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39 Cards in this Set
- Front
- Back
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membrane functions |
1) separate cells from the external medium to create an intracellular environment of unique and defined composition 2) allow selective transport of substrates in and out of the cell 3) provide a location for specialized pathways and processes (energy conversion of mitochondrin) 4) rapid changes in electric potential across the membranes of neurons as basis of the nervous system 5) localization of receptors to facilitate response to physiological signals 6) mediate cell-cell recognition and interaction |
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lipid bilayer
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type of lipid aggregated formed depends on the ratio of cross-sections of the polar head group and the hydrophobic tail exposure of hydrophobic tails to water is energetically unfavorable |
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biological membranes |
-impermeabled to charged and polar molecules -5 to 8 nm thick (two dimensional structures -asymmetrical (each face has a diff composition_ -fluid (fluid mosaic model) and dynamic |
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membrane composition and architecture |
membranes are primarily composed of lipids and proteins (more active membranes have a higher ratio of protein) lipids include phospholipids, glycoshingolipids and sterols membrane composition varies considerably across species and cell types cells have mechanisms to control lipid production and localization |
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distribution of lipids in membranes |
plasma membranes are asymmetrically distributed which indicates the ability to place and maintain membrane lipids in a specific orientation
movement of phosphatiylserine |
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three classes of membrane proteins |
peripheral integral lipid anchored |
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peripheral |
associate with membrane through charge-charge or hydrogen bonding interactions to intergral proteins or membrane lipids change in pH or ionic strength often releases these proteins from the membrane may functional physiologically as regulators or tethers for integral membrane proteins |
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membrane proteins description |
span the lipid bilayer are immersed and usually span the membrane extracted from membrane with detergent protein positioning within a membrane is specific and directional trans membrane region hydrophobic |
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hydrogen bonding |
polar unpaired carbonyl and amide groups in the non polar bilayer core are energentically unfavorable, therefore carbonyl and amide groups of the protein backnbone inside the bilayer are hydrogen bonding |
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integral membrane proteins |
lipid soluable (hydrophobic) portions of the protein span the membrane specific orientation (receptors) membrane spanning region often a hydrophobic alpha helix diff classes depending on the number and direction of membrane spanning region |
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membrane spanning |
difficult to determine the 3D structures of membrane proteins very but membrane spanning regions can be predicted from the amino acid sequence stretches of 20 hydrophobic residues in a row are likely membrane spanning a hydropathy index looks at the hydophobic characteristics of a protein to predict transmembrane regions - |
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tyrosine and tryptonphan as interface anchors |
often positioned at the interface between the polar face and the non polar intermembrane region charged amino acids (blue) are located in regions of the protein that are in contact with the aqueous state |
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covalently attached lipids |
lipids can serve as anchors to line the protein to the membrane "greasy fingers" (when covalently attached to the protein) |
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fluid mosaic model |
membranes are dynamic structures due to the nature of the non-covalently interactions lateral movement of proteins and lipids within the membrane is very rapid freedom of movement within it because of the non-covanletn interactions |
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membrane acyl groups |
molecules within the membrane that have freedom of motion and under go phase transition with raising temperature below the phase transition temp the membrane is an ordered paracrystallaine gel state well above the phase transition temp the membrane is in a liquid disordered state near the phase transition temp, the membrane is in a liquid-ordered state where the hydrocarbon chains are partially ordered but lateral diffusion still possible cells can adjust membrane composition to maintain liquid ordered state |
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transbilayer movement of lipids |
requires catalysis spontaneous "flip-flop" diffusion very slow process transbilayer movement requires a polar head group to pass through hydrophobic environment membrane lipids are initially produced into inner face and must be flipped (flipasses catalyze flop flop diffusion) |
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lateral movement of some membrane lipids is restricted |
patches are function aggregates on the membrane surface in which the movement of proteins is restricted "fenced" higher order structures within membrane acetylchloline receptors on neuron plasma membranes at synapses membrane proteins can also be linked to internal structures to limit movement |
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sphinglolipis and cholesterol |
cluster in rafts lipid distribution is not random within a membrane leaflet glycosphingolipids form clusters that excluse glycerophospholipids the longer the saturated acyl groups of sphingolipids form stable associations with cholesterol in the outer layer (thicker and more ordered) rafts are enriched in lipid anchored proteins |
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maurice hilleman |
born 1918, the year of the last great plague maurice was abandoned by his father and raised my neighbours to work on a chicken farm developed an influenza vaccine to minimize the impact of the 1957 pandemic developed vaccines for mumps, measles and rubella (mmr) his vaccines save millions of children every year` |
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influenza pandemics |
influenza- periodic occurance of the influence of the heavenly bodies frequency: 10 influenza pandemics in last 300 years severity: pandemic of 1918 killed 100 million people, aids has killed 25 million since 1970 hemagglutinin is the most important target for stopping the virus influenza has 16 gradually shifting HA proteins (yearly vaccines) when these undergo a dramatic shift so that noone is immune there is a potential there is the potential for a pandemic |
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membrane fusion |
