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BIOL*1090 > Biological Membranes > Flashcards

Biological Membranes Flashcards

1
Q

What is the main component of cell membranes?

A

Lipids

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2
Q

What is often embedded in or associated with the cell membrane?

A

Proteins

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3
Q

What are carbohydrates called when they attach to lipids and proteins in the cell membrane?

A

Glycolipids and glycoproteins

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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

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5
Q

What is the major type of lipid found in cell membranes?

A

Phospholipids

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6
Q

What does it mean for phospholipids to be amphipathic?

A

They have both hydrophilic and hydrophobic regions

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7
Q

What three things make up a phospholipid?

A

A glycerol backbone attached to a phosphate group and two fatty acids

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8
Q

Which region of a phospholipid is hydrophobic?

A

The fatty acid tails

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9
Q

Is the hydrophobic region of a phospholipid polar or non-polar?

A

Non-polar

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10
Q

Which region of a phospholipid is hydrophilic?

A

The phosphate head group

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11
Q

Is the hydrophilic region of a phospholipid polar or non-polar?

A

Polar

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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

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13
Q

What determines the shape of the phospholipid structure?

A

The bulkiness of the head group relative to the tails

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14
Q

What is a micelle?

A

A spherical structure in which lipids can arrange themselves

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15
Q

What is the structure of phospholipids that form micelles?

A

Those with bulky heads and a single hydrophobic tail

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16
Q

How do phospholipids that are roughly rectangular with less bulky head groups and two hydrophobic tails arrange themselves?

A

A bilayer

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17
Q

Where does phospholipid synthesis occur?

A

The interface of the cytosol and outer endoplasmic reticulum membrane

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18
Q

Two of which molecule always starts phospholipid synthesis?

A

Two fatty acids

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19
Q

Where are the two fatty acids in a phospholipid initially derived from?

A

Carbohydrates via the glycolytic pathway

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20
Q

Where are fatty acids activated during phospholipid synthesis?

A

In the cytosol

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21
Q

During phospholipid synthesis, how are fatty acids activated?

A

By the attachment of a CoA molecule

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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

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23
Q

During phospholipid synthesis, what does the phosphatase enzyme do?

A

Removes the phosphate from a protein

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24
Q

During phospholipid synthesis, what is attached via choline phosphotransferase?

A

A choline already linked to a phosphate

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25
Q

What is the difference between flippases and floppases?

A
  • Flippases: transfer phospholipids from the outer leaflet to the inside
  • Floppases: transfer phospholipids from the inner leaflet to the outside
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26
Q

After being synthesized, phospholipids destined for the cytoplasmic cellular membrane will be on which leaflet of a vesicle?

A

The exterior leaflet

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27
Q

After being synthesized, phospholipids destined for the exoplasmic cellular membrane will be on which leaflet of a vesicle?

A

The interior leaflet

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28
Q

T or F: The lipid bilayer is self-healing.

A

True

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29
Q

How are small tears in the bilayer sealed?

A

Spontaneous rearrangement of the lipids surrounding the damaged region

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30
Q

T or F: The bilayer forms spontaneously.

A

True

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31
Q

What is the structure of the bilayer dependent on?

A

Properties of the phospholipid

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32
Q

T or F: The formation of the bilayer relies on the action of enzymes.

A

False

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33
Q

Why is the pH of a solution important for phospholipids to arrange in a bilayer?

A

The pH ensures the head groups are in their ionized (charged) form and are suitably hydrophilic

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34
Q

What structures do phospholipids form when they are in environments with a neutral pH like water?

A

Liposomes

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35
Q

Can liposomes form, break, and re-form?

A

Yes

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36
Q

How can liposomes grow?

A

By incorporating lipids from the environment and capturing molecules in their interiors

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37
Q

What is proposed about the creation and evolution of membranes?

A

Membranes formed originally by straightforward physical processes, then their composition and function evolved overtime

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38
Q

T or F: Early membranes may have been either leaky or impermeable to molecules.

