1. The Plasma Membrane and Membrane Potential
Chapter 3
The Plasma Membrane and Membrane Potential
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

2. New Review Membrane structure and composition Cell to cell adhesions
Membrane transport
Pgs 52-73
New
Membrane potentials
Pgs 73-83
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

3. Plasma Membrane Forms outer boundary of every cell
Controls movement of molecules between the cell and its environment
Joins cells to form tissues and organs
Plays important role in the ability of a cell to respond to changes in the cell’s environment
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

4. Plasma Membrane Structure
Fluid lipid bilayer embedded with proteins
Most abundant lipids are phospholipids
Also has small amount of carbohydrates
On outer surface only
Cholesterol
Tucked between phospholipid molecules
Contributes to fluidity and stability of cell membrane
Proteins
Attached to or inserted within lipid bilayer
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

5. Plasma Membrane Structure
Channels
Carrier molecules
Docking marker acceptors
Membrane bound enzymes
Receptor sites
Cell adhesion molecules (CAMs)
Integrin, cadherin
Cell surface markers
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

6. Cell-To-Cell Adhesions
Extracellular matrix
Serves as biological “glue”
Major types of protein fibers interwoven in matrix
Collagen, elastin, fibronectin
CAMs in cells’ plasma membranes
Specialized cell junctions
Desmosomes
Tight junctions (impermeable junctions)
Gap junctions (communicating junctions
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

7. Specialized Cell Junctions
Desmosomes
Act like “spot rivets” that anchor two closely adjacent nontouching cells
Most abundant in tissues that are subject to considerable stretching
Gap junctions
Small connecting tunnels formed by connexons
Especially abundant in cardiac and smooth muscle
In nonmuscle tissues permit unrestricted passage of small nutrient molecules between cells
Also serve as method for direct transfer of small signaling molecules from one cell to the next
Tight junctions
Firmly bond adjacent cells together
Seal off the passageway between the two cells
Found primarily in sheets of epithelial tissue
Prevent undesirable leaks within epithelial sheets C
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

8. Membrane Transport Unassisted membrane transport Diffusion Osmosis
Carrier-mediated transport
Facilitated transport
Active transport
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

9. Membrane Transport Diffusion
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

10. Membrane Transport
Factors affecting rate of diffusion collectively make up Fick’s law of diffusion:
Magnitude (or steepness) of the concentration gradient
Permeability of the membrane to the substance
Charge?
Surface area of the membrane across which diffusion is taking place
Molecular weight of the substance
Distance through which diffusion takes place
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

11. Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Table 3-1, p. 62

12. Membrane Transport Osmosis Net diffusion of water down its
own concentration
gradient
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

13. Figure 3.9: Relationship between solute and water concentration in a solution.
(a) Pure water. (b) Solution.
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Fig. 3-9, p. 63

14. Membrane Transport Tonicity of a solution
Determines whether cell remains same size, swells, or shrinks when a solution surrounds the cell
Isotonic solution
Has same concentration of nonpenetrating solutes as normal body cells
Cell volume remains constant
Hypotonic solution
Lower concentration of nonpenetrating solutes than normal body cells
Water enters cell causing cell to swell or perhaps rupture
Hypertonic solution
Higher concentration of nonpenetrating solutes than normal body cells
Cells shrink as they lose water by osmosis
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

15. Membrane Transport Assisted membrane transport
Carrier-mediated transport
Accomplished by membrane carrier flipping its shape
Can be active or passive
Characteristics that determine the kind and amount of material that can be transferred across the membrane
Specificity
Saturation
Competition
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

16. Membrane Transport Types of assisted membrane transport
Facilitated diffusion
Active transport
Vesicular transport
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

17. Membrane Transport Facilitated diffusion
Substances move from a higher concentration to a lower concentration
Requires carrier molecule
Means by which glucose is transported into cells
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

18. Membrane Transport Active transport
Moves a substance against its concentration gradient
Requires a carrier molecule
Primary active transport
Requires direct use of ATP
Secondary active transport
Driven by an ion concentration gradient established by a primary active transport system
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

19. Active Transport Concentration gradient ECF (High) Na+ ICF (Low)
Phosphorylated
conformation Y
of carrier
Dephosphorylated
conformation X
of carrier
Direction of
transport
Molecule to be
transported
Step 1
Step 2
Phosphorylated conformation Y of
carrier has high affinity for passenger.
Molecule to be transported binds to
carrier on low-concentration side.
Dephosphorylated conformation X
of carrier has low affinity for
passenger. Transported molecule
detaches from carrier on high-concentration side.
= phosphate
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Fig. 3-16, p. 70

20. side and drops off K+ on its high-concentration side
Sodium Potassium Pump
When open to the ECF, the carrier drops off Na+ on its high-concentration
side and picks up K+ from its low-concentration side
ECF
ICF
When open to the ICF, the carrier picks up Na+ from its low-concentration
side and drops off K+ on its high-concentration side
Phosphorylated conformation Y
of Na+–K+ pump has high affinity
for Na+ and low affinity for K+
when exposed to ICF
Dephosphorylated
conformation X of Na+–K+
pump has high affinity for
K+ and low affinity for Na+
when exposed to ECF
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
= Sodium (Na+)
= Potassium (K+)
= Phosphate
Fig. 3-17, p. 70

