Chapter 4 Flashcards
The plasma membrane exhibits a tri_____ appearance
trilaminar
7 functions of the plasma membrane
1) compartmentalization
2) scaffold for biochemical activities: membranes provide a framework that organizes enzymes for effective interactions (ex/ photosynthetic enzymes are all enclosed in a membrane and held in the chloroplast
3) selectively permeable barrier
4) transporting solutes
5) responding to external stimuli ex/ signal transduction
6) cell-cell recognition (intracellular interactions)
7) energy transduction
example of how a membrane conducts enerygy transduction
oxidative phosphorylation occurs in the mitochondrial membranes
intracellular organelles are also known as ______
membrane bound organelles
why are red blood cells best for studying membrane structures?
1) plentiful
2) easy to obtain
3) anucleate
4) no organelles
How did gorter and grendel propose the lipid bilayer?
realized that there was 2 times as much membrane lipids as there was surface area
what technique was used to find embedded proteins of the lipid bilayer?
the freeze fracture technique; freezing the membrane of RBC, using a knide to separate the 2 layers. used molten metal to create a cast to analyze and find integral proteins embedded in the membrane.
prood of embedded proteins
1) proteins that were isolated had hydrophobic regions
2) labelling proteins showed portions that were exposed on both sides
3) proteins wre mobile in the plane of the membrane
4) freeze fracture techniques confirmed existence of transmembrane proteisn
Fluid mosaic model
the core lipid bilayer exists in a fluid state, and is capable of movement. the membrane proteins form a mosaic of particles penetrating the lipids. Membranes are DYNAMIC
T/F: lipid to protein ratio are the same for all cells membanes
false. the composition of membranes are dependent on their roles in the cell
how are lipids and proteins often bound together?
usually through non-covalent bonds (vanderwaal interactions). allows for migration around the membrane.
3 main types of membrane lipids
1) phospholipids/ phosphoglycerides
2) sphingolipids
3) cholesterol
what is a phosphoglycerides
membrane lipids that contain a phosphate group with a glycerol backbone and two hydrocarbon chains
What kind of glycerids are membrane lipids?
Di glycerides. the third site has a phosphate group attached to create a polar head
examples of phospholipids
phosphatidyl choline
phosphatidul serine
phosphatidyl ethanolamine
phosphatidyl inositol
phosphatidic acid
a fatty acid that has no additional group added to the phosphate on the glycerol backbone
CH-hydrocarbon
CH-hydrocarbon
CH-phosphate
What is a sphingolipid
a ceraminde formed by the attachment of sphingosine to fatty acid by the sphingosine’s amino group
what is a sphingosine
amino alcohol containing a long hydrocarbon chain
what kind of lipid arises if a carbohydrate is attached to sphingosine?
a glycolipid
what is sphingo myelin
a phosphocholine attached to a sphingosine, which is an amino alcohol with a hydrocarbon chain
what is a cerebroside
a simple sugar attached to sphingosine (a type of glycolipid)
if a complex sugar or saalic acid is bound to a spingoside, a _____lipid is formed
a ganglioside glycolipid
what would happen if there are no gangliosides in a body
severe neurodegeneration
how is cholesterol oriented in the membrane
the hydroxylgroup of cholesterol is on the membrane surface, with the hydrophobic ring structure in the inner portion of the membrane.
why are hydrophobic tails never in the aqueous face?
because it is not thermodynamically favorable
liposome
a continuous lipid bilayer that is formed SPONTANEOUSLY when lipids are placed in aqueous solution
T/F: both faces of the lipid membranes are symmetrical
false; each face has different lipid and protein composition
T/F; membrane lipids flip flop easily
false, they can move around laterally but very rarely flip flop
where are carbohydrates found on the membrane
on the OUTSIDE face, facing the EXTRACELLULAR space
what process attaches carbohydrates onto a lipid? what kind of linkage?
glycosylation, covalent linkages hold the oligosaccharide in place
roles of glycoproteins and glycolipids
glycoproteins have SHORTER branches of carbs for other interactions with other cells
glycolipids have LONGER branches for cell to cell recognition.
what two types of linkages connect carbohydrates to a protein?
