Presentation by Andreas Schleicher Tackling the School Absenteeism Crisis 30 ...
AS CIE Cell Membranes
1. D1: The Cell Membranes
Plan
1 Introduction:
1.1 Where are membranes found in the cell ?
1.2 Roles of the Cell Membranes
1.3 The fluid mosaic model
2 Membrane lipids:
2.1 Types of membrane lipids
2.2 Roles of membrane lipids
2.3 Examples
2
3
4
1
5
3 Membrane proteins:
3.1 Types of membrane proteins
3.2 Roles of membrane proteins
3.3 Examples
4 Membrane carbohydrates:
4.1 Types of membrane carbohydrates
4.2 Roles of membrane carbohydrates
4.3 Examples
5 Conclusions and Overviews:
Xavier DANIEL, Ph.D.
AS
2. D1: The Cell Membranes
Plan
1 Introduction:
1.1 Where are membranes found in the cell ?
1.2 Roles of the Cell Membranes
1.3 The fluid mosaic model
2 Membrane lipids:
2.1 Types of membrane lipids
2.2 Roles of membrane lipids
2.3 Examples
2
3
4
1
5
3 Membrane proteins:
3.1 Types of membrane proteins
3.2 Roles of membrane proteins
3.3 Examples
4 Membrane carbohydrates:
4.1 Types of membrane carbohydrates
4.2 Roles of membrane carbohydrates
4.3 Examples
5 Conclusions and Overviews:
Xavier DANIEL, Ph.D.
AS
3. • Cell wall
• Plasma membrane
• Cytoplasm
• Free DNA
• Ribosomes
A Typical Prokaryotic Cell
0.1 – 10mm
Depending on the species
outside
inside
Where are membranes found in the cell ?
1
Xavier DANIEL, Ph.D.
AS
4. Rough ER Smooth ER
Centrosome
CYTOSKELETON
Microfilaments
Microtubules
Microvilli
Peroxisome
Lysosome
Golgi apparatus
Ribosomes
In animal cells but not plant cells:
Lysosomes
Centrioles
Flagella (in some plant sperm)
Nucleolus
Chromatin
NUCLEUS
Flagellum
Intermediate filaments
ENDOPLASMIC RETICULUM (ER)
Mitochondrion
Nuclear envelope
Plasma membrane
A Typical Animal Cell
Where are membranes found in the cell ?
1
Xavier DANIEL, Ph.D.
AS
6. In plant cells but not animal cells:
Chloroplasts
Central vacuole and tonoplast
Cell wall
Plasmodesmata
CYTOSKELETON
Ribosomes (small brown dots)
Central vacuole
Microfilaments
Intermediate
filaments
Microtubules
Rough
endoplasmic
reticulum Smooth
endoplasmic
reticulum
Chromatin
NUCLEUS
Nuclear envelope
Nucleolus
Chloroplast
Plasmodesmata
Wall of adjacent cell
Cell wall
Golgi apparatus
Peroxisome
Tonoplast
Centrosome
Plasma membrane
Mitochondrion
A Typical Plant Cell
Where are membranes found in the cell ?
1
Xavier DANIEL, Ph.D.
AS
7. D1: The Cell Membranes
Plan
1 Introduction:
1.1 Where are membranes found in the cell ?
1.2 Roles of the Cell Membranes
1.3 The fluid mosaic model
2 Membrane lipids:
2.1 Types of membrane lipids
2.2 Roles of membrane lipids
2.3 Examples
2
3
4
1
5
3 Membrane proteins:
3.1 Types of membrane proteins
3.2 Roles of membrane proteins
3.3 Examples
4 Membrane carbohydrates:
4.1 Types of membrane carbohydrates
4.2 Roles of membrane carbohydrates
4.3 Examples
5 Conclusions and Overviews:
Xavier DANIEL, Ph.D.
AS
8. Cell (plasma) membrane
1. Separates the components of a cell from its
environment
Surrounds the cell
The cell membrane is the boundary
IN
food
- sugars
- proteins
- fats
salts
O2
H2O
OUT
waste
- ammonia
- salts
- CO2
- H2O
products
- proteins
Cell needs materials in & products or waste out
Roles of the cell membranes
1
Controls what goes in
and what goes out of
the cell
Xavier DANIEL, Ph.D.
