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transport across cell membranes - Coggle Diagram
transport across cell membranes
fluid mosaic model of cell membranes:
-proteins:
-for:
-structure
-cell surface receptor (cell recognition)
adhesion of cells
-receptor sites (eg, for hourmones)
-extrinsic: on the surface of the bilayer
-intrinsic: go through the bilayer (carrier and channel)
-carrier: allow active transport
-channel: allows transport of water soluble substances
-chloresterol:
-reduce lateral movement, increase strength and stability
-reduce fluidity at high temperatures
-prevents leakage of water and dissolved ions in the cell
-glycolipids and glycoproteins:
-act as recognition sites
-maintain stability of membrane
-help cells attach to form tissues
-glycoproteins form receptors for hourmones and nuerotransmitters
-characteristics:
-fluid:
-phospholipids can move latterly relative to each other (flexible and constantly changes shape)
-mosaic:
-proteins embedded are varied in size, shape and pattern
-partial permeability:
-the cell surface membrane controls the movement of substancess in/out of the cell
-membranes in organells also control entry in/out
diffusion:
-"the net movement of a substance down a concentration gradient"
-substances move from areas of higher to lower concentration
-a passive process that requires no additional energy
facilitated diffusion:
-protein channels:
-a hydrophillic channel through the plasma membrane
-open and closed
specific
-carrier proteins:
-molecules bind to proteins
-protein then changes shape
-molecule is released
-specific
-movement still occurs down the concentration gradient
-still passive
-protein channels and carrier proteins are intrinsic
osmosis:
-"the net movement of water molecules from an area of higher water potential to that of a lower water potential through a partially permeable membrane"
-water potential:
-water molecules move and collide with the cell membrane
-this creates a pressure build up called water potential pressure
-pure water has the highest water potential
-solutes lower the water potential
the water potential is usually negative in value
-solute potential:
-solutes restrict the movement of water molecules due to hydration shells
-lowers the water potential by an amount called the solute potential
-solutions have a negative water potential
-pressure potential:
-pressure potential is the positive contribution made by pressure to water potential
-raises water potential
-important for turgidity in plant cells
-hypotonic: bursts animal cells (lysis) and expands plant cells (higher WP in than out)
-isotonic: does nothing to either cell (WP in = WP out)
-hypertonic: animal cell shrivels (crenation) and plant undergoes plasmolysis (WP in higher than out)
-incipient plasmolysis: when the protoplast pulls away from the cell wall no longer applying pressure
WP=PP+SP
active transport:
-carrier proteins:
1-the molecule binds to receptor sites on one side of the carrier protein
2-on the inside of the membrane ATP binds to the carrier protein and is converted to ADP and a free Pi- the carrier protein changes shape
3-the shape change causes the carrier protein to open to the other side of the membrane
4-the Pi is released from the protein so it reverts to the original shape
-carrier protiens are highly specific- different protein pumps for each ion/molecule
-protein pumps are also ATPase enzumes
-Na-K pump explained:
1) 3 Na and 1 ATP bind to pump
2) ADP is released causing a shape change
3) 3 Na are released as 2 K bind to the pump
4) Pi is released causing shape reversion so the 2 K can move through
adaptations for transport:
-ficks law: rate of diffusion=(surface area*conc difference) / distance
-most effective exchange sufaces:
-have high surface area
-maintain a high concentration gradient
-have thin, short diffusion pathways
-absorbtion of glucose in the ileum:
1) Na ions are actively transported out of the epithelial cells by the Na - K ion pump into the blood lowering the Na concentration in the cells
2) Na ions diffuse from the lumen of intestines into the epithelial cells down the concentration gradient
3) as the Na ions diffuse through the co-transporter protein they carry glucose molecules with them into the cell
4) the glucose pass into the blood plasma by facilitated diffusion by using another type of carrier protein