BIOL 1090 Study Guide - Final Guide: Integral Membrane Protein, Lipid Bilayer, Lipid Raft

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Published on 26 Sep 2012
University of Guelph
BIOL 1090
of 7
Two classes of cells
1. Prokaryotic bacteria; structurally simpler; don‟t have membrane-
bound organelles
2. Eukaryotic protists, fungi, plants, animals; more complex;
membrane-bound organelles
Nuclear Pore Complex
Enables movement of molecules into and out of nucleus
Cytoskeletal Elements (actin & intermediate filaments, microtubules)
Contribute to cell shape; supports structure, transport of material
Non-cellular macromolecular packages; can function and reproduce
ONLY within living cells
Outside of cells = virion (inanimate particle - inactive) comprised of
small amount of DNA or RNA (encoding a few to hundreds of genes),
protein capsule = capsid, does not have a nucleus
Bind to cell surface via specific proteins then enter cell this defines
the cell types the virus can infect and host range
When inside cell, utilized cellular machinery to synthesize nucleic acids
and proteins assembles new virus particles
Two types of viral infection 1) Lytic production of virus particles
ruptures, kills cell 2) Non-lytic (Integrative) viral DNA is inserted in
host genome = provirus; viral progeny bud at cell surface; cell can
survive, often w/ impaired function cell can still survive, but does not
function properly
Plasma Membrane ONLY
Cell boundary
Control movement of material into/out of cell
Allow response to external stimuli
Enable interactions b/w cells
Provide scaffold for biochemical activities including energy transduction
Biological Membranes
Bilayer of amphipathic lipids
Proteins integral (trans membrane proteins span the lipid bilayer),
peripheral (membrane proteins associate with the outer surfaces of the
lipid bilayer), lipid-anchored (proteins are covalently attached to a lipid
in the bilayer, prion protein)
Asymmetrical two leaflets have distinct lipid composition; outer
leaflet = glycolipids, glycoproteins (lipids, proteins with carbohydrate
Lipids move easily, laterally within leaflet
Lipid movement to other leaflet = slow, not easy
Membrane proteins can diffuse within bilayer movement of proteins is
restricted; some don‟t move; rapid movement = spatially limited; long
range diffusion = slow; biochemical transduction can dramatically alter
protein‟s mobility in the membrane;
Fluid-Mosaic Model
Hydrophobic alpha helix
Membrane Fluidity
Determined by temp & type
Saturated fluidity
Unsaturated fluidity
temperature, fluidity = liquid crystal
temp, fluidity = crystalline gel
Balance allows mechanical support; flexibility; dynamic interactions
b/w membrane components; membrane assembly, modification;
ordered = rigid, disordered = flexible (relate to a person)
Must be maintained; in response to temperature change, lipid
composition can be changed by 1) desaturation of lipids 2) exchange
of lipid chains
Regulated by cholesterol alters packing and flexibility of lipids; if
added to a liquid crystal membrane, fluidity will decrease; if added to a
crystalline gel membrane, fluidity will increase;
Lipid rafts
Small areas of PM enriched in certain types of lipids
Relatively rigid
Some membrane proteins accumulate in rafts
May form „functional compartment‟
High in cholesterol
Ion Channels
Formed by integral membrane proteins that line an aqueous pore
Selective, allowing only one type of ion to pass
Ions move down concentration gradient
Often „gated‟ (can be opened or closed)
Types of Gated Channels
1. Voltage-gated Channels (eg. K+ channel) channel responds to
change in charge across membrane move down gradient, non-
passive, mediated
2. Ligand-gated Channels (eg. CFTR) channels responds to binding of
specific molecule (the „ligand‟ – an ion or molecule that binds to
another, usually larger, molecule (metal))
3. Mechano-gated Channel (eg cation channels in inner ear) channel
responds to physical force on membrane (eg stretch)
Simple Diffusion
Very small molecules
Down a concentration gradient (flow is „downhill‟)
Eg. O2, CO2, H2O (osmosis)
Passive, non-mediated
Diffusion through a Channel
Small, charged molecules (ions)
Down a concentration gradient
Eg. Na+, K+, Ca2+, Cl-
Passive, non-mediated
Channels -
Facilitated Diffusion
Compound binds specifically to integral membrane protein called
„facilitative transporter‟
Change In conformation of transporter allows compound to be
released on other side of membrane
Compound moves down concentration gradient
Ex. Glucose transporter
Passive (doesn‟t require energy), mediated (requires something else to
get through, needs to bind to something)
Active Transport
Compound binds specifically to integral membrane protein called
„active transporter‟
Change in conformation of transporter allows compound to be released
on other side of membrane