Transcript Slide 1 - nimitz163

Membrane
• Different membranes
– All have similar functions & structures
– Plasma membrane separates inside of cell
from outside of cell
– Other membrane define organelles to form
compartments of eukaryotic cells
• Forms a selectively permeable layer
– Lets some things in or out but not all
– Like a window screen
Membrane
• Phospholipid bilayer
– Phosphate group facing outward
• hydrophillic
– Fatty acid tails face each other
• hydrophobic
• Proteins also in membrane
– Lots of functions
• Signaling
• Transport
• Enzymatic
– Peripheral- on inside or outside surface
– Integral- proteins stick out on both sides
Permeability in membranes
• Selectively permeable
– Some move easily through the lipid layer
• Non polar molecules (O2, alcohols)
• Small polar molecules (H2O, CO2)
• Move with (or down) a concentration gradient
– From areas of high to low concentration
– Some need help to get through
• Like ions and larger polar molecules (sugar, a.a.)
• Transport proteins assist
– Channel proteins - allow passage of charged particles
– Carrier proteins- transport specific molecules
Diffusion
Defined as passive movement of
molecules down a concentration
gradient
from areas of high to low conc.
This does not require energy - (passive)
Eventually the molecules will be equally
distributed (equillibrium is reached)
Osmosis
• Movement of water molecules from high to low concentration across a
semi-permeable membrane
• Or diffusion of water
• Hypotonic solution outside cell
– Low solute concentration
– High water concentration
– Water moves into cell
• Hypertonic solution outside cell
– High solute concentration
– Low water concentration
– Water leaves cell
• Isotonic solution
– Concentration of water equal on both sides of membrane
– No change in concentration will occur
Water in Plants
• Plant cells normally in hypotonic
environment
– Central vacuole full
– Puts pressure on cell wall
– Cell doesn’t burst because of cell wall
• Plants in hypertonic solution
– Lose water and usually kills cell
Passive transport
• Involves movement of molecules across
a membrane
• From areas of high concentration to
areas of lower concentration across a
membrane
– Spilled perfume example
• Without energy
Facilitated transport
• Like passive transport but requires a
membrane protein to help (facilitate) the
movement
• Does not require energy
• Moves with concentration gradient
Active Transport
• Moves molecules across a membrane
– Via a membrane protein
– Can move molecules against their
concentration gradient
• From low to high concentration
• Not easy to put spilled perfume back into bottle
– Requires energy (ATP)
Exo or endocytosis
• Exocytosis- molecules exiting cell
– Ex. Transport vesicle releasing contents outside
cell
• Endocytosis- molecules entering cell
– Phagocytosis - cell eating
• Ex. White blood cell eating bacteria
– Pinocytosis - cell drinking
– Receptor mediated endocytosis
• Molecule binds to protein receptor
Ex. Cholesterol in liver cells
Cell signaling
• Signal transduction pathway
– How cells talk to each other
– Reception
• Outside molecule binds to receptor
• Ex. Adrenaline to muscle cells
– Transduction
• Message relayed inside cell via chemicals
– Response
• Chemical action
• Ex. Breakdown glycogen to release glucose