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BMSC 200 > Chapter 9 > Flashcards

Chapter 9 Flashcards

1
Q

what are the membrane functions

A

-separate cells from external medium to create an intracellular environment of unique
-allows selective transport of substances in and out of the cell
-provides a location for specialized pathways and processed (e.g energy conversion of mitochondria
-rapid changes in electric potential across the membranes of neurons as basis of the nervous system
-localization of receptors to facilitate response to physiological signals (why enzymes are located together)
-mediate cell-cell recognition and interaction

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2
Q

what are the membrane characteristics

A
  • they are sheet-like structures, two molecules thick, that form closed boundaries between compartments
    -they consist of mainly lipids and proteins with carbohydrates linked to the molecules
    -they are built from amphipathic molecules
    -membranes are largely impermeable to polar molecules
    -specific membrane proteins mediate particular biological functions
    -they are self assembling, non covalent structures
  • they are fluid and dynamic structures
    -membranes and highly specialized in their composition and distribution (asymetric)
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3
Q

what is membrane formation a consequence of

A

-the amphipathic nature of the membrane lipids
-they are self assembling through hydrophobic effect

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4
Q

what does the structure of a membrane form based off of

A

on the ratio of the cross sectional areas of the polar head and the hydrophobic tail

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5
Q

what do lipids with to hydrocarbon tails tend to form (glycerophospholipids and sphingolipids)

A

bilayers

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6
Q

what formation do fatty acids favor

A

the micelle formation of micelles

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7
Q

exposure of hydrophobic tails at the edge of the bilayer to water is…

A

energetically unfavourable

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8
Q

what do flat bilayer sheets tend to do

A

-they are unstable and spontaneously form membrane vesicles with internal volume
-the vesicles are the basis of cells and organelles

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9
Q

what molecules can and cant pass through a lipid bilayer vesicle

A

-only hydrophobic molecules can pass
-very low permability to ions and most polar molecs
-some smaller non-polar gases (O2 and CO2 for example) and small hydrophobic molecules (like fat soluble hormomes) can pass directly through the membrane

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10
Q

what is the permeability of small molecules correlated with

A

their relative solubility in water

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11
Q

what challenge can membranes have for drugs

A

it can represent a critical barrier for polar drugs intended for intercellular targets

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12
Q

how can polar drugs make it across the cell membrane

A

encapsulation of a drug within a liposome can facilitate transport across the membrane

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13
Q

what thing can liposomes deliver drug molecules to

A

it will deliver specific molecules to specific cell types but also different organelles within different cell types

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14
Q

what are membranes mostly composed of

A

lipids and proteins

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15
Q

what do more active membranes have

A

they have a higher ratio of protein to lipid

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16
Q

can compositions of membranes change?

A

yes composition of membranes can be dynamic, especially for prokaryotes

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17
Q

why are membranes dynamic structures

A

due to the nature of the non-covalent interaction

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18
Q

where are lipids and proteins on the membrane

A

they are freely diffused in the plane of the membrane

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19
Q

how can proteins and lipids move in the membrane

A

-lateral movement of proteins and lipids within the membrane is very rapid
-movement across the membrane is restricted

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20
Q

what does transbilayer movement require

A

a polar head group to pass through hydrophobic environment

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21
Q

what is the rate of uncatalyzed lipid molecule crossing from one sheet to another

A

it is very slow (t 1/2 in days)

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22
Q

what is it called when a uncatalyzed lipid molecule crosses from one sheet to another

A

flip flop diffusion

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23
Q

what is the translocation of lipids from one side of bilayer to catalyzed by and how fast is it

A

and enzyme called flippases
and it is fast (t 1/2 in seconds)

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24
Q

what allows for specialization of membrane faces

A

how lipid composition of inner and outer sheets of the bilayer can be different

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25
Q

what must cells maintain

A

an appropreate level of membrane fluidity

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26
Q

membranes undergo temperature dependent…

A

phase transitions

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27
Q

below the phase transition temp the membrane is

A

too solid

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28
Q

above the phase transition temp the membrane is

A

too fluid

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29
Q

at the phase transition temp…

A

they hydrocarbon chains are partially ordered but lateral diffusion is still possible (just right)

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30
Q

how do cells adjust there membrane composition to maintain liquid ordered state

A

-bacteria vary the length and saturation of the hydrocarbon tails of membrane lipids
-animals use cholesterol to mediate membrane fluidity

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31
Q

while the basic features of the bilayer are simple and consistant what are the mechanisms that enable specification

A

-composition of membrane components
lipids and proteins
-distribution of membrane components
static and dynamic
-specialized membrane rings
lipid rafts

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32
Q

the lipid composition of membranes varies across…

A

species and cell types (highly specialized compositions and functions)

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33
Q

in cell membranes what things does highly specialized compositions and functions include

A

the dynamic changes to composition and/or positioning to regulate biological events
for example the movement of phosphatidylserine to outer leaf functions initiating cell destruction (apoptosis)

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34
Q

what do lipid rafts arise form

A

the spontaneous association of lipid molecules whose hydrocarbons are simular length

