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Cell membrane •Cells are highly dynamic and integrated (Phospholipid…
Cell membrane
•Cells are highly dynamic and integrated
Cytoskeleton
:
•Organize structure
•Activity in cell
•a network of protein fibers
•highly dynamic
supports and maintain cell shape
transport material
cell movement
microtubules (cell division in metaphrase)
< intermediate filaments
< microfilaments
not total random movement
Graph
Phospholipid bilayer
:
highly dynamic
• Form cell’s boundary and intracellular compartments
• Provide a place of communication and transport between compartments
• Cellular membranes are fluid mosaics of lipids and proteins
Integral protein can absorb water faster in kidney cells rather than diffusion(too slow)
Selective permeability:
O2, CO2,N2(non-polar) >
H2O, glycerol(small uncharged polar) >
Glucose, sucrose(large uncharged polar) >
Cl- , K+, Na+(Ions)
(can use specialize protein to pass trough)
Integral protein - larger
a) Transport
b) Enzymatic activity
c) Signal transduction
d) cell-cell recognition
e) intercellular joining
f) Atachement to the cytoskeleton and extracellular matrix
Membrane fluidity - Factors
1) Saturated HC tails is well packed - more fluid
2) Cholesterol within cell membrane - black ramdom movement
3) Protein avoids movement
Peripheral protein -smaller
Mechanism of membrane transport
Passive transport
no energy investment
Diffusion
• Substances diffuse down their concentration gradient
• At dynamic equilibrium, molecules cross the membrane in one direction as in the other
Facilitated diffusion
• Speeds the transport of a solute by providing efficient passage
• Channel proteins, have a hydrophilic channel that certain molecules or ions can use as a tunnel
• Carrier proteins, bind to molecules and change shape to
shuttle them across the membrane
Active transport
use energy to move solutes against their gradients
allows cells to maintain concentration gradients that differ from their surroundings
e.g. Na+/K+ - ATPase in animal cell
protein change its shape and gate is opened, release all Na+ ion
ATP hydrolysis
ATP => ADP + P
(graph)
Na+ / K+ ATPase
• Transport of 3 Na+ out of the cell and 2 K+ into the cell creates membrane potential o outside the membrane: more positive o Inside the cell: more negative
• When ions build up on one side of a plasma membrane, they establish both a concentration gradient and a charge gradient, collectively called the electrochemical gradient.
• Electrochemical gradients store energy for cellular work
e.g. drives movement of ions involved in nerve impulse transmission
Toxin and ion channels
Scorpion venom
interfere Na+-, K+- and Ca2+- channels of excitable cells, causing muscle paralysis麻痺(no breath) and death.
Cholera Toxin(霍亂菌)
activate the cystic fibrosis transmembrane conductance regulator (CFTR), causing a dramatic efflux(流出) of Cl- ions and
water
from infected intestinal cells, leading to diarrhoea(腹瀉)
Botox
: muscle contraction
Bulk Transport
- require energy
Large molecules(polysaccharides/proteins) cross the membrane in bulk via vesicles
Exocytosis
- transport vesicles migrate to the membrane, fuse with it, and release their contents
Endocytosis
- cell takes in macromolecules by forming vesicles from the plasma membrane
Recetpor-medicated endocytosis
Binding of ligands to receptors triggers
coated
vesicles formation
Phagocytosis
A cell engulfs a particle(food/bacteria) in a vacuole (pseudopodium) which will hen fuse with a lysosome for digestion
Pinocytosis
Molecules are taken up when extracellular fluid is "gulped"大口地吃 into tiny vesicles