A

True

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39
Q

What does it mean to say that a cell membrane is dynamic?

A

They are continually moving, forming, and re-forming during the lifetime of a cell

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40
Q

Why are lipids able to freely associate with each other?

A

Because of the extensive van der waals forces between their fatty acid tails

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41
Q

Why is the cell membrane said to be fluid?

A

Because membrane lipids are able to move in the plane of the membrane

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42
Q

What two factors influence membrane fluidity?

A
  • Lipid composition
  • Temperature
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43
Q

In a single layer of the lipid bilayer, what does the strength of van der waals interactions depend on?

A

The length of the fatty acid tails and the presence of double bonds between neighbouring carbon atoms

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44
Q

How do longer fatty acid tails affect membrane fluidity?

A

They result in tighter packing of lipids and reduced mobility

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45
Q

In terms of temperature, what changes the membrane into a liquid crystal state?

A

An increase in temperature

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46
Q

In terms of temperature, what changes the membrane into a crystalline gel state?

A

A decrease in temperature

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47
Q

In response to changes in temperature, how is the lipid composition of membranes affected?

A

By desaturation of lipids and change of lipid chains

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48
Q

What is the difference between saturated and unsaturated fatty acids?

A
  • Saturated: Fatty acid tails don’t have double bonds
  • Unsaturated: Fatty acid tails have double bonds, causing kinks
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49
Q

Do saturated or unsaturated fatty acid tails reduce lipid mobility in the membrane?

A

Saturated

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50
Q

Do saturated or unsaturated fatty acid tails enhance lipid mobility in the membrane?

A

Unsaturated

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51
Q

Is cholesterol amphipathic?

A

Yes

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52
Q

Which region on a cholesterol molecule is hydrophilic?

A

The hydroxyl group (-OH)

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53
Q

What is the hydrophobic region of cholesterol composed of?

A

Four carbon rings with an attached hydrocarbon chain

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54
Q

Which region of cholesterol interacts with the head groups of phospholipids in the bilayer?

A

The hydroxyl head group

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55
Q

Which region of cholesterol participates in van der waals interactions with the fatty acid tails of the phospholipids in the bilayer?

A

The carbon ring structure

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56
Q

What component of animal cell membranes acts as a bidirectional regulator of membrane fluidity?

A

Cholesterol

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57
Q

How does cholesterol affect membrane fluidity at high temperatures?

A

It decreases fluidity

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58
Q

How does cholesterol affect membrane fluidity at low temperatures?

A

It increases fluidity

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59
Q

If cholesterol is added to a liquid crystal membrane, what will happen to the membrane’s fluidity?

A

Membrane fluidity will decrease

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60
Q

If cholesterol is added to a crystalline gel membrane, what will happen to the membrane’s fluidity?

A

Membrane fluidity will increase

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61
Q

What are lipid rafts?

A

Lipids that have assembles in a defined patch in the cell membrane

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62
Q

What tends to accumulate around lipid rafts?

A

Cholesterol and other membrane components like proteins

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63
Q

What is lipid flip-flop?

A

The spontaneous transfer of a lipid between layers of the bilayer

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64
Q

Why is it not surprising that lipid flip-flop is rare?

A

Because flip-flop requires the hydrophilic head group to pass through the hydrophobic interior of the membrane

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65
Q

Why does a lack of lipid flip-flop allow the two membrane layers to differ in composition?

A

Because there is little exchange of components between layers

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66
Q

What are the three classes of membrane proteins?

A
  • Integral membrane proteins
  • Peripheral membrane proteins
  • Lipid-anchored proteins
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67
Q

What are peripheral membrane proteins?

A

A protein that is temporarily associated with the lipid bilayer or with integral membrane proteins through weak non-covalent bonds

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68
Q

T or F: Peripheral membrane proteins can only be associated with the external side of the membrane.