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35
Q

what do sphingopilids (with longer tails) form

A

clusters that exclude that exclude glycerophospholipids

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36
Q

what do the longer saturated hydrocarbons of sphingolipids form

A

stable associations making the rafts thicker and more ordered than the rest of the membrane

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37
Q

what are rafts

A

they are the docking point in lipid-anchored proteins that contain long chain saturated fatty acid anchors

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38
Q

what do the lipid linked proteins that assoceate with rafts often serve as

A

signalling functions

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39
Q

how do GPI linked proteins work

A

-GPI tail is a lipid anchor
-the GPI tail wants to burry itself in a hydrophobic environment
-doing so tethers itself to the membrane

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40
Q

what do proteins with GPI anchors tend to be involved in

A

signal transduction (involved in how the cell is communicating with the extra cellular environment

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41
Q

what are active roles of membranes often preformed by proteins

A

receptors and transporters

42
Q

three categories of membrane proteins are defined based on different mechanisms of association with the membrane. what are they

A

-peripheral (just on the surface of either side of the membrane
-lipid-anchorred (just on the surface of the membrane attached to a embedded lipid)
-integral membrane proteins (embedded across the bilayer)

43
Q

what forces do peripheral membrane proteins associate with the membrane through

A

electrostatic of hydrogen bonding interactions

44
Q

what can peripheral membrane proteins dock to

A

either membrane lipids or integral membrane proteins

45
Q

where is the bulk of the peripheral membrane proteins found

A

in the cytosol or extracellular space

46
Q

what things can release the peripheral membrane proteins from the membrane

A

changes in pH or ionic strength often releases these proteins form the membrane

47
Q

where can covalently attached lipids anchor proteins

A

to the membrane

48
Q

are lipid anchor membrane proteins reversible

A

sometimes these modifications are allowing fro regulation of cellular location

49
Q

where are GPI anchored proteins facing

A

they always at the outer face

50
Q

how many residues in the membrane do GPI anchored proteins have

A

two

51
Q

proteins with single chain hydrocarbon anchored in the membrane proteins are always on the…

A

inner face

52
Q

is there one kind of fatty acid chain that acts as lipid anchored membrane proteins

A

-no there are different types of fatty acids
-different fatty acids are attracted to different points on the protein

53
Q

where are integral membrane proteins found

A

they are immersed in, and usually span the membrane

54
Q

how are proteins positioned in the membrane in integral proteins

A

positioning within a membrane is specific and directional

55
Q

what are the 3 varieties that integral membrane proteins tend to be

A

-single pass a-helical
-a-helical bundles
-B-barrels

56
Q

how many passes do a-bundles tend to have

A

they tend to have around 7

57
Q

what tends to be the context in which you see B barrels

A

-you have BBs from amphipathic B sheets
-youll get nonpolar residues pointing out and interacting in the membrane
-you have the polar residues on the inside
-through the inside region youll have have water
-represents a pore passageway to get through the membrane

58
Q

what is the distribution of proteins like for the distribution of amino acids in integral membrane proteins

A

-charged residues are usually located mostly within the intra and extra cellular portions of the protein
-residues with non-polar side chains dominate inside the hydrophobic slab of the bilayer
-tryptophan and tyrosine cluster at the interface between the hydrocarbon chain and polar head region

59
Q

how many on the proteins in out body are integral membranes

A

-30%
-of those only 1% have had there structures determined by procedures like X ray crystallography and NMP (they are very important but very hard to study)

60
Q

what can membrane spanning regions be predicted from

A

the amino acid sequence of integral mem proteins

61
Q

sequences of how many and what kind of amino acids are likely to be membrane spanning

A

20-24 hydrophobic residues

62
Q

what technology can be used to look at the hydrophobic characteristics of a protein to predict transmembrane regions for integral proteins

A

a hydropathy index

63
Q

amino acids within the teansmembrane region tend to be non-polar how ever something attached is polar what is it

A

the carbonyl and amide groups of each peptide bond are polar

64
Q

polar unpaired carbonyl and amide groups in the bilayer core are…

A

energetically unfavorable

65
Q

carbonyl and amide groups of the protein backbone within the bilayer have to be…

A

hydrogen bonded

66
Q

what are the categories of membrane transport

A

-simple diffusion
-facilitated diffusion
-active transport
-ion transporters

67
Q

what are the different kinds of facilitated diffusion

A

-carriers
-channels

68
Q

what are the different kinds of active transport

A

primary and secondary

69
Q

what molecules can directly cross the membrane for simple diffusion

A

non-polar gases (O2 and CO2) and hydrophobic molecules

70
Q

for the things that can cross the membrane through simple diffusion what is the direction and rate of the movement determined by

A

their concentrations on either side of the membrane

71
Q

diffusion can only result in the net movement…

A

down a concentration gradient

72
Q

how does facilitated diffusion work

A

-membrane transporters lower the activation energy barrier of crossing bilayer
-activation energy for removing the hydration shell form a polar solute and transferring it into the non-polar environment in the core of the bilayer is very hard
-membrane transporters lower the activation energy for crossing the membrane by replacing the hydration shell with interactions with polar groups along the transfer path in the protein interior

