Plasma Membrane and Movement in and out of cell membrane
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Prokaryotic Cell No nucleus No nuclear membrane One circular
chromosome ribosomes No membrane bound organelles
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Eukaryotic Cell nucleus Nuclear membrane Chromosomes are linear
Membrane bound organelles
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History: Discovery of membrane Structure 1895: Overton: lipids
and lipid soluble materials enter the cell more rapidly than
non-soluble lipid substances
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History: Discovery of membrane Structure 1925 Gorter and
Grerndel reasoned the membrane was a phospholipid bilayer.
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History: Discovery of membrane Structure 1935: Davson and
Danielli membrane model was a sandwich: a phospholipid bilayer
between 2 layers of globular proteins
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History: Discovery of membrane Structure Problems with Davson
and Danielli Model 1.Not all membranes of all cells are the same
2.Problems with placement of the proteins
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History: Discovery of membrane Structure 1972: Singer &
Nicolson developed Fluid Mosaic Model Proteins are embedded in the
phospholipid bi- layer due to the amphipathic nature of some
protein molecules. hydrophilichydrophilic (water-loving) and
lipophilic (fat-loving) propertieslipophilic
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History: Discovery of membrane Structure Singer & Nicolson
cont. Membrane is about as fluid as salad dressing. Composed of
various lipids, proteins, and carbohydrates The arrangement due to
the bonding properties of the molecules that make up the
membrane.
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History: Discovery of membrane Structure
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Plasma Membrane Video
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3 Types of Membrane Proteins Transmembrane Proteins- Straddle
bilayer with protruding parts on both faces Most bear
oligosaccharide side chains that function as receptors Allow cell
to cell recognition
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3 Types of Membrane Proteins Integral Proteins Imbedded to
different degrees in the bilayer Some span into the membrane Can
form channels/pores through the entire membrane Allow H2O/dissolved
materials to move in and out Swerve as selective channels for
certain materials (ions, amino acids, glucose)
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3 Types of Membrane Proteins Peripheral Proteins Not embedded,
but attached to membrane surfaces Function as enzymes
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Ligands Ligand: means to bind, like a key into a lock They
combine with specific receptors of transmembrane proteins
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Ligands continues Ligands include substrates, activators,
inhibitors, hormones, drugs and neurotransmitters.
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Cell Membranes Cell or plasma membranes can be described as
selectively permeable and in a dynamic state.
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Functions of Plasma Membrane 1. shape and mechanical strength
to cell, serves as an anchor to cytoskeletal fibers.
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Functions of Plasma Membrane 2. Inactivate foreign substances
(pathogens and poisons often need to pass through to cause harm)
Illustration of HIV virus tricking an Integral Protein to let it
in
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Functions of Plasma Membrane 3. Catalyzes membrane/cellular
reactions
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Functions of Plasma Membrane Regulates every interaction
between cell and environment. Movement of materials through
membrane Conveys messages EX: hormones Links cells together
Maintains electric potential difference across membrane
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Transport across Cell Membrane Diffusion net movement from
areas from high to low concentrationunhampered movement!
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Transport across Cell Membrane Facilitated transport: Diffusion
helped by a transport protein Usually work by shape transformation,
not catalyzed by enzymes
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Transport across Cell Membrane Permeation diffusion hampered by
a permeability barrier Ex: water through a lipid bilayer
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Transport across Cell Membrane Active Transport: movement of
materials across a concentration gradient.
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Transport across Cell Membrane Osmosis: diffusion of water
through a selectively permeable barrier.
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Transport across Cell Membrane Endocytosis/Exocytosis:
physiological process of moving macromolecules through the plasma
membrane. 1.Phagocytosis engulfing of solid particles using a
pseudopod 2.Pinocytosis engulfing of liquid droplets
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Transport across Cell Membrane Receptor-Mediated Endocytosis:
Importing specific macromolecules by way of vesicles in response to
the binding of specific ligands to receptors on cell surfaces.
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Transport across Cell Membrane Vesicular transport: Movement of
substances in vesicles (vacuoles)
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Transport across Cell Membrane Gating: movement of substances
through selective channels in transport proteinstype of facilitated
transport
