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BIOL 266 > Unit 3 > Flashcards

Unit 3 Flashcards

1
Q

If bilayers are fluid, why do they not spontaneously fuse?

A

The cage-like structure around the polar heads acts as an insulator and is not easily displaced. Membrane fusion requires many factors as well as energy. Thus, the hydration shell around the membrane contributes to keeping the organelles distinct and prevents uncontrolled fusion.

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2
Q

why important for membranes to be fluid?

A

for movement
for seperation of daughter cells
particularly for proteins in membrane to be able to move and change conformation

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3
Q

Membrane fluidity is also determined by

A

the types of lipids

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4
Q

Two main properties of lipids contribute to fluidity:

A

(1) the length of the hydrocarbon tails (2) their degree of saturation (double bonds or not).

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5
Q

Membrane fluidity is also determined by the types of lipids:A shorter chain length:

A

reduces the tendency of the hydrocarbon tails to interact with one another and therefore increases the fluidity of the bilayer.

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6
Q

Membrane fluidity is also determined by the types of lipids:Unsaturated hydrocarbon tails introduce

A

kinks into the chain, making them more difficult to pack together, increasing the fluidity of the bilayer. Such membranes are less viscous.

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7
Q

Cholesterol inserts into the membrane with :

A

its polar hydroxyl group close to the polar head groups of the phospholipids

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8
Q

The rigid hydrocarbon rings of cholesterol interact with, and partly immobilize:

A

the regions of the fatty acid chains that are adjacent to the phospholipid head groups

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9
Q

Cholesterol makes the bilayer

A

less fluid at high temperature, but keeps it fluid at low temperature.

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10
Q

The lipid composition influences

A

the properties of the membranes

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11
Q

The lipid composition influences the properties of the membranes. Relatively small polar head groups (e.g. phosphatidylethanolamine) give the lipid a

A

“cone” structure

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12
Q

The lipid composition influences the properties of the membranes:hose with larger head groups (e.g. phosphatidylcholine, phosphatidylinositol) give the lipid a

A

cylindrical structure.

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13
Q

An abundance of conical lipids(small polar head groups) on the inner leaflet as opposed to the outer leaflet could allow for

A

natural curvature of the membranes.

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14
Q

where are glycolipids synthesized?

A

golgi apparatus

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15
Q

__could allow for natural curvature of the membranes.

A

An abundance of conical lipids on the inner leaflet as opposed to the outer leaflet could allow for natural curvature of the membranes.

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16
Q

Glycolipids and sphingomyelin are only in the

A

extracellular (outside) leaflet.

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17
Q

Both glycolipids and sphingomyelin are produced by

A

enzymes exposed to the Golgi lumen

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18
Q

Both glycolipids and sphingomyelin are produced by enzymes exposed to the Golgi lumen and are not

A

substrates for flippases.

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19
Q

two glycolipids:

A

cerebrosides
gangliosides

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20
Q

Asymmetric distribution of lipids in the plasma membrane:Phosphatidylcholine is mostly found in:

A

the outer leaflet.

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21
Q

Asymmetric distribution of lipids in the plasma membrane:Phosphoglycerides with terminal primary amine groups in the polar heads (phosphatidylserine and phosphatidylethanolamine) are mainly found in:

A

the inner leaflet.

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22
Q

Phosphatidylcholine is mostly found in the outer leaflet.
Phosphoglycerides with terminal primary amine groups in the polar heads (phosphatidylserine and phosphatidylethanolamine) are mainly found in the inner leaflet. This asymmetry is due to:

A

The action of flippases.

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23
Q

Asymmetric distribution of lipids in the plasma membrane:Phosphatidylinositols are:

A

minor constituents of the inner leaflet of the plasma membrane, with a role in cell signaling.

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24
Q

Phosphatidylinositols are minor constituents of the inner leaflet of the plasma membrane, with a role in cell signaling. This asymmetry is due to

A

the action of flippases.

