Chapter 12 Flashcards
1
Q
Membranes are ____________ that form _______ between inside and outside of the cell
A
lipid bilayers; membranes
2
Q
True or False: Membranes are two molecule thick boundaries
A
True
3
Q
Membranes are composed of _______ and _______, either of which can be decorated with ____________
A
lipids; protein; carbohydrates
4
Q
True or False: Membranes are fluid like, but are not flexible sheet-like structures
A
False: membranes are fluid like and flexible sheet-like structures
5
Q
Most cell membranes are electrically ___________; meaning inside is __________
A
polarized; negative
6
Q
What are membrane lipids?
A
Membrane lipids are small amphipathic molecules that form closed biomolecular sheets which prevent the movement of polar or uncharged molecules
7
Q
Water molecules are released from the __________ tails of membrane lipids as these tails become sequestered in the ________ interior of the bilayer
A
hydrocarbon; nonpolar
8
Q
_____________ attractive forces between the ___________ favor close packing of the tails
A
van der Waals; hydrocarbon tails
9
Q
There are _________ and __________ attractions between the polar head groups and water molecules
A
Electrostatic; hydrogen-bonding
10
Q
Membrane lipids are _________ molecules with a __________ head group and a ___________ tail
A
amphipathic; hydrophilic (polar); hydrophobic hydrocarbon
11
Q
The formation of the phospholipid bilayer is driven by the _____________
A
Hydrophobic effect
12
Q
Recall, what is the hydrophobic effect?
A
- Nonpolar molecules in an aqueous solution are driven together b/c of the resulting increase in entropy of water molecules
- Nonpolar solute molecules are driven together in water not primarily b/c they have high affinity for each other, but b/c when they associate, they release water molecules
13
Q
Hydrocarbon tails of phospholipid bilayer interact via _______________ which contribute to membrane being a somewhat stable structure
A
Van der Waals forces
14
Q
Adding a correct mixture of phospholipids to water can form _________
A
Liposomes
They created by the joining of phospholipids to form a small spherical entity with an internal aqueous compartment
15
Q
Describe the steps to preparation of glycine-containing liposomes
A
- First breaker contains solution of glycine with a layer of phospholipids at the bottom of the beaker
- Sonication is than applied to disrupt the phospholipids
- Hydrophobic forces cause the liposomes containing glycine molecules to form
- Filtration is than used to extract the liposomes
16
Q
True or False: Membrane bilayers are straight membranes. This follows w/ the understanding of cells being spherical structures and the curvature of organelles
A
False: Membrane bilayers are curved membranes. This follows with the understanding of cells being spherical structures and the curvature of organelles
17
Q
What features/things help the membrane achieve a curved nature?
A
- To get a curved configuration, the inner leaflet will contain phospholipids with smaller polar head groups
- Different phospholipids with slightly different chain lengths and degree of saturation can help accomplish curved nature
18
Q
True or False: Cell membranes are selectively permeable
A
True
19
Q
Lipid bilayers will be highly impermeable to ____and most _____________ molecules
A
ions; large uncharged polar
20
Q
______________ molecules and _________ molecules can easily pass through the membrane via simple diffusion
A
small uncharged polar; hydrophobic
21
Q
True or False: Non-polar core of membranes inhibits the crossing of charged and/or polar molecules
A
True
22
Q
The function of selective permeability is related to hydrophobicity, which refers to…
A
The association of nonpolar molecules/groups in an aqueous environment which arises from the tendency of water to exclude nonpolar molecules
23
Q
The ability of molecules to cross the cell membrane can be captured in the quantitative measure of _____________
A
permeability coefficients
24
Q
Permeability coefficients are expressed in ________ and provide a quantitative estimate of the ____________ of molecules across a membrane
A
cm per second; rate of passage
25
True or False: For permeability coefficients, as the value gets smaller (bigger numbers), passage of molecule will be slower
True
26
List of order of following molecules/ions from slowest passage to fastest passage through the membrane
Na+, glucose, Cl-, K+, H2O, indole, tryptophan, urea glycerol
Na+, K+, Cl-, glucose, tryptophan, urea glycerol, indole, H2O
27
Why will sodium be the slowest when passing through the cell membrane?
Because sodium (Na+) is a charged ion and will be surrounded by a salvation shell, which comprises the passage of sodium through the cell membrane
28
What are examples of hydrophobic molecules that can pass through the membrane?
