Fluid mosaic membranes
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Describe the arrangement of phospholipids in the fluid mosaic model and explain the interactions that drive this arrangement.
Phospholipids form a bilayer with hydrophilic phosphate heads facing outwards, interacting with water, and hydrophobic fatty acid tails facing inwards, shielded from water. This arrangement is driven by the hydrophobic effect and hydrophilic interactions, minimizing free energy.
What role does cholesterol play in the cell surface membrane?
Cholesterol regulates membrane fluidity by preventing the phospholipid fatty acid tails from packing too closely at low temperatures (increasing fluidity) and by stabilizing the membrane at high temperatures (decreasing fluidity).
Distinguish between the roles of channel proteins and carrier proteins in membrane transport.
Channel proteins form pores that allow specific molecules to passively diffuse across the membrane, following the concentration gradient. Carrier proteins bind to specific molecules and undergo conformational changes to actively or passively transport them across the membrane.
How do glycoproteins and glycolipids contribute to cell recognition?
Glycoproteins and glycolipids, located on the cell surface, have carbohydrate chains that act as cell surface antigens. These antigens allow cells to identify each other, which is important in immune responses and tissue formation.
Outline the role of a cell surface receptor in cell signalling.
Cell surface receptors bind to specific ligands (
Explain how the fluid mosaic model contributes to the permeability of the cell membrane.
The fluid nature of the phospholipid bilayer allows small, nonpolar molecules (like oxygen and carbon dioxide) to easily diffuse across the membrane. Membrane proteins also contribute to permeability by selectively transporting larger or charged molecules.
Describe how proteins contribute to the stability of the fluid mosaic membrane.
Proteins, specifically integral proteins, can interact with the phospholipid heads and cytoskeleton, providing structural support and maintaining the membrane's integrity. These interactions contribute to overall membrane stability.
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