1. Membrane Structure and Function

2. Membrane Function Membranes organize the chemical activities of cells.
The outer plasma membrane
forms a boundary between a living cell and its surroundings
Exhibits selective permeability
Controls traffic of molecules in and out

3. Membrane Function
Internal membranes provide structural order for metabolism
Form the cell's organelles
Compartmentalize chemical reactions

4. Membrane Structure
Phospholipid
Phospholipids are the major structural component of membranes.

5. Membrane Structure
All membranes are phospholipid bilayers with embedded proteins.
Phospholipid Bilayer
Label the:
Hydrophilic heads
Hydrophobic tails

6. Membrane Structure Embedded in the bilayer are proteins
Most of the membrane’s functions are accomplished by the embedded proteins.
Integral proteins span the membrane
Peripheral proteins are on one side or the other of the membrane

7. Plasma Membrane
Glycoproteins and glycolipids are proteins/lipids with short chain carbohydrates attached on the extracellular side of the membrane.

8. Carbohydrate of
glycoprotein
Glycoprotein
Glycolipid
Integrin
Phospholipid
Microfilaments
of cytoskeleton
Cholesterol

9. Membrane Proteins Types of Membrane Proteins Recognition proteins
Integrins
Cell junction proteins
Enzymes
Receptor proteins
Transport proteins
Passive and active

10. Recognition Proteins - identify type of cell and identify a cell as “self” versus foreign
Most are glycoproteins
Carbohydrate chains vary between species, individuals, and even between cell types in a given individual.
Glycolipids also play a role in cell recognition

11. Integrins Integrins are a type of integral protein
The cytoskeleton attaches to integrins on the cytoplasmic side of the membrane
Integrins strengthen the membrane
Cell Junction proteins - help like cells stick together to form tissues

12. Many membrane proteins are enzymes
This is especially important
on the membranes of organelles.

13. Receptor Proteins
Receptor proteins bind hormones and other substances on the outside of the cell.
Binding triggers a change inside the cell.
Called signal transduction
Example: The binding of insulin to insulin receptors causes the cell to put glucose transport proteins into the membrane.

14. Messenger molecule
Receptor
Activated
molecule

15. Transport Proteins Passive Transport Proteins
allow water soluble substances (small polar molecules and ions) to pass through the membrane without any energy cost
Active Transport Proteins
The cell expends energy to transport water soluble substances against their concentration gradient

17. Transport of Substances Across the Plasma Membrane (PM)
Passive Transport
(Simple) Diffusion
Facilitated diffusion
Osmosis
Active Transport
Bulk Flow - endocytosis and exocytosis

18. Passive Transport
In passive transport substances cross the membrane by diffusion
Diffusion - net movement of substances from an area of high concentration to low concentration
no energy required

19. Factors Affecting Diffusion Rate
Steepness of concentration gradient
Steeper gradient, faster diffusion
Molecular size
Smaller molecules, faster diffusion
Temperature
Higher temperature, faster diffusion

20. Simple Diffusion
Nonpolar, hydrophobic molecules diffuse directly through the lipid bilayer
Simple diffusion does not require the use of transport proteins.
Examples: O2, CO2, steroids
Polar, hydrophilic substances cannot pass directly through the lipid bilayer
Examples: water, ions, carbohydrates

21. Simple Diffusion Polar molecules ions small, nonpolar molecules
(ex. Glucose, water)
ions
(ex. H+, Na+, K+)
small, nonpolar molecules
(ex. O2, CO2)
LIPID-SOLUBLE
WATER-SOLUBLE
LIPID-SOLUBLE

22. Facilitated Diffusion
In facilitated diffusion small polar molecules and ions diffuse through passive transport proteins.
No energy needed
Most passive transport proteins are solute specific
Example: glucose enter/leaves cells through facilitated diffusion

23. Facilitated Diffusion
Higher concentration of
Passive transport protein
Lower concentration

24. Osmosis
Osmosis – diffusion of water across a selectively permeable membrane
Water moves from an area of _______ water concentration to an area of _____ water conc.
Is energy required ?

25. Consider two solutions separated
Osmosis Terms
Consider two solutions separated
by a plasma membrane.
Hypertonic
solution with a relatively high concentration of solute
Hypotonic
solution with a relatively low concentration of solute
Isotonic
solutions with the same solute concentration

26. cluster of water molecules
Lower
concentration
of solute
Higher
concentration
of solute
Equal
concentration
of solute
H2O
Solute
molecule
Selectively
permeable
membrane
Water
molecule
Solute molecule with
cluster of water molecules
Net flow of water

27. Osmosis and Animal Cells

28. Osmosis and Plant Cells

29. Osmosis When a Cell is Placed in a Hypotonic Solution
Water concentration is _________ the cell.
Water flows ___________ the cell.

