1. Ms. Napolitano & Mrs. Haas CP Biology
The Cell Membrane
Ms. Napolitano & Mrs. Haas
CP Biology

2. The Cell Membrane Thin, flexible barrier that surrounds the cell
AKA plasma membrane
Selectively permeable – allows some substances to cross more easily than others
Usually ~8nm thick

3. The Phospholipid Bilayer

4. Fluid Mosaic Model Used to describe the structure of the membrane
Fluid structure of phospholipids with a mosaic of various proteins embedded in it
Cholesterol helps maintain fluidity
Membrane becomes less fluid as temperature increases by restricting movement
Membrane becomes more fluid as temperature decreases by maintaining space

5. Structure of the Membrane

6. Membrane Proteins
Different types of cells contain different types of membrane proteins
Integral proteins – embedded into the hydrophobic core of the lipid bilayer
May or may not go all the way through the membrane
Peripheral proteins – on the bilayer surface
Integral
Peripheral

7. Types of Membrane Proteins (1 of 2)
Transport
Channel or carrier proteins (hydrophilic tunnels) allow polar molecules and ions to pass through the hydrophobic layer
Proteins are specific for the substance they transport
Enzymatic
Signal Transduction (chemical messages)
Receptor proteins transmit information from outside of the cell to inside of the cell

8. Types of Membrane Proteins (2 of 2)
4. Recognition
ID tags – glycolipids or glycoproteins
5. Intercellular Joining
Join together adjacent cells
6. Support
Attach to cytoskeleton or extracellular matrix for stability

9. The phospholipid bilayer is __________ in the middle and __________ on the outsides.
Hydrophobic, hydrophilic
Hydrophilic, hydrophobic
Hydrophobic, hydrophobic
Hydrophilic, hydrophilic

10. What is the function of cholesterol in the cell membrane?
Identification
Transport
Membrane fluidity
Recognition

11. The picture shows a peripheral protein.
True
False

12. Which of the following is NOT a function of membrane proteins?
Signal transduction
Identification
Transport
Support

13. Passive Transport
Passive Transport – the movement across the cell membrane that does not require energy
Types:
Diffusion
Osmosis
Facilitated Diffusion

14. Diffusion
Diffusion – the movement of particles from an area of high concentration to an area of low concentration until an equilibrium is reached
Transports small, nonpolar molecules such as CO2 and O2
Concentration Gradient – the difference in the concentration of a substance across a space
Equilibrium – concentration of a substance is equal throughout a space

15. Osmosis
Osmosis – diffusion of free water across a selectively permeable membrane
Water diffuses across the cell membrane from the region of low solute concentration to that of a higher solute concentration until it reaches equilibrium

16. Which way will water flow?
U-Tube (not YouTube!)
Which way will water flow?

17. U-Tube (not YouTube!)
This way!

18. Osmoregulation in Cells Without Cell Walls
Osmoregulation: control of water balance
Tonicity: the ability of a solution to cause a cell to gain/lose water
Isotonic solution: no net movement of water across the cell membrane
Hypertonic solution: more free water inside the cell (cells lose water & shrivel)
Hypotonic solution: less free water inside the cell (cells gain water & lyse)
Some cells have a contractile vacuole to pump water out of the cell

20. Osmoregulation of Cells With Cell Walls
Plant cells are healthiest in a hypotonic solution
Osmotic pressure keeps cell walls turgid (very firm)
Plant cells are flaccid (limp) in an isotonic solution
In a hypertonic solution, the cell membrane will shrink and pull away from the cell wall
AKA plasmolysis (wilting)

22. Facilitated Diffusion
Facilitated Diffusion: passive transport aided by proteins
Molecules travel from high  low concentration
Transports small, polar molecules
Glucose
Salts
Ions
Amino Acids
Water (aquaporins)

23. Channel Proteins Hydrophilic passageways
Some are always open for diffusion
Rate of movement is determined by the concentration gradient
Some ion channels have gates that can be opened by:
Cell membrane stretching
Change in electrical charge
Binding of specific molecules

24. Carrier Proteins Specific substance binds to carrier protein
Protein changes shape & transports substances across the cell membrane
Molecule is released into the cell, and carrier protein returns to its original shape

25. Active Transport
Uses energy to move solutes AGAINST the concentration gradient
Carrier proteins act as “pumps” powered by ATP
Examples:
Sodium Potassium Pump
Proton Pump
Cotransport

26. Sodium Potassium Pump
Pumps 3 Na+ out of the cell and 2 K+ into the cell
Actively transports both ions against their concentration gradient
Powered by ATP

28. Proton Pump
Actively transport protons (H+) through the internal membranes of mitochondria & chloroplasts

29. Cotransport (Coupled Transport)
Cotransport: The transport of one solute indirectly drives the transport of several other solutes (using ATP)
Example: As proton pump pumps H+ out, H+ ions diffuse back in pulling sucrose with it

30. Bulk Transport
Substances that are too large to be transported by carrier proteins
Example: proteins leaving/entering the cell
Uses vesicles
Types:
Exocytosis
Endocytosis

31. Exocytosis Exo = Export (recall exo means outside!!)
Vesicles fuse with the cell membrane, releasing the contents outside of the cell

32. Endocytosis Recall endo means inside!! Cell membrane engulfs particles
Pinches off to form vesicles inside of the cell