Cells (transport across cell membranes) Flashcards
describe the fluid mosaic model of the membranes
-states that membranes are composed of a phospholipid bilayer in which the phospholipids, as amphipathic molecules, have a hydrophilic head and a hydrophobic tail
-the membrane is fluid as the individual phospholipids can move side to side within the layer, meaning the membrane has a flexible shape
-the membrane is described as mosaic because intrinsic and extrinsic proteins of different shapes and sized are embedded
explain three features of a plasma membrane which make it adapted to its function
-phospholipid bilayer acts as a barrier to prevent polar substances from entering the cell
-membrane contains cholesterol which connects phospholipids and reduces fluidity to make the bilayer more stable by restricting the movement of the phospholipids
-membrane contains glycolipids which act as cell signalling receptors, and allows drugs, hormones and antibodies to bind to the cell
explain the role of extrinsic proteins
-these proteins are partly embedded in the bilayer
-glycoproteins allow cell signalling to occur as they have binding sites/receptors which can receive messages such as hormones
-individuals cells have their own glycoproteins called antigens which are recognisable to the immune system.
explain the role of intrinsic proteins.
-these proteins span the width of the bilayer
-channel proteins allow the movement of too large or hydrophilic molecules to pass through the bilayer by facilitated diffusion
-carrier proteins allow selected molecules through by facilitated diffusion or active transport
describe simple diffusion.
-it’s a passive process as it requires no energy from ATP hydrolysis
-it is the net movement small, lipid soluble molecules directly though the bilayer from an area of high concentration to an area of low concentration until they reach equilibrium
what factors influence simple diffusion
-thinner exchange surfaces give a faster rate of diffusion because the particles don’t have to travel as far
-larger surface area gives a faster rate of diffusion
-the higher the concentration gradient the faster the rate of diffusion
describe facilitated diffusion.
-large, polar molecules are transported down their concentration gradient via specific channel or carrier proteins with complementary binding sites.
-it’s a passive process as it requires no energy from ATP hydrolysis -channel proteins are hydrophilic channels which bind to a specific ion in order for one side of the protein to open and the other closes
-carrier proteins have a binding site which specific molecules bind to causing a conformational change to occur which releases the molecule on the other side of the membrane.
describe active transport through carrier proteins.
-ion binds to receptors on its specific carrier protein
-ATP binds to the side of the protein on the inside of the cell
-ATP is broken down into ADP and a phosphate molecule causing the carrier protein to change shape
-carrier protein releases the ion on the other side of the membrane
-the phosphate molecule and ADP are released from the protein causing the carrier protein to return to its original configuration
what three factors affect the rate of active transport
-speed of carrier proteins
-number of carrier proteins present
-rate of respiration in the cells
if it has a slower rate there is less ATP produced
if there is less ATP there is slower active transport
how are cells adapted to maximise the rate of transport across the membrane?
-contain many carrier/channel proteins for faster facilitated diffusion on active transport
-have a folded membrane or microvilli which increases the surface area
-large number of mitochondria so to synthesise more ATP in aerobic respiration and release energy for active transport
define osmosis
the net movement of water molecules from an area of high water potential to an area of lower water potential until dynamic equilibrium is reached, across a selectively permeable barrier
define an isotonic solution
the same water potential as inside of the cell
means there is no net movement of water particles into the cell
define hypotonic solution
water potential is higher than inside the cells
means the water moves into the cell by osmosis
in a plant cell this causes the cell to become turgid as the protoplast swells
in an animal cell this cause the animal cell to undergo lysis
define hypertonic solution
water potential is lower than inside the cell
means the water moves out of the cell by osmosis
in a plant cell this causes the cell to become plasmolysed as the protoplast to shrink
in an animal cell this causes the cell to become crenated
what three factors affect membrane permeability
-high temperatures denature membrane proteins and they provide phospholipid molecules with more kinetic energy
-pH changes the tertiary structure of membrane proteins
-use of solvent may dissolve membrane