O2, CO2, N2, steroids
29
What are examples of small uncharged polar molecules that can pass through the membrane?
H2O, glycerol, urea, ethanol
30
What are examples of large uncharged polar molecules that can't pass through the membrane?
glucose, sucrose
31
What are examples of Ions that can't pass through the membrane?
Na+, K+, H+, Ca2+, Cl-
32
Membrane fluidity is attributed to properties of fatty acid chains including, which include...
1. The length of fatty acids
2. The degree of cis-unsaturated bonds along the fatty acid tails
33
True or False:Membrane processes and functions are dependent on the fluidity of the membrane
True
34
Describe melting temperature (Tm) and factors Tm is dependant upon
Tm is where the membrane transitions from being highly ordered to very fluid
Melting temp is dependent upon:
(1) the length of the fatty acids in membrane
(2) The degree of cis-unsaturated bonds along the fatty acid tails
35
True or False: Cholesterol helps maintain appropriate membrane fluidity in the cell membrane and stabilize membrane
True
36
Longer fatty acid chains that are _______ without any _______ bonds will create more ________ structures because of the extent of __________ forces between the tails
saturated; double; solid-like; van der waals
37
Shorter fatty acids that are __________ with at least 1-cis double bond will allow for a more _________ membrane
unsaturated; cis double; fluid-like
38
Temperatures above the Tm will be more ________
fluid-like
39
Temperatures below the Tm will be more _________
solid-like
40
In animals’ __________ is the key modulator of membrane fluidity
cholesterol
41
Cholesterol is a polycyclic structure with a _______ group with a bulky steroid ________
hydroxyl; nucleus
42
________ group of the carbohydrate will interact with __________ of phospholipid head groups within cell membrane. ______ components of cholesterol will be inserted into non-polar core of lipid bilayer
Hydroxyl; carbonyl oxygen; hydrophobic
43
True or False: overall shape of cholesterol is the same as phospholipids
False: Overall shape of cholesterol is different from phospholipids
44
What are lipid rafts?
Also called cell membrane microdomains, lipid rafts are dense areas that are rich in lipids and select biomolecules - important components for signal transduction cascades
45
Describe the roles lipid rafts have
- Lipid rafts play important roles in helping regulate membrane curvature and budding
- Lipid rafts can facilitate multiple types of interactions between extracellular matrix and cytoskeleton
46
Describe features/parts to lipid rafts
- Microdomains (localized regions) will be dynamic
- lipid rafts can be enriched in cholesterol and glycosphingolipids
- lipid rafts can interact w/ the cell cytoskeleton
- lipid rafts may contain actin-binding proteins
47
True or False: Membrane lipids do not establish a barrier
False: Membrane lipids establish a barrier
48
Membrane proteins allow for _______ of molecules and ___________ across the cell membrane
transport; information
49
True or False: Membranes that differ in function differ in their protein content. Protein content depends on the role or function of membranes
True
50
Myelin has a protein content of _______%
a) 20%
b) 16%
c) 25%
d) 18%
d) 18%
51
Plasma membrane has a protein content of _______%
a) 80%
b) 60%
c) 50%
d) 15%
c) 50%
52
Energy transduction membranes have a protein content of _________%
a) 25%
b) 75%
c) 30%
d) 60%
b) 75%
53
True or False: A membrane can be made up of 18% to as much as 75% protein content
True
54
What two ways can proteins be associated with lipid bilayers in?
1. Integral membrane proteins
2. Peripheral membrane proteins
55
Describe integral membrane proteins?
- Found in membranes that interact w/ and are embedded in the hydrocarbon chains of membrane lipids
- can be released only when membrane is physically disrupted
- most span over the lipid bilayer
56
Describe peripheral membrane proteins?
