1. Membrane Structure/ Function and Cell Transport Ms. Day AP Biology
Chapter 7
Membrane Structure/ Function and Cell Transport
Ms. Day
AP Biology

2. Overview of Cell Membrane
The plasma (cell) membrane
boundary  separates living cell from nonliving surroundings
Also called the phospholipid bilayer

3. Plasma membrane exhibits selective permeability. It is semi-permeable
It allows some substances to cross it more easily than others
Wow…
it’s so
detailed!

4. Cellular membranes are made of 2 types of lipids and proteins
LIPID #1: Phospholipids
most abundant lipid in membrane
They are amphipathic
have both hydrophobic and hydrophilic regions

5. Phospholipid Bilayer Phosphate Groups in “head” (- charge)
Figure 7.2
Hydrophilic
head
Hydrophobic
tail
WATER
Phosphate Groups in “head” (- charge)
2 Fatty Acids in “tail” (hydrocarbon)
NO WATER

7. Fluid Mosaic Model of the cell membrane
Polar heads love water & dissolve.
Fluid Mosaic Model of the cell membrane
Non-polar tails “hide” from water.
Membrane movement animation
Carbohydrate cell markers
Proteins

8. The Fluidity of Membranes
Phospholipids in the plasma membrane
Can move within the bilayer
Proteins are larger & drift (move) less
Figure 7.5 A
Lateral movement
(~107 times per second)
Flip-flop
(~ once per month)
(a) Movement of phospholipids

9. Another view…

10. So hydrocarbon tails in phospholipids
Temperature decreases  so does fluidity
So hydrocarbon tails in phospholipids
Affects fluidity of the plasma membrane
Need to have some unsaturated fatty acid tails
Fluidity is enhanced
Figure 7.5 B
Fluid
Viscous
Unsaturated hydrocarbon
tails with kinks
Saturated hydro-
Carbon tails
(b) Membrane fluidity

11. (c) Cholesterol within the animal cell membrane
LIPID #2: Use a steroid called cholesterol *increases membrane fluidity (only in animal cells) - cholesterol in membrane  stops solidification **acts as a temp “buffer”
(c) Cholesterol within the animal cell membrane
Cholesterol

12. Hydrophobic region of protein
Membrane Proteins
Hey, that
looks like a
sandwich!
Phospholipid
bilayer
Hydrophobic region
of protein
Hydrophobic region of protein

13. Span of 1+ stretches of Nonpolar amino acids
1. Integral proteins
Go through hydrophobic core of membrane
Aka- transmembrane proteins
Wait…what’s
that
word for a polar &
nonpolar
molecule?
Figure 7.8
a Helix
CYTOPLASMIC
SIDE
Span of 1+ stretches of Nonpolar amino acids
EXTRACELLULAR
SIDE

14. 2. Peripheral proteins
loosely bound to the surface of the membrane

15. An overview of six major functions of membrane proteins
Transport.
Enzymatic
activity.
Signal
transduction.
(a)
(b)
(c)
Enzymes
Receptor

16. Cell-cell recognition. Intercellular joining Attachment to
cytoskeleton &
extracellular
matrix (ECM)
(d)
(e)
(f)
Glyco-
protein
ECM

17. Why Carbohydrates on Proteins?
Cell-cell recognition
Helps distinguish neighboring cell from another
It’s their “ID” tag

18. Membrane carbohydrates
short, branched carbohydrates
Bind with surface molecules of other cells
Function as cell “markers”
Ex: Blood types (A, B, AB, and O)

19. 2 different types membrane carbohydrates
Glycolipids
Carbohydrates covalently attached to lipids
Glycoproteins
Carbohydrates covalently attached to proteins (most abundant)

20. Review…

22. Cell Transport Ms. Day AP Biology
Chapter 7
Cell Transport
Ms. Day
AP Biology

23. Cell Transport Means moving things INTO and OUT of the cell
Food, gases, water
Get rid of waste products (excretion)
Give out such useful substances as hormones and enzymes (secretion).

