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BIOL 331 Midterm > Cellular Membranes (Ch. 4) > Flashcards

Cellular Membranes (Ch. 4) Flashcards

1
Q

How does the lipid bilayer prevent random movement of substances in and out of the cell?

A

It creates a nonpolar barrier that prevents aqueous solutes from freely diffusing across without help

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2
Q

What are some properties of fatty acids?

A
  • long, unbranched carbohydrate chains
  • can be saturated or unsaturated
  • unsaturated fatty acids have naturally-occurring cis double bonds
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3
Q

What is a phosphoglyceride?

A

Phospholipid with a glycerol backbone. Glycerol has both a saturated and unsaturated FA tail and an additional group attached to the phosphate.

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4
Q

What are the basic units of a phosphoglyceride?

A

Additional group, phosphate, glycerol, and 2 fatty acid chains

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5
Q

What are the 5 phosphoglycerides found in membranes?

A

PA, PC, PS, PE, and PI

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6
Q

What are the phosphoglycerides with negatively charged head groups?

A

PA, PS, and PI

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7
Q

What are the phosphoglycerides with neutral head groups?

A

PC and PE

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8
Q

What are sphingolipids? Give an example

A

They are sphingosine molecules with a fatty acid tail (ex. Ceramide)

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9
Q

What are the properties of sphingolipids?

A
  • amphipathic
  • longer and more highly saturated tails than phosphoglycerides
  • decrease membrane fluidity
  • may have phospholipids attached
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10
Q

True/False? Phospoglycerides and sphingolipids are phospholipids

A

False. Phospholipids are, but not every sphingolipid has a phosphate group

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11
Q

What is an example of a sphingolipid that is also a phospholipid?

A

Sphingomyelin

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12
Q

What is a glycosphingolipid, and where are they usually found? Give two examples

A

A sphingolipid with the addition of a carbohydrate that is usually found in nervous tissue membranes (ex. cerebroside and ganglioside)

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13
Q

What is Tay-Sachs disease?

A

The deficiency of an enzyme that breaks down gangliosides, leading to an accumulation of gangliosides and impaired brain and nerve function

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14
Q

What is cholesterol?

A

An amphipathic membrane lipid that impairs fatty acid tail movement which has a role in membrane fluidity and rigidity

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15
Q

Which membrane lipids are exoplasmic?

A

SM, PC, and cholesterol

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16
Q

Which membrane lipids are cytosolic?

A

PS, PE, PI, and cholesterol

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17
Q

Where are membrane carbohydrates found?

A

Extracellular space

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18
Q

What is the proportion of glycolipids to glycoproteins? What is the interaction that links carbohydrates to lipids and proteins?

A

1:9. Covalently linked

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19
Q

What can membrane lipid composition determine?

A
  • physical state of the membrane
  • facilitate protein interactions
  • roles in signal transduction
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20
Q

What are the 7 functions of the membrane?

A
  1. Compartmentalization
  2. Scaffold for biochemical activities
  3. Selectively permeable barrier
  4. Solute transport
  5. Response to external stimuli
  6. Cell-cell communication
  7. Energy transduction (allows for electrochemical gradient)
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21
Q

Describe what influences membrane fluidity

A

Temperature, FA tail saturation and length, and cholesterol content

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22
Q

How does cholesterol effect membrane fluidity?

A

Rigid hydrophobic rings impair movement of FA tails, which decreases fluidity at high temperatures and disrupts VW interactions at low temp, increasing fluidity. It also eliminates a sharp transition melting temperature

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23
Q

How does a cell respond to a sudden drop in temperature regarding its membrane fluidity?

A
  1. Desaturase creates double bonds in the FA tails
  2. FA tails are reshuffled to create lipids with 2 unsaturated tails
  3. Shorter and more unsaturated FAs are synthesized
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24
Q

Does increasing the percentage of saturated fatty acids in a membrane increase or decrease the transition temp?

A

Increase

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25
Q

Linoleic acid has 2 cis double bonds, and stearic acid has 0. Both are the same length.
a) Which is more likely to be liquid at lower temperatures?
b) Which has a higher transition temperature?

A

a) Linoleic acid
b) Stearic acid

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26
Q

What are the three classes of membrane proteins?

A
  1. Integral
  2. Peripheral
  3. Lipid-anchored
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27
Q

What is an integral membrane protein?