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25
Asymmetric distribution of lipids in the plasma membrane:Cholesterol is
evenly distributed between both leaflets and spontaneously shuttles between both leaflets without the need for flippases.
26
Phosphoglycerides are synthesized on :
the outer leaflet of the endoplasmic reticulum (A)
27
Phosphoglycerides are synthesized on the outer leaflet of the endoplasmic reticulum (A). An enzyme called __ randomly transfers the lipids to the inner leaflet, preventing buildup in the outer leaflet.
SCRAMBLASE
28
Phosphoglycerides are synthesized on the outer leaflet of the ENDOPLASMIC RETICULUM (A). An enzyme called SCRAMBLASE randomly transfers the lipids to the inner leaflet, preventing buildup in the outer leaflet. At the GOLGI COMPLEX (B), :
flippases then distribute the lipids in a specific pattern.
29
Membrane orientation ___ during transfer between compartments.
does NOT change
30
Membrane orientation does not change during transfer between compartments. Lipids facing the cytosol
remain cytosolic even at the plasma membrane.
31
Membrane orientation does not change during transfer between compartments. Lipids facing the lumen of a compartment:
will face the extracellular space
32
Membrane orientation does not change during transfer between compartments. The same is true for:
proteins
33
Membrane orientation does not change during transfer between compartments.The same is true for proteins:those in the lumen of the organelle (or with parts in the lumen) will be:
released into the extracellular space
34
Membrane orientation does not change during transfer between compartments.The same is true for proteins:the cytosolic portion remains
facing the cytosol.
35
Phospholipids can be broken down at:
specific ester bonds
36
Phospholipids can be broken down at specific ester bonds by
phospholipases
37
Phospholipase D releases
the polar head group
38
phospholipase C releases
the polar head group attached to the phosphate
39
Phospholipase A1 releases:
the hydrophobic fatty acid chain from the C1 position
40
Phospholipase A2 releases:
The hydrophobic fatty acid chains from C2 position
41
Products produced by phospholipases are:
important signaling molecules.
42
PLD – generates
phosphatidic acid
43
PLA1 and A2 – generate
lysophospholipids
44
History of biological membranes: 1 - cells must be :
SURROUNDED BY LIPIDS
45
History of biological membranes: 1. cells must be surrounded by lipids since:
lipid soluble substances penetrated cells but polar substances did not
46
History of biological membranes: 2. Lipids __
LIPID ARRANGE THEMSELVES into a layer called a monolayer
47
History of biological membranes: 2. LIPIDS ARRANGE THEMSELVES into a layer, called a :
monolayer
48
History of biological membranes: 3. The membrane is composed of a :
lipid bilayeer
49
Erythrocyte plasma membrane occupies:
twice the expected area
50
When erythrocytes (red blood cells) were lysed and their membranes were spread out, the measured surface area was found to be approximately twice the estimated surface area of the intact cells. This supported the idea that
the membrane is composed of a bilayer rather than a single lipid monolayer.
51
When erythrocytes (red blood cells) were lysed and their membranes were spread out, the measured surface area was found to be approximately twice the estimated surface area of the intact cells. This supported the idea that
The membrane is composed of a bilayer rather than a single lipid monolayer.
52
History of biological membranes: 4. sandwich model
Proteins must account for the selective permeability of membranes. Proposed to coat both sides as a sheet
53
History of biological membranes: 5. Fluid-mosaic model:
Some proteins are hydrophobic and must embed in the membrane The fluid-mosaic model proposes an underlying fluid-like bilayer with a mosaic of proteins embedded within the lipids
54
Functions of biological membranes (7):
1. Compartmentalization 2. Scaffold for biochemical activitie 3. Selectively permeable barrier 4.Transporting solutes 5. Responding to external signals 6. Intercellular interaction 7. Energy transduction
55