30. Osmosis When a Cell is Placed in a Hypertonic Solution
Water concentration is _________ the cell.
Water flows ___________ the cell.

31. See page 83 Isotonic solution Hypotonic solution Hypertonic solution
H2O
H2O
H2O
H2O
Animal
cell
(1) Normal
(2) Lysed
(3) Shriveled
H2O
H2O
H2O
Plasma
membrane
H2O
Plant
cell
(4) Flaccid
(5) Turgid
(6) Shriveled
(plasmolyzed)
See page 83

32. Osmosis Summary When a cell is placed in a Hypotonic solution:
Cell gains water through osmosis
Animal cell lyses; plant cell becomes turgid (firm)
When a cell is placed a Hypertonic solution:
Cell loses water through osmosis
Animal cell shrivels; plant cell plasmolyzes

33. Active Transport
Active transport proteins move substances across the PM against their concentration gradient.
Requires energy (ATP)
Active transport proteins are highly selective
Active transport is needed for proper functioning of nerves and muscles

34. Active Transport of “X”
Active transport proteins span the plasma membrane
They have openings for “X” on only one side of the membrane
“X” enters the channel and binds to functional groups inside the transport protein.
Cytoplasmic ATP binds to the transport protein

35. Active Transport of “X”
A phosphate group is transferred from ATP to the transport protein
protein is energized by the added –P.
The energized transport protein changes shape and releases “X” on the other side of the cell.
The phosphate group is released from the transport protein and it resumes its original shape.
Process repeats.

36. Transport
protein
Solute 1
Solute binding

37. Transport
protein
Solute 1
Solute binding 2
Phosphorylation

38. Transport
protein
Protein
changes shape
Solute 1
Solute binding 2
Phosphorylation 3
Transport

39. Transport
protein
Protein
changes shape
Phosphate
detaches
Solute 1
Solute binding 2
Phosphorylation 3
Transport 4
Protein reversion

40. Active Transport tell the story…
ATP P
ADP

42. Bulk Flow
Vesicles are used to transport large particles across the PM.
Requires energy
Types:
Exocytosis
Endocytosis
Phagocytosis, pinocytosis, receptor-mediated

43. Exocytosis
Fluid outside cell
Vesicle
Protein
Cytoplasm

44. Bulk Flow
Exocytosis
Cytoplasmic vesicle merges with the PM and releases its contents
Example:
Golgi body vesicles merge with the PM an release their contents
How nerve cells release neurotransmittors

45. Endocytosis Endocytosis can occur in three ways
Vesicle forming
Endocytosis can occur in three ways
Phagocytosis ("cell eating")
Pinocytosis ("cell drinking")
Receptor-mediated endocytosis

46. Endocytosis Endocytosis
PM sinks inward, pinches off and forms a vesicle
Vesicle often merges with Golgi for processing and sorting of its contents

47. Endocytosis - terms Phagocytosis – cell eating
Membrane sinks in and captures solid particles for transport into the cell
Examples:
Solid particles often include: bacteria, cell debris, or food
Pinocytosis – cell drinking
Cell brings in a liquid

48. Endocytosis - comments
Phagocytosis and pinocytosis are not selective
Membrane sinks inward and captures whatever particles/fluid present.
Vesicle forms and merges with the Golgi body…

49. Receptor Mediated Endocytosis
Receptor Mediated Endocytosis is a highly specific form of endocytosis.
Receptor proteins on the outside of the cell bind specific substances and bring them into the cell by endocytosis

50. Receptor Mediated Endocytosis
Receptor proteins on PM bind specific substances (vitamins, hormones..)
Membrane sinks in and forms a pit
Called a coated pit
Pit pinches closed to form a vesicle around bound substances
Cytoskeleton aids in pulling in the membrane and vesicle formation

51. Plasma membrane
Receptor-mediated endocytosis
Coat protein
Receptor
Coated
vesicle
Coated
pit
Coated
pit
Specific
molecule
Material bound
to receptor proteins

53. Phagocytosis
EXTRACELLULAR
FLUID
CYTOPLASM
Food
being
ingested
Pseudopodium
“Food” or
other particle
Food
vacuole
Pinocytosis
Plasma
membrane
Vesicle
Receptor-mediated endocytosis
Plasma membrane
Coat protein
Receptor
Coated
vesicle
Coated
pit
Coated
pit
Specific
molecule
Material bound
to receptor proteins

56. Plasma Membrane Notes Continued…
The Plasma Membrane
Plasma Membrane Notes Continued…
What Are Three Forms of Transport Across the Membrane ?
4/19/2017
G. Podgorski, Biol. 1010

57. Objective: Compare active transport with passive transport.
The Plasma Membrane
4/19/2017
Objective:
Compare active transport with passive transport.
Distinquish between endocytosis and exocytosis
G. Podgorski, Biol. 1010