1) N-linkages
2) O-linkages
what is an N linkage
a linkage that connects a carb to a protein. linked through N-acetylglucosamine to asparagine
What is an Olinkage
a linkage that connects a carb to a membrane protein. linked through N-acetylgalactoseamine to serine or threonine
how do glycolipids determine blood type?
Blood type O; no terminal sugar
Blood type A; N-Acetylglucosamine attached to end.
Blood type B; galatose at end
how is an integral membrane protein able to transport a hydrophillic solute across the interior of the membrane?
the protein may have a hydrophillic core that forms aqueous channels in the membrane spanning region
three main functions of transmembrane proteins
1) as receptors
2) as channels
3) as electron transport agents (ex/ succinate dehydrognase)
how are integral membranes sealed into the lipid “wall”
amino acids in the transmembrane domain form vanderwaal forces with the fatty acyl chains of the bilayer, allowing the protein to be anchored
portions of the integral membrane protein that span on either the extracellular or intercellular space are more ____ in shape
globular
How is integral membrane distribution studied?
freeze fracture analysis
how does a non-ionic detergent allow for the study of integral membrane proteins?
they won’t ionize the membrane protein and allows the native conformation to be seen. ex/ Trition-X
how does an ionic detergent allow for the study of integral membrane protein
it denatures the protein and usually coats it with negative charge (SDS), allows for gel electrophoresis conduction (PAGE)
the more negative the charge coated, the larger the protein is, allows you to characterize size based on how far it moves down the gel
______ crystallography allows you to determine integral membrane protein structure. What is necessary to conduct this?
X ray crystallography. you need a really pure smaple
what shape is the transmembrane domain of an integral membrane?
alpha helix
how is amino acid sequence determined in an integral membrane protein?
by a hydropathy plot. each site along the polypeptide is ranked on hydrophobicity based on FREE ENERGY in a PARTICULAR SOLVENT
how are spatial relationships/conformation determined in an integral membrane protein? (2 types)
1) site directed mutagenesis
2) electrone resonance
what feature of a protein is studied when site directed mutagenesis is conducted? what is site directed mutagenesis?
site directed mutagenesis is a form of studying the spatial relationships of an integral protein. it is done by changing the GENETIC CODE of a protein so that a different amino acid is coded, resulting in a DIFFERENT AMINO ACID SEQUENCE, resulting in a DIFFERENT CONFORMATION.
what premise does site directed mutagenesis operate on?
on the fact that proteins are dynamic and that a change in AA sequence will change their conformation AND INTERACTIONS WITH THEIR ENVIRONMENT, and thus their function
What is electron spin resonance?
a method of determining a protein’s spatial relationship/conformation. can be conducted WHEN THE PROTEIN IS STILL FUNCTIONING.
T/F: peripheral proteins are connected to the lipid membrane by covlent bonds
false. they are held by weak bonds. they can be easily removed with a solvent
how can a peripheral protein be attached to the membrane (two ways_
1) by NON COVALENTLY bonding to the polar head of a lipid
2) by NON COVALENTLY bonding to an integral protein
a GPI-linked protein is an example of a ______ protein. where are they found? how are they removed?
a GPI-linked protein is an example of a LIPID ANCHORED protein. found on the outer leafelet. removed by inositol specific phospholipases
GPI-linked= glucophosphatidylnositol-proteins.
Src and Ras proteins are an example of ____ proteins
example of a lipid anchored protein, attached to the CYTOPLASMIC side. involved in transforming cells to malignant state
3 types of membrane protein
1) integral
2) peripheral
3) lipid anchored proteins
unsaturated fatty acids and cholesterol _____ the transition temperature of a membrane. what does this do?
lowers the transition temperatuer. the membrane stays fluid at lower temperatures.
