Biological Membranes Flashcards
(170 cards)
1
Q
What is the main component of cell membranes?
A
Lipids
2
Q
What is often embedded in or associated with the cell membrane?
A
Proteins
3
Q
What are carbohydrates called when they attach to lipids and proteins in the cell membrane?
A
Glycolipids and glycoproteins
4
Q
Why have red blood cells been a particularly useful model for studying membrane structures?
A
They don’t contain nuclei or internal membranes
5
Q
What is the major type of lipid found in cell membranes?
A
Phospholipids
6
Q
What does it mean for phospholipids to be amphipathic?
A
They have both hydrophilic and hydrophobic regions
7
Q
What three things make up a phospholipid?
A
A glycerol backbone attached to a phosphate group and two fatty acids
8
Q
Which region of a phospholipid is hydrophobic?
A
The fatty acid tails
9
Q
Is the hydrophobic region of a phospholipid polar or non-polar?
A
Non-polar
10
Q
Which region of a phospholipid is hydrophilic?
A
The phosphate head group
11
Q
Is the hydrophilic region of a phospholipid polar or non-polar?
A
Polar
12
Q
When phospholipids spontaneously arrange themselves, which region faces out and which region faces inwards?
A
The polar head groups face outwards and the non-polar tail groups come together inside away from the water
13
Q
What determines the shape of the phospholipid structure?
A
The bulkiness of the head group relative to the tails
14
Q
What is a micelle?
A
A spherical structure in which lipids can arrange themselves
15
Q
What is the structure of phospholipids that form micelles?
A
Those with bulky heads and a single hydrophobic tail
16
Q
How do phospholipids that are roughly rectangular with less bulky head groups and two hydrophobic tails arrange themselves?
A
A bilayer
17
Q
Where does phospholipid synthesis occur?
A
The interface of the cytosol and outer endoplasmic reticulum membrane
18
Q
Two of which molecule always starts phospholipid synthesis?
A
Two fatty acids
19
Q
Where are the two fatty acids in a phospholipid initially derived from?
A
Carbohydrates via the glycolytic pathway
20
Q
Where are fatty acids activated during phospholipid synthesis?
A
In the cytosol
21
Q
During phospholipid synthesis, how are fatty acids activated?
A
By the attachment of a CoA molecule
22
Q
What causes activated fatty acids to bind to glycerol-phosphate and inserted themselves into the cytosolic leaflet of the ER membrane?
A
Acyl transferase
23
Q
During phospholipid synthesis, what does the phosphatase enzyme do?
A
Removes the phosphate from a protein
24
Q
During phospholipid synthesis, what is attached via choline phosphotransferase?
A
A choline already linked to a phosphate
25
What is the difference between flippases and floppases?
- Flippases: transfer phospholipids from the outer leaflet to the inside
- Floppases: transfer phospholipids from the inner leaflet to the outside
26
After being synthesized, phospholipids destined for the cytoplasmic cellular membrane will be on which leaflet of a vesicle?
The exterior leaflet
27
After being synthesized, phospholipids destined for the exoplasmic cellular membrane will be on which leaflet of a vesicle?
The interior leaflet
28
T or F: The lipid bilayer is self-healing.
True
29
How are small tears in the bilayer sealed?
Spontaneous rearrangement of the lipids surrounding the damaged region
30
T or F: The bilayer forms spontaneously.
True
31
What is the structure of the bilayer dependent on?
Properties of the phospholipid
32
T or F: The formation of the bilayer relies on the action of enzymes.
False
33
Why is the pH of a solution important for phospholipids to arrange in a bilayer?
The pH ensures the head groups are in their ionized (charged) form and are suitably hydrophilic
34
What structures do phospholipids form when they are in environments with a neutral pH like water?
Liposomes
35
Can liposomes form, break, and re-form?
Yes
36
How can liposomes grow?
By incorporating lipids from the environment and capturing molecules in their interiors
37
What is proposed about the creation and evolution of membranes?
Membranes formed originally by straightforward physical processes, then their composition and function evolved overtime
38
T or F: Early membranes may have been either leaky or impermeable to molecules.
True
39
What does it mean to say that a cell membrane is dynamic?
They are continually moving, forming, and re-forming during the lifetime of a cell
40
Why are lipids able to freely associate with each other?
Because of the extensive van der waals forces between their fatty acid tails
41
Why is the cell membrane said to be fluid?
Because membrane lipids are able to move in the plane of the membrane
42
What two factors influence membrane fluidity?
- Lipid composition
- Temperature
43
In a single layer of the lipid bilayer, what does the strength of van der waals interactions depend on?