58. is a type of Simple Diffusion which…
The Plasma Membrane
Review…
Passive Transport
4/19/2017
is a type of Simple Diffusion which…
Doesn’t require energy
Moves solids, liquids and gases from high to low concentration
Biological connection
Oxygen or water diffusing into lung cells and carbon dioxide diffusing out.
G. Podgorski, Biol. 1010

59. Passive Transport can also occur as … Facilitated diffusion which…
The Plasma Membrane
4/19/2017
Passive Transport can also occur as …
Facilitated diffusion which…
Doesn’t require energy
Uses transport proteins to move high to low concentration
Biological connection:
Glucose or Protein in the form of amino acids move from blood into a cell.
G. Podgorski, Biol. 1010

60. The Plasma Membrane
4/19/2017
In cells proteins (amino acids) are Critical to Membrane Function because of 4 main reasons which are…
G. Podgorski, Biol. 1010

61. 2 Types of Transport Proteins are…
The Plasma Membrane
4/19/2017
2 Types of Transport Proteins are…
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
G. Podgorski, Biol. 1010

62. Facilitated Diffusion
The Plasma Membrane
4/19/2017
Facilitated Diffusion
Molecules will randomly move through the pores in Channel Proteins.
G. Podgorski, Biol. 1010

63. Facilitated Diffusion
The Plasma Membrane
4/19/2017
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.
G. Podgorski, Biol. 1010

64. The Plasma Membrane
4/19/2017
Carrier Proteins
Other carrier proteins change shape to move materials across the cell membrane
G. Podgorski, Biol. 1010

65. Active Transport Requires energy or ATP
The Plasma Membrane
4/19/2017
Active Transport
Requires energy or ATP
Moves materials from LOW to HIGH concentration
AGAINST concentration gradient
G. Podgorski, Biol. 1010

66. What is the name of this organelle?
The Plasma Membrane
4/19/2017
What is the name of this organelle?
What is the mitochondria function?
How does it transport the materials it needs to function?
Why is this important?
G. Podgorski, Biol. 1010

67. Exocytosis- moving things out.
The Plasma Membrane
Moving the “Big Stuff”
4/19/2017
Exocytosis- moving things out.
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.
G. Podgorski, Biol. 1010

68. The Plasma Membrane
Exocytosis
4/19/2017
Exocytic vesicle immediately after fusion with plasma membrane.
G. Podgorski, Biol. 1010

69. The Plasma Membrane
Moving the “Big Stuff”
4/19/2017
Large molecules move materials into the cell by one of three forms of endocytosis.
G. Podgorski, Biol. 1010

70. Pinocytosis Most common form of endocytosis.
The Plasma Membrane
Pinocytosis
4/19/2017
Most common form of endocytosis.
Takes in dissolved molecules as a vesicle.
G. Podgorski, Biol. 1010

71. Pinocytosis Cell forms an invagination
The Plasma Membrane
4/19/2017
Pinocytosis
Cell forms an invagination
Materials dissolve in water to be brought into cell
Called “Cell Drinking”
G. Podgorski, Biol. 1010

72. Example of Pinocytosis
The Plasma Membrane
Example of Pinocytosis
4/19/2017
mature transport vesicle
pinocytic vesicles forming
Transport across a capillary cell (blue).
G. Podgorski, Biol. 1010

73. Receptor-Mediated Endocytosis
The Plasma Membrane
4/19/2017
Receptor-Mediated Endocytosis
Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol, etc.
G. Podgorski, Biol. 1010

74. Receptor-Mediated Endocytosis
The Plasma Membrane
Receptor-Mediated Endocytosis
4/19/2017
G. Podgorski, Biol. 1010

75. Endocytosis – Phagocytosis
The Plasma Membrane
4/19/2017
Endocytosis – Phagocytosis
Used to engulf large particles such as food, bacteria, etc. into vesicles
Called “Cell Eating”
G. Podgorski, Biol. 1010

76. Phagocytosis About to Occur
The Plasma Membrane
Phagocytosis About to Occur
4/19/2017
This is a picture of a White Blood Cell…
about to flow around and eat a Prokaryotic Bacteria
G. Podgorski, Biol. 1010

77. Phagocytosis - Capture of a Yeast Cell (round yellow object ) by
The Plasma Membrane
4/19/2017
Phagocytosis - Capture of a
Yeast Cell (round yellow object ) by
the White Blood Cells (BLUE)
extending found in the Immune System Cell
G. Podgorski, Biol. 1010

78. The Plasma Membrane
4/19/2017
Exocytosis The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane.
From inside the Cell out to the …
cells environment which will then distribute the molecule to the proper system to get rid of the material
G. Podgorski, Biol. 1010