Chapter 4 Cell Membranes

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Chapter 4 Cell Membranes
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
www.cellsalive.com/
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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
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Cell Membranes

• Surround all cells
• Fluid-like compositionlike 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).

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The Cell Membrane
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The Cell Membrane
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• Liposome ???
• artificial lipid vesicle
• Model of membrane study
• Carrier of drug
• Use in Gene treatment

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Cell Membrane
At Very High Magnification in color
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Cell Membrane

• Plasma membrane
• Endomembrane system
• Nuclear membrane
• Endoplasmic reticulum
• Vessicles
• Golgi apparatus

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• 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????membrane

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Fluid Mosaic Membrane
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Diversity of Molecules make a Mozaic
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Mozaic

• Integral proteins embedded in membrane
• Amphipathic!

Hydrophilic
Hydrophobic
Hydrophilic
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4.1.3 Composition of the Cell Membrane

• CM is composed of A) Lipids
• B) Proteins
• C) Carbohydrates

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????????
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Phospholipids
Glycolipid
A Membrane lipid
Cholesterol
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Phospholipids

• 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
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Phospholipid Bilayer
H2O
H2O
amphipathic
Organization of the cell membrane relies on water!
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Membrane Lipids

• 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
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Membrane lipids ??

• ??
• ??
• ???

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Membrane Lipidsform a Bilayer
Outside layer
Inside Layer
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Phospholipid Molecule Model

phosphate (hydrophilic???)
glycerol fatty acids (hydrophobic???)
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Quiz

• If Phospholipids are polar, which end seeks out
  water and which avoids water?

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B Membrane Proteins

• Various shapes and sizes, depending on function
  in the membrane
• 2 main kinds
• 1) Peripheral Proteins 2) Integral Proteins

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Membrane Proteins

• Integral embedded within bilayer
• Peripheral reside outside hydrophobic region of
  lipids

Text pg. 80
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Peripheral Proteins

• 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

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Integral Proteins

• 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

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Membrane Proteins
Text pg 80
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Integral membrane proteins
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Peripheral membrane proteins
Integral
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Membrane Protein Functions
Every cell membrane is a unique, two-sided work
surface
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• Control factor of membrane protein movement
• Cytoskeleton ????Protein Congregation ?????
• Interlink with extracelluar??????????

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C Carbohydrates

• Polar hydrophilic
• Found attached to outer surface of membrane only
• Carbohydrate protein glycoprotein
• Carobhydrate lipid glycolipid

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Review of last lesson

• Which component do take part in forming CM?

• Lipids
• Proteins
• C) Carbohydrates

what is prominent point of every components?
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two-dimensional liquid, emphasize
fluidity, asymmetrical membrane
Please give conclusion of the fluid mosaic 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
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Phospholipids

• 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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How many types Could membrane protein divide
into? What is special points of every type
membrane protein?
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4.1.3 Evidence for the Fluid Mosaic Model (Cell
Fusion)
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Phospholipid Molecule Model

phosphate (hydrophilic???)
glycerol fatty acids (hydrophobic???)
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Experimental Observation of Fluidity
Fluorescence recovery after photobleaching FRAP)
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Control of Membrane Fluidity

• Plants
• unsaturated fatty acids
• type of fatty acid adjusted seasonally
• Animals- Cholesterol
• buffers membrane at hi temp
• prevents membrane from crystalizing at low temp

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• Influence factor of membrane fluidity
• Fatty acids length
• Saturation of fatty acids
• Temperature
• Cholesterol concentration

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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
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• 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 enzymes,
  nutrients inside cell

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• Membrane Functions
• 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
• allows for different conditions between inside
  and outside of cell
• allows release of substances from cell via
  vesicle fusion with outer membrane
• Form special structure on cell surface

http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
exocyt.gif
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Membrane function conclusion of text book

• 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

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Cellular Membranes

• REVIEW
• Importance of Membranes
• Fluid Mosaic model
• Membrane Structure
• Membrane function