- are bound to the polar head groups of membrane lipids
- can be exposed to surfaces of integral membrane proteins by electrostatic and hydrogen bond
- can be anchored to the bilayer with a covalently bound lipid anchor attached to hydrophobic chains
- these interactions may occur on the cytoplasmic or extracellular side of membrane
57
__________ and __________ are common structural features of integral membrane proteins that allow proteins to be embedded within the cell membrane
Alpha helices; beta sheets
58
Bacteriorhodopsin is almost entirely ____________. _________ bacteriorhodopsin associates with the ______ core of lipid bilayer
alpha helices; Nonpolar; hydrocarbon
59
Bacteriorhodopsin is important for generating ....
a) the formation of beta sheets along the membrane
b) a proton gradient for ATP in bacterial cells
c) the formation of a lipid bilayer
b) a proton gradient for ATP in bacterial cells
60
True or False: Membrane spanning bacteriorhodopsin = common structural motif in integral membrane proteins
True
61
What are porin?
bacterial protein, also another integral membrane protein
62
Porin is predominately made up of _________. Arrangement of beta sheets is that each sheet is _________ to its neighbor in a _______ arrangement
beta sheets; H-bonded; antiparallel
63
Porins create ________ through cell membranes to allow for passage of biomolecules
pores
64
Exterior of porin will be _______ to allow for interaction with the hydrocarbon core of membrane. Interior channel of pore is _____ and will be filled with water
non-polar; hydrophilic
65
________ regions of the protein interacting with _______ regions of cell membrane is another way for an integral membrane protein to associate with a membrane
Hydrophobic; hydrophobic
66
True or False: Hydrophobic amino acid side chains that are associated with the alpha helix of prostaglandin H2-synthase 1 allow this enzyme to be securely anchored into the membrane of the endoplasmic reticulum
True
67
True or False: The cyclooxygenase (COX) activity of prostaglandin H2 synthase-1 is dependent on a channel connecting the active site, with a serine residue, to the membrane interior
True
68
True or False: Aspirin inhibits the cyclooxygenase activity of prostaglandin H2 synthase-1 by transferring an acetyl group to the serine residue in prostaglandin H2 synthase-1 thereby obstructing the activity of this channel. This inhibitory effect prevents arachidonic acid from being converted to prostaglandin H2
True
69
Lipid bilayer has a dual role: List the two roles.
(1) is a solvent for integral membrane proteins
(2) is a permeability barrier
70
Membrane fluidity showing the movement of lipids was elucidated by experiments using ___________________
Fluorescence recovery after photobleaching (FRAP technique)
71
Describe the FRAP technique
- A fluorescent molecule or label can be attached to either the lipids or proteins of cell membranes
- The label can be destroyed, or bleached w/ a high intensity light administered via a laser.
- When this is applied to a small portion of the membrane and during visualization under a microscope, fluorescently labeled membrane molecules from regions adjacent to the region that was bleached can be observed to move into that area that was bleached
- Gradually, the intensity of the fluorescence intensity can be measured as a function of time
- The return in fluorescence intensity can be measured as a function of time. This is demonstrated with graph above which shows high levels of fluorescence intensity across entire cell membrane at the start of the experiment. After bleaching, fluorescence intensity drops, but as time progresses, fluorescence intensity returns as nearby fluorescently labeled molecules move into area that was bleached during recovery portion of experiment
72
Lipids are not able to diffuse laterally in the membrane
False: Lipids can diffuse laterally in the membrane
73
Lateral diffusion...
a) is constant
b) can occur with little to no constraint
c) is relatively rapid
d) is the movement of lipids laterally across the bilayer
e) all of the above
e) all of the above
74
Transverse diffusion or flip-flopping.....
a) is very slow
b) requires activity of flipases, which help move phospholipids from outer leaflet to inner leaflet
c) the transition of a molecule from one membrane surface to another
d) all of the above
d) all of the above
75
Phospholipid molecules takes about _____ times as long to flip-flop across a membrane as it takes to diffuse a distance of _______ in the lateral direction
10^9; 50 A
76
True or False: The free-energy barriers to flip-flopping are larger for protein molecules than for lipids because proteins have more extensive polar regions
True
77
True or False: Flip-flopping of a protein molecule has been observed
Flip-flopping of a protein molecule has not been observed, thus membrane symmetry can be preserved for long periods
78
True or False: Movements will be variable in speed and rate, with lateral movements being more rapid than transverse movement
True
79
Major role of membrane proteins is to function as _________
transporters
80
True or False: Transporter proteins are a specific class of pump or channels that facilitate the movement of molecules across a membrane
True
81
True or False: Each cell expresses the same set of transporters in its plasma membrane
False: Each cell expresses a specific set of transporters in its plasma membrane
82
Transporters are crucial because they largely determine the _________ inside a cell and the compounds that can be taken up from the cell’s environment
ionic composition
83
In accordance to the second law of thermodynamics, molecules spontaneously move from an area of ______ concentration to one of _____ concentration
high; low
84
What are lipophilic molecules?
