Transport and membrane CAQ

Transport and Cell membrane Created Tags Describe how the carrier protein works June 13 , 2025 132 AM T ranspor t and Cell membrane 1

Notes molecule to be transported is complementary to binding site of carrier protein and will bind to binding site of carrier protein This induced a conformational change on the carrier protein and hence molecule is taken into carrier protein and released to other side of plasma membrane Channel proteins are constantly open the rate of transport of molecules across plasma membrane with increasing concentration of molecules The rate of transport increases with increasing concentration However, it is limited by the number of transport proteins embedded in cell membrane Note that rate of transport by carrier protein is lower than channel protein due to limited number if channel protein being saturated with ions T ranspor t and Cell membrane 2

Significance of transport proteins To transport charged, hydrophilic and polar molecules that are unable to transverse the hydrophobic core of phospholipid bilayer and hence interior of channels are lined with hydrophilic residues for transport of these molecules across cell membrane Why is the rate of transport (that involves ATP hydrolysis) expected to stay constant, even if the concentration difference changes? Notes  ATP provides energy: The process uses energy from ATP hydrolysis (breaking ATP into ADP  Pi) to power the transport. This energy input is fixed and doesnʼt depend on how much more or less concentrated the molecules are outside/inside the cell. T ranspor t and Cell membrane 3

 Works against the gradient: This type of transport (e.g., active transport) moves molecules against their natural concentration gradient (from low to high concentration). Since the energy comes from ATP (not the gradient), the rate stays steady regardless of how big the concentration difference is.  Bulk transport exception: For processes like endocytosis/exocytosis (where large amounts are moved at once), the concentration gradient doesnʼt matter because the cell "decides" to move a set amount Passive Transport: Rate depends on gradient (e.g., diffusion). Active Transport: Rate depends only on ATP availability (fixed speed). Bulk Transport: Gradient irrelevant; cell decides how much to move. Features of active transport Requires ATP to provide energy for reaction to occur Requires a carrier protein Note that channel protein is used in facilitated diffusion as no confrontational change is needed to open the gate of protein Carrier protein has specific binding sites Binding causes conformational changes in carrier proteins Function of hydrocarbon tails in phospholipid bilayer of cell membrane Provides a hydrophobic core which acts as a selective barrier, restricting movement of charged ions, polar or hydrophilic molecules across membrane into cell Describing and explaining the process of endocytosis Endocytosis is a process of bulk transport whic