21. Secondary Active transport Fig. 3-18, p. 72
Figure 3.18: Secondary active transport.
Glucose (as well as amino acids) is transported across intestinal and kidney cells against its concentration gradient by means of secondary active transport.
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Fig. 3-18, p. 72

22. Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Table 3-2c, p. 74

23. Membrane Transport Vesicular transport
Material is moved into or out of the cell wrapped in membrane
Active method of membrane transport
Two types of vesicular transport
Endocytosis
Process by which substances move into cell
Pinocytosis – nonselective uptake of ECF
Phagocytosis – selective uptake of multimolecular particle
Exocytosis
Provides mechanism for secreting large polar molecules
Enables cell to add specific components to membrane
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

24. Carrier-mediated transport:
(a) involves a specific membrane protein that serves as a carrier molecule.
(b) always moves substances against a concentration gradient.
(c) always requires energy expenditure.
(d) two of these answers.
(e) all of these answers.
Facilitated diffusion:
(a) involves a carrier molecule.
(b) requires energy expenditure.
(c) is how glucose enters the cells.
(d) both (a) and (c) above.
Select the correct statement about diffusion.
(a) It depends on the random motion
(b) It involves active forces.
(c) Its rate increases as the temperature decreases.
(d) Molecules move from a lower concentration to a higher concentration.
(e) The chemical gradient of a substance does not affect it.
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

25. Membrane Potential
Plasma membrane of all living cells has a membrane potential (polarized electrically)
Separation of opposite charges across plasma membrane
Due to differences in concentration and permeability of key ions
Separated charges create the ability to do work ( hydroelectric dam) millivolt- 1/1000 volt
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

26. Membrane Potential Which has the greatest membrane potential?
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

27. Membrane Potential Nerve and muscle cells Resting membrane potential
Excitable cells
Have ability to produce rapid, transient changes in their membrane potential when excited
Resting membrane potential
Constant membrane potential present in cells of nonexcitable tissues and those of excitable tissues when they are at rest
Na+, K+, A-
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

28. Membrane Potential
Effect of sodium-potassium pump on membrane potential
Makes only a small direct contribution to membrane potential through its unequal transport of positive ions
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

29. Table 3-3, p. 75

30. Resting potential (Er)
Rp + -75mv
Variable from one cell to another
Poison eliminates this potential
Generated by the imbalance of ions in the intracellular and extracellular spaces.
Ion
Out mM In
Pot mV K
5.5
150
-90 Na 15 60 Cl
125 9
-70
Perm.
50-75 1
Chapter 3 The Plasma Membrane and Membrane Potential Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

31. Ion Concentration

32. Resting Potential

33. Figure 3.22: Effect of concurrent K+ and Na+ movement on establishing the resting membrane potential.
Fig. 3-22, p. 78

34. Plasma membrane ECF ICF Electrical gradient for K+ Concentration
EK+ = –90 mV
Fig. 3-20, p. 76

35. Plasma membrane ECF ICF Concentration gradient for Na+ Electrical
ENa+ = +60 mV
Fig. 3-21, p. 78

36. Resting membrane potential = –70 mV
Plasma membrane
ECF
ICF
Relatively large net
diffusion of K+
outward establishes
an EK+ of –90 mV
No diffusion of A–
across membrane
Relatively small net
diffusion of Na+
inward neutralizes
some of the
potential created by
K+ alone
Resting membrane potential = –70 mV
(A– = Large intracellular anionic proteins)
Fig. 3-22, p. 78

37. Figure 3.23: Counterbalance between passive Na+ and K+ leaks and the active Na+–K+ pump. At resting membrane potential, the passive leaks of Na+ and K+ down their electrochemical gradients are counterbalanced by the active Na+–K+ pump, so no net movement of Na+ and K+ takes place, and membrane potential remains constant.
Fig. 3-23, p. 79

38. ECF Na+–K+ pump (Passive) (Active) Na+ channel K+ channel (Passive)
ICF
Fig. 3-23, p. 79

39. Which of the following methods of transport is being used to transfer the substance into the cell in the accompanying graph?
a. diffusion down a concentration gradient b. osmosis c. facilitated diffusion d. active transport e. vesicular transport f. It is impossible to tell with the information provided.
Points to Ponder 3, p. 83

40. Nernst equation E=(61) log Co/Ci For Potassium Ek=(61) log 5mM/150mM
For sodium ENa=(61) log 150mM/15mM
Co concentration in the ECF
Ci concentration in the ICF
Used to calculate the contribution of ions to the resting potential of -70mv

41. Resting potential EK = -90mv ENa = 60mv ECl = -70mv
K and Na drive Cl gradient

42. Usefulness?
Neurons and muscle fibers can alter membrane potential to send signals and create motion.