Adhesion Junctions – Intercellular filaments between cells
Desmosomes – internal cytoplasmic plaques
Tight junctions – form impermeable barriers
Gap Junctions
Plasma membrane channels are joined (allows communication)
Important in heart muscle and smooth muscle

26. Junctions Between Cells of the Intestinal Wall
 Adhesion
 Tight
 Gap

27. Modifications of Cell Surfaces
Plant Cell Walls
Plants have a freely permeable cell wall, with cellulose as the main component.
Plasmodesmata penetrate the cell wall
Each contains a strand of cytoplasm
Allow passage of material between cells

28. Plasmodesmata