Functions of biological membranes 1. Compartmentalization:
Membranes form continuous sheets that enclose intracellular compartments.
56
Functions of biological membranes: 2. Scaffold for biochemical activities
Membranes provide a framework that organizes enzymes for effective interaction.
57
Functions of biological membranes:3. Selectively permeable barrier
Membranes allow regulated exchange of substances between compartments.
58
Functions of biological membranes 4. Transporting solutes
Membrane proteins facilitate the movement of substances between compartments.
59
Functions of biological membranes:5. Responding to external signals
Membrane receptors transduce signals from outside the cell in response to specific ligands.
60
Functions of biological membranes: 6: intercellular interaction:
Membranes mediate recognition and interaction between adjacent cells.
61
Functions of biological membranes: 7. Energy transduction:
Membranes transduce photosynthetic energy, convert chemical energy to ATP, and store energy.
62
Plasma membrane-specific functions (3):
1. Import and export of molecules 2. Receiving information 3. Capacity for movement and expansion
63
Plasma membrane-specific functions 1. Import and export of molecules:
Nutrients pass inward across the plasma membrane, waste products pass outward
64
Plasma membrane-specific functions: 2. Receiving information
Some proteins in the plasma membrane act as sensors (receptors) to enable the cell to respond to changes in its environment
65
Plasma membrane-specific functions:3. Capacity for movement and expansion
When the cell grows or changes shape, the plasma membrane enlarges its area by addition of new membrane and it can deform without tearing
66
The membranes that surround the organelles of eukaryotic cells separate
one aqueous phase (the cell cytosol) from another (the interior of the organelle)
67
Internal membranes serve as
SELECTIVE BARRIERS between the cell cytosol and the interior of individual orgnaelles
68
The membranes of the organelles maintain
the characteristic differences in composition between these organelles.
69
Subtle differences between the membrane of organelles, especially __ are largely responsible for giving each organelle its distinct character
DIFFERENCES IN THE MEMBRANE PROTEINS
70
Subtle differences between the membrane of organelles,especially differences in the membrane proteins, are largely responsible for
giving each organelle its distinct character.
71
All cell membranes are composed of
lipids and proteins
72
All cell membranes are composed of lipids and proteins and have a common
general structure
73
The lipid component of cell membranes consists of:
many millions of lipid molecules arranged in two closely apposed sheets, forming a lipid bilayer, ~5 nm thick.
74
lipid bilayer thickness:
~5 nm thick.
75
The plasma membrane is visible by
electron microscopy.
76
The lipids in cell membranes combine two very different properties in a single molecule:
a hydrophilic (“water-loving”) head and one or two hydrophobic (“water-hating”) hydrocarbon tails
77
Molecules with both hydrophilic and hydrophobic properties are termed
amphipathic
78
The simplest lipids:
fatty acids
79
A fatty acid consists of
a long hydrocarbon chain (16 to 18 carbon atoms) terminating in a carboxyl group at one end
80
introduces a kink in the hydrocarbon chain
double bond
81
In saturated fatty acids
all of the carbon atoms are bonded to the maximum number of hydrogen atoms (no double bonds between carbon atoms)
82
Unsaturated fatty acids contain
one or more double bonds between carbon atoms
83
Chemical composition of membrane lipids: __ main types
Three
84
Chemical composition of membrane lipids : three main types:
(1) Phosphoglycerides (2) Spingholipids (3) Chlolesterol
85
Phosphoglycerides are:
Diacylglycerides with small functional head groups linked to the glycerol backbone by phosphate ester bonds. 1/3 of the main types of chemical components of membrane lipids
86
Sphingolipids are:
Ceramides formed by the attachment of sphingosine to fatty acids.
87
Cholesterol is:
A smaller and less amphipathic lipid that is only found in animals.
88
