Chapter 10: Membrane Structure Flashcards
1
Q
Membranes are essential for what?
A
Cell viability
2
Q
Membranes are used to establish what that have distinct and diverse functions?
A
Compartments
3
Q
Name three functions of membranes
A
- Synthesizing ATP
- Transmitting electrical signals
- Acting as sensor to extracellular cues
4
Q
All biological membranes have a common what?
A
General structure
5
Q
Basic structure of all cellular membranes include what?
A
Lipid molecules and membrane associated proteins
6
Q
The most abundant membrane lipids are what?
A
Phospholipids
7
Q
What are phospholipids composed of?
A
A polar (water loving) head group and two hydrophobic (water fearing) hydrocarbon tails
8
Q
The nonpolar tails of phospholipids vary in their what?
A
Length (13-24 carbons)
9
Q
One of the hydrocarbon tails of a phospholipid may contain one or more whats which impacts lipid packing within the bilayer?
A
Double bonds
10
Q
The differences in the length of the tail plus the number of double bonds influence what?
A
The fluidity of the membrane
11
Q
What are these structures?
A
Phospholipids
12
Q
What are the main phospholipids?
A
Phosphoglycerides
13
Q
Phosphoglycerides contain what kind of backbone?
A
A 3 carbon glycerol backbone
14
Q
In a phosphoglyceride, 2 carbons of the glycerol are linked to what?
A
Fatty acid tails
15
Q
In a phosphoglyceride, the 3rd carbon is linked to a phosphate group which is linked to a what?
A
Head group
16
Q
Give an example of a phosphoglyceride
A
Phosphotidylcholine
17
Q
What is this structure?
A
Lipid Bilayer
18
Q
Identify structure
A
Phosphatidylethanolamine
19
Q
What is this structure?
A
Cholesterol
20
Q
What is A and B?
A
A: Lipid Micelle; B: Lipid Bilayer
21
Q
What is a rigid ring structure attached to a polar hydroxyl head group and short nonpolar hydrocarbon tail?
A
Cholesterol
22
Q
What packs in between phospholipids close to the nonpolar head groups?
A
Cholesterol
23
Q
How many cholesterol molecules are present per phospholipid?
A
One cholesterol molecule present per phospholipid
24
Q
Cholesterol has an impact on what property of the lipid bilayer?
A
The permeability-barrier properties of the bilayer
25
Cholesterol makes the bilayer less permeable to what?
Small water soluble molecules
26
Yes or No: Does cholesterol change the fluid properties of the membrane?
No
27
Membrane fluidity is influenced by two factors
Composition and temperature
28
Membranes with short hydrocarbon tails/multiple double bonds are more fluid at lower temperatures than membranes composed of what? Due to differences in what?
Long, saturated hydrocarbon tails due to differences in phospholipid packing
29
Which one has unsaturated hydrocarbon chains with cis-double bonds or saturated hydrocarbon chains?
A: unsaturated hydrocarbon chains with cis-double bonds B: saturated hydrocarbon chains
30
Which are thinner: Membranes composed of unsaturated phospholipids or membranes composed of saturated phospholipids?
Unsaturated phospholipids
31
Where does most of the movement in a layer of phospholipid occur?
Within the plane of each monolayer
32
Lipids rotate on their what?
Axis
33
Lipids exchange positions with neighboring lipids by what?
Lateral diffusion
34
Which motion in the lipid layer occurs most often?
A: Lateral diffusion
35
Which motion in the lipid layer is rare?
B: Flip-flop
36
Lipids molecules in the plasma membrane associate in specialized lipid subdomains referred to as what?
Lipid rafts
37
What regions are enriched with sphingolipids and cholesterol and are involved in organizing membrane proteins?
Lipid rafts
38
Lipid composition of membrane proteins differ how?
From organism to organism and organelle to organelle
39
Cholesterol is absent from what organism?
E. coli
40
What organism's plasma membrane is composed primarily of phosphotidylethanolamine?
E. coli
41
A typical cell membrane can contain upwards of how many different lipid types that vary in their head groups, hydrocarbon chain length and saturation?
1, 000
42
The two leaflets of a lipid bilayer differ in their what?
Composition
43
What are sugar modified lipids?
Glycolipids
44
What is this structure?
Glycolipid
45
What are localized to the outer leaflet of the plasma membrane bilayer?
Glycolipids
46
Asymmetry is because sugar addition occurs only within the lumen of the what?
ER/Golgi
47
Glycolipids make up how much of all plasma membrane lipids?
~5%
48
What three things happen after the exposure of sugar molecules to the extracellular environment?
1. It protects the membrane from low pH and degradative enzymes 2. It modulates the electrical properties of the membrane 3. It functions in cell-cell adhesion
49
One difference in the composition of the bilayers was the presence of glycolipids. What is the second difference?
The second difference is in the distribution of phospholipid head groups
50
What localizes only to the inner leaflet of a plasma membrane?
Phosphotidylserine
51
Phosphotidylserine gives a what kind of charge to the inner leaflet?
Negative charge
52
The difference in the composition of each leaflet of the lipid bilayer is extremely important for what?
Cell function
53
In addition to cell function, lipid layer asymmetry is used for what other two functions?
1. Propagation of an external signal into an intracellular response 2. Distinction of live versus dead cells
54
Identify the membrane proteins
1. Single-pass alpha helix
2. Multipass alpha-helix
3. Beta-sheet (Beta-barrel)
4. alpha-helix anchor
5. Fatty acid or prenyl group anchor
6. Oligosaccharide linker (GPI)
7. Noncovalent interactions
8. Noncovalent interactions
55
Number and type of proteins present in a membrane will vary from what to what?
