Membranes of Cells
Major features of the lipid bilayer:
• Main part of the membrane had molecules on both sides
(bilayer)
- round parts at the outer edge
- legs facing toward middle
• Highly mobile at level of individual molecules (agitation,
kicking)
• Contains "lipid rafts" -
- mobile unit that contained cholesterol
- had proteins stuck through it
Functions of the membrane:
• Defines boundaries and serves as a permeability barrier
- it compartmentalizes by either separating the
-
inside of the cell (separating the inside of the
organelles from the cytoplasm) or from the outside
-
of the cell
-
- in simple terms, it keeps things out and in--
• serves as an organization and localization of functions
- membranes are defined by the proteins and lipids
that are embedded in them, and also gives them
different characteristics and functions from each
of the organelles
- EX: the membrane of the mitochondria has ATP
synthases embedded in it which defined its
functions as being different from another
organelle, such as the membrane of the golgi
apparatus
• Regulates the transportation of solutes
- there are proteins in the plasma membrane that
allow some things to go in and out, regulating
solutes
- EX: cellular organelle membrane may transport
in nutrients, ions, water, and other
substances, and transfer out waste that the
cell produces
, Function of the membrane (con't)
• detect and transmit signals
- there are receptor proteins that are located on
membrane cell organelle receive information in a
form of either a chemical or electrical signal
- EX: receptors on white blood cells that help
identify an infectious agent and initiate a
response to protect the organism
• Helps cell adhere to other cells by forming junctions
- These junctions allow tissues to be formed as well
as the exchange of materials between cells
- Helps in cell to cell communication
Phospholipids:
• Amphipathic:
- Head: "water-loving" (hydrophilic)
- Tail: "Water-fearing" (hydrophobic)
• "Hydrophobic effect": the driving force of the
spontaneous bilayer assembly
- Polar molecules cluster together
- in this case, H2 O molecules via hydrogen bonding
- The polar clusters repel the non-polar molecules,
pushing the non-polar molecules together
- The hydrophobic effect causes lipids in aqueous
solutions to form bilayer, or micelles
THIS FORMATION IS NOT DUE TO NON-POLAR ATTRACTIONS.
"HYDROPHOBIC BONDING" IS A MISNOMER
Major features of the lipid bilayer:
• Main part of the membrane had molecules on both sides
(bilayer)
- round parts at the outer edge
- legs facing toward middle
• Highly mobile at level of individual molecules (agitation,
kicking)
• Contains "lipid rafts" -
- mobile unit that contained cholesterol
- had proteins stuck through it
Functions of the membrane:
• Defines boundaries and serves as a permeability barrier
- it compartmentalizes by either separating the
-
inside of the cell (separating the inside of the
organelles from the cytoplasm) or from the outside
-
of the cell
-
- in simple terms, it keeps things out and in--
• serves as an organization and localization of functions
- membranes are defined by the proteins and lipids
that are embedded in them, and also gives them
different characteristics and functions from each
of the organelles
- EX: the membrane of the mitochondria has ATP
synthases embedded in it which defined its
functions as being different from another
organelle, such as the membrane of the golgi
apparatus
• Regulates the transportation of solutes
- there are proteins in the plasma membrane that
allow some things to go in and out, regulating
solutes
- EX: cellular organelle membrane may transport
in nutrients, ions, water, and other
substances, and transfer out waste that the
cell produces
, Function of the membrane (con't)
• detect and transmit signals
- there are receptor proteins that are located on
membrane cell organelle receive information in a
form of either a chemical or electrical signal
- EX: receptors on white blood cells that help
identify an infectious agent and initiate a
response to protect the organism
• Helps cell adhere to other cells by forming junctions
- These junctions allow tissues to be formed as well
as the exchange of materials between cells
- Helps in cell to cell communication
Phospholipids:
• Amphipathic:
- Head: "water-loving" (hydrophilic)
- Tail: "Water-fearing" (hydrophobic)
• "Hydrophobic effect": the driving force of the
spontaneous bilayer assembly
- Polar molecules cluster together
- in this case, H2 O molecules via hydrogen bonding
- The polar clusters repel the non-polar molecules,
pushing the non-polar molecules together
- The hydrophobic effect causes lipids in aqueous
solutions to form bilayer, or micelles
THIS FORMATION IS NOT DUE TO NON-POLAR ATTRACTIONS.
"HYDROPHOBIC BONDING" IS A MISNOMER