The most abundant membrane lipids are:
the phospholipids
89
Phospholipids consist of:
Two fatty acids linked to a polar head group
90
Phospholipid structure:
Most phospholipids are built on a glycerol molecule (a three-carbon structure). Two of the glycerol's carbon atoms are attached to fatty acids through ester bonds. The third carbon is attached to a phosphate group (phosphatidic acid).
91
The phosphate group in membrane lipids id frequently attached to another small molecule, such as:
serine (phosphatidylserine), choline (phosphatidylcholine) , inositol (phosphatidylinositol) and ethanolamine (phosphatidylethanolamine)
92
The most common type of phospholipid in most cell membranes is
phosphatidylcholine
93
Phosphatidylcholine: The net charge of the polar head:
= (+1) + (-1) = 0
94
Phosphatidylethanolamine:The net charge of the polar head:
= (+1) + (-1) = 0
95
Phosphatidylserine: The net charge of the polar head =
(+1) + (-1) + (-1) = -1
96
Phosphatidylinositol:nThe net charge of the polar head =
(0) + (-1) = -1
97
Sphingolipids are derived from:
Sphingosine
98
The addition of a second fatty acid to sphingosine through the amine group results in:
a lipid called ceramide
99
The addition of phosphorylcholine to ceramide results in:
A lipid called sphingomyelin
100
The addition of galactose to ceramide results in:
a lipid called a cerebroside.
101
The addition of complex carbohydrates including sialic acid to ceramide results in
a lipid called a ganglioside.
102
sugar-substituted lipids are called
glycolipids
103
In addition to phosphoglycerides, sphingolipids and glycolipids, all cell membranes contain:
cholesterol
104
Hydrophilic molecules dissolve in water because :
They contain charged atoms or polar groups and therefore can form electrostatic (hydrogen) bonds with water molecules.
105
Hydrophobic molecules are insoluble in water because:
all of their atoms are uncharged and nonpolar and therefore cannot form bonds with water molecules. The water forms a cage-like structure around the hydrophobic molecule.
106
The formation of the cage structure of water molecules around the hydrophobic molecule requires energy. The energy cost is minimized if
the hydrophobic molecules cluster together (smaller number of water molecules are needed for the cage).
107
depending on the shape of the fatty acid tail, lipids can form:
micelles (tails inwards) or bilayers (tails sandwiched between the head groups).
108
Why membranes naturally seal into enclosed structures
These same forces provide a bilayer with self-sealing properties. The exposed edges will rearrange spontaneously to the energetically more favourable state where they are not exposed to water.
109
planar phospholipid bilayer with edges exposed to water
energetically unfavourable
110
sealed compartment formed by phospholipid bilayer : aqueous solution inside and outside
energetically favourable
111
Pure phospholipids in water will spontaneously form
liposomes
112
The lipid bilayer behaves as
a two-dimensional fluid
113
The lipid bilayer behaves as a two-dimensional fluid. Three types of lipid mobility account for this:
1. Lateral diffusion 2. Rotation 3. Flip-flop
114
lipid mobility: lateral diffusion:
Lipids rapidly exchange places with their neighbors (107 times per second). Gives rise to rapid diffusion (diffusion coefficient of 10-8 cm2/sec) → A lipid can move the length of a bacterial cell in 1 second.
115
lipid mobility: rotation:
lipids can rotate around their axis at speeds as high as 500 rpm.
116
lipid mobility: Flip-flop:
rarely occurs, on the time scale of hours, assisted by enzymes called flippases. The exception is cholesterol which can flip rapidly on its own.
117
Flip-flop: cholesterol:
cholesterol can flip rapidly on its own.
118
The fluid nature of membranes can be demonstrated by
FRAP: fluorescence recovery after photobleaching
119
FRAP: fluorescence recovery after photobleaching
1. unlabeled cell surface 2.cell surface labeled with fluorescent due 3. laser beam bleaches an area of the cell surface 4. Fluorescent labeled molecules diffuse into bleached are

BIOL 266 (17 decks)

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