1. The Cell Membrane and Transport Across the Cell Membrane

2. Cell Membrane

3. Cell Membrane
Fluid at physiological temperatures and allows cells to change shape due to physical constraints or changing cellular volumes.
Provides protection and support for the cell
Regulates movement of molecules from one side to the other

4. Cell membrane is composed of Phospholipid bilayer -contains embedded proteins and carbohydrate molecules attached to proteins
The phospholipid membrane allows free diffusion of some small molecules such as oxygen, carbon dioxide, and small hydrocarbons, but not charged ions, polar molecules or other larger molecules such as glucose, salt .
Semi-permeable – allows some things to pass through and not other things

6. Figure 7-15 The Structure of the Cell Membrane Fluid Mosaic Model
Outside
of cell
Cell
membrane
Proteins
Protein
channel
Lipid bilayer
Carbohydrate
chains
Inside
of cell
(cytoplasm)
Period 4 stopped here

7. Diffusion
Diffusion causes many substances to move across a cell membrane but does not require energy.
From an area of high to low concentration

8. Facilitated Diffusion- Diffusion of larger molecules (glucose, starch, salts) using protein channels in the cell membrane, does not require energy
Glucose
molecules
High
Concentration
Cell
Membrane
Protein
channel
Low
Concentration

10. until equilibrium is reached
Osmosis – water moves from a higher concentration to a lower concentration
until equilibrium is reached
Water molecules
Higher Concentration
of Water
Cell
membrane
Lower Concentration
of Water
Sugar molecules

11. What is Osmosis?
The movement of water across a semi permeable membrane.
Osmosis is the movement of water (red dots) through a semipermeable membrane to a higher concentration of solutes (blue dots).
Osmosis does not require energy.

16. Passive Transport Particles Water Diffusion Facilitated Diffusion
When material move from areas of high concentration to low concentration they don’t requires energy.
Examples
Diffusion
Facilitated Diffusion
Osmosis
Particles
Periods stopped here
Water

17. What if we have to bike uphill?
Connect to Passive transport aka biking downhill!

18. Active Transport
Moving particles AGAINST the concentration gradient i.e. biking uphill!
Takes energy in the form of ATP
Example: Sodium/Potassium Pump—uses ATP to maintain Na+ and K+ ions
ATP is the cell’s energy currency! We’ll talk about this later.
One example is the Sodium/Potassium Pump – this is not the only type of pump for active transport.

19. Notice the phosphate molecule!

20. Endocytosis and Exocytosis
Endocytosis—the process by which a cell surrounds a substance and encloses it in the plasma membrane to bring it into the cell
Exocytosis—the secretion of materials outside the plasma membrane
Why would substances move like this? Too large. Not shown here but they do require ATP.
Two types of endo (write on board): Pino (solutes and fluids) and phago (large molecules and whole cells—we’ll revisit this in the immune system!).

21. Types of Endocytosis Phagocytosis – large molecules and entire cells
Pinocytosis – small molecules and fluids

22. Pinocytosis

23. An example different from the NA+/K+

24. Name the 2 reasons cells cannot be the size of a basketball.
Geometry: Volume increases faster than surface area which makes it hard for membrane to keep up with needs of the cell
Practical aspects: Nucleus can’t handle that big of a job.

25. SA:V – it’s all about TRANSPORT
What was that ratio we talked about? What’s good, big or small SA:V? Transport.