1. The Cell Membrane
Mader Biology, Chapter 5

2. Membrane Structure: Fluid Mosaic Model

3. The Membrane is Selectively Permeable
The ability to allow some substances to cross more easily than others
Allows the cell to maintain an internal environment different from the external one

4. Membrane Components Phospholipids Proteins
Cholesterol Carbohydrates (glucose)

5. Phospholipids

6. Cholesterol Steroid (lipid) found within the phospholipid bilayer
Keeps membrane solid when under heat

7. Membrane Proteins Integral Proteins: Peripheral Proteins:
Glycoproteins:

8. Glycocalyx
Polysaccharides (chains of glucose) attached to glycoproteins Functions:

9. Membrane Transport

10. Modes of Membrane Transport
Passive Transport
Diffusion
Osmosis
Facilitated Diffusion
Active Transport
Protein Pumps
Endocytosis
Exocytosis

11. Goes “with” the concentration gradient; no ATP energy required
Passive Transport
Goes “with” the concentration gradient; no ATP energy required

12. Simple Diffusion
The tendency for molecules of any substance to spread out into the available space
Molecules move from a region of high concentration to low concentration
moving down the concentration gradient

13. Osmosis
Osmosis is the diffusion of water across a semi- permeable membrane
Water travels
through protein
pores called
aquaporins

14. Effects of Tonicity on Cell Membranes
Hypotonic solution
higher concentration of water outside of cell results in hemolysis
Hypertonic solution
lower concentration of water outside of cell causes crenation
Isotonic solution
water concentration the same inside & outside of cell results in no net movement of water across cell membrane

15. Osmosis
Water always moves from a hypotonic solution to a hypertonic solution
What happens to cells when placed in:
Hypotonic solutions?
Hypertonic solutions?
Isotonic solutions?

16. (equal amounts entering & leaving)
Cells in Solutions
Isotonic Solution
Hypotonic Solution
Hypertonic Solution
No net movement of H2O
(equal amounts entering & leaving)
CYTOLYSIS
PLASMOLYSIS

17. Facilitated Diffusion
Diffusion with the assistance of integral transport proteins. (Still Passive transport)
Note: Carrier proteins allow both passive and active transport

18. Facilitated Diffusion
Transport proteins
Provide corridors allowing a specific molecule or ion to cross membrane
Undergo a shape change that translocates the molecule across the membrane
Still Passive Transport
Process requires no energy
Particles are moving from an area of high concentration to low concentration

19. Channel Proteins
Channel Proteins – allow certain materials to flow in and out (down their concentration gradient.)
Aquaporin – channel protein that only lets water in.
Ion Channels – also called gated channels, open and close in response to a chemical or electrical stimulus

20. Carrier Proteins
Carrier Proteins – change shape to escort certain material in and out of the cell. (Passive- down their concentration gradients; Active- against). Passive is shown below. How do you know?

21. Active Transport
Goes “against” the concentration gradient (“low to high”); requires ATP energy

22. Active Transport
Movement of solutes AGAINST the concentration gradient. Goes from low to high concentration.
Requires energy input by the cell
ATP supplies this energy

23. Active Transport
Carrier proteins are needed to transport molecules across the membrane against the concentration gradient and require an expenditure of energy
ATP ADP +P (ATP must release energy to go [low] to [high]
Often referred to as “pumps”.
Ex: Na+ and K+ for nerve (neuron) impulses

24. Active Transport Active transport - requires energy
Proteins act as pumps to move material from low to high concentration. Ex. Proton Pumps (Hydrogen Pumps) going against the gradient

25. Pumps continued
Sodium-Potassium pump – pumps sodium out and potassium in. (low to high concentration)

26. Moving Large Objects
Endocytosis – Cells take in materials by forming vesicles from the plasma membrane
Exocytosis – Cell secretes macromolecules by the fusion of vesicles with plasma membrane

27. 3 Types of Endocytosis 1. Phagocytosis: engulfing solid particles
2. Pinocytosis: engulfing liquid substances (extracellular fluid)

28. 3 Types of Endocytosis
Receptor mediated endocytosis – particles called ligands bind to receptors, which signals the engulfing of the particles.

29. Membrane Proteins

30. Membrane Proteins Integral Proteins – go through the whole membrane
Peripheral Proteins – sit on the outside of the membrane (inside of the cell).

31. Membrane Proteins and their Functions
Membrane proteins do six main things:
Transport
Enzymatic Activity
Signal Transduction
Cell Recognition
Cell-Cell Joining
Attachment to the cytoskeleton and extracellular matrix

32. Transport Proteins Channel Proteins: Passive
Have a pore for materials to cross
Carrier Proteins: Passive and Active
Can change shape to move material from one side of the membrane to the other

33. Enzymatic Proteins
Initiate reactions directly at membrane site. Ex- converting ATP->ADP +P (and vice versa)

34. Receptor Proteins Glycoproteins: “Alert” if being invaded by pathogens
Initiate immune response

35. Cell Recognition Proteins
May be embedded in membrane or in cytoplasm
Ligand (signal molecule) binds to receptor (H bonding)
Changes shape and starts cellular response (further reactions inside cell called signal transduction).
Ex- hormones.

36. Cell Signaling

37. The Three Stages of Cell Signaling
There are 3 stages at the “receiving end” of a cellular conversation:
Reception
Transduction
Response

38. Transport across membrane: Signal Transduction
A signal transduction pathway is a series of steps by which a signal on a cell’s surface is converted into a specific cellular response
Molecules that are small enough or hydrophobic and pass through the membrane - directly activate intracellular receptors in the cytoplasm or nucleus of target cell
Molecules that are too large or too hydrophilic to cross the plasma membrane - rely on membrane receptors
Ligand- Signaling Molecule