Describe the Fluid Mosaic Model Flashcards

Fluid-mosaic model proposes that the membrane is a fluid phospholipid bilayer in which protein moleculse are either partially or wholly embedded. This was proven through a freeze-fracture of the membrane and viewing under an electron micrograph. Other models include the sandwich model and the unit membrane model.

The hydrophilic polar heads of the phospholipid molecule face the ouside and inside of the cell where water is found. The hydorphobic non-polar tails face each other. Cholesterol is another lipid found in animal plasma membrane that stiffens and strengthens the membrane and thereby helping to regulate it fluidity.

Peripheral proteins are on the inside surface of the membrane held in place by cytoskeletal filaments. Integral proteins are embedded in the membrane but they can move back and forth. some integral proteins protrude from only one surface of the bi-layer, but most span the membrane with a hydorphilic and hydrophobic region. A mouse cell and a human cell were fused toghther, after 40 minutes both mouse and human proteins had diffused across the cell.

Receptor protein, Enzymatic Protein, Carrier protein, Channel Protein, Cell Recognition Protein

Diffusion is the movement of molecule from a higher concentration to a lower concentration--down their concentration gradient. Water, gases, and non-charged molecules can diffuse through a differentially permeable membrane.

Osmosis is the diffusion of water across a differentially permable membrane due to concentration differences. An animal cell placed in a isotonic solution has neither a net gain or loss of water so nothing happens. An animal cell placed in a hypotinic solution will have a net gain of water and the cell may burst (lysis). An animal cell placed in a hypertonic solution will have a net loss of water and the cell shrivles (crenation).

Most substances must be assisted across the plasma membrane because the plasma membrane impedes all but a very few substances. In facilitated transport, no energy is required for the molecule to pass through the plasma membrane. They are simply following their concentration gradient. In active transport molecules move to a region of higher concentration, exactly the opposite of diffusion.

1. Carrier protein has a shape that allows it to take up 3Na+ 2. ATP is split and phosphate group attaches to the carrier protein. 3. Change is shape results and causes carrier to release 3Na+ outside the cell. 4. Carrier protein now has a shape that allows it to take up 2K+. 5. Phosphate group is release from the carrier protein. 6. Change in shape results and causes carrier to release 2K+ inside the cell. Back to #1.

Phagocytosis-- when large material such as food, or antother cell is taken by endocytosis. Pinocytosis -- occurs when vesicles form around a liquid or around a very small particle. Receptor-Mediated Endocytosis-- a form of pinocytosis that is quite specific because it uses a receptor protein shaped in such a way that a specific molecule can bind to it.

Adhesion junctions -- internal cytoplasmic plaques, firmly attached to the cytoskeleton within each cell are joined by intercellular filaments. The result is a sturdy, but flexible, sheet of cells such as the stomach, bladder and heart. Tight Junctions--plasma membrane proteins actually attached to each adjecent cell producing a zipper-like fastening Cells of tissues that serve as barriers are held together in tight junctions. (intestine, kidneys) Gap Junction--lends strength to the cells, but allows molecules and ions to pass between them. Gap junction are important in the heart.

B. some proteins span the membrane

B. in the interior of the membrane

There is a net movement of molecules from the area of higher to lower concentration.

Water enters the cell toward the area of higher solute concentration

Water exits the cell toward the area of higher solute concentration.