24. Permeability and Cell Transport
Hydrophobic (non polar) molecules
lipid soluble (can dissolve)
can pass through membrane easily
Ex: Hydrocarbons, CO2, O2
Hydrophilic (Polar) molecules
NOT lipid soluble (can’t dissolve)
Lipid INsoluble
Do not cross membrane easily
Ex: Na+, Cl- , Glucose/ other sugars
NOTE: CHARGED molecules need “help” to cross membrane

25. http://www. sumanasinc. com/webcontent/animations/content/diffusion

26. Types of Cellular Transport
high
low
Weee!
Passive Transport
cell do NOT use energy
Diffusion
Facilitated Diffusion
Osmosis
Active Transport
cell DOESuse energy
Protein Pumps
Endocytosis/Exocytosis
Receptor Mediated
high
low
This is going to be hard!

27. Types of Passive Transport
Diffusion= tendency for a population of molecules (of ANY substance) to spread out evenly into available space
[High]  [Low]
A “net” movement
Ex: Perfume, tea, food coloring in water

28. DIFFUSION In absence of other forces…
Molecules diffuse from area of HIGH [ ] to an area of lower [ ]
A.k.a. Molecules move DOWN its OWN concentration gradient
the difference in [ ] of a substance from one area to another
No chemical work (ATP energy) is used diffusion is spontaneous!

29. Substances diffuse down their OWN concentration gradient
Figure 7.11 B
(b)
Net diffusion
Equilibrium

30. Factors Affecting Diffusion
1. Temperature
Higher temperature  more kinetic energy  molecules move faster (Example: Tea)
2. Pressure
Higher pressure  molecules move faster

31. Introduction to Osmosis

32. Effects of Osmosis on Water Balance
Movement of water (water diffusion) across a semipermeable membrane
Involves the movement of FREE water molecules down a water [ ] gradient
High solute low “free” water [ ] or….
Low solute  high free water [ ]

33. Tonicity= the measure of the amount of dissolved particles in a solution

34. Osmosis is affected by the concentration gradient of dissolved substances (solutes)
Osmosis animation

35. 1. If a solution is isotonic to a cell
3 Different Types of Solutions Recall: SOLUTION = a uniform mixture of 2 or more substances ** compare solutions OUTSIDE cell to inside cell
1. If a solution is isotonic to a cell
[solutes] is the same outside as inside the cell
“iso-” means “same”
There will be NO net movement of water

36. ISOTONIC SOLUTION
Result: Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium)

37. 2. If a solution is hypertonic to a cell
[solutes] is greater outside than inside the cell
Cell will lose water and shrivel or wilt
“hyper” means more
(high [solute])
Ex: when salinity increases in lake, fish can die!

38. HYPERTONIC SOLUTION
Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis)!

39. 3. If a solution is hypotonic to a cell
[solutes] is less outside than inside cell
The cell will gain water and swell (and maybe lyse or burst)
“hypo” means “less”
(low [solute])
Think: Hypo- sounds like hippo…
hippos are big & round; cells in
hypotonic solutions get big & round
Also, think “hypo” is “low” meaning “low” solutes SURROUNDING cell
“Hypo” is
LOW!!!

40. HYP0TONIC SOLUTION
Result: Water moves from the solution to inside the cell): Cell Swells and bursts open (cytolysis)!

41. Now…let’s review tonicity using Gummy Bears!

42. Osmosis Animations for isotonic, hypertonic, and hypotonic solutions

43. Water Balance of Cells with Walls
Cell walls
Help maintain water balance
Cell walls are in:
Plants
Prokaryotes
Fungi
Some protists

44. If a plant cell is turgid
It is in a hypotonic environment
It is very firm
A healthy state in most plants
If a plant cell is flaccid
It is in an isotonic or hypertonic environment
Cells are limp
Plasmolysis= when plasma membrane pulls away from cell wall in hypertonic solutions ; causes cell with walls to wilt & can be lethal.

45. Water balance in cells with walls
Plant cell. Plant cells
are turgid (firm) and
generally healthiest in
a hypotonic environ-
ment, where the
uptake of water is
eventually balanced
by the elastic wall
pushing back on the
cell.
(b)
H2O
Turgid (normal)
Flaccid
Plasmolyzed
Figure 7.13

46. How Organisms Deal with Osmotic Pressure
Bacteria and plants have cell walls that prevent them from over-expanding.
In plants the pressure exerted on the cell wall is called tugor pressure.
A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from bursting.
Salt water fish pump salt out of their specialized gills so they do not dehydrate.
Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.