AS
9. Roles of the cell membranes
1
Cell (plasma) membrane
1. Separates the components of a cell from its environment
Controls what goes in
and what goes out of
the cell
2. Keeps a stable environment inside the cell
Homeostasis of the cell
Xavier DANIEL, Ph.D.
AS
10. Organelle’s membranes
1’. Separate the components of an organelle from its environment
=
Cytoplasm
Surrounds the organelle
Organelle’s membrane is the boundary
Roles of the cell membranes
1
What goes in ? What goes out ?
Depends on the organelle
Controls what goes in and what
goes out of each organelle
Xavier DANIEL, Ph.D.
AS
11. Organelle’s membranes
1’. Separate the components of an organelle from its environment
Roles of the cell membranes
1
Controls what goes in and what
goes out of each organelle
2. Keeps a stable environment inside each organelle
Homeostasis of all organelles
Xavier DANIEL, Ph.D.
AS
12. Organelle’s membranes
2. Compartimentalize the molecules
What is needed in the nucleus may not be needed elsewhere
Genomic DNA
What is needed in the chloroplast may not be needed elsewhere
Chlorophyll
What is needed in the cytoplasm may not be needed elsewhere
Cytoskeleton
What is needed in the vacuole may not be needed elsewhere
Water and waste products
etc...
Roles of the cell membranes
1
Xavier DANIEL, Ph.D.
AS
13. Organelle’s membranes
3. Compartimentalize the chemical reactions
Each organelle is specialized for some reactions only
More efficient ! No mutual inhibition !
Lysosome
Hydrolysis of molecules
Chloroplast
Photosynthesis
Mitochondrion
Last steps of Cellular respiration
Golgi
Modification of proteins
etc...
Roles of the cell membranes
1
Xavier DANIEL, Ph.D.
AS
14. Roles of the cell membranes
1
4. Different cellular compartments
can have different conditions
Organelle’s membranes
2. Compartimentalize the molecules
3. Compartimentalize the chemical reactions
+
Xavier DANIEL, Ph.D.
AS
15. pH 4.8
Contains digestive
enzymes, optimum pH
4.5 - 4.8
pH 7.2
lysosome
cytosol
Membrane = tonoplast
acts as
a barrier
Roles of the cell membranes
1
4. Different cellular compartments
can have different conditions
Xavier DANIEL, Ph.D.
AS
16. D1: The Cell Membranes
Plan
1 Introduction:
1.1 Where are membranes found in the cell ?
1.2 Roles of the Cell Membranes
1.3 The fluid mosaic model
2 Membrane lipids:
2.1 Types of membrane lipids
2.2 Roles of membrane lipids
2.3 Examples
2
3
4
1
5
3 Membrane proteins:
3.1 Types of membrane proteins
3.2 Roles of membrane proteins
3.3 Examples
4 Membrane carbohydrates:
4.1 Types of membrane carbohydrates
4.2 Roles of membrane carbohydrates
4.3 Examples
5 Conclusions and Overviews:
Xavier DANIEL, Ph.D.
AS
17. Phospholipids are
the major structural
component of
membranes
Phospholipid
The fluid mosaic model
1
Xavier DANIEL, Ph.D.
AS
18. aqueous solution
Hydrophilic head
Hydrophobic tail
Phospholipids form
micelles when submerged
in water
air
One-layer membrane ? Impossible !
The fluid mosaic model
1
Xavier DANIEL, Ph.D.
AS
21. All membranes are phospholipid bilayers
with embedded proteins
The fluid mosaic model
1
Transmembrane (intrinsic) proteins span the membrane
Integral (extrinsic) proteins are on either side of the membrane
Xavier DANIEL, Ph.D.
AS
22. All membranes are phospholipid bilayers
with embedded proteins
The fluid mosaic model
1
Xavier DANIEL, Ph.D.
