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1. The Plasma Membrane -
Gateway to the Cell 1

2. Photograph of a Cell
Membrane
2

3. Cell Membrane
The cell
membrane is
flexible and
allows a
unicellular
organism to
move
3

4. Homeostasis
• Balanced internal condition of
cells
• Also called equilibrium
• Maintained by plasma (or cell)
membrane controlling what
enters & leaves the cell
4

5. Functions of Plasma
Membrane
 Protective fence
 Controls transport in & out of cell
(selectively permeable)
 Allow cells recognize “friend or Foe”
 Provide anchoring sites the
cytoskeleton support framework
5

6. Functions of Plasma
Membrane
 Provide a tie on site for enzymes
 Place for cells to bind together
Contains the cytoplasm (fluid in cell)
6

7. Structure of the Cell Membrane
Peripheral
protein
Lipid Bilayer
Integral
Protein
7

8. Phospholipids-3 models
Make up the cell
membrane
Contains 2 fatty
acid chains that
are nonpolar
Head is polar &
contains a –PO4
group
8

9. FLUID MOSAIC MODEL
Fluid mosaic model
FLUID- because individual phospholipids and
proteins can move around freely within the
layer, like it’s a liquid.
MOSAIC-little pieces put together in a pattern
9

10. • Mosaic
10

11. Cell Membrane
Polar heads are hydrophilic “water loving”
Nonpolar tails are hydrophobic “water fearing”
Makes membrane “Selective” in what crosses11

12. Cell Membrane
The cell membrane is made
of 2 layers of Hydrophobic molecules
phospholipids called the pass easily; hydrophillic
lipid bilayer DO NOT
12

13. Solubility
• Materials that
are soluble in
lipids can pass
through the
cell membrane
easily
13

14. Selectively Permeable
Membrane
Small molecules like water move across
easily, most larger molecules need help-
and need energy to be added so they can
cross. 14

15. IMPORTANT!
Kinds of Transport
Across Cell
Membranes
15

16. 1. Passive Transport
Movement of substances across the
cell membrane without any input of
energy on the part of the cell.
16

17. 2. Simple Diffusion
• Requires NO
energy
• Molecules move
from area of
HIGH to LOW
concentration or
down the
concentration
gradient.
17

18. Simple Diffusion continued
• Concentration Gradient is the
difference ( change) in the
concentration of a substance from
one location to another.
18

19. DIFFUSION
Diffusion is a
PASSIVE process
which means no
energy is used to
make the
molecules move,
they have a
natural KINETIC
ENERGY
19

20. Diffusion of Liquids
20

21. Diffusion through a
Membrane
Cell membrane
Solute moves DOWN concentration gradient (HIGH to
LOW) until equilibrium is reached
21

22. Osmosis
Diffusion across a membrane
• Diffusion of water
across a
membrane
• Moves from HIGH
Semipermeable
water potential membrane
(low solute) to
LOW water
potential (high
solute)
22

23. A Hypertonic solution has a higher
concentration of dissolved particles
than the cell.
A Hypotonic solution has a lower
concentration of dissolved particles
than the cell.
An Isotonic solution has the same
concentration of dissolved particles
as the cell.
23

24. Diffusion of H2O Across A
Membrane
High H2O potential Low H2O potential
Low solute concentration High solute concentration
24

25. Cell in Isotonic Solution
10% NaCL ENVIRONMENT
90% H2O
CELL
NO NET
10% NaCL MOVEMENT
90% H2O
What is the direction of water movement?
equilibrium
The cell is at _______________. 25

26. Cell in Hypotonic Solution
10% NaCL
90% H2O
CELL
20% NaCL
80% H2O
What is the direction of water movement?
26

27. Cell in Hypertonic Solution
15% NaCL ENVIRONMENT
85% H2O
CELL
5% NaCL
95% H2O
What is the direction of water movement?
27

28. Cells in Solutions
28

29. Isotonic Solution Hypotonic Hypertonic
Solution Solution
NO NET
MOVEMENT OF
H2O (equal amounts CYTOLYSIS PLASMOLYSIS
entering & leaving) (cell rupture) (cell shrinkage)
29