2 main states of a membrane
1) liquid crystal
2) gel phase
what role does cholesterol play in the membrane?
abolishes the sharp transition temperature to create an “intermediate fluid,” membrane will be fluid at lower temps.
the longer/shorter the fatty acyl chain of the membrane, the lower it’s melting point
the SHORTER the FA chain, the lower its melting temperature. Short FAs will melt at lower temperatures
how are membranes made?
by preexisting membranes
how do membranes cope with new environments?
by changing their fatty acid composition
what type of enzyme desaturates single bonds to double bonds?
desaturases
what do phospholipases and acyltransferases do?
phospholipases: spilt FAs from glycerol backbone
acyltransferrases: transfer FAs between phospholipids
two ways to remodel a lipid bilayer
1) switching from single to double bonds (desaturases)
2) switching acyl groups among the phospholipids (phospholipases and acyl transferases)
what are lipid rafts?
patches of cholesterol and sphingolipids that float within more fluid and disordered portions of the bilayer
what portions of the lipid bilayer are GPI-anchored proteins found?
found on the outer leaflet on a LIPID RAFT.
purpose of lipid rafts
to serve as an organizer and provides an environment for cell-surface receptrs to interact with other membrane proteins
what experiment proved that proteins could move?
a cell fusion experiment. at the beginning of fusion, the proteins of the respective celled remained on their half of the new cell. But as time went on, the proteins from human and rat cells began to intermingle
what would you see if you conducted the cell fusion experiment at a low temperature
there would be less intermingling of the two proteins because the lipid membrane will be frozen (hard for eveyrthing to move)
What is FRAP?
fluorecense recovery after photobleaching. used to detect protein movement. bleach a spot on the cell with a laser. see fluorecent tagged proteins move into the spot, you can no longer see the bleached spot– shows that the proteins moved
Rate of fluorecence recovery = rate of diffusion of mobile proteins
findings of FRAP
1) membrane proteins move SLOWER than liposome proteins
2) some proteins will not diffuse back into the photobleached spot, indicating some proteins are stationary
T/F; membrane proteins move slower than liposome proteins
true, probs due to hinderance
disadvantages of FRAP?
1) need a high protein concentration
2) hard to distinguish TRUE protein mobility. protein studied might just be too far away to fill the photobleached spot
in single particle tracking, how are proteins labelled? How are protein movement seen?
labelled with gold particles. movement seen with video microscopy
ways of watching protein movement
1) FRAP
2) single particle tracking
3) genetic modification
T/F: larger proteins move faster than smaller proteins
false
strongest force that makes a protein stay stationary
integral membrane protein is thought to be bound to he MEMBRANE SKELETON
What are optical tweezers?
generally found that proteins can be dragged for a certain distance until the protein encounters a barrier in the membrane.
how can genetic modification be used to study mobility
cells whos cytoplasmic proteins have been genetically delted often move greater distances, indicating that barriers reside on the CYTOPLASMIC side of the membrane
which side do most membrane barriers reside
on the cytoplasmic side (the membrane skeleton in the cell)
how are phospholipids mobility hindered?
by integral protein fences that prevent mobility.
3 main cells making up epithelia
1) apical cells: regulation of nutrient intake. faces the lumen
2) lateral cells: cell cell recognition, adhesion
3) basal membrane: cell-muscle connection, generation of ion gradients.
how can you get a membrane ghost for analyss?
use a red blood cell. make it undergo hemolysis by placing it in a hypotonic solution. water will enter cell and burst cell. all cell contents will be removed, leaving the membrane.
how can you separate proteins from a red blood cell membrane?
make cell undergo hemolysis by placing it in hypotonic solution, then after a ghost membrane is obtained, use PAGE electrophoresis (SDS to coat with negative charge).
three main proteins of the RBC
1) glycoprotein/ BAND THREE
2) glycoporin A
3) spectrin
purpose of band 3/glycoprotein in RBC
exchanged Cl- and HCO3- across a red cell membrane. When Co2 is released in the lungs, HCO3- moves out of RBC and CL- moves in through the glycophorin channel
How does glycophorin A help an RBC?
prevents RBC’s from clumping by containing negatively charged oligosaccharide chains, which repel each other
Role of spectrin in RBC? HOw is it attached?