AS
24. Membranes are not static
They have a fluid consistency
Most membrane lipids and proteins can drift about
laterally in the plane of the membrane
Cholesterol enhances membrane fluidity
(animal membranes mostly)
The fluid mosaic model
1
Xavier DANIEL, Ph.D.
AS
25. The membranes’ “fluid” is
the double layer of phospholipids
The fluid mosaic model
1
Xavier DANIEL, Ph.D.
AS
26. The membranes’ “mosaic” is
a collection of various proteins
The fluid mosaic model
1
Xavier DANIEL, Ph.D.
AS
27. Membrane is a collage of proteins & other molecules
embedded in the fluid matrix of the lipid bilayer
Extracellular fluid
Cholesterol
Cytoplasm
Glycolipid
Transmembrane
proteins
Filaments of
cytoskeleton
Peripheral
protein
Glycoprotein
Phospholipids
The fluid mosaic model
1
Xavier DANIEL, Ph.D.
AS
28. The Fluidity of Membranes
Phospholipids in the membranes
Can move within the bilayer
Lateral movement
(~107 times per second) Flip-flop
(~ once per month)
(a) Movement of phospholipids
The fluid mosaic model
1
Xavier DANIEL, Ph.D.
AS
29. Proteins in the membranes
Can drift within the bilayer
EXPERIMENT
Researchers labeled the plasma membrane proteins of a mouse
cell and a human cell with two different markers and fused the cells.
Using a microscope, they observed the markers on the hybrid cell.
Membrane proteins
Mouse cell
Human cell
Hybrid cell
Mixed
proteins
after
1 hour
RESULTS
CONCLUSION
The mixing of the mouse and human membrane proteins
indicates that at least some membrane proteins move sideways within the plane
of the plasma membrane.
+
The fluid mosaic model
1
Xavier DANIEL, Ph.D.
AS
30. Overview
Cell membranes separate living cell from non-living
surroundings and separate different organelles
thin barrier = 8nm thick
Controls traffic in & out of the cell/organelle
Made of phospholipids, proteins & other macromolecules
Is a fluid mosaic
The fluid mosaic model
1
Xavier DANIEL, Ph.D.
AS
32. D1: The Cell Membranes
Plan
1 Introduction:
1.1 Where are membranes found in the cell ?
1.2 Roles of the Cell Membranes
1.3 The fluid mosaic model
2 Membrane lipids:
2.1 Types of membrane lipids
2.2 Roles of membrane lipids
2.3 Examples
2
3
4
1
5
3 Membrane proteins:
3.1 Types of membrane proteins
3.2 Roles of membrane proteins
3.3 Examples
4 Membrane carbohydrates:
4.1 Types of membrane carbohydrates
4.2 Roles of membrane carbohydrates
4.3 Examples
5 Conclusions and Overviews:
Xavier DANIEL, Ph.D.
AS
33. Types of membrane lipids
2
Two types of lipids in the membranes
Phospholipids Cholesterol
Mostly in animal cels
Xavier DANIEL, Ph.D.
AS
34. Phospholipids
Triglycerides that contain a Phosphate Group
One of the 3 fatty acids is replaced by a phosphate group
Variable
2
Types of membrane lipids
Xavier DANIEL, Ph.D.
AS
37. 2
Types of membrane lipids
Most common Phospholipids in membranes
Xavier DANIEL, Ph.D.
AS
38. 2
Types of membrane lipids
Most common Phospholipids in membranes
Outer side
of membranes
Phosphatidylcholine = Lecithin
Proeminent phospholipid in membranes
Xavier DANIEL, Ph.D.
AS
39. 2
Types of membrane lipids
Most common Phospholipids in membranes
Inner side
of membranes
Phosphatidylserine
Xavier DANIEL, Ph.D.
AS
40. 2
Types of membrane lipids
Most common Phospholipids in membranes
Inner side
of membranes
Phosphatidylethanolamine = Cephalin
Xavier DANIEL, Ph.D.
AS
41. 2
Types of membrane lipids
Most common Phospholipids in membranes
Inner and Outer sides
of membranes
Phosphatidylinositol
Xavier DANIEL, Ph.D.
