lipid bilayers and cell membranes Flashcards
What is the primary function of the plasma membrane?
The plasma membrane forms the border between a cell and its environment, controlling the passage of substances in and out of the cell.
What is the basic structure of all biological membranes?
The basic structure of biological membranes is a bilayer of phospholipids and other amphipathic molecules that form a continuous sheet, controlling the passage of substances.
What are the components of a phospholipid molecule?
A phospholipid consists of a phosphate head (hydrophilic) and two hydrocarbon tails (hydrophobic).
How do the hydrophobic tails of phospholipids affect the membrane structure?
The hydrophobic tails interact to form the core of the membrane, which creates a barrier that is low in permeability to hydrophilic substances like ions and polar molecules.
Why do the hydrophobic tails of phospholipids not repel solutes?
The hydrophobic tails do not repel solutes; instead, they are more attracted to each other and the solutes in the aqueous solution, which can influence membrane permeability.
How does the membrane permeability vary with the size of molecules?
Larger molecules have lower membrane permeability, meaning they find it harder to pass through the lipid bilayer. For example, water molecules (slightly larger than a single oxygen atom) pass through the membrane more easily than larger molecules like glycogen or proteins.
How do the aqueous solutions on either side of the membrane affect the permeability of the lipid bilayer?
The aqueous solutions on both sides of the membrane contain water molecules and hydrophilic solutes in continuous random motion. Hydrophilic solutes can penetrate between the hydrophilic heads, but if they reach the hydrophobic core, they are typically drawn back to the aqueous solution, preventing their passage.
Why does the hydrophobic core of the lipid bilayer have low permeability to hydrophilic molecules?
The hydrophobic core of the lipid bilayer creates a barrier to hydrophilic molecules, including ions and polar molecules, preventing them from passing through easily due to the repulsive interaction between the hydrophobic tails and the hydrophilic solutes.