The length of the fatty acid tails and the presence of double bonds between neighbouring carbon atoms
44
How do longer fatty acid tails affect membrane fluidity?
They result in tighter packing of lipids and reduced mobility
45
In terms of temperature, what changes the membrane into a liquid crystal state?
An increase in temperature
46
In terms of temperature, what changes the membrane into a crystalline gel state?
A decrease in temperature
47
In response to changes in temperature, how is the lipid composition of membranes affected?
By desaturation of lipids and change of lipid chains
48
What is the difference between saturated and unsaturated fatty acids?
- Saturated: Fatty acid tails don't have double bonds
- Unsaturated: Fatty acid tails have double bonds, causing kinks
49
Do saturated or unsaturated fatty acid tails reduce lipid mobility in the membrane?
Saturated
50
Do saturated or unsaturated fatty acid tails enhance lipid mobility in the membrane?
Unsaturated
51
Is cholesterol amphipathic?
Yes
52
Which region on a cholesterol molecule is hydrophilic?
The hydroxyl group (-OH)
53
What is the hydrophobic region of cholesterol composed of?
Four carbon rings with an attached hydrocarbon chain
54
Which region of cholesterol interacts with the head groups of phospholipids in the bilayer?
The hydroxyl head group
55
Which region of cholesterol participates in van der waals interactions with the fatty acid tails of the phospholipids in the bilayer?
The carbon ring structure
56
What component of animal cell membranes acts as a bidirectional regulator of membrane fluidity?
Cholesterol
57
How does cholesterol affect membrane fluidity at high temperatures?
It decreases fluidity
58
How does cholesterol affect membrane fluidity at low temperatures?
It increases fluidity
59
If cholesterol is added to a liquid crystal membrane, what will happen to the membrane's fluidity?
Membrane fluidity will decrease
60
If cholesterol is added to a crystalline gel membrane, what will happen to the membrane's fluidity?
Membrane fluidity will increase
61
What are lipid rafts?
Lipids that have assembles in a defined patch in the cell membrane
62
What tends to accumulate around lipid rafts?
Cholesterol and other membrane components like proteins
63
What is lipid flip-flop?
The spontaneous transfer of a lipid between layers of the bilayer
64
Why is it not surprising that lipid flip-flop is rare?
Because flip-flop requires the hydrophilic head group to pass through the hydrophobic interior of the membrane
65
Why does a lack of lipid flip-flop allow the two membrane layers to differ in composition?
Because there is little exchange of components between layers
66
What are the three classes of membrane proteins?
- Integral membrane proteins
- Peripheral membrane proteins
- Lipid-anchored proteins
67
What are peripheral membrane proteins?
A protein that is temporarily associated with the lipid bilayer or with integral membrane proteins through weak non-covalent bonds
68
T or F: Peripheral membrane proteins can only be associated with the external side of the membrane.
False. They can be associated with either the internal or external side of the membrane.
69
Which type of membrane protein is transiently associated with the membrane and can play a role in transmitting information received from external signals?
Peripheral membrane proteins
70
What is an integral membrane protein?
A protein that is permanently associated with the cell membrane
71
What are three different examples of functions played by different integral membrane proteins?
- Transport of nutrients and ions
- Cell-to-cell communication
- Attachment
72
What are transmembrane proteins?
Proteins that span the entire lipid bilayer
73
T or F: Most integral proteins are transmembrane proteins.
True
74
What are the three regions composing transmembrane proteins?
- Two hydrophilic regions (one protruding from each face of the membrane)
- A connecting hydrophobic region that spans the membrane
75
What is the most common protein structure element crossing biological membranes?
The alpha-helix
76
What is a transmembrane protein domain?
A peptide sequence that is largely hydrophobic (uncharged) spans across the plasma membrane
77
What does the transmembrane protein domain do?
This sequence permanently attaches the protein to the plasma membrane
78
What are tetraspanins (TM4SFs)?
A family of membrane proteins found in all multicellular eukaryotes
79
What are tetraspanins composed of?
Four transmembrane alpha-helices and two extracellular domains
80
Which extracellular domain of a tetraspanin is shorter and which one is longer?
- EC1 is shorter
- EC2 is longer
81
On which extracellular domain/loop can tetraspanins be glycosylated?
The long extracellular domain (EC2)
82
What does it mean for a tetraspanin extracellular domain to be glycosylated?
There is a carbohydrate molecule attached to it
83
What do tertraspanins play a role in?
Cell adhesion, motility, proliferation, and more
84
What are transporters?
A transmembrane protein that moves ions or other molecules across the cell membrane
85
What are transmembrane receptors?
A transmembrane protein that allows the cell to receive signals from the environment
86
What are transmembrane enzymes?