A

False. They can be associated with either the internal or external side of the membrane.

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69
Q

Which type of membrane protein is transiently associated with the membrane and can play a role in transmitting information received from external signals?

A

Peripheral membrane proteins

70
Q

What is an integral membrane protein?

A

A protein that is permanently associated with the cell membrane

71
Q

What are three different examples of functions played by different integral membrane proteins?

A
  • Transport of nutrients and ions
  • Cell-to-cell communication
  • Attachment
72
Q

What are transmembrane proteins?

A

Proteins that span the entire lipid bilayer

73
Q

T or F: Most integral proteins are transmembrane proteins.

A

True

74
Q

What are the three regions composing transmembrane proteins?

A
  • Two hydrophilic regions (one protruding from each face of the membrane)
  • A connecting hydrophobic region that spans the membrane
75
Q

What is the most common protein structure element crossing biological membranes?

A

The alpha-helix

76
Q

What is a transmembrane protein domain?

A

A peptide sequence that is largely hydrophobic (uncharged) spans across the plasma membrane

77
Q

What does the transmembrane protein domain do?

A

This sequence permanently attaches the protein to the plasma membrane

78
Q

What are tetraspanins (TM4SFs)?

A

A family of membrane proteins found in all multicellular eukaryotes

79
Q

What are tetraspanins composed of?

A

Four transmembrane alpha-helices and two extracellular domains

80
Q

Which extracellular domain of a tetraspanin is shorter and which one is longer?

A
  • EC1 is shorter
  • EC2 is longer
81
Q

On which extracellular domain/loop can tetraspanins be glycosylated?

A

The long extracellular domain (EC2)

82
Q

What does it mean for a tetraspanin extracellular domain to be glycosylated?

A

There is a carbohydrate molecule attached to it

83
Q

What do tertraspanins play a role in?

A

Cell adhesion, motility, proliferation, and more

84
Q

What are transporters?

A

A transmembrane protein that moves ions or other molecules across the cell membrane

85
Q

What are transmembrane receptors?

A

A transmembrane protein that allows the cell to receive signals from the environment

86
Q

What are transmembrane enzymes?

A

A transmembrane protein that functions as a catalyst to accelerate the rate of a chemical reaction

87
Q

What are transmembrane anchors?

A

A transmembrane protein that attaches to other proteins and helps maintain cell structure and shape

88
Q

What are lipid-anchored proteins?

A

Proteins that attach to a lipid in the bilayer

89
Q

Are biological membranes symmetrical or asymmetrical?

A

Asymmetrical

90
Q

Which leaflet of biological membranes often contains glycolipids and glycoproteins?

A

The outer leaflet

91
Q

What did the Frye-Edidin experiment prove?

A

That the membrane is dynamic

92
Q

What was the procedure of the Frye-Edidin experiment and what observations were made?

A
  • 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
Q

What is fluorescence recovery after photobleaching?

A

A technique used to measure the mobility of molecules in the plane of the membrane

94
Q

During fluorescence recovery after photobleaching, what is labelling?

A

A process in which a fluorescent dye is attached to proteins embedded in the cell membrane

95
Q

What does the fluorescence recovery after photobleaching procedure involve?

A
  • 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
Q

What was the hypothesis of the fluorescence recovery after photobleaching procedure?

A

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
Q

What observations and conclusions were made using fluorescence recovery after photobleaching?

A
  • Observations: Overtime, fluorescence appeared in the bleached area
  • Conclusions: Proteins move in the plane of the membrane
98
Q

What is the fluid mosaic model?

A

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
Q

What is the plasma membrane?

A

The membrane that surrounds the cytoplasm of the cell

100
Q

The plasma membrane is what kind of structure?

A

A trilaminar structure made up of a phospholipid bilayer

101
Q

What is the most studied cell membrane?

A

The plasma membrane

102
Q

What is homeostasis?

