Transcript Cell Membranes: Chapt. 6

Chapter 4 Cell Membranes
www.cellsalive.com/
4.1Cell membrane structure
4.1.1 Model structure
4.1.2 Composition of the Cell
Membrane
4.1.3 Fluidity of membrane
4.1.4 Asymmery membrane
4.1.5 Membrane function
4.1.6 Cell cytoskeleton
interaction with cellmembrane
4.1.1 stucture of Cell
Membrane
Every cell is encircled by a membrane and most cells
contain an extensive intracellular membrane system.
Membranes fence off the cell's interior from its
surroundings. Membranes let in water, certain ions and
substrates and they excrete waste substances. They act
to protect the cell.
Without a membrane the cell contents would diffuse
into the surroundings, information containing molecules
would be lost and many metabolic pathways would
cease to work:
The cell would die!
www.biologie.uni-hamburg.de/b-online/e22/22.htm
Cell Membranes:
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Surround all cells
Fluid-like composition…like soap
bubbles
Composed of:
• Lipids in a bilayer
• Proteins embedded in lipid layer
(called transmembrane proteins)
• And, Proteins floating within the lipid
sea (called integral proteins)
• And Proteins associated outside the
lipid bilayer (peripheral).
The Cell
Membrane
The Cell Membrane
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Liposome 脂质体
artificial lipid vesicle
• Model of membrane study
• Carrier of drug
• Use in Gene treatment
Cell Membrane:
At Very High
Magnification
& in color
Cell Membrane
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Plasma membrane
Endomembrane
system
• Nuclear membrane
• Endoplasmic
reticulum
• Vessicles
• Golgi apparatus
Choloplast
Mitochondron
4.1.2 Molecular structure model of cell
membrane
1 sandwich model
Danielli and Davison，1930
Protein-lipid –protein
2 Robertson，1950 suugest unit membrane
model
structure of dark-bright－dark under
electron microscope
3 Fluid Mosaic Membrane model
1972，Singer and Nicolson suggest
two-dimensional liquid, emphasize
fluidity,asymmetrical非对称的membrane
Fluid Mosaic Membrane
Diversity of Molecules make a Mozaic
Mozaic
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Integral proteins embedded in membrane
Amphipathic!
Hydrophilic
Hydrophobic
Hydrophilic
4.1.3 Composition of the Cell Membrane
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CM is composed of
A) Lipids
B) Proteins
C) Carbohydrates
细胞膜的化学组成
Phospholipids
A Membrane lipid
Glycolipid
Cholesterol
Phospholipids
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The chemical nature of
the Phosphate-Nitrogen
chain, and the small
glycerol part of the
molecule are polar, while
the fatty acid parts of the
molecule are non polar
CM is essentially a double
layer (bilayer) of a type of
lipid called a phospholipid
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The dual nature of the phospholipid
molecule, the cell membrane is
formed of a double later of these
molecules, arranged “tail-to-tail” =
phospholipid bilayer
Head
Tails
Head
Phospholipid Bilayer
H
H
O
H2O
O
H
H
H
H
O
hydrophilic
hydrophobic
H2O
amphipathic
Organization of the cell membrane relies on water!
Membrane Lipids
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Composed largely of phospholipids
Phospholipids composed
of….glycerol and two fatty acids +
PO4 group
P-Lipids are polar molecules…
P-Lipids are represented like this
Membrane lipids 膜脂
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磷脂
糖脂
胆固醇
Membrane Lipids
form a Bilayer
Outside layer
Inside Layer
Phospholipid Molecule
Model
phosphate (hydrophilic亲水的)
glycerol
fatty acids (hydrophobic疏水的)
Quiz
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If Phospholipids are polar, which end
seeks out water and which avoids
water?
