Unit 2 - Transport Across Membranes Flashcards
What is the role of the cell surface plasma membrane?
It controls the entry and exit of substances to cells and membrane bound organelles.
What does the cell membrane consist of?
A phospholipid bilayer, proteins, glycoproteins, glycolipids and cholesterol.
Why is the membrane classed as a fluid-mosaic model?
Fluid-the components can move around within the membrane.
Mosaic-due to the pattern produced by the proteins embedded throughout the membrane.
The membrane is partially permeable. What does this mean?
It only allows certain molecules through it.
What molecules are allowed through the membrane without using anything else?
Allows lipid soluble and small non-polar molecules to diffuse through as they all dissolve in lipids. Charged and water soluble molecules won’t make it past the hydrophobic barrier.
Role of phospholipids in the cell membrane?
They form a bilayer. Allows lipid soluble and small, non-polar molecules to diffuse through and prevents the passage of charged and water soluble molecules.
Role of transport proteins in the cell membrane?
Their shape and charge determines which specific molecule passes through. Allows the passage of water soluble and charged molecules.
Role of protein channels in the cell membrane?
They’re used in facilitated diffusion only. Form a water filled channel for molecules like ions to move through by facilitated diffusion.
Role of carrier proteins in the cell membrane?
They’re used in facilitated diffusion and active transport. Molecules bind and protein changes shape to allow molecule through.
Role of enzymes in the cell membrane?
Disaccharidases.
Role of receptor proteins in the cell membrane?
They bind complementary molecules to cause a response, e.g. T cell receptors.
Role of antigens in the cell membrane?
They’re used to determine if a cell is foreign to initiate an immune response.
Role of glycoproteins in the cell membrane?
They’re a carbohydrate bound to a protein. The carbohydrate acts as a recognition site.
Role of glycolipids in the cell membrane?
They’re a carbohydrate bound to a phospholipid. The carbohydrate acts as a recognition site.
Role of cholesterol in the cell membrane?
They reduce the fluidity of the membrane by restricting the movement of other molecules. Makes the membrane more rigid and less permeable. Maintains the shape of the membrane.
What is the definition of diffusion?
Diffusion is the passive, net movement of small non-polar, or lipid soluble molecules from a higher concentration to a lower concentration.
What does a passive process mean?
It does not require extra energy from the hydrolysis of ATP.
Why can lipid soluble molecules diffuse through?
Because they dissolve into the phospholipids.
Why can’t water soluble or charged molecules diffuse through?
The fatty acid tails of phospholipids are hydrophobic, so they won’t let them dissolve.
Definition of facilitated diffusion?
Facilitated diffusion is the passive, net movement of larger, charged, or water-soluble molecules from a higher concentration to a lower concentration l, using a channel or carrier protein.
Channel and carrier proteins are specific. What does this determine?
Their specific shape and charge determines which specific molecules passes through (the tertiary structure determines the shape).
How does concentration affect the rate of absorption via diffusion?
They’re directly proportional. As one increases so does the other.
