1. Unit 3 topic 3: cell transport
By the end of this topic, you should be able to…
Label a cell membrane with its components and explain the function of each component (carbohydrates, phospholipid head/tail, proteins)
Explain what “a cell membrane is selectively permeable means”
Explain why the cell membrane is known as the Fluid Mosaic Model
Compare and contrast passive transport (diffusion, facilitated diffusion, osmosis) with active transport (endocytosis, exocytosis)
Discuss the importance of surface area to volume ratio

2. The cell membrane
Task: regulate movement of materials into and out of the cell
Parts you need to know:
Phospholipid bilayer
Carbohydrate Chains
Proteins (integral and peripheral)
Cholesterol

3. The cell membrane - labeling
Task: regulate movement of materials into and out of the cell
Parts you need to know:
Phospholipid bilayer
Carbohydrate Chains
Proteins (integral and peripheral)
Cholesterol

4. Arrangement of lipid bilayer
1. Two sheets of phospholipids (a lipid with a head & two tails)
Head = hydrophilic
Hydro: water
Philia: love, fondness, affinity for
Arranged on the outsides of the bilayer due to it’s love for water (constant contact)
Tails = hydrophobic
Phobia: fear of or aversion to
Arranged on the inside of the bilayer so it is away from water

5. Components in the lipid bilayer
2. Carbohydrate Chains
Attach as a chain to membrane proteins or lipids
Glycoprotein- carbohydrates attached to protein
Glycolipid- carbohydrates attached to lipid
Protect the cell
These are used for cell recognition
Differentiate between things that can enter the cell and things that cannot enter the cell

6. Components in the lipid bilayer
3. Proteins
Allow for interactions between cells and transport of materials
Integral proteins: embedded within the cell membrane
Usually transmembrane (extends the length of the membrane to connect the inside of the cell with the outside)
Can act as pathways for materials to enter and exit the cell
Peripheral proteins: attached to the exterior (outside) of the lipid bilayer (or other membrane)
Wingmen for other membrane proteins (partner with other proteins- can be used for transport from one part of the cell to another by attaching to these other proteins)

7. Components of the lipid bilayer
4. Cholesterol
Maintains the integrity of cell membranes
Without cholesterol, cell membranes would be too fluid and too permeable
Used to maintain fluidity of the cell membrane by preventing crystallization of the tails in the bilayer
Involved with cell to cell communication (due to closeness with proteins on the cell membrane)

8. Fluid mosaic model
Fluid combination of phospholipids, cholesterol, and proteins
Separate but loosely attached molecules
Dynamic and scattered with these different molecules (mosaic-like)
This fluid characteristic allows it to be SEMI—PERMEABLE (certain things can pass through freely, but not others)

9. how do things get into/out of cells?
By moving across a concentration gradient (moving from one side of the cell to the other)
Concentration: mass of solute in a given volume of solution
Cell transport
Passive: no energy required, solutes move down the concentration gradient (from high to low)
Active: energy required, solutes move up the concentration gradient (from low to high)

10. Simple diffusion
Molecules move from an area of high concentration to an area of low concentration
This means they are moving DOWN the CONCENTRATION GRADIENT
PASSIVE
No energy required
Oxygen and carbon dioxide move through cells using simple diffusion

12. Simple Diffusion of a Solute Across a Membrane

13. Can all solutes cross the membrane by simple diffusion?
NO!
The membrane is selectively permeable, this means only certain solutes (typically small ones) can pass across by simple diffusion
The solution? – Channel Proteins!

14. Facilitated diffusion
Diffusion of certain molecules through a selectively permeable membrane, made possible by protein channels
Some substances, like glucose, are too large to fit through the cell membrane on their own
DOWN the CONCENTRATION GRADIENT (high to low)
PASSIVE process (no energy
required)

15. osmosis This is the diffusion of water across a cell membrane
Passive process
WATER molecules move down their concentration gradient
Movement depends on type of solution (hypertonic, isotonic, hypotonic)

16. Solution types
hypertonic
hypotonic
Solution outside the cell has a higher solute concentration and lower water concentration than inside the cell
Water LEAVES the cell
Solution outside the cell has a lower solute concentration and higher water concentration than inside the cell
Water ENTERS the cell

17. Solution types, cont. isotonic
The concentration of solute (and water) is the same outside the cell as inside the cell
Water moves equally in both directions
No NET movement

18. NO NET MOVEMENT OF H2O (equal amounts entering & leaving)
The Plasma Membrane
2/19/2019
Hypotonic Solution
Hypertonic Solution
Isotonic Solution
NO NET MOVEMENT OF H2O (equal amounts entering & leaving)
Cell Shrinking
Cell Bursting
G. Podgorski, Biol. 1010

19. Real life example: Red blood cells
Red blood cells
Plant cells

20. Real life example: plant cell

21. Active transport Movement up the concentration gradient
From areas of low concentration to areas of high concentration
Active because this requires energy (ATP)
Molecular pumps are used to transport materials across the membrane
Each pump moves one type of molecule

22. Endocytosis and exocytosis
Endo = within
Cyto = cell
Taking large amounts of material INTO the cell
Exocytosis
Exo = exit/leave
Sending large amounts of material OUT OF the cell

23. Endocytosis: Phagocytosis & pinocytosis
Phagocytosis: essentially, cell eating (bringing solids into the cell)
Ph sounds like fuh… same start as food (solid)
Pinocytosis: essentially, cell drinking (bringing liquids into the cell)
Think pina colada, which is a drink!

24. In endocytosis, the membrane pinches in to form a vesicle
The vesicle may later join with a lysosome so that particles can be “digested”
Vesicles

25. exocytosis
Products of the ER are packaged into vesicles at the Golgi and are then sent to and released at the cell membrane

26. Surface area to volume ratio
Each part of the cell relies on the cell surface. As a cell grows, its volume grows and the cell membrane expands. The volume increases quicker than the surface area.
Surface area available to pass materials to a unit volume of the cell steadily decreases.

27. Surface area to volume ratio
If the cell grows too big, not enough material can come into the cell to accommodate the larger cell volume.
cell must divide into smaller cells with favorable surface area/volume ratios, or cease to function.
The important point is that the surface area to the volume ratio gets smaller as the cell gets larger.