non covalent nature of membranes allows fusing of membranes which is essential for many biological events 1) appropriate recognition 2)close association of membrane surfaces with exclusion of water molecules 3) localization disruption of the membrane to allow fusion of outer leaf lets (hemi fusion) 4) fusion of bilayers to form a single bilayer 5) regulation |
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botulism and botox |
clostridium botulinum is an anerobic bacteria that is sometimes found in canned foods and improper handled meats produces botulinic toxin botulinic toxin is a protease that cleaves the SNARE and SNAP25 proteins blocking neurotransmission and causing paralysis and death the isolated toxin has medicinal value in the o reduce treatment of muscle spasms as well as cosmetic applications to reduce wrinkles and prevent under arm sweating |
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solute transport across membranes |
1) simple diffusion 2) facilitated diffusion - channels and carriers 3) active transport -primary and secondary |
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simple diffusion |
small, non polar gases (O2 and CO2) and hydrophobic molecules can directly cross the membrane down a concentration gradient. no specialized systems required high->low concentration (down gradient) |
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facilitated diffusion |
membrane transporters lower the activation energy barrier of crossing the bilayer activation energy for removing the hydration shell from a polar solute and transferring it into the apolar environment in the core of the bilayer is very high membrane transporters lower the activation energy for crossing the membrane by replacing the hydration shell of the substrated with polar groups along the transfer path in the protein interior |
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facilitated diffusion (channels vs carriers) |
-channels are membrane pores that can only transport molecules and ions down the electrochemical gradient -channels can have very high conduction rates because they bind the substrate weakly -channels do not show saturation behavior.rate of transport through the channel is proportional to the substrate concentration -carriers have a kinetically distinct (rate limiting) step where substrate is bound to the protein. this produces saturation kinetics similar to enzymes that catalyze chemical reactions. rate of membrane transport catalyzed by carriers generally can be described by michaelis-menten equation -carriers generally have lower rate of transport than channels -carriers can catalyze both active (against electrochemical gradient) and passive (down the electrochemical gradient) transport |
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facilitated diffusion channels |
-transmembrane proteins with central passage for the transport of ions and small molecules -assist in the movement of polar molecules through the membrane by replacing the hydration shell of the substrate with polar groups along the transfer path in the protein interior -moleucles and ions of appropriate size, charge and geometry tranverse the membrane down a concentration gradient -no energy required and does not saturate with substrate |
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facilitated diffusion carriers |
-protein binds specific to solute and transports it down a concentration gradient -also called facilitated diffusion, does not require an energy source -can be saturated with substrate -glucose permase of red blood cells |
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erythrocytes (carrier) |
facilitated diffusion of glucoseat 50,000 x faster than simple diffusion -specific for movement of d-glucose -the rate of uptake follows a pattern resembling m-m kinetics -kt (k-transport) is about 1/3 the concentration of blood glucose so the transporter is nearly saturated andoperates near v max
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coupled transport |
electroneutral exchange of ions prevents changing the electric potential across the membrane (ie chloride bicarbonate exchange protein) |
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active transport |
input of energy allows movement of molecules against their concentration gradient primary active transport-driven by direct source of energy (ATP) secondary active transport- driven by ion gradient |
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atp hydrolysis |
the energy of ATP is used to drive conformational change in the protein required to translocate the ions across the membrane |
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active transport |
reversible ATP-driven proton pumps (uses energy of ATP to move protons against a concentration gradient\0
f-type ATPases- in reverse, a proton gradient can be used to generate ATP (mitochondria and chloroplasts) v-type ATPases- acidification of intracellular compartments |
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active transport (ABC transporters) |
-transport of a variety of biomolecules (amino acids, peptides, drugs) out of the cell against a concentration gradient -multi-drug transporter pumps drugs (chemotherapeutic) out of the cell rendering them ineffective -these proteins contain two ATP-binding domains ATP-binding Cassette transporters |
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secondary active transport |
-utilizing the movement of ions down their concentration gradients as a source of energy to co-transport other molucles UP their concentration gradients -secondary active transport is dependent upon primary active transport for the initial formation of these ion gradients -bacterial system for uptake of lactose against its concentration gradient -proton pump which established proton gradient is inhibited by CN- |
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secondary active transport (glucose uptake) |
-in intestinal epithelial cells, glucose uptake driven through symport with NA down its concentration gradient -the movement of glucose against its concentration gradient is facilitated by the movement of 2 NA ions down their concentration and electrical gradient
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voltage-gated ion selective channels |
-rapid changes in the activity of ion channels cause the changes in membrane potential (action potentials) in neurons -ion channels differ from ion transporters in three ways: 1) much faster 2) no saturation limits 3) gated (open and close in response to cellular event ie voltage gated or ligand gated) |
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ion selective channels (mechanism of specificity) |
-voltage gates (k+) channel of neurons allows k+ ions to pass through 10,000 times faster than Na+ ions -narrow channel region acts as selectively filter backbone.carbonyls can replace water molecules for hydrogen bond formation |
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neuronal Na+ channel is voltaged gated |
the neural Na+ channel is a single polypeptide of 4 domains and surrounding a central pore. the channel opens in response to membrane depolarization. opening the channel is triggered by movement of the voltage sensor (helix iV). heliz IV has high concentration of positive changes and moves across the membrane in response to changes in electric potential |
