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Biol 130 > Membranes > Flashcards

Membranes Flashcards

1
Q

In a fluid membrane, there is…

A
  • free lateral movement of phospholipids within each leaflet
  • free lateral movement of proteins, maintaining their orientations
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2
Q

Compared to plants in normal conditions, plants adapted to cold would…

A
  • a higher proportion of unsaturated fatty acids
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3
Q

Transmembrane proteins stay embedded in membranes because of…

A
  • the locations of their polar and non-polar amino acids
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4
Q

Rank the following based on their ability to diffuse through the membrane most to least readily…

CO2, glucose, ethanol, H2O, and Ca2+

A
  1. CO2
  2. H2O
  3. ethanol
  4. glucose
  5. Ca2+
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5
Q

What features distinguish membrane carrier proteins from ion channels

A

Membrane carrier proteins become saturated if the concentration of their cargo molecule is high, whereas channels allow passage of ions at very high rates as long as there is a diffusion gradient

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6
Q

Transport of glucose across apical surface of epithelial cells can be referred to as secondary active transport because…

A

It is co-transported with Na+ via symport, such that it indirectly depends on the Na+ gradient maintained by the K+/Na+ pump

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7
Q

Why don’t bacteria cells burst in hypotonic solutions

A

Bacteria cells have cell walls that prevent lysis

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8
Q

What is the function of the plasma membrane

A
  • Encloses all cell contents
  • Provide semi-permeable membrane
  • Transport solutes
  • Energy transduction
  • Respond to external signals
  • Scaffold for biochemical activities
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9
Q

Membrane Phospholipids

A

PC - Phosphadityl choline
PS - Phosphadityl serine
PE - Phosphadityl ethanolamine
PI - Phosphadityl inisitol

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10
Q

Are all membrane proteins amphipathic

A

Yes

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11
Q

Lipid bilayers are…

A
  • closed
  • no free edges
  • self sealing
  • important for cell fusion, locomotion, and budding
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12
Q

Amphiatic molecules are subject to _____ forces

A

Conlficting
- these opposing forces are solved by the formation of a bilayer

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13
Q

What is the fluid mosiac model

A

How scientists explain what the cell membrane looks and functions like

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14
Q

Lipid bilayers are made up of ____ and ____ leaflets

A

Outer and innner

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15
Q

Movement of phospholipids

A

Constantly moving, spinning in place, travelling laterally through the leaflet, and can be flipped to opposite leaflet (but rarely flop back)

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16
Q

Membrane fluidity is affected by…

A
  • temperature
  • changes in lipid composition that affect the alignment of tails
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17
Q

Tighly packed tails leads to

A

Less fluidity

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18
Q

Loosly packed tails lead to

A

More fluidity

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19
Q

Transition temperature

A

The temperature at which membrane transitions between fluid phase and gel phase
- above the Tm; membrane “melts” and lipids move more freely through the leaflet
- below Tm; membrane “gels” and tails pack together

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20
Q

With lower Tm you notice ______ fatty acids while with higher Tm you notice ______ fatty acids, and can also be affected by ______

A

Lower: altered degree of fatty acids (more double bonds)
Higher: altered length of fatty acids (longer chains)
Also affected by: amount of sterol (cholesterol) (lots of cholesterol in animal cells)

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21
Q

How does cholesterol act as a buffer

A

Inhibits phase transitions when temperature changes
- higher cholesterol at cool temps (more fluid)
- lower cholesterol at high temps (less fluid)

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22
Q

Home viscous adaptation

A

Maintaining membrane fluidity at temps low enough to cause membrane to enter gel phase by altering membrane lipid composition

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23
Q

Dealing with low temps (fluidity regulation)

A

Shorter fatty acid chain length (eg. enzymes that cut C18 to C16)

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24
Q

Increase in double bonds (fluidity regulation)

A

Decreases saturation (eg. desaturase enzymes triggered by low temps)