A

A protein that is permanently anchored to, or is a part of the membrane

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28
Q

What are the two types of integral proteins? Describe them

A
  1. Monotopic (protein does not completely cross membrane)
  2. Transmembrane (bitopic and polytopic completely cross membrane at least once and contain one or more transmembrane domains)
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29
Q

Are transmembrane proteins hydrophilic, hydrophobic, or amphipathic?

A

Amphipathic

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30
Q

What is glycoporin A?

A

A bitopic transmembrane protein found in red blood cells

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31
Q

Which amino acids are most likely to be found in the hydrophobic domain of transmembrane proteins? How many can be found in one domain?

A

About 20 nonpolar/hydrophobic amino acids (G, A, V, L, I, M, F, W, P)

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32
Q

What is a peripheral membrane protein?

A

A protein associated to the membrane by weak non-covalent bonds (ionic interactions, hydrogen bonds), which may be composed of multiple polypeptides

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33
Q

Are peripheral membrane proteins dynamic?

A

Yes! Their weak interactions with the membrane allow them to be recruited and released

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34
Q

Are peripheral membrane proteins hydrophilic, hydrophobic, or amphipathic?

A

Hydrophilic

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35
Q

What are the roles of peripheral membrane proteins?

A

Signal transduction, mechanical support, anchor for integral membrane proteins, and enzymes

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36
Q

What is spectrin?

A

A peripheral membrane protein found on the cytosolic side of red blood cell membranes that give them their concave shape

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37
Q

What are lipid-anchored proteins?

A

Proteins covalently linked to lipids that can be found on either side of the membrane

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38
Q

What are 2 classes of lipid-anchored proteins?

A
  1. GPI-anchored proteins
  2. Embedded hydrocarbon chains
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39
Q

What is a GPI-anchored protein?

A

Proteins attached to the membrane by a small, complex oligosaccharide linked to PI in the membrane. It faces the extracellular space and has roles in cell adhesion and receptors

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40
Q

Explain phospholipid dynamics, cholesterols exception to these dynamics, and the role of flippase

A

Phospholipids can move laterally, but it is not thermodynamically favourable for them to flip to the other side of the membrane (transverse diffusion). Flippase helps to establish membrane asymmetry. Cholesterol can readily flip due to its small polar head

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41
Q

Describe the 6 modes of membrane protein mobility

A
  1. Random diffusion
  2. Immobilized
  3. Particular direction (motor proteins)
  4. Restricted by other integral membrane proteins
  5. Restricted by membrane skeleton proteins
  6. Restrained by extracellular materials
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42
Q

What are the passive transport mechanisms across membranes?

A

Diffusion, channel, and facilitative transporters

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43
Q

Which molecules can diffuse through the lipid bilayer? Which molecules can’t?

A

Small, inorganic solutes (O2, CO2, H2O) and solutes with high lipid solubility can. Ions, polar organic solutes, and large molecules cannot.

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44
Q

What is aquaporin?

A

A channel protein that allows for the bulk flow of water

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45
Q

Describe an ion channel

A

A highly selective transmembrane protein that is usually gated

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46
Q

What are the 3 types of gated ion channels?

A
  1. Voltage-gated
  2. Ligand-gated
  3. Mechano-gated
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47
Q

Describe a voltage-gated channel

A

Conformation depends on the difference in ionic charge on either side of the membrane

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48
Q

Describe a ligand-gated channel

A

Conformation depends on the binding of a specific molecule that is not the solute

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49
Q

Describe a mechano-gated channel

A

Conformation depends on mechanical forces imposed on it

50
Q

How does a facilitative transporter work?

A

The binding of a solute causes a conformational change that exposes the solute to the other side

51
Q

What does facilitative transport look like as solute concentration increases?

A

Exhibits saturation-type kinetics (like enzymes), where the maximum number of solutes being transported levels off. Transporters can generally transport 100-1000 molecules per second

52
Q

What is GLUT4 and how does it work?

A

A facilitative transporter for glucose which can move glucose in or out of the cell depending on the chemical gradient (bidirectional). Glucose is phosphorylated after transport, so there is constant movement into/out of the cell

53
Q

What are the 3 types of pumps?