A

The active regulation and maintenance of a constant environment within cells

103
Q

Why is the plasma membrane able to maintain homeostasis?

A

Because it is selectively permeable

104
Q

What does it mean for the plasma membrane to be selectively permeable?

A

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
Q

What allows the plasma membrane to be selectively permeable?

A

The lipids and embedded proteins of which it is composed

106
Q

What types of molecules are able to move unassisted across the plasma membrane?

A

Gases (ex. oxygen and CO2) and non-polar molecules (ex. lipids)

107
Q

What types of molecules require assistance to move across the plasma membrane?

A

Ions and charged polar molecules

108
Q

What is the simplest form of movement into and out of cells?

A

Passive transport

109
Q

Which type of transport works by diffusion?

A

Passive transport

110
Q

What is diffusion?

A

The random motion of molecules, with net movement occurring from areas of higher to lower concentration

111
Q

In terms of diffusion, what happens when there is no longer a concentration gradient?

A

Net movement stops, but movement of molecules in both directions continues

112
Q

What is facilitated diffusion?

A

Diffusion of a molecule through a membrane protein, bypassing the lipid bilayer

113
Q

What are the two membrane transporters that can be used for facilitated diffusion?

A
  • Channels
  • Carriers
114
Q

What is the difference between channel and carrier proteins?

A
  • Channels: Only transport ions and molecules down the concentration gradient
  • Carriers: Transport substances both down and against the concentration gradient
115
Q

What is a protein channel?

A

A transporter with a passage that allows the movement of molecules through it, depending on their shape and charge

116
Q

What does it mean for a channel to be gated?

A

They open in response to some sort of chemical or electrical signal

117
Q

What are voltage-gated channels?

A

Channels that respond to changes in charge across the membrane

118
Q

What are ligand-gated channels?

A

Channels that respond to binding of a specific molecule on its surface

119
Q

What the molecule called that binds to and activates ligand-gated channels?

A

A ligand

120
Q

T or F: Any ligand can bind to a ligand-gated channel and cause the proper conformational change.

A

False. Only a ligand adapted to the binding site can produce an effect (lock-and-key model)

121
Q

Under what conditions can molecules flow through an open channel?

A

Molecules can only flow through channels when a concentration gradient is present

122
Q

What is tetrodotoxin?

A

A very potent neurotoxin

123
Q

What type of ion channels do tetrodotoxin target?

A

Binds to voltage-gated sodium channels

124
Q

What is curare?

A

A mixture of organic compounds found in plants

125
Q

What does it mean for curare to be a competitive antagonist?

A

It binds to the same site on the receptor with an equal or greater affinity to the actual ligand, but elicits no response

126
Q

What are the three types of protein carriers?

A
  • Uniporter
  • Symporter
  • Antiporter
127
Q

What is a uniporter?

A

A type of carrier that passively transports molecules across the cell membrane

128
Q

What is a symporter?

A

A carrier protein that uses the chemical gradient of one molecule to transport a second molecule in the same direction

129
Q

What is an antiporter?

A

A carrier protein that uses the chemical gradient of one molecule to transport a second molecule in the opposite direction

130
Q

What is osmosis?

A

The net movement of a solvent (ex. water) across a selectively permeable membrane from regions of high solute concentration to low solute concentration

131
Q

What are aquaporins?

A

A protein channel that allows water to cross the plasma membrane

132
Q

What is osmotic pressure?

A

The pressure needed to prevent water from moving into a solution by osmosis

133
Q

What is active transport?

A

The movement of substances against the concentration gradient that requires the input of energy

134
Q

What is the role of proteins in active transport?

A

They act as pumps, using energy directly to move a substance into or out of a cell

135
Q

Within cells, how do sodium and potassium concentrations differ?

A
  • Sodium concentration is much lower that the external environment
  • Potassium concentration is much higher than the external environment
136
Q

What is the sodium-potassium pump?