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25
Membrane lipids of eukaryotes and eubacteria
Consists of phospholipids that have fatty acid chains ester linked to D-glycerol
26
Membrane lipids of archaea
Consist of branched isoprene chains (instead of fatty acids) ether (instead of ester) linked to L-glycerol (instead of D-glycerol)
27
Polypeptide chains usually cross over as...
A-Helices
28
Where are pores common in bilayers
Common in outer membranes of gram negative bacteria and endosymbiont-derived organelles
29
Can cells restrict the movement of proteins within the membrane
Yes
30
What functions does the rough ER provide
Synthesis of proteins for - export - insertion into membranes - lysosomes
31
What function does the Golgi body provide
Collection, packaging, and distribution
32
What is membrane assembly with the role of ER
The rough ER takes free fatty acids in the cytosol and catalyzes them (using enzymes bound to the cytosolic side of ER) to create new phospholipids added to the cytosolic side, and scramblases transfer random phospholipids to the non-cytosolic side
33
What is membrane assembly with the role of Golgi
Membranes with evenly distributed phospholipids arrive from ER, flipases move PS and PE to cytosolic leaflet, and due to this action the phospholipids are no longer symmetrically distributed (however from here on the symmetry is maintained)
34
What makes the composition of membrane leaflets asymmetrical
PE, PI, and PS are on the non-cytosolic side only
35
What does PS on the outer membrane indicate
The cell is going to die
36
What is the best understood plasma membrane
Red blood cells
37
What substances require movement in/out of cells
Ions, wastes, gases, nutrients
38
What are the three ways substances can enter cell
- pass directly through the bilayer - pass with the help of membrane proteins by channels or carriers - being engulfed by the cell, avoiding passing through the membrane
39
How does solubility work
Dissolved solutes spread out (high entropy) in their volume to create equal concentration amongst all locations
40
When is there no NET flux
When the dissolved solutes have spread out evenly enough to create even concentrations across the entire volume of solution
41
If the solute cannot cross the membrane, what happens to an unevenly concentrated volume
The water volume will increase on the side containing more solute, and will decrease on the side containing less solute - concentrations become equal on both sides, making volume unequal
42
How does NET flux work?
NET flux of water moves into the chamber with more water (flux is the forward movement of water, not the reduction) - water moves equally across both sides once at equilibrium
43
What is osmosis
The movement of water in cells based on concentration of solutes
44
What are osmotically active particles
Solutes
45
What is the water concentration of intracellular and extracellular fluids
Isotonic - have an even level of water to solute (no water movement)
46
What happens to animal cells when they become hypertonic
The shrivel up
47
What happens to animal cells when they become hypotonic
They inflate, sometimes bursting
48
What happens to a plant cell when it becomes hypertonic
Same as animal, it shrinks and shrivels
49
What happens to a plant cell when it becomes hypotonic
It is lysed - means the membrane is broken down due to osmotic properties
50
What are osmoconformers
Used by marine animals to adjust their inner salt concentrations to match sea water (so they dont shrivel up and die)
51
What are osmoregulators
Some single-celled eukaryotes have contractile vacuoles that periodically pump out water Terrestrial organisms carefully regulate the osmolarity of a fluid they circulate through their bodies such that it is so iso-osmotic with their cytoplasm
52
What is turgor
Most plants are hyper-osmotic to their environment - water is pulled into cells and pushes the membrane outward to cell wall
53
What molecules can pass DIRECTLY through membranes
- small non-polar molecules - small uncharged or polar molecules - larger uncharged or polar molecules - ions
54
Carrier protein and channel protein similarities
Passageways for particular molecules or classes of molecules - most are multipass proteins
55
Carrier protein and channel protein differences
- Channels detect size/charge, as long as the channel is open the molecule with that size/charge can pass no matter how big/small - Carriers require molecules that fit a particular binding site, therefore must be a specific size/shape, and only one molecule at a time
56
Functions of ion channels