A
  1. P-type
  2. V-type
  3. ABC transporter
54
Q

Describe a P-type pump and provide 2 examples

A

Becomes phosphorylated by ATP. Na+/K+-ATPase transports 3Na+ out and 2 K+ in per ATP. H+/K+-ATPase is another example

55
Q

Explain the steps of the Na+/K+-ATPase mechanism

A
  1. E1 conformation: Ion binding sites have a high affinity for Na+ ions. In this conformation the pump is open to the cytosol. ATP is already bound
  2. The pump enters the occluded E1 state (closes)
  3. ATP is hydrolyzed which causes the pump to be phosphorylated
  4. Release of ADP and conformation change to E2. K+ ions on the outside of the cell bind to the pump on the outside of the cell
  5. Pump enters occluded E2 state (closes) and dephosphorylation occurs
  6. ATP binds, which returns the pump to E1 conformation and opens it to the cytosol
56
Q

Why is the rate of transport for Na+/K+-ATPase slow?

A

Complex conformational changes

57
Q

What is the H+/K+-ATPase pump?

A

A P-type ion pump found in the stomach which pumps K+ into the cell and H+ out into the extracellular space, which makes the environment more acidic to digest food

58
Q

What is a V-type ion pump? What is it used for?

A

Utilizes ATP energy without becoming phosphorylated. It transports H+ across organelles and vacuoles to maintain the low pH of lysosomes

59
Q

What is an ABC transporter?

A

“ATP-binding cassette” transporters share a similar structure of ATP-binding domains and they transport ions, lipids, peptides, and nucleosides

60
Q

Describe secondary active transport

A

A way to move solutes against their concentration gradient without using ATP through symporters or antiporters. One solute moves with its concentration gradient (provides potential energy), and the other solute moves against it

61
Q

What is a symporter?

A

A protein that transports two substances in the same direction, also called a cotransporter

62
Q

What is an antiporter?

A

A protein that transports two substances in opposite directions, also called an exchanger

63
Q

What is an example of a symporter?

A

Na+/glucose cotransporter: Na+ ions move with their concentration gradient into the cell, and glucose molecules move against their concentration gradients into the cell

64
Q

What form of transport establishes the Na+ concentration gradient for Na+/glucose cotransport?

A

Active transport via Na+/K+-ATPase

65
Q

Diffusion during which a substance to be transported binds selectively to a membrane-spanning protein and results in a conformational change is called ___________

A

Diffusion via a facilitative transporter

66
Q

What is FRAP used to study for? What is an advantage of it?

A

Protein movements and dynamics within membranes. It can be used in vivo

67
Q

What is gel electrophoresis used to study for?

A

Isolated membrane proteins. It is studied in vitro

68
Q

Describe the steps of FRAP

A
  1. Label the membrane component with a fluorescent dye (ex. fluorescent antibody specific to a protein)
  2. Photobleach (remove fluorescence) from a small part of the cell (~1micrometer)
    3.Monitor reappearance of fluorescence in previously bleached portion, rate of recovery of fluorescence is a measure of the rate of diffusion of the protein
69
Q

Describe step 1 of isolating membrane proteins. What is produced after centrifugation?

A

Lyse the cells by mechanical disruption, freezing/thawing, or a hypotonic solution. It is separated into pellet 1 and supernatant 1

70
Q

What is contained in pellet 1 (after lysing)?

A

Insoluble membrane material (all membrane proteins)

71
Q

What is contained in supernatant 1 (after lysing)?

A

Aqueous soluble materials

72
Q

Describe step 2 of isolating membrane proteins. What is produced after centrifugation?

A

Isolate peripheral membrane proteins using high salt concentrations. It is separated into pellet 2 and supernatant 2

73
Q

How does using high salt concentrations in step 2 of isolating membrane proteins work? What protein does it isolate?

A

The salt ions will compete with the charged amino acids of the peripheral membrane proteins to disrupt noncovalent interactions with the membrane, which releases the peripheral proteins.

74
Q

What is contained in pellet 2 (after adding salt)?

A

Transmembrane proteins and lipid-anchored proteins (GPI-anchored)

75
Q

What is contained in supernatant 2 (after adding salt)?

A

Peripheral membrane proteins

76
Q

Describe step 3 of isolating membrane proteins. What is produced after centrifugation?

A

Isolate transmembrane proteins with strong detergent (ionic or nonionic). Pellet 3 and supernatant 3 are formed.

77
Q

How does using a detergent in step 3 of isolating membrane proteins work? What protein does it isolate?