Molecules that can pass through the membrane because they dissolve in the lipid bilayer
85
What are the three types of transport through a cell membrane?
1. Simple diffusion
2. Facilitated diffusion
3. active transport
86
What is simple diffusion?
Movement of molecules down a concentration gradient, concentration is higher on one side than the other
87
Small molecules that meet the criteria can simply diffuse and spontaneously across the membrane if. What is the criteria?
1. If the concentration of the molecule is higher on one side of the membrane than the other
2. If the molecule is soluble in non-polar solutions
88
What is facilitated diffusion?
polar molecules can diffuse across a membrane down their concentration gradient with the assistance of a particular protein, called channel
also called passive transport
89
Facilitated diffusion is the transport of an ion or a molecule down a concentration gradient, where deltaG for the transport species is _____
negative
90
What is active transport?
using an energy source to move the molecule against a concentration gradient
- This process must be coupled to an input of free energy from a source such as ATP, an electrical gradient, or light
91
Active transport is the transport of molecules against a gradient, where deltaG for the transport species is ______
positive
92
________ and __________ require transport proteins that can act or function as pumps or channels to facilitate the movement of molecules
Facilitated diffusion; active transport
93
True or False: Sodium potassium ATPase is an important pump in cells
True
94
Most animal cells contain a high concentration of ________ and low concentration of ________
potassium; sodium
95
How does the Sodium potassium pump work?
The sodium potassium pump uses energy from ATP hydrolysis to simultaneously pump 3-sodium ions out of cell and 2-potassium ions into cell against concentration gradient
96
True or False: Because the Na/K pump reaction includes an intermediate in which ATPase enzyme is phosphorylated, pump is called P-type ATPases
True
97
Explain how MDR works
- MDR is a (multi-drug resistance or p-glycoprotein)
- When cells are exposed to a drug, the MDR protein pumps the drug out of the cell before the drug can exert its effects
98
The MDR protein comprises four domains: two __________ domains and two ________ domains (called ATP-binding cassettes)
membrane-spanning; ATP-binding
99
Explain how CFTR works
- CFTR (cystic fibrosis transmembrane regulator)
- CFTR acts as ATP-regulated chloride channel in plasma membrane of epithelial cells
- Mutations in gene for CFTR cause decrease in fluid and salt secretion by CFTR, which leads to cystic fibrosis
- As a consequence of the malfunctioning CFTR, secretion from pancreas is blocked, and heavy and dehydrated mucus accumulates in lungs, which leads to chronic lung infections
100
True or False: Secondary transporters use one concentration gradient to the power formation of another concentration gradient
True
101
Second transporters use the energy of the downhill (_________) flow of one ion or molecule to power the uphill (________) flow of another
exergonic; endergonic
102
What are second transporters also called?
cotransporters
103
What are the 3 types of second transport?
1. Symporter
2. Antiporter
3. Uniporter
104
What is a uniporter
- one molecule is transported
- This is a type of facilitated diffusion and would be exemplified w/ the transport of glucose
105
What is a symporter?
- two molecules move in the same direction
- Transport system where a molecule is carried across a membrane against its concentration gradient (LOW TO HIGH) in the same direction as an ion moving down its concentration gradient (high to low)
106
What is an antiporter?
- two molecules moving in opposite directions
- Use one concentration gradient to power formation of another
- Transport system where a molecule is carried across a membrane in the direction opposite of an ion
107
Describe how glucose is a symporter?
Glucose is moved into some animal cells by the sodium glucose linked transporter (SGLT), a symporter powered by the simultaneous entre of Na+
Symporter moves glucose against concentration gradient along w/ sodium
108
What are ion channels?
