Membrane Structure and Cellular Transport Flashcards
Why is it named fluid mosaic model?
Fluid: The individual protein and lipid molecules on the phospholipid have lateral mobility due to the weak bonds that hold them together.
What are the features of the fluid mosaic model?
- The hydrophilic phosphate head faces outwards into the aqueous environment while the hydrophobic fatty acid tail faces inwards creating a hydrophobic core.
- Peripheral proteins occur on the surface of the membrane and does not penetrate through it. They are bound to the membrane via ionic bonds and hydrogen bonds interaction with the phospholipid phosphate head.
- Integral proteins penetrate through the cell membrane and maintain in their position via hydrophobic interaction and ionic bonds.
How does cholesterol regulate fluidity of membrane?
At high temperatures , phospholipids tend to gain kinetic energy and move further apart from one another. Cholesterol restrains the movements of the phospholipids , preventing the membrane from breaking apart.
At low temperatures , cholesterol disturbs the close packing of phospholipids to prevent them from freezing.
Cholesterol also limits the uncontrolled leakage of ions and small polar molecules through the membrane.
What are the importance of regulating membrane fluidity?
When a membrane solidifies , its permeability changes and enzymatic proteins may become inactive.
The lipid composition of a cell can change as an adjustment to changing temperature.
What are the factors affecting membrane fluidity?
Temperature - At low temperatures , molecules have low kinetic energy and thus the membrane becomes less fluid. At high temperatures , molecules have high kinetic energy , vibrate faster causing the membrane to be more fluid and permeable.
Lipid composition - Unsaturated fats have kinks at the site of double C=C bonds. This prevents the membrane from packing closely together , making it more fluid.
Presence of cholesterol - At higher temperatures , cholesterol prevents phospholipids from moving too far by forming hydrophobic interactions with interactions with the hydrocarbon fatty acid tail.
At low temperatures , cholesterol disturbs the close packing of phospholipids to prevent freezing.
What are the functions of membranes?
-Compartmentalization
-Transport of materials in and out of the cell
-Cell signaling
-Cell-cell recognition
-Cell-cell adhesions
-Form of boundary
Define simple diffusion.
The net movement of particles from a region of higher concentration to a region of lower concentration , down a concentration gradient.
What molecules cant diffuse through the membranes?
-Charged ions and molecules as they repel the hydrophobic region of the membrane.
Define facilitated diffusion.
The movement of molecules or ions down from high concentration to low concentration across a biological membrane passing through specific transmembrane transport proteins.
It transports ions and hydrophilic molecules (eg.glucose) as they are insoluble in lipids.
What are the two types of transmembrane transport proteins?
Channel proteins: Transports ions in and out of cells. The lining of the channel is hydrophilic so that water soluble molecules can pass through it. Channel proteins have a fixed shape unlike carrier proteins that undergoes conformational change during transportation.
Carrier protein: Binds the specific solute and undergoes conformational change.
How are transport protein similar to enzymes?
-they are specific and only transports certain molecules
-molecules that resemble the usual molecules that are transported can inhibit the transport protein
-they can be saturated
HOWEVER , transport proteins speeds up a PHYSICAL reaction while enzymes speed up a CHEMICAL reaction.
Define osmosis.
The movement of water molecules from a region of high water potential to a region of low water potential through a selectively permeable membrane.
Define active transport.
The movement of ions or molecules across a membrane against a concentration gradient , from low to high by means of a protein pump with the use of energy by hydrolysis of ATP.
What is the diff between facilitated diffusion and active transport?
The conformational change of protein pump in active transport requires energy frm the hydrolysis of ATP while facilitated diffusion does not.
What is the importance of active trasport?
-Allows plants to take up nutrient even when the concentration of nutrients outside the cell is lower than in the cell.
-It enables cells to remove waste products even when the concentration outside the cell is higher than inside the cell.