73
Q

how do channels and carriers for facilitated diffusion differ interns of saturation

A

channels dont saturate
carriers do

74
Q

how do channels and carriers for facilitated diffusion differ interms of speed of thing passing through

A

-channels have high conductance rates because they bind the substrate very weakly
-carriers are slower because they bind the substrate quite strongly

75
Q

how do channels and carriers for facilitated diffusion differ interms of how they move thing from one side of the membrane to the other

A

-channels: membrane pores to transport molecules down the conc gradient
-carriers: membrane proteins that undergo substrate induced conformational changes or membrane repositioning to release substrate to the other side of the membrane

76
Q

what is the rate difference of facilitated diffusion and simple diffusion of glucose

A

facilitated diffusion of glucose is 50,000x faster the simple

77
Q

what is Kt for facilitated diffusion of glucose

A

Kt is about 1/3 the concentration of blood glucose so the transporter is nearly saturated and operates near Vmax

78
Q

what is the glucose carrier of the RBC

A

glucose permease (works kinda like an enzyme)
-alway regenerated
-velocity of transport is going to vary as a function of the substrate of the concentration of the substrate out side the cell

79
Q

why does the glucose permease work at about 75% its max capacity

A

-enzymes work at around 50% max capacity to make them more responsive at a time of need (if needed they can go faster)
-in RBC theres nothing really going on it has low energy requirements
-cells know there wont be any demands placed on that RBC its ok to run the system a little closer to the red zone
-no situation that the RBC would need something that requires extra energy

80
Q

what is transport on a single molecule called

A

uniport

81
Q

what are antiports

A

transporters that couple the movement of two molecules. they move the molecules in different directions

82
Q

what are symporters

A

transporters that couple the movement of two molecules. they move molecules in the same direction

83
Q

what does the diffusion co-transport through antiport or symport depend on

A

the charge of the molecules in order to have a net neutral charge

84
Q

how does active transport work

A

input of energy allows movement of molecules against the concentration gradients

85
Q

what is primary active transport

A

-its driven by a direct source or energy (ATP)
-includes P-type, V-type, and ABC transporters (p=phosphorolatred v=vaccuole)

86
Q

what is secondary active transport

A

it couples the movement of one molecule down it concentration gradient within the movement of another molecule down its gradient

87
Q

what concentrations of Na+ and K+ does the cell like to maintain. what does this concentration gradient control

A

-the cells likes to maintain high gradients of Na+ outside the cell and K+ inside the cell
-this controls the cell volume, electrical excitability, and enables uptake of nutrients through secondary active transport systems

88
Q

how much of your energy does maintaining the Na+ and k+ pump require

A

about 1/3 of your energy

89
Q

k+,Na+ ATPase uses the energy of…

A

ATP hydrolysis to pump three Na+ out of the cell and two K+ into the cell

90
Q

what is P-type transporter called P type

A

because it undergoes a phosphorolayted intermediate from aspartate

91
Q

what is V-type ATPase and what does it do

A

-used the energy of ATP to move protons against the concentration gradient
-acidification or organelles (lysosomes)
-in chloroplast and mitochondria F-type ATP synthases reverse this reaction to use proton gradients to generate ATP

92
Q

what are ABC transporters and how do they work

A

-contain ATP-binding domains (ATP-Binding Cassette)
-transport a variety of biomolecules out of the cell against a concentration graident
-multi-drug resistance protein pums drug (chemotheraputic) out of the cell rendering the drugs ineffective)

93
Q

what is glucose uptake form the gut driven by? how does it work? and what is it dependent on?

A

-in intestinal epithelial cells glucose uptake form the gut is driven through symport with Na+
-the movement of glucose up its concentration gradient is enabled by the movement of Na+ ions down there concentration gradient
- it is dependent on the action of the Na+ -K+ ATPase to establish the gradient of Na+ ions

94
Q

what do ion channels do

A

-they enable rapid movement of ions across the membrane

95
Q

what does the action of ion channels cause

A

-action of ion channels can cause changes in membrane potential (action potential in neurons)

96
Q

how and what are ion channels regulated by

A

they are tightly regulated by voltage gated channels and ligand-gated channels

97
Q

what are the three ways that ion channels differ from ion transporters

A

-they are faster
-have no saturation limits
-gated/regulated (open and close in response to signal)

98
Q

ion channels are highly…

A

selective for the molecules to be transported

99
Q

how do K+ channels work

A

-they allow rapid movement of K+ ions out of cell
-although Na+ is smaller the channel is 100-fold more permeable to K

100
Q

how does selectivity work for specificity of ion channels

A

-selectivity filter discriminates K and Na based on there ability to shed water molecules to form electrostatic interactions within backbone carbonyls

101
Q

what helps with the speed of ion channels for K+ channels

A

-selectivity filter have four equivalent binding sites for K+
–as K+ ions enter the filter the electrostatic repulsion form the other incoming K+ ions helps to push the flow of ions form inside to outside the cell

BMSC 200 (10 decks)

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