AS
42. 2
Types of membrane lipids
Most common Phospholipids in membranes
Phosphatidyl
inositol
Phosphatidyl
ethanolamine
Phosphatidyl
serine
Phosphatidyl
choline
Xavier DANIEL, Ph.D.
AS
43. 2
Types of membrane lipids
Most common Phospholipids in membranes
Xavier DANIEL, Ph.D.
AS
44. 2
Types of membrane lipids
The lipid bilayer is asymmetric
Xavier DANIEL, Ph.D.
AS
45. Roles of Phospholipids
2
The kind of phospholipids influences
the movement of molecules in the membrane
Xavier DANIEL, Ph.D.
AS
47. The type of hydrocarbon tails in phospholipids
affects the fluidity and viscosity of the membranes
Fluid Viscous
Unsaturated hydrocarbon
tails with kinks
Saturated hydro-
Carbon tails
2
1. Fluid membrane
Not tight
Molecules can drift
1. Viscous membrane
Tight
Molecules cannot drift
Roles of Phospholipids
Xavier DANIEL, Ph.D.
AS
48. 1. Fluid membrane
Not tight
Molecules can drift
2
Roles of Phospholipids
Xavier DANIEL, Ph.D.
AS
50. 2
Aqueous
Aqueous
“Organic”
Can water go through ?
?
Phospholipids regulate the passage of molecules through membranes
YES
Can hydrophilic molecules
go through ?
?
NO
Membranes are selectively permeable
Hydrophilic molecules
do not mix with lipids
Roles of Phospholipids
Xavier DANIEL, Ph.D.
AS
51. 2
Phospholipids regulate the passage of molecules through membranes
Membranes are selectively permeable
Phospholipids restrict the passage of
hydrophilic molecules
through membranes
Phospholipids make membranes become
Barriers between
1. Cells and their environment
2. Organelles and the cytoplasm
Aqueous
Aqueous
“Organic”
Roles of Phospholipids
Xavier DANIEL, Ph.D.
AS
52. Types of membrane lipids
2
Two types of lipids in the membranes
Phospholipids Cholesterol
Only in animal cels
Xavier DANIEL, Ph.D.
AS
53. Lipids
Steroids
Basic form = CHOLESTEROL
In animal membranes
Mostly in the plasma membrane
2
Types of membrane lipids
Xavier DANIEL, Ph.D.
AS
54. 2
Types of membrane lipids
Cholesterol is amphipathic
Hydrophobic
Hydrophilic
Xavier DANIEL, Ph.D.
AS
57. 2
Roles of cholesterol
1. Cholesterol maintains the integrity of the Cell Membrane
Part of the steroid ring
(the four hydrocarbon rings in between the hydroxyl group and the hydrocarbon "tail")
is closely attracted to part of the fatty acid chain on the nearest phospholipid
1. This helps slightly immobilize the surface of the membrane
Xavier DANIEL, Ph.D.
AS
58. 2
2. Cholesterol regulates the fluidity of the membranes
Part of the steroid ring
(the four hydrocarbon rings in between the hydroxyl group and the hydrocarbon "tail")
is closely attracted to part of the fatty acid chain on the nearest phospholipid
1. This helps slightly immobilize the surface of the membrane
More cholesterol
Membrane is more ………
Less cholesterol
Membrane is more …….
Roles of cholesterol
Xavier DANIEL, Ph.D.
AS
59. 2
3. Cholesterol reduces membranes’ permeability
to hydrophilic molecules
Part of the steroid ring
(the four hydrocarbon rings in between the hydroxyl group and the hydrocarbon "tail")
is closely attracted to part of the fatty acid chain on the nearest phospholipid
2. Makes the membrane less soluble to very small water-soluble molecules
that could otherwise pass through more easily
Very small hydrophilic molecules
Roles of cholesterol
Xavier DANIEL, Ph.D.
AS
60. 2
Types of membrane lipids
Membranes contain many important proteins
Sometimes the “normal” phospholipid bilayer is not suitable
“islands” of Cholesterol + Sphingolipids make up Lipid Rafts
Xavier DANIEL, Ph.D.