a major component of the membrane skeleton. attached to membrane surfacce by NON COVALENT BONDS TO ANKYRIN (another peripheral protein that is non covalently bonded to band 3/glycoprotein)
what is Ankryrin
another peripheral protein that is non covalently bonded to band 3/glycoprotein)
2 means for substance movement
1) passively via diffusion
2) actively via energy coupling
diffusion is a _____ process that moves material from a region of high to low concentration
diffusion is a SPONTANEOUS PROCESS
free energy chanrge during difusion of NON electrolytes depends on the ____ gradient, while free energy change during diffusion of ELECTROLYTES depends on the ____- gradient
free energy chanrge during difusion of NON electrolytes depends on the CONCENTRATION gradient, while free energy change during diffusion of ELECTROLYTES depends on the ELECTROCHEMICAL gradient
two types of non mediated diffusion,
1) simple diffusion. no proteins. small molecules can pass through the membrane
2) channels. no conformatinal change, but a channel protein is needed. no energy used. used to move ions
how does transporter mediated passive transport work
uses a protein and binding of a substrate triggers conformational change, making it release the substrate onto the other side of the membrane. no energy is needed.
three things that determine the lipid permeability of a molecule
1) partition coefficient
2) molecular size
3) polarity
what is partition coefficient
helps determine how lipid soluble a molecule is. solubility of a substance in a NON POLAR solvent OVER its solubility in WATER
Osmosis
diffusion of WATER through a SEMIPERMEABLE MEMBRANE from HIGH TO LOW concentrsion
turgor pressut
internal pressure that plants develop that pushes against the surrounding cell wall
in hypertonic solutions, the plant cell will_____
plasmolyze. plasma membrane pulls away from surrounding cellw all due to water loss.
How does osmosis work?
in salt solution, water forms a hydration shell around Na+/Cl- ions. water molecules are immobile in a hydration shell. the less amount of salt, the more water molecules are free to move, therefore, water will move from hypo to hyper tonic solutions
aquaporins are associated with _____ transport of water in plants
passive transport.
How do aquaporins remain specific to water and not allow protons to flow through?
they have N203 and N68 amino acids that ATTRACTS the oxygen atom of each water molecule as it speeds through the constriction of the protein. This interactions prevents H2O from Hbonding with it’s neighbors at this point in the protein, preventing proton hopping and closes the bridge that normally allows protons to move from one water molecule to the next.
conductance
rapid movement of ions across the concentration gradient. important for nerves
what did patch clamp technique find?
discovered ion channels by measuring the voltage of oe cell/
three types of gated ion channels
1) voltage gated
2) ligand gated
3) mechanogated
What type of organism does KsCa belong to?
it is a potassium channel of a prokaryotic cell
the KsCa channel is made up of ____ subunits arranged to create a pore. only ___ K+ ions can be present at the filter at once.
the KsCa channel is made up of 4 subunits arranged to create a pore. only 2 K+ ions can be present at the filter at once.
T/F potassium channels can pump K+ against its gradient.
false. it’s a channel. it only allows potassium to flow across its gradient
what amino acids line the selectivity filter of KsCa?
GYGVT
2 domains of the eukaryotic potassium channel
1) pore domain. permits the selective passage of K+ ions
2) voltage sensing domain: helices S1-S4 that senses charge across the plasma membrane
What kind of gated channel is a potassium channel
voltage gated
how many helices make up Kv (eukaryotic potassium channel)
6 membrane spanning helices
in a prokaryotic potassium channel, which helices are moved in order to open the channel
the M2 and M1 helices must swing open
3 different conformatinal states of a eukaryotic K+ ion channel?
1) rest: all subunits are closed
2) open: ions can move
3) inactivated: cytoplasmic inactivation peptide fits inside and BLOCKS the pore
four characteristics of facilitated diffussion
1) passive
2) saturable
3) regulated
4) specific
which types of molecules would need to undergo facilitated diffusion
large substances that need to cross the membrane across their gradient
How does facilitate diffusion transport molecules?
binding of a solute to the facilitative transporter on one side of the membrane thought to trigger conformational change in the protein, allowing it to diffuse down its concentration gradient to the other side.