A

Detergents can substitute for phospholipids to stabilize transmembrane proteins and make them soluble in aqueous solution because the detergents are amphipathic

78
Q

What is contained in pellet 3 (after adding detergent)?

A

Lipid-anchored proteins (GPI-anchored)

79
Q

What is contained in supernatant 3 (after adding detergent)?

A

Transmembrane proteins

80
Q

Describe step 4 of isolating membrane proteins. What is produced after centrifugation?

A

Phosphatidylinositol-specific phospholipase C (PI-PLC) is used to isolate GPI-anchored proteins. Pellet 4 and supernatant 4 are produced

81
Q

How does using PI-PLC in step 4 of isolating membrane proteins work? What protein does it isolate?

A

PI-PLC cleaves a linkage between the GPI-anchored protein and PI located in the membrane

82
Q

What is contained in pellet 4 (after PI-PLC is added)?

A

Insoluble materials

83
Q

What is contained in supernatant 4 (after PI-PLC is added)?

A

GPI-anchored proteins

84
Q

Describe the order in which membrane proteins are isolated from the membrane preceding gel electrophoresis

A
  1. Peripheral
  2. Transmembrane
  3. GPI-anchored
85
Q

What does PAGE stand for and what is it?

A

Polyacrylamide gel electrophoresis. Proteins migrate through a gel matrix made of cross-linked acrylamide polymers following denaturation

86
Q

How are proteins sorted in gel electrophoresis?

A

By size

87
Q

How does SDS help in the denaturation of proteins?

A

SDS is a negatively charged amphipathic detergent that gives proteins a uniform negative charge (which causes repulsion), which disrupts protein folding

88
Q

What dye is used to visualize proteins in SDS-PAGE?

A

Coomassie blue

89
Q

What can we determine from an SDS-PAGE?

A

Approximate size of protein and protein concentration (expression) by analyzing band intensity

90
Q

What is a neuron?

A

A nerve cell that is specialized for communication with other cells with electrical impulses caused by ion gradients

91
Q

What are the components of neuron structure? What are their functions?

A
  1. Dendrites receive information
  2. Axon conducts outgoing information
  3. Terminal knobs are where impulses are transmitted to the target cell
  4. Myelin sheath wraps most vertebrate axons for protection and insulation. It is lipid-rich and protein-poor
92
Q

What is the resting potential for a neuron?

A

The membrane potential when a nerve cell is in an unexcited state (-70mV)

93
Q

What is the overall charge of the outside of the cell membrane vs. the inside?

A

Positive

94
Q

What is the overall charge of the inside of the cell membrane vs. the outside?

A

Negative

95
Q

What contributes to the difference in charge across the neuron membrane?

A
  1. More positive ions are pumped outside than inside
  2. K+ ions are the charged substance with the most permeability in a resting nerve cell (ions diffuse out through potassium leak channels)
96
Q

What establishes the equilibrium in a resting nerve cell?

A

The concentration gradient favouring K+ leaving the cell and the electrical gradient favouring K+ staying in the cell

97
Q

If you applied poison that specifically inhibits the Na+/K+ ATPase pump, predict the overall long-term change in resting membrane potential this would cause (considering the impact of the pump only):
a) no change
b) resting potential will be less negative
c) resting potential will be more negative

A

B. Resting membrane potential will be less negative as the Na+ ions will not be able to leave in a 3:2 ratio, so the difference in charge between each side of the membrane will begin to stabilize

98
Q

Define an action potential

A

A change in the membrane potential after a stimulus is sensed. It includes depolarization and repolarization and takes 5ms to complete

99
Q

Describe what happens during depolarization

A

Once the threshold value has surpassed (-50mV), depolarization occurs where voltage-gated sodium channels open and sodium is allowed to diffuse into the nerve cell, which results in a membrane potential of +40mV. The channels close after 1ms

100
Q

Describe what occurs during repolarization

A

Depolarization causes voltage-gated potassium channels to open, allowing K+ to diffuse outwards, and the voltage-gated sodium channels close. The membrane potential lowers to -80mV, which causes the potassium channels to close

101
Q

Define hyperpolarization

A

This occurs after repolarization, where the membrane potential decreases past its equilibrium point, so the Na+/K+ ATPase pumps restore equilibrium

102
Q

How are the concentration gradients of each of the ions in an action potential effected by the time hyperpolarization occurs?