AS
61. 2
Types of membrane lipids
Sphingolipid
=
Shingosine + fatty acid (+ phosphate)
Shingosine
Xavier DANIEL, Ph.D.
AS
62. 2
Types of membrane lipids
Sphingolipid
=
Shingosine + fatty acid + X
Shingosine
Fatty acid
can vary
X
Varies: carbohydrate, phosphate...
If X is a carbohydrate
Sphingolipid = Glycosphingolipid
Xavier DANIEL, Ph.D.
AS
63. 2
Types of membrane lipids
Sphingolipid
=
Shingosine + fatty acid + R
Xavier DANIEL, Ph.D.
AS
64. 2
Types of membrane lipids
Sphingolipid
=
Shingosine + fatty acid + X
Xavier DANIEL, Ph.D.
AS
65. 2
Types of membrane lipids
Lipid rafts
=
Cholesterol + Sphingolipids
a) Shingolipid
b) Cholesterol
Xavier DANIEL, Ph.D.
AS
68. D1: The Cell Membranes
Plan
1 Introduction:
1.1 Where are membranes found in the cell ?
1.2 Roles of the Cell Membranes
1.3 The fluid mosaic model
2 Membrane lipids:
2.1 Types of membrane lipids
2.2 Roles of membrane lipids
2.3 Examples
2
3
4
1
5
3 Membrane proteins:
3.1 Types of membrane proteins
3.2 Roles of membrane proteins
3.3 Examples
4 Membrane carbohydrates:
4.1 Types of membrane carbohydrates
4.2 Roles of membrane carbohydrates
4.3 Examples
5 Conclusions and Overviews:
Xavier DANIEL, Ph.D.
AS
69. Types of membrane proteins
Two types of proteins in the membranes
Integral
3
Span the membrane:
transmembrane
On either side
of the membrane
Peripheral
Bound to protein Bound to lipids
Xavier DANIEL, Ph.D.
AS
70. Within membrane
nonpolar amino acids
hydrophobic
anchors protein
into membrane
On outer surfaces of
membrane
polar amino acids
hydrophilic
extend into extracellular
fluid & into cytosol
Polar areas
of protein
Nonpolar areas of protein
Types of membrane proteins
3
Transmembrane proteins
Xavier DANIEL, Ph.D.
AS
71. Functions of membrane proteins
Six main functions for proteins in the membranes
3
Transportation Enzymes
Receptor Cell adhesion Attachment
to cytoskeleton
/ ECM
Recognition
outside outside outside inside / outside
inside
Xavier DANIEL, Ph.D.
AS
72. Channel proteins have pores that allow passage of
ions and small water-soluble molecules
Passive transport
Carrier proteins bind to molecules and change
shape for delivery across membrane
Active transport
3
1. Transport proteins
Regulate movement of ions and small hydrophilic molecules across the membranes
Functions of membrane proteins
Xavier DANIEL, Ph.D.
AS
73. 3
2. Receptor proteins = Signal transduction proteins
Usually after the cell received a signal from outside the cell
Signal = hormone and other substances
Pass on a signal from outside to inside the cell
The cell will respond to the signal that was passed on
Messenger molecule
Activated
molecule
Receptor
Functions of membrane proteins
Xavier DANIEL, Ph.D.
AS
74. 3
3. Enzymes = Effector proteins
Catalyze reactions inside the cell
One or more than one different enzymes grouped together
Functions of membrane proteins
Xavier DANIEL, Ph.D.
AS
76. 3
4. Recognition proteins
“Identification tags” “Cell signature”
Very important in Immunity
Usually glycoproteins
To differentiate between “self” and “non-self”
Glyco-protein
Cell A
Cell B
Functions of membrane proteins
Xavier DANIEL, Ph.D.
AS
77. 3
5. Cell adhesion proteins
“intercellular compatibility”
Important in Gap junctions and Tight junctions
Cell A
Cell B
Functions of membrane proteins
Xavier DANIEL, Ph.D.