Membrane to membrane
56
Membrane proteins vary in their structure and in the way they associate with the what?
Lipid bilayer
57
What kind of proteins span the membrane at least once to generate domains that localize to both sides of the membrane?
Transmembrane proteins
58
What proteins pass through the membrane as either an amphipathic alpha-helix or a beta-sheet?
Transmembrane proteins
59
Some membrane proteins are exposed to only one side of the membrane via what? (Two answers)
1. Noncovalent interaction with other membrane proteins 2. Attachment by a carbohydrate, fatty acid or prenyl anchor
60
Identify the lipid anchors
A. Myristoyl anchor B. Palmitoyl anchor C. Farnesyl anchor
61
What type of lipid anchor contains a saturated 14 carbon fatty acid added to N-terminal glycine during translation?
Myristic acid
62
What type of lipid anchor contains saturated 16 carbon fatty acid added to cysteine?
Palmitic acid
63
What contains farnesyl or geranylgeranyl, has an unsaturated 15 carbon fatty acid added to C-terminal cysteine?
Prenyl group
64
What are attached to a membrane through a fatty acid or prenyl group are often involved in converting an extracellular signal into an intracellular response
Proteins
65
What types of proteins are typically localized to the cytosolic side of the plasma membrane?
Lipid anchors
66
What are reversible; converting a membrane bound protein into a soluble cytosolic one?
Lipid modifications
67
What is this structure?
\_-helix containing transmembrane protein
68
Most membrane proteins span the lipid bilayer as what?
Alpha helices
69
Alpha helices are composed of amino acids having what?
Hydrophobic side chains
70
In a lipid environment these amino acids form hydrogen bonds with each other to exclude what?
Water
71
Hydrogen bonding is maximized if the polypeptide adopts what shape as it crosses the membrane?
Alpha helix
72
On average, how many amino acids are required to cross a lipid bilayer
20-30 amino acids
73
What plots are an example program used to predict alpha helical transmembrane domains
Kyte Doolittle hydropathy plots
74
TheKyte Doolittle hydropathy program can not be used to identify what?
A beta barrel containing transmembrane regions
75
The calculated hydrophobicity for a stretch of amino acids is plotted on what axis?
Y-axis
76
The amino acid window is plotted on what axis?
X-axis
77
Values with a positive hydropathy score indicate what?
Hydrophobic regions and putative transmembrane domains
78
Will this membrane protein still function normally after getting cut by the protease?
Yes
79
Identify the Beta barrel proteins
1. 8 stranded OmpA
2. 12 stranded OMPLA
3. 16 stranded porin
4. 22 stranded FepA
80
Beta barrels are composed of 8-22 antiparallel what?
Beta strands
81
Where do you find Beta barrels?
Outer membrane of mitochondria, chloroplast and bacteria
82
Which two Beta barrels are used for transport of small hydrophilic molecules?
3 and 4
83
Which two Beta barrels are used for receptor or enzyme activities?
1 and 2
84
Average length of a beta strand is how long?
10 amino acids
85
The study of membrane proteins requires the use of various what?
Detergents
86
Detergents cover the hydrophobic domains of membrane spanning segments generating what complexes?
Protein-detergent-lipid
87
Detergents are what making them ideal for solubilizing the transmembrane proteins?
Amphiphilic
88
Name the two types of detergents
1. Strong ionic detergents (SDS) 2. Nonionic detergents (TritonX-100 or beta-octylglucoside)
89
Which detergents completely denature proteins?
Strong ionic detergents (SDS)
90
Which detergents are gentle and used to isolate membrane proteins in an active state?
Nonionic detergents (TritonX-100 or beta-octylglucoside)
91
What two tests are used to measure the lateral diffusion rates of membrane proteins in a lipid bilayer?
1. FRAP (fluorescence recovery after photobleaching) 2. FLIP (fluorescence loss in photobleaching)
92
The rate of diffusion of membrane proteins will vary from protein to protein due to their interaction with what?
Other proteins and cytoskeletal elements
93
FRAP and FLIP measure the bulk flow of what?
Membrane protein movement
94
What is the limitation of both the FRAP and FLIP tests?
These methods can not be used to follow the movement of an individual protein molecule
95
What is this structure?
A single-pass transmembrane protein
96
What test is this? FRAP or FLIP?
FRAP
97
What test is this? FRAP or FLIP?
FLIP
98
What with its associated membrane proteins is not a free flowing sea of lipid and membrane proteins?
A plasma membrane
99
Cells with what (apical, lateral and basal) have membrane domains with distinctly different functions?
Polarity
100
What is established by the asymmetric distribution of both lipid and membrane proteins?
Polarity
101
Differential localization is essential for what?
Cellular function
102
Several mechanisms generate and maintain what?
An asymmetric distribution pattern
103
What is A? It is an intercellular junction that maintains the separation of both protein and lipid molecules
Tight junction
104
What are four mechanisms to restrict membrane protein motility?
Proteins can self-assemble into large aggregates
They can be tethered by interactions with assemblies of macromolecules:
1. Outside the cell
2. Inside the cell
3. They can interact with proteins on the surface of another cell
105
Mammalian cells have a what just below their plasma membrane?
A complex cytoskeletal network
106
What are two functions of the actin based network?
1. Restricts movement of membrane proteins that are directly linked. 2. Establishes a barrier for other membrane proteins
107
The actin network is closely associated with the membrane forming a mechanical barrier for what purpose?
The free diffusion of other membrane proteins
108
What is A?
An example 'corral' formed by cytoskeletal elements
109
What is B?
A trace for the movement for a single membrane protein