B Membrane Proteins
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Various shapes and sizes, depending on
function in the membrane
2 main kinds:
1) Peripheral Proteins
2) Integral
Proteins
Membrane Proteins
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Integral: embedded within bilayer
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Peripheral: reside outside hydrophobic
region of lipids
Text pg. 80
Peripheral Proteins
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Hydrophobic (water-loving)
Are attached to inner and outer
surface of membrane
In contact wit hydrophilic heads of
phospholipids and watery
interior/exterior of cell
Integral Proteins
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Have both hydrophilic
and hydrophobic areas
Penetrate completely
through or partially
into the phospholipid
bilayer
Hydrophobic areas
contact watery interior
& exterior of cell
Hydrophobic areas are
embedded inside the
bilayer to avoid
contact with water
Membrane Proteins
Text pg 80
Integral membrane
proteins
Peripheral membrane
proteins
Integral
Membrane Protein Functions
Every cell membrane is a unique, two-sided work surface
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Control factor of membrane protein
movement
Cytoskeleton 细胞骨架Protein
Congregation 蛋白的聚集
Interlink with extracelluar细胞与外侧结构
的连结
C Carbohydrates
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Polar – hydrophilic
Found attached to outer surface of
membrane only
Carbohydrate + protein =
glycoprotein
Carobhydrate + lipid = glycolipid
Review of last lesson
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Which component do take
part in forming CM?
A) Lipids
B) Proteins
C) Carbohydrates
what is prominent point
of every components?
two-dimensional liquid,
emphasize fluidity,
asymmetrical membrane
Please give conclusion of the fluid mo
model
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The dual nature of the phospholipid
molecule, the cell membrane is
formed of a double later of these
molecules, arranged “tail-to-tail” =
phospholipid bilayer
Head
Tails
Head
Phospholipids
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The chemical nature of
the Phosphate-Nitrogen
chain, and the small
glycerol part of the
molecule are polar, while
the fatty acid parts of the
molecule are non polar
CM is essentially a double
layer (bilayer) of a type of
lipid called a phospholipid
How many types Could membrane protein
divide into?
What is special points of every type
membrane protein?
4.1.3 Evidence for the Fluid Mosaic
Model (Cell Fusion)
Phospholipid Molecule
Model
phosphate (hydrophilic亲水的)
glycerol
fatty acids (hydrophobic疏水的)
Experimental Observation of
Fluidity
Fluorescence
recovery after photobleaching
FRAP)
Control of Membrane Fluidity
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Plants
• unsaturated fatty
acids
• type of fatty acid
adjusted seasonally
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AnimalsCholesterol
• buffers membrane
at hi temp
• prevents membrane
from crystalizing at
low temp
Influence factor of membrane
fluidity
Fatty acids length
Saturation of fatty acids
Temperature
Cholesterol concentration
4.1.4 Asymmetry of membrane
Membrane lipid asymmetry: distribution
Membrane protein asymmetry :directional
signal
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4.1.5 membrane function
In essence membranes are essential
for the integrity and function of the
cell.
CM is material exchange gateway of
the cell
Functions
1) Transport raw materials into the cell from
the surrounding Extra Cellular Fluid (ECF)
e.g – O2,H2O,glucose,aa
2) Transport manufactured products and
wastes out of the cell into the ECF
e.g. – hormones, enzymes, CO2
3) Prevent entry of unwanted matter into the
cell
e.g. – bacteria, poisons
4) Prevents the escape of matter needed
within the cell to perform cellular functions
e.g. – keep cell parts, needed
Membrane Functions
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be protective ,material exchage gateway
regulate transport in and out of cell or
organelle
allow selective receptivity and signal
transduction by providing transmembrane
receptors that bind signaling molecules
allow cell recognition
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subdivides cell into compartments with
different internal conditions
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allows for different conditions between
inside and outside of cell
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allows release of substances from cell via
vesicle fusion with outer membrane
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Form special structure on cell surface
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/exocyt.gif
Membrane function conclusion
of text book
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provide anchoring sites for cytoskeletal
components. This allows the cell to maintain its
shape and perhaps move to distant sites.
provide a stable site for the binding and catalysis
of enzymes.
regulate the fusion of the membrane with other
membranes in the cell via specialized junctions
provide a passageway across the membrane for
certain molecules
allow directed cell or organelle motility
Cellular Membranes
REVIEW
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Importance of Membranes
Fluid Mosaic model
Membrane Structure
Membrane function