A

A transmembrane protein that actively moves sodium out of the cell and potassium into the cell

137
Q

How many sodium and potassium ions can be transported via the sodium-potassium pump with one ATP molecule?

A

1 ATP allows 3 sodium ions out and 2 potassium ions in

138
Q

What is a hypertonic solution?

A

A solution with a higher solute concentration than the cell surrounded by it

139
Q

What would happen to a human red blood cell if placed in a hypertonic solution?

A

Water leaves the cell by osmosis and it shrinks

140
Q

What is a hypotonic solution?

A

A solution with a lower solute concentration than the cell surrounded by it

141
Q

What would happen to a human red blood cell if placed in a hypotonic solution?

A

Water moves into it the cell by osmosis and it lyses/bursts

142
Q

What are contractile vacuoles?

A

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
Q

What is an example of a single-celled organism that exists in hypotonic environments

A

Paramecium

144
Q

How do single-celled organisms existing in hypotonic solutions avoid bursting from water intake by osmosis?

A

Contractile vesicles take up and expel excess water from inside the cell

145
Q

What is the cell wall?

A

The structural layer external to the plasma membrane

146
Q

What is turgor pressure?

A

The force exerted by water pressing against the cell wall

147
Q

How does turgor pressure build?

A

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
Q

What is the membrane bound organelle that can absorb water and contribute to turgor pressure?

A

Vacuoles

149
Q

Why do plants wilt when dehydrated?

A

The loss of water in vacuoles reduces turgor pressure and the cell can no longer maintain its shape

150
Q

What type of cell wall is composed of polysaccharides, including cellulose?

A

Plant cell walls

151
Q

What is the most abundant biological material in nature?

A

Cellulose

152
Q

What type of cell wall is composed of cellulose, silicon, or calcium carbonate?

A

Algae cell walls

153
Q

What type of cell wall is composed of chitin?

A

Fungi cell walls

154
Q

What type of cell wall is composed primarily of peptidoglycan?

A

Bacteria cell walls

155
Q

How do membrane proteins play a major role in signal transduction?

A

Convert extracellular signals into intracellular signals

156
Q

What are the three stages of signal transduction?

A
  • Binding of ligand to receptor
  • Signal transduction via secondary messengers
  • Cellular response
157
Q

Does the ligand fully enter the cell during signal transduction?

A

No

158
Q

What causes signal transduction via secondary messengers?

A

Caused by cytosolic side of receptor protein being affected by ligand induced conformational change

159
Q

What is gycogenolysis?

A

The process in which epinephrine/adrenaline activates the conversion of glycogen stored in the liver to glucose

160
Q

What is glycogen?

A

A molecule with a glycogenin protein at its core surrounded by branches of glucose

161
Q

What is glycogenin?

A

An enzyme that acts as a primer to polymerize the first glucose molecules before other enzymes take over

162
Q

What is the signal that starts glygogenolysis?

A

Epinephrine

163
Q

Where does epinephrine bind to during gygogenolysis?

A

The adrenergic receptor on the liver cell

164
Q

What activates the adrenergic receptor on the liver cell during gygogenolysis?

A

The binding of epinephrine

165
Q

During the process of gygogenolysis, what does the active receptor do?

A

Recruits G-protein and allows the binding of GTP to turn that G-protein on

166
Q

During gygogenolysis, what occurs after the G-protein is turned on?

A

One of the G-protein subunits will dissociate and turn on adenyl cyclase

167
Q

What is the role of adenyl cyclase during gygogenolysis?

A

Turns ATP into cyclic AMP (cAMP)

168
Q

What is the secondary messenger during gygogenolysis?

A

Cyclic AMP (cAMP)

169
Q

During gygogenolysis, what causes the cellular response?

A

The accumulation of cAMP

170
Q

What does the accumulation of cAMP lead to as the final step of gygogenolysis?

A

Causes a molecular cascade that eventually results in the release of a glucose unit from the glycogen

BIOL*1090 (15 decks)

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