A

The concentration gradients of both Na+ and K+ are barely effected

103
Q

How do Na+ ions enter a neuron when an action potential is initiated (after the threshold voltage has been reached)?
a) the Na+/K+-ATPase
b) gated Na+ pump
c) voltage-gated Na+ channel
d) ligand-gated Na+ channel

A

C

104
Q

Define a nerve impulse. What are the 2 types of conduction?

A

An action potential is propagated along a neuron by triggering action potentials in adjacent portions of the membrane. Continuous conduction in unmyelinated axons, and Saltatory conduction in myelinated axons

105
Q

Describe continuous conduction

A

The flow of current causes the membrane of the region just ahead to become depolarized. An action potential at one area triggers an action potential at the next

106
Q

Where does the refractory period occur in relation to the area of the neuron becoming depolarized?

A

Towards the end with the dendrites (usually to the left)

107
Q

Describe saltatory conduction

A

Depolarization occurs at a node of Ranvier, which causes depolarization to occur at the next node of Ranvier, propagating the impulse along the axon. An action potential at one node triggers an action potential at the next

108
Q

Is there a difference in speed of nerve impulse between the two levels of conduction?

A

Yes. In myelinated axons, nerve impulses travel 20x faster

109
Q

Myelination is associated with (select all that apply):
a) amplification of nerve impulses
b) prevention of passage of ions across the plasma membrane
c) higher speeds of conduction of impulses along axons
d) determining the direction of the impulse

A

B and C

110
Q

Protein Z is a transmembrane protein that transports a large polar drug across the plasma membrane into cells. However, once the concentration of the drug inside and outside of the cell are equal, there is no further intracellular accumulation. Which of the options below best describes Protein Z?
a) it requires ATP hydrolysis to transport the drug
b) it is a facilitative transporter
c) it is an ABC transporter
d) it is a ligand-gated channel
e) it is a symporter (secondary pump)

A

B

111
Q

Define a synapse

A

The specialized junction of a neuron with its target cell

112
Q

Define a presynaptic cell

A

Conducts the impulse towards a synapse

113
Q

What are synaptic vesicles?

A

Storage for neurotransmitters in the terminal knobs of presynaptic cells

114
Q

What is a neurotransmitter?

A

A chemical that binds to the postsynaptic cell

115
Q

What is the synaptic cleft?

A

The space between two nerve cells

116
Q

What is a postsynaptic cell?

A

It receives the impulse from the presynaptic cell

117
Q

Describe the steps of synaptic transmission

A
  1. The nerve impulse (depolarization) causes voltage-gated Ca2+ channels to open in the presynaptic cell, which then diffuses into the cell from the synaptic cleft
  2. Increased Ca2+ in the presynaptic cell triggers synaptic vesicles to fuse with the plasma membrane, releasing the neurotransmitters it holds into the cleft to bind with receptors on the postsynaptic cell
  3. (Excitatory) The binding of the neurotransmitters to their receptors causes an influx of Na+ ions, which may cause an action potential and the postsynaptic cell is depolarized as the nerve impulse is carried from the presynaptic cell to the postsynaptic cell
  4. (Inhibitory) The binding of neurotransmitters causes an influx of Cl- ions, causing hyperpolarization, and the nerve impulse is cut off
118
Q

What limits the uptake of neurotransmitters in the synaptic cleft?

A
  1. Enzymes destroy the neurotransmitter in the cleft
  2. They are reuptaken by the presynaptic cell
119
Q

Acetylcholine is a neurotransmitter that stimulates the contraction of skeletal muscles. What would be the effect of a poison that inhibits acetylcholinesterase?
a) overstimulation of muscle fibers
b) under stimulation of muscle fibers
c) no effect

A

A. A poison that inhibits the enzyme that destroys the neurotransmitter will allow for acetylcholine to be uptaken by the postsynaptic cell for longer, increasing muscle activity

120
Q

Stimulatory/excitatory neurotransmitters released from the terminal knobs of a presynaptic cell will have which effect?
a) increase sodium influx into presynaptic cell
b) increase sodium influx into postsynaptic cell
c) increase chloride influx into presynaptic cell
d) increase chloride influx into postsynaptic cell

A

B. Chloride has an inhibitory effect

BIOL 331 Midterm (3 decks)

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