Bio 2
Bio 2 VL
Bio 2 VL
Membrane Fluidity:
Mechanisms
two states: Fluid / Viscous
Mechanisms: Unsaturated hydrocarbon tails with kinks (knick), Cholesterol (only mammalians)
Cholesterol influence on luidity
- Warm (e.g. 37C): restricts the movement of phospholipids
- Cold: maintains fluidity by hindering a tighter packing of phospholipids
Transmembrane Proteins
Integral Proteins with parts on both sides of a membrane.
If used to transport Ions through the membrane, the channel is between alpha-helices
Use of Membrane Proteins
• Proteins determine most functions of the different membranes
• Membrane fluidity strongly influences the function of membrane proteins
• Membrane proteins may be integral (transmembrane) or peripheral (attached) to the membrane
Function of Membrane Proteins
- Transport
- Enzyme activity
- Signal transition
- Cell-Cell-recognition
- Cell-Cell binding
- Mechanical binding
Often membrane proteins have multiple such functions
(eg transport and binding of the cytoskeleton)
Carbohydrates in Cell-Cell Recognition
• Cells recognize each other through binding of
molecules on their surface, often these are short
carbohydrate chains on the plasma membrane
• Typically these are branched
heteropolysaccharides (ie consist of different
sugars)
• Covalently bound to lipids (glycolipids) or, more
frequently, to proteins (glycoproteins)
• Carbohydrates on outside of plasmamembrane
vary between species, individuals (eg autoimmune
response to reject transplanted organs), and between
different cell types in an individual
Membrane: Selective Permeability
• Non polar molecules can pass freely (eg O2, CO2)
How does water get into the cell?
• Slowly through diffusion
• Through specific pore
proteins (aquaporins)
when higher rates of
transfer are necessary
• a single channel
• 3 x 109 H2O molecules per
aquaporin and second
• greatly increases the water
transfer capacity per unit of
membrane area
Membrane: Transport Proteins
• transfer hydrophilic molecules
across membranes
• are specific for particular
molecules or ions
• channel proteins:
hydrophiler Kanal (eg aquaporin)
• carrier proteins: binding
affects conformation change,
which allows release of the
molecules on the other side
(shuttle)
Channel and carrier Proteins are so called "Facilitated diffusion" because it doesnt need ATP
Tonicity
the osmotic pressure within cells
• Isotonic solution:
concentration of ions/molecules inside and outside
of cells is identical –> no net movement of water
• Hypertonic solution: ion/molecule concentration
lower inside cells -> cell looses water
• Hypotonic solution: ion/molecule concentration
higher inside cells -> cell takes up water
Cellular Water Balance
Animal Cell: has no Cell wall, lives in Isotonic solution
Plant cell: normal situation is under "overpressure"
Active Transport:
Mostly when acting against concentration gradient
requires atp
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Flashcards
Membrane Fluidity:
Mechanisms
two states: Fluid / Viscous
Mechanisms: Unsaturated hydrocarbon tails with kinks (knick), Cholesterol (only mammalians)
Cholesterol influence on luidity
- Warm (e.g. 37C): restricts the movement of phospholipids
- Cold: maintains fluidity by hindering a tighter packing of phospholipids
Transmembrane Proteins
Integral Proteins with parts on both sides of a membrane.
If used to transport Ions through the membrane, the channel is between alpha-helices
Use of Membrane Proteins
• Proteins determine most functions of the different membranes
• Membrane fluidity strongly influences the function of membrane proteins
• Membrane proteins may be integral (transmembrane) or peripheral (attached) to the membrane
Function of Membrane Proteins
- Transport
- Enzyme activity
- Signal transition
- Cell-Cell-recognition
- Cell-Cell binding
- Mechanical binding
Often membrane proteins have multiple such functions
(eg transport and binding of the cytoskeleton)
Carbohydrates in Cell-Cell Recognition
• Cells recognize each other through binding of
molecules on their surface, often these are short
carbohydrate chains on the plasma membrane
• Typically these are branched
heteropolysaccharides (ie consist of different
sugars)
• Covalently bound to lipids (glycolipids) or, more
frequently, to proteins (glycoproteins)
• Carbohydrates on outside of plasmamembrane
vary between species, individuals (eg autoimmune
response to reject transplanted organs), and between
different cell types in an individual
Membrane: Selective Permeability
• Non polar molecules can pass freely (eg O2, CO2)
How does water get into the cell?
• Slowly through diffusion
• Through specific pore
proteins (aquaporins)
when higher rates of
transfer are necessary
• a single channel
• 3 x 109 H2O molecules per
aquaporin and second
• greatly increases the water
transfer capacity per unit of
membrane area
Membrane: Transport Proteins
• transfer hydrophilic molecules
across membranes
• are specific for particular
molecules or ions
• channel proteins:
hydrophiler Kanal (eg aquaporin)
• carrier proteins: binding
affects conformation change,
which allows release of the
molecules on the other side
(shuttle)
Channel and carrier Proteins are so called "Facilitated diffusion" because it doesnt need ATP
Tonicity
the osmotic pressure within cells
• Isotonic solution:
concentration of ions/molecules inside and outside
of cells is identical –> no net movement of water
• Hypertonic solution: ion/molecule concentration
lower inside cells -> cell looses water
• Hypotonic solution: ion/molecule concentration
higher inside cells -> cell takes up water
Cellular Water Balance
Animal Cell: has no Cell wall, lives in Isotonic solution
Plant cell: normal situation is under "overpressure"
Active Transport:
Mostly when acting against concentration gradient
requires atp