A transmembrane protein that functions as a catalyst to accelerate the rate of a chemical reaction
87
What are transmembrane anchors?
A transmembrane protein that attaches to other proteins and helps maintain cell structure and shape
88
What are lipid-anchored proteins?
Proteins that attach to a lipid in the bilayer
89
Are biological membranes symmetrical or asymmetrical?
Asymmetrical
90
Which leaflet of biological membranes often contains glycolipids and glycoproteins?
The outer leaflet
91
What did the Frye-Edidin experiment prove?
That the membrane is dynamic
92
What was the procedure of the Frye-Edidin experiment and what observations were made?
- The surface proteins of mouse and human cells were dyed different colours
- The cells were fused together
- The surface proteins of the mouse and human cell diffused around the unified membrane
93
What is fluorescence recovery after photobleaching?
A technique used to measure the mobility of molecules in the plane of the membrane
94
During fluorescence recovery after photobleaching, what is labelling?
A process in which a fluorescent dye is attached to proteins embedded in the cell membrane
95
What does the fluorescence recovery after photobleaching procedure involve?
- Membrane proteins are labelled
- A laser is used to bleach a small area of the membrane, leaving a non-fluorescent spot on the cell surface
96
What was the hypothesis of the fluorescence recovery after photobleaching procedure?
If membrane components move in the plane of the membrane, the bleached spot should become fluorescent overtime as unbleached fluorescent molecules move into the bleached area
97
What observations and conclusions were made using fluorescence recovery after photobleaching?
- Observations: Overtime, fluorescence appeared in the bleached area
- Conclusions: Proteins move in the plane of the membrane
98
What is the fluid mosaic model?
The idea that the lipid bilayer is a fluid structure that allows molecules to move laterally within the membrane and is a mosaic of lipids and proteins
99
What is the plasma membrane?
The membrane that surrounds the cytoplasm of the cell
100
The plasma membrane is what kind of structure?
A trilaminar structure made up of a phospholipid bilayer
101
What is the most studied cell membrane?
The plasma membrane
102
What is homeostasis?
The active regulation and maintenance of a constant environment within cells
103
Why is the plasma membrane able to maintain homeostasis?
Because it is selectively permeable
104
What does it mean for the plasma membrane to be selectively permeable?
It lets some molecules in and out freely, some in and out only under certain conditions, and prevents others from passing through at all
105
What allows the plasma membrane to be selectively permeable?
The lipids and embedded proteins of which it is composed
106
What types of molecules are able to move unassisted across the plasma membrane?
Gases (ex. oxygen and CO2) and non-polar molecules (ex. lipids)
107
What types of molecules require assistance to move across the plasma membrane?
Ions and charged polar molecules
108
What is the simplest form of movement into and out of cells?
Passive transport
109
Which type of transport works by diffusion?
Passive transport
110
What is diffusion?
The random motion of molecules, with net movement occurring from areas of higher to lower concentration
111
In terms of diffusion, what happens when there is no longer a concentration gradient?
Net movement stops, but movement of molecules in both directions continues
112
What is facilitated diffusion?
Diffusion of a molecule through a membrane protein, bypassing the lipid bilayer
113
What are the two membrane transporters that can be used for facilitated diffusion?
- Channels
- Carriers
114
What is the difference between channel and carrier proteins?
- Channels: Only transport ions and molecules down the concentration gradient
- Carriers: Transport substances both down and against the concentration gradient
115
What is a protein channel?
A transporter with a passage that allows the movement of molecules through it, depending on their shape and charge
116
What does it mean for a channel to be gated?
They open in response to some sort of chemical or electrical signal
117
What are voltage-gated channels?
Channels that respond to changes in charge across the membrane
118
What are ligand-gated channels?
Channels that respond to binding of a specific molecule on its surface
119
What the molecule called that binds to and activates ligand-gated channels?
A ligand
120
T or F: Any ligand can bind to a ligand-gated channel and cause the proper conformational change.
False. Only a ligand adapted to the binding site can produce an effect (lock-and-key model)
121
Under what conditions can molecules flow through an open channel?
Molecules can only flow through channels when a concentration gradient is present
122
What is tetrodotoxin?
A very potent neurotoxin
123
What type of ion channels do tetrodotoxin target?
Binds to voltage-gated sodium channels
124
What is curare?
A mixture of organic compounds found in plants
125
What does it mean for curare to be a competitive antagonist?
It binds to the same site on the receptor with an equal or greater affinity to the actual ligand, but elicits no response
126
What are the three types of protein carriers?
- Uniporter
- Symporter
- Antiporter
127
What is a uniporter?
