PSYC 2110 Chapter Notes -Tonicity, List Of Lakes By Volume, Electrochemical Gradient

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Published on 9 Oct 2012
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CH 3: THE PLASAM MEMBRANE AND MEMBRANE POTENTIAL
MEMBRANE STRUCTURE AND COMPOSTION
The p.m. is a trilaminar structure which can only be seen using an electron
microscope
o There are 2 dark layers that surround a 3rd light layer (this is bc the
outer layers can be stained more than the inside nonpolar area which
is lighter under an electron microscope)
Plasma membrane (composition)
Phospholipids: the most abundant lipid in the membrane (have a non-polar
tail and polar heads)
o Made of a phosphate group (head) and 2 nonpolar fatty acid tails
Cholesterol: found in b/w the phospholipids they are used to inhibit the
fatty acids from binding and crystalizing (which wouldn’t allow the
membrane to be so fluid)
o Since the membrane is fluid, it is able to change shape when needed;
i.e. muscle cells that contract or RBCells that change shape to fit
through the capillaries
Membrane proteins: inserted in the lipid bilayer proteins are larger than
lipids so they account for half of the mass of the membrane, although there
are 50 times more lipids
Fluid mosaic model: the membrane is fluid and looks mosaic bc of the
different shaped proteins
Carbs: found only on the ECF portion of the p.m. (so the membrane is sugar
coated) only have glycoproteins and glycolipids (based on what there
attached to): the carbs are used as self recognition molecules - discuss later
Lipid bilayer (3 functions)
Structure of membrane
Hydrophobic interior: barrier for passage of water-soluble substances from
the ECF cell can maintain what goes in and out
Allows fluidity
Membrane proteins different specialized proteins are used for different fn’s
Channels: used for small, water-soluble things to pass without going through
the nonpolar barrier there are HIGHLY selective
Carrier molecules: transfer things across the membrane that cant go alone
can transport a particular molecule or one that resembles it
Docking-marker acceptors: found in the ICF and bind to secretory vesicles
(lock and key) allows secretion through exocytosis
Membrane-bound enzymes: control chemical rxns on both sides of the p.m.
i.e. enzymes that destroy chemical messengers that trigger muscle
contractions, so they can relax
Receptor sites: able to bind with a specific molecule (outside the cell) and
alter activity in the cell
Cell adhesion molecules (CAMs): looks like loops protruding from the ICF
to the ECF and can grip fibers on other cells holds cells w/in tissue and
organs together this way
o CAMs also act as signaling molecules signal cells to grow and
interact w/ the right type of cells
Bind w/carbs (glycoproteins) for the cells ability to recognize “self” and in
cell-to-cell interactions
Self-recognition glycoproteins and glycolipids
Allow cells to identify and interact w/each other in different ways:
Different cells have different markers based on their unique sugar chain
allows cells to recognize others that are their own kind this allows the same
type of cells to become tissues (especially important for embryo
development)
Also allow for tissue growth cells wont grow and trespass to neighbored
cells (exception is cancer cells - they will invade the space of other cells)
CELL-TO-CELL ADHESION
Allow cells to bind together and become tissue (which become organs)
Biological “Glue”
ECM (extracellular matrix): fibrous proteins found in the interstitial fluid
used to hold neighbouring cells together (like glue)
Protein fibers are:
o Collagen: cable-like fibers that provide tensile (resistance) to
longitudinal stress scurvy causes these fibers to not form, so tissue
is fragile and leads to bleeding
o Elastin: rubber like fiber which allows tissue to stretch and recoil
(like the lungs)
o Fibronectin: holds cells in position cancer cells have reduced
amounts of this which is why they can grow on top of each other and
break loose and metastasize
The ECM is useful for creating different environments for different
specialized cells and also allows for cell growth only blood cells can survive
and function without attaching to the ECM
Cell Junctions
Cell adhesion molecules (surface proteins on the p.m) are used to hold the
different cells together through 3 different types of junctions
Desmosomes: anchor close distance cells together; ADHERING JUNCTIONS
Has 2 components (1) dense button like thickenings (plaque) which is
found on the inner surface of each cell and (2) glycoproteins which are used
to attach the two plaques together
Tight junctions: firmly bind to seal off a passageway b/w 2 cells
Found in epithelial cells used to seal off the different internal cavities and
the skin so bodily chemicals don’t mix together
Kiss sites: sites of tight seal around the border
The junction is impermeable passage of things has to go through the cells,
not b/w them (regulated by the channels and carriers)
Gap Junctions: gap found b/ adjacent cells, which are linked by connexon’s
Connexon: a 6-protein subunit that creates a hollow tube like structure
(A connexon from different cells will join to make a tunnel b/w the cells)
Only small water soluble particles can pass this way (ions and small
particles can be exchanged without having to enter the ECF)
Found often in cardiac and smooth muscle allows synchronized
contractions of the muscles and heart
Also allow small nutrients to pass glucose, a.a., etc. to things like a
developing egg in the ovaries
Allows communication of cells
OVERVIEW OF MEMBRANE TRANSPORT
Substances that can pass the membrane = permeable
Impermeable = cant pass the membrane
P.m. = selectively permeable (something’s can pass while others cant)
Things that are too big in size and not lipid soluble are able to only pass the
membrane through assisted transport (i.e. glucose)
Something’s need a force to move (active) whereas some do not need any
energy (passive)
UNASSISTED MEMBRANE TRANSPORT
Can take place either with diffusion or moving down an electrical gradient
Passive diffusion of particles:
Takes place when there are different [ ] gradients in different areas when
this happens diffusion occurs from high [ ] to low
o Net diffusion: the difference b/w 2 opposing movements if 10
molecules move from A to B and 2 move from B to A, then the net
diffusion = 8 molecules from A to B (molecules keep moving until
there is no [ ] gradient anymore, in which case they will move in
exactly in the same amount, which is known as a steady state)
Fick’s Law of Diffusion: shows the factors that influence diffusion across the
membrane (find in course kit page 127)
Passive diffusion of ions
Differences in charges make areas have electrical gradients (cations in ve
areas, and anions in +ve areas)

Document Summary

Ch 3: the plasam membrane and membrane potential. Phospholipids: the most abundant lipid in the membrane (have a non-polar tail and polar heads: made of a phosphate group (head) and 2 nonpolar fatty acid tails. Membrane proteins: inserted in the lipid bilayer proteins are larger than lipids so they account for half of the mass of the membrane, although there are 50 times more lipids. Fluid mosaic model: the membrane is fluid and looks mosaic bc of the different shaped proteins. Hydrophobic interior: barrier for passage of water-soluble substances from the ecf cell can maintain what goes in and out. Membrane proteins different specialized proteins are used for different fn"s. Channels: used for small, water-soluble things to pass without going through the nonpolar barrier there are highly selective. Carrier molecules: transfer things across the membrane that cant go alone can transport a particular molecule or one that resembles it.