47. Types of Passive Transport
DOES NOT require chemical energy (ATP)
Moves DOWN (WITH) [ ] gradient
Kinetic energy drives movement
#2 Active Transport
DOES require chemical energy (ATP)
Moves AGAINST its [ ] gradient

48. 2 Types of PASSIVE TRANSPORT
1. SIMPLE DIFFUSION
**INCLUDES DIFFUSION
Uses NO membrane proteins
GOES DOWN CONCENTRATION GRADIENT (no ATP needed)
Molecules move HIGH [ ]low [ ]
Uncharged & lipid-soluble molecules also pass freely through bilayer.
solutes move down a concentration gradient
Examples: CO2, O2…H2O
WAIT!!!
Isn’t
water
polar?

49. Aquaporins water is polar but very small
It can pass easily through membrane
uses aquaporins
Oh…now
I get it!
EXTRACELLULAR
FLUID
AQUAPORIN
Channel protein
Water
CYTOPLASM

50. 2 Types of PASSIVE TRANSPORT
2. FACILITATED DIFFUSION
needs a little “help”
Uses help of channel or carrier proteins
GOES DOWN CONCENTRATION GRADIENT (no ATP needed)
Moves POLAR molecules  can NOT easily pass through HYDROPHOBIC region of membrane.
Example: ions, smaller polar molecules (ex: sugar)
Channel/carrier proteins specific receptor site for substances they “help.”

51. Channel proteins -Provide “tunnels”
Channel Proteins animations
Channel proteins -Provide “tunnels”
Figure 7.15
EXTRACELLULAR
FLUID
Channel protein
Solute
CYTOPLASM
A channel protein (purple) has a channel through which
water molecules or a specific solute can pass.
(a)

52. Carrier proteins -Undergo a subtle change in shape “carry” solute across the membrane

53. 2 Types of Passive Transport

54. Active transport
Uses energy to move solutes against their [ ] gradients across the cell membrane
Energy required  usually ATP
Carrier proteins are used…NEVER channel proteins
Ex: sodium-potassium pump

55. Passive vs. Active Transport
Figure 7.17

56. Sodium Potassium Pumps (Active Transport using proteins)
1. PROTEIN PUMPS
Sodium Potassium Pumps (Active Transport using proteins)
Protein Pumps -transport proteins that require energy to do work
Examples:
Na+/K+ Pumps are important in nerve responses
Antiports and Symports (Cotransport)
H+ (proton) pump
Protein changes conformational shape to move molecules: this requires energy!

58. Cotransport, Proton Pumps and Sodium/Potassium Pumps… ANIMATIONS
REVIEW OF ACTIVE TRANSPORT… ANIMATIONS
Cotransport, Proton Pumps and Sodium/Potassium Pumps… ANIMATIONS

59. 2. Bulk transport across the plasma membrane
Occurs by exocytosis and endocytosis
BOTH MOVE “BIG” AMOUNTS OF STUFF in OR out OF THE CELL

60. Exocytosis In exocytosis
Transport vesicles move to the plasma membrane, fuse with it, and release their contents
“exo-” means “exit”
Ex: hormone excretion; nerve cells and transmitters; removal of wastes

62. ROUGH ER GOLGI APPARATUS Glycolipid Vesicle Secreted protein
Membrane glycolipid
Secreted
protein 4 1 2 3
GOLGI
APPARATUS

63. Endocytosis In endocytosis
Cell takes in macromolecules by forming new vesicles from the plasma membrane
“endo-” means “enter”

64. 2 types of Endocytosis 1. Phagocytosis
“cell eating”
Cell engulfs SOLIDS into vesicle & “digests” it
2. Pinocytosis (think “pineapple juice)
“cell drinking”
Cell engulfs LIQUIDS into vesicle & “digests” it

65. http://highered. mcgraw-hill

66. Endocytosis and Exocytosis Animations

67. REVIEW ANIMATIONS http://www.hippocampus.org/Biology
Click on “Membranes and Transport”
Listen to animation #3 (7 minutes long)
Excellent Review all Passive (simple/facilitated diffusion) and Active Transport 
No verbal explanation…you have to read the tutorial!