AS
78. 3
6. Attachment to Cytoskeleton / ECM
ECM
Microfilaments
Maintain cell shape
and
Stabilizes the location of
some membrane proteins
coordinate extracellular and
intracellular changes
Integrins
Functions of membrane proteins
Xavier DANIEL, Ph.D.
AS
80. D1: The Cell Membranes
Plan
1 Introduction:
1.1 Where are membranes found in the cell ?
1.2 Roles of the Cell Membranes
1.3 The fluid mosaic model
2 Membrane lipids:
2.1 Types of membrane lipids
2.2 Roles of membrane lipids
2.3 Examples
2
3
4
1
5
3 Membrane proteins:
3.1 Types of membrane proteins
3.2 Roles of membrane proteins
3.3 Examples
4 Membrane carbohydrates:
4.1 Types of membrane carbohydrates
4.2 Roles of membrane carbohydrates
4.3 Examples
5 Conclusions and Overviews:
Xavier DANIEL, Ph.D.
AS
81. Usually branched molecules of 15 or less sugar units
Some are bonded to lipids: Glycolipids
Most are bonded to proteins: Glycoproteins
Glycolipids + Glycoproteins = Glycocalyx
Function: Cell-cell recognition
Membrane Carbohydrates
4
Xavier DANIEL, Ph.D.
AS
82. D1: The Cell Membranes
Plan
1 Introduction:
1.1 Where are membranes found in the cell ?
1.2 Roles of the Cell Membranes
1.3 The fluid mosaic model
2 Membrane lipids:
2.1 Types of membrane lipids
2.2 Roles of membrane lipids
2.3 Examples
2
3
4
1
5
3 Membrane proteins:
3.1 Types of membrane proteins
3.2 Roles of membrane proteins
3.3 Examples
4 Membrane carbohydrates:
4.1 Types of membrane carbohydrates
4.2 Roles of membrane carbohydrates
4.3 Examples
5 Conclusions and Overviews:
Xavier DANIEL, Ph.D.
AS
83. Membrane proteins and lipids
Are synthesized in the ER and Golgi apparatus
ER
Transmembrane
glycoproteins
Secretory
protein
Glycolipid
Golgi
apparatus
Vesicle
Transmembrane
glycoprotein
Membrane glycolipid
Plasma membrane:
Cytoplasmic face
Extracellular face
Secreted
protein
4
1
2
3
Conclusion and Overviews
5
Xavier DANIEL, Ph.D.
AS
84. Summary
The unit membrane consists of a phospholipid bilayer
Phospholipids consist of a polar, hydrophilic phosphate head and a non-polar,
hydrophobic tail consisting of fatty acid chains.
Proteins also occur in the membrane and float freely throughout it.
The model for membrane structure is known as the fluid mosaic model.
Peripheral proteins occur on the inner or outer face of the membrane and integral
proteins extend through both lipid layers.
Membrane bound enzymes occur allowing structured metabolic pathways.
5
Conclusion and overviews
Xavier DANIEL, Ph.D.
AS
85. Summary
Glycoproteins form the glycocalyx and allow cell to cell recognition.
Receptor proteins can act as binding sites for hormones and other substances and
can transmit the information to the interior of the cell.
A variety of carrier proteins allow for the controlled movement of substance
through the membrane using both passive diffusion or active transport.
Non-polar, lipid soluble molecules diffuse through the phospholipid bilayer.
Ionic, polar molecules require carrier proteins to enable them to pass through the
membrane.
Membrane structure loses integrity with high temperature or presence of organic
solvents such as alcohol, thereby increasing permeability.
5
Conclusion and overviews
Xavier DANIEL, Ph.D.
AS
86. Macromolecules found in Membranes
Lipids
Phospholipid bilayer
Cholesterol Sphingolipids
Proteins
Transport Receptor
Enzymes Recognition
Cell adhesion Attachment to Cytoskelton / ECM
Carbohydrates
Oligosaccharides on glycoproteins
Oligosaccharides on glycolipids
5
Conclusion and overviews
Xavier DANIEL, Ph.D.
AS