a passive transport system for ions capable of very high transport rates; ion channels often display a high degree of specificity for the transported ion
109
True or False: Voltage gated channels open in response to changes in membrane potential
True
110
True or False: Ligand-gated channels open in response to the binding of small molecules (ligands) such as neurotransmitters
True
111
The potassium channel _______and ________ transports potassium ions across the cell membrane
selectively; rapidly
112
True or False: Larger ions are NOT transported b/c they are too big to enter channel
True
113
True or False: Small ions are excluded b/c they CANNOT interact with the selectivity filter
True
114
The interior diameter of potassium ion channel changes from inside of cell at ______ through to the outside of cell with narrowest part of pore constructed at ________
10 A; 3A
115
Ions having a radius larger than ____- cannot pass into the narrow diameter (3 Å) of the selectivity filter of the channel
a) 1.5 Å
b) 2 Å
c) 1.2 Å
a) 1.5 Å
116
Describe potassium channel selectivity
POTASSIUM
- Potassium will approach the channel with water molecules. The water molecules are given up as potassium enters the channel and specifically interacts with the carbonyl oxygens of the amino acids within the channel
(The carbonyl groups will be on the amino acids of the proteins that make up the channel; this creates the selectivity filter = a region of the ion channel that determines the specificity of a particular channel)
SODIUM:
- The sodium ion is too small to fit through the channel as this ion is unable to interact with the carbonyl oxygens and thus will not be able to pass through the channel
117
True or False: The opening to the outside and the central cavity pore of the potassium channel are filled w/ water, and a potassium ion can fit in the pore w/o losing its shell of bound water molecules. About 2/3 of the way, the pore becomes constricted (3 A diameter). At that point, any K+ ions must give up their water molecules and interact directly w/ groups from the protein
True
118
True or False: Potassium ion channels are 100 -fold more permeable to K+ than to Na+
True
119
The potassium channel pays the cost ______ potassium ions by providing compensating interactions w/ the carbonyl oxygen atoms lining the selectively filter
dehydrating
120
Sodium ions are rejected from the potassium channel because....
The energy required to dehydrate them would not be recovered
- The potassium channel does not closely interact with sodium ions, which must stay hydrated and, hence, cannot pass through the channel
121
True or False: Potassium ion will approach the channel in a hydration shell and the energy cost of dehydrating this potassium ion compensated by the favorable interactions within the selectivity filter. In comparison, sodium has a high energy for dissolving the sodium ion, but the energy for resolving the sodium is not enough to compensate for the energy of dissolution since the sodium ion is too small to interact with the selectivity filter
True
122
True or False: Charge repulsion among the four ion binding sites in the potassium channel accounts for the rapid transport of potassium ions down their concentration gradient
True
123
There are two different models which have been proposed and both depend on charge repulsion as the driving force for rapid ion movement across the channel. Name the two models and what they do.
(1) hard-knock model
step 1: a hydrated potassium ion goes into the channel and through the relatively unrestricted part of the channel
step 2: The ion gives up its coordinated water molecules and binds to a site within the selectivity filter region
step 3: As each subsequent potassium ion moves into the selectivity filter, its positive charge will repel the potassium ion at the nearest site, causing it to shift to a site farther up the channel and in turn push upward any potassium ion already bound to a site farther up
- A criticism of this model is that the charge repulsion between the ions would be too great for the ions to be in such close contact
(2) knock-on mode
- this model suggests that the ions never occupy adjacent sites. Instead, the four sites are occupied by a potassium ion and a water molecule.
- This model reduces excessive charge repulsion between the ions, but still allows charge repulsion to be the driving force for conductance
- Regardless of the model, this multiple-binding-site mechanism solves the apparent paradox of high ion selectivity and rapid flow
124
True or False: Of the four binding sites in the selectivity filter, hydrated potassium ions can enter these sites one at a time after losing their hydration shells
True
125
Which are necessary steps in the contraction of heart muscles?
- movement of K+ into the cell
- Movement of Ca+ out of the cell
- movement of Na+ into the cell
126
Longer fatty acids interact more strongly b/c of the increased number of vaderwaals interactions. A cis double bond present produces a bend in the hydrocarbon chain, which interferes w/ the highly ordered lacking of fatty acids, so Tm is lowered
True
127
Cells exposed to a newly discovered toxin show elevated levels of cAMP. Which of the following could be a mechanism of action of the toxin.
a) The toxin chemically modifies a G protein, so it can no longer hydrolyze GDP to GTP.
b) The toxin chemically modifies a G protein, so the α subunit can no longer bind to β-adrenergic receptors.
c) The toxin activates an inhibitory G protein that turns off the activity of adenylate cyclase.
a) The toxin chemically modifies a G protein, so it can no longer hydrolyze GDP to GTP
This would prevent the α subunit from dissociating and activating the next step in cAMP production.