A type of carrier that passively transports molecules across the cell membrane
128
What is a symporter?
A carrier protein that uses the chemical gradient of one molecule to transport a second molecule in the same direction
129
What is an antiporter?
A carrier protein that uses the chemical gradient of one molecule to transport a second molecule in the opposite direction
130
What is osmosis?
The net movement of a solvent (ex. water) across a selectively permeable membrane from regions of high solute concentration to low solute concentration
131
What are aquaporins?
A protein channel that allows water to cross the plasma membrane
132
What is osmotic pressure?
The pressure needed to prevent water from moving into a solution by osmosis
133
What is active transport?
The movement of substances against the concentration gradient that requires the input of energy
134
What is the role of proteins in active transport?
They act as pumps, using energy directly to move a substance into or out of a cell
135
Within cells, how do sodium and potassium concentrations differ?
- Sodium concentration is much lower that the external environment
- Potassium concentration is much higher than the external environment
136
What is the sodium-potassium pump?
A transmembrane protein that actively moves sodium out of the cell and potassium into the cell
137
How many sodium and potassium ions can be transported via the sodium-potassium pump with one ATP molecule?
1 ATP allows 3 sodium ions out and 2 potassium ions in
138
What is a hypertonic solution?
A solution with a higher solute concentration than the cell surrounded by it
139
What would happen to a human red blood cell if placed in a hypertonic solution?
Water leaves the cell by osmosis and it shrinks
140
What is a hypotonic solution?
A solution with a lower solute concentration than the cell surrounded by it
141
What would happen to a human red blood cell if placed in a hypotonic solution?
Water moves into it the cell by osmosis and it lyses/bursts
142
What are contractile vacuoles?
A type of cellular compartment that takes up excess water and waste products from inside the cell and expels them into the external environment
143
What is an example of a single-celled organism that exists in hypotonic environments
Paramecium
144
How do single-celled organisms existing in hypotonic solutions avoid bursting from water intake by osmosis?
Contractile vesicles take up and expel excess water from inside the cell
145
What is the cell wall?
The structural layer external to the plasma membrane
146
What is turgor pressure?
The force exerted by water pressing against the cell wall
147
How does turgor pressure build?
Turgor pressure builds as a result of water moving into the cell by osmosis and the tendency of the cell wall to resist deformation
148
What is the membrane bound organelle that can absorb water and contribute to turgor pressure?
Vacuoles
149
Why do plants wilt when dehydrated?
The loss of water in vacuoles reduces turgor pressure and the cell can no longer maintain its shape
150
What type of cell wall is composed of polysaccharides, including cellulose?
Plant cell walls
151
What is the most abundant biological material in nature?
Cellulose
152
What type of cell wall is composed of cellulose, silicon, or calcium carbonate?
Algae cell walls
153
What type of cell wall is composed of chitin?
Fungi cell walls
154
What type of cell wall is composed primarily of peptidoglycan?
Bacteria cell walls
155
How do membrane proteins play a major role in signal transduction?
Convert extracellular signals into intracellular signals
156
What are the three stages of signal transduction?
- Binding of ligand to receptor
- Signal transduction via secondary messengers
- Cellular response
157
Does the ligand fully enter the cell during signal transduction?
No
158
What causes signal transduction via secondary messengers?
Caused by cytosolic side of receptor protein being affected by ligand induced conformational change
159
What is gycogenolysis?
The process in which epinephrine/adrenaline activates the conversion of glycogen stored in the liver to glucose
160
What is glycogen?
A molecule with a glycogenin protein at its core surrounded by branches of glucose
161
What is glycogenin?
An enzyme that acts as a primer to polymerize the first glucose molecules before other enzymes take over
162
What is the signal that starts glygogenolysis?
Epinephrine
163
Where does epinephrine bind to during gygogenolysis?
The adrenergic receptor on the liver cell
164
What activates the adrenergic receptor on the liver cell during gygogenolysis?
The binding of epinephrine
165
During the process of gygogenolysis, what does the active receptor do?
Recruits G-protein and allows the binding of GTP to turn that G-protein on
166
During gygogenolysis, what occurs after the G-protein is turned on?
One of the G-protein subunits will dissociate and turn on adenyl cyclase
167
What is the role of adenyl cyclase during gygogenolysis?
Turns ATP into cyclic AMP (cAMP)
168
What is the secondary messenger during gygogenolysis?
Cyclic AMP (cAMP)
169
During gygogenolysis, what causes the cellular response?
The accumulation of cAMP
170
What does the accumulation of cAMP lead to as the final step of gygogenolysis?
Causes a molecular cascade that eventually results in the release of a glucose unit from the glycogen