T/F facilitated diffusion exhibit michalis menton kinetics
true. it can be saturated when all the transport proteins are being used.
provide an example of facilitated diffusion
GLUT1 or GLUT2. moves glucose with its concentration gradient
how does insulin stimulate the uptake of glucose into the blood
insulin binds to its receptor and causes vesicles containing glucose transporteers to bind to the membrane, allowing GLUTs to be membrane bound and active (facilitated diffusion)
Proteins associated with active transport are called ____
pumps
example of a protein pump
Na+/K+ ATP ase
P type pump
phosphorylation causes changes in conformation and ion affinity that allows transport against gradients
T/F: plants have Na+/K+ ATPase to keep their solutes in check
false. Na+/K+ ATPase pumps are only found in animals
What are the conformation states of Na+/K+ ATPase
E1 conformation. high affinity for Na+, low affinity for K+
ATP hydrolysis phosphorylates ATPase, becomes E2
E2 conformation. low affinity for Na+, releases Na+, high affinity for K+, binds K+.
phosphate group is removed and ATPase goes back to E1.
potassium binding dephosphorylates the protein
Has a low affinity for K+, so it released K+ into the cell.
Ca2+ ATPase
a P type pump. found in ER, transports Ca2+ out of the cytosol
H+ ATPase
P type pump. seen in plants, used for secondary transport
H+/K+ ATPase
secretes solution of concentrated acid into the stomach.
Which type of pump is responsible for stomach acidity? Which cells have this pump?
H+/K+ ATPase P type pump. Parietal cells have this pump, located in active vesicles
mechanism for stomach acid secretion
parietal cells contain vesicles of H+/K+ ATPase pump. When food is injested, histamine is released and triggers these vesicles to fuse to with cell membrane of parietal cells and the H+/K+ATPase pumps get activated.
H+ is pumped out of the cell, and potassium enters the cell.
Example of an antiport system
Na+/K+ ATPase, H+/K+ ATPase
How does prilosec treat acid reflux?
blocks H+/K+ ATPase
How does Zantac treat acid reflux?
prevents the binding of histamine, cannot activate H+/K+ ATPase at all.
Vtype pumps
use energy from ATP but the protein pump itself does not get phosphorylated.
ABC transporters
ATP-binding cassette transporters have regulatory ATP binding sites
what is secondary active transport
using ionic gradients created by primary active transport to drive another molecule against its concentration gradient.
example of secondary active transport
ex/ using sodium to drive glucose against its gradient. sodium ionic gradient was created by Na+/K+ ATPase (active transport). Sodium then flows back into the cell (across its cocnentration gradient), bringing a glucose with it. the glucose moves AGAINST its concentration gradient. the glucose was transported by SECONDARY active transport
co transport
moving two different molcules the same direction (ex/ sodium and glucose secondary active transport)
refer back to drawing of sodium glucose secondary transporter in epithelial cells
glucose moves into apical cells by secondary active transport via cotransport with sodium. once in the cells, glucose moves out of the basal cells to the blood stream using GLUT FACILITATED diffusion transporter
how can light be used for active transport?
absorb light energy to transport protons out of the cell. proton gradient can be used to make ATP/cellular processes
4 types of active transport
1) ATP hydrolysis
2) using co transport (ex/ sodium glucose secondary transport)
3) light
4) using electrons
irritability
reponding to external stimulation
schwann cells
cells with myelin wrapped aroung it
how can cell resting potential be monitored?
using a microelectrode
T/F: K+ leak channels move potassium along the gradient
true. K+ moves out of cell through leak channels because Na+/K+ ATPase has been pumping K+ into cell
T/F: K+ leak channels open and close depending on potassium concentration
false. they are ALWAYS OPEN. K+ leak channels are not responsive to electrochemical concentration signals.
all or none law
there is no in-between. as soon as a membrane is depolarized to -50mV from -70, the maximum reponse AP will occur. NOTHING will occur at -49mV.
how does the diameter of an axon affect the speed of AP
increased diameter= decreased resistance = increased speed of action potential
saltatory conduction
sodium ion flow from na+ channels in Node of Ranvier depolarized the next node of ranview. Conductive activity jumps from node to node
neuromuscular junction
site where branches from motor axon form synapses with the muscle fibers of the skeletal muscle.
an AP triggers the opening of a ____ channel, which causes the exocytosis of a vesicle holding neurotransmitters
triggers the opening of a calcium channel