When open, allows movement of Na+, Ca+, Cl- and K+ DOWN their gradients (like sodium-potassium pump)
57
Why are channels critical
- regulation in cell volume - formation and propagation of nerve impulses - secretion of substances into extracellular space - muscle contraction
58
Ion channel features
- discriminate on both charge and size - highly selective - much faster than carriers - bidirectional - ion flux determined by both concentration and electrical gradients: electrochemical gradient
59
Chemical gradient
Concentration inside vs outside
60
Electrical gradient
Whether attracted or repulsed across gradients (based on same/opposing charges)
61
What makes ion channels selective
The aqueous pore at the bottom of the channel has a selectivity filter - once the channel opens the select ion can enter and trigger the selectivity filter, allowing it to be filtered through
62
How does a voltage gated channel work
Opposite charges on either side of the membrane (eg. positive intra and negative outer) pull the "arms" of the protein apart, opening the channel
63
How does an extracellular ligand-gated channel work
Similar to binding sites, small enzymes bind to sites on the channel outside the cytosol and opens the arms of the channel
64
How does an intracellular ligand-gated channel work
Similar to binding sites, small enzymes bind to sites on the channel inside the cytosol and open the arms of the channel
65
How does a mechanically gated channel work
Two arms on the outer membrane pull apart to open the channel and allow flow to the inner cytosolic membrane
66
What type of diffusion do carrier proteins mediate
Facilitated diffusion
67
How does the facilitated diffusion of carrier proteins work
Binding sites on the protein match solutes intended to be moved across, so the binding of the solute to the site temporarily changes the shape of the protein, allowing the solute to move through, then repositioning to accept next matching solute
68
In carrier proteins, do solutes move up or down the gradient
Down
69
As solutes move down the concentration gradient in carrier proteins, what specific diffusion is mediated
Passive facilitated diffusion
70
What is GLUT1
A glucose transporter in mammalian cells that will move glucose but not fructose, more specifically D-glucose but NOT L-glucose
71
What are the features of membrane carrier proteins
- Specificity - Facilitates diffusion (passive) - Saturable - Can be inhibited/blocked by substances to stop the function when needed (controllable)
72
What is active transport
The type of transport against the gradient, that requires energy to be successfully completed
73
What are examples of energy used in active transport
ATP hydrolysis, light absorption, movement of electrons
74
What is the first pump to be discovered in mammalian cells
The sodium-potassium ATPase - in nerve cells of a crab
75
What is the function of sodium-potassium ATPase
Moves Na+ out and K+ in, with the help of ATP hydrolysis for energy (moves 3 Na+ out for every 2 K+)
76
What is the signifigance of Na-K ATPase
- both a membrane protein AND an enzyme - present in ALL animal cells - a major contributor to basal metabolic rate - helps maintain Na+ gradient - uses this pump to facilitate movement of other particles (like glucose or amino acids)
77
What pump is found in muscle cells of animals
Ca2+ -ATPase
78
What pump is found in parietal cells lining the stomach
H+/K+ ATPase (proton pump)
79
What is symport
When two molecules move in the same direction across the membrane in facilitated diffusion
80
What is antiport
When two molecules move in opposing directions across the membrane in facilitated diffusion
81
What symport tactic is used in epithelial cells of the intestines
Glucose/Na+ symport
82
What are the features of coupled transport
Membrane carrier protein uses the driving force of an ion moving down its gradient to facilitate the movement of a small molecule/ion down or even up its gradient Gradient for the ion is created by active transport Coupled-mediated transport is also known as indirect active transport (secondary)
83
Do different types of membranes (lysosomal, plasma, mitochondrial, etc.) have different types of channels and carriers
Yes, each membrane has its own specific set of channels and carriers based on the function required
84
Transporters are proteins encoded by _____
Genes
85
How do the transporters on membranes vary type to type
- Dependant on the genes present in the organism - Whether or not those genes are expressed in the cell in that membrane at that given point
86
What is the term for ion channel diseases
Channelopathies

Biol 130 (5 decks)

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