30. Osmosis in Red Blood Cells
Isotonic Hypotonic Hypertonic
30

31. Osmosis in plant cells
In plant cells, plasmolysis
results in wilting and
osmotic pressure results
in turgor pressure.
31

32. hypotonic hypertonic isotonic
hypertonic isotonic hypotonic
32

33. Three Forms of Transport Across the Membrane
33

34. Passive Transport
Simple Diffusion
 Doesn’t require energy
 Moves high to low
concentration
 Example: Oxygen or
water diffusing into a
cell and carbon dioxide
diffusing out. 34

35. Facilitated diffusion
Doesn’t require energy
Uses transport
proteins to move high to
low concentration
Examples: Glucose or
amino acids moving from
blood into a cell.
35

36. Proteins Are Critical to
Membrane Function
36

37. Types of Transport Proteins
• Channel proteins are embedded
in the cell membrane & have a
pore for materials to cross
• Carrier proteins can change
shape to move material from
one side of the membrane to
the other
37

38. Facilitated Diffusion
Molecules will randomly move through
the pores in Channel Proteins.
38

39. Facilitated Diffusion
• Some Carrier
proteins do not
extend through
the membrane.
• They bond and
drag molecules
through the lipid
bilayer and
release them on
the opposite side. 39

40. Carrier Proteins
• Other carrier
proteins
change shape
to move
materials
across the cell
membrane
40

41. Remember this? It’s
Facilitated Passive
Transport.
41

42. Passive Transport Review
Movement of particles across the cell
membrane without energy input on
the part of the cell.
42

43. Passive Transport Review
Three major types:
1) Diffusion
2) Osmosis
3) Facilitated Diffusion
43

44. Active Transport
44

45. Active Transport
Requires energy or
ATP
Moves materials from
LOW to HIGH
concentration
AGAINST
concentration gradient
45

46. Major Types
• Endocytosis (including
pinocytosis and phagocytosis)
• Exocytosis
• Pumps (including proton pump
and sodium-potassium pump)
46

47. Endocytosis
47

48. Endocytosis
• Endocytosis is the process of taking
liquids or larger molecules into a cell
by engulfing them in a membrane.
• This is done when the cell membrane
makes a pocket around the substance
that breaks off inside the cell.
• This pocket is called a vesicle.
48

49. Moving the “Big Stuff”
Large molecules move materials into the cell by
one of three forms of endocytosis.
49

50. Pinocytosis
• Endocytosis
that involves
movement of
liquids.
• Called “Cell
Drinking”
50

51. Pinocytosis
Most common form of endocytosis.
Takes in dissolved molecules as a vesicle.
51

52. Example of Pinocytosis
pinocytic vesicles forming mature transport vesicle
52
Transport across a capillary cell (blue).

53. Endocytosis – Phagocytosis
•Endocytosis that involves taking
in large particles such as
food, bacteria, etc. into vesicles
•Called “Cell Eating”
53

54. Phagocytosis About to Occur
54

55. Phagocytosis
- Capture
of a Yeast
Cell (yellow)
by
Membrane
Extensions
of an
Immune
System Cell
(blue)
55

56. Exocytosis
• moving things out
• essentially the opposite of endocytosis
• Molecules are moved out of the cell by
vesicles that fuse with the plasma
membrane.
• This is how many hormones are secreted
and how nerve cells communicate with
one another
56

57. Exocytosis
57

58. Exocytosis
Exocytic
vesicle
immediately
after fusion
with plasma
membrane.
58

59. Exocytosis
The opposite of endocytosis is exocytosis. Large
molecules that are manufactured in the cell are
released through the cell membrane.
Inside Cell Cell environment 59

60. Pumps
• Pumps are similar to
facilitated diffusion in
that they use transport
proteins.
• Pumps use proteins to
move materials against
the concentration
gradient.
60

61. Three Types of Pumps
• Sodium-Potassium Pump (3 Na out,
2 K in)
• Proton Pump
• Contractile Vacuole (pumps excess
water out of single-cell organisms)
61

62. Sodium-Potassium Pump
3 Na+ pumped out for every 2 K+
pumped in; creates a membrane potential
62