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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
Q

Membrane lipids of eukaryotes and eubacteria

A

Consists of phospholipids that have fatty acid chains ester linked to D-glycerol

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26
Q

Membrane lipids of archaea

A

Consist of branched isoprene chains (instead of fatty acids) ether (instead of ester) linked to L-glycerol (instead of D-glycerol)

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27
Q

Polypeptide chains usually cross over as…

A

A-Helices

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28
Q

Where are pores common in bilayers

A

Common in outer membranes of gram negative bacteria and endosymbiont-derived organelles

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29
Q

Can cells restrict the movement of proteins within the membrane

A

Yes

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30
Q

What functions does the rough ER provide

A

Synthesis of proteins for
- export
- insertion into membranes
- lysosomes

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31
Q

What function does the Golgi body provide

A

Collection, packaging, and distribution

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32
Q

What is membrane assembly with the role of ER

A

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

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33
Q

What is membrane assembly with the role of Golgi

A

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)

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34
Q

What makes the composition of membrane leaflets asymmetrical

A

PE, PI, and PS are on the non-cytosolic side only

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35
Q

What does PS on the outer membrane indicate

A

The cell is going to die

36
Q

What is the best understood plasma membrane

A

Red blood cells

37
Q

What substances require movement in/out of cells

A

Ions, wastes, gases, nutrients

38
Q

What are the three ways substances can enter cell

A
  • 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
Q

How does solubility work

A

Dissolved solutes spread out (high entropy) in their volume to create equal concentration amongst all locations

40
Q

When is there no NET flux

A

When the dissolved solutes have spread out evenly enough to create even concentrations across the entire volume of solution

41
Q

If the solute cannot cross the membrane, what happens to an unevenly concentrated volume

A

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
Q

How does NET flux work?

A

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
Q

What is osmosis

A

The movement of water in cells based on concentration of solutes

44
Q

What are osmotically active particles

A

Solutes

45
Q

What is the water concentration of intracellular and extracellular fluids

A

Isotonic - have an even level of water to solute (no water movement)

46
Q

What happens to animal cells when they become hypertonic

A

The shrivel up

47
Q

What happens to animal cells when they become hypotonic

A

They inflate, sometimes bursting

48
Q

What happens to a plant cell when it becomes hypertonic

A

Same as animal, it shrinks and shrivels

49
Q

What happens to a plant cell when it becomes hypotonic

A

It is lysed - means the membrane is broken down due to osmotic properties

50
Q

What are osmoconformers

A

Used by marine animals to adjust their inner salt concentrations to match sea water (so they dont shrivel up and die)

51
Q

What are osmoregulators

A

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
Q

What is turgor

A

Most plants are hyper-osmotic to their environment - water is pulled into cells and pushes the membrane outward to cell wall

53
Q

What molecules can pass DIRECTLY through membranes

A
  • small non-polar molecules
  • small uncharged or polar molecules
  • larger uncharged or polar molecules
  • ions
54
Q

Carrier protein and channel protein similarities

A

Passageways for particular molecules or classes of molecules - most are multipass proteins

55
Q

Carrier protein and channel protein differences

A
  • 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
Q

Functions of ion channels

A

When open, allows movement of Na+, Ca+, Cl- and K+ DOWN their gradients (like sodium-potassium pump)

57
Q

Why are channels critical

A
  • regulation in cell volume
  • formation and propagation of nerve impulses
  • secretion of substances into extracellular space
  • muscle contraction
58
Q

Ion channel features

A
  • 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
Q

Chemical gradient

A

Concentration inside vs outside

60
Q

Electrical gradient

A

Whether attracted or repulsed across gradients (based on same/opposing charges)

61
Q

What makes ion channels selective

A

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
Q

How does a voltage gated channel work

A

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
Q

How does an extracellular ligand-gated channel work

A

Similar to binding sites, small enzymes bind to sites on the channel outside the cytosol and opens the arms of the channel

64
Q

How does an intracellular ligand-gated channel work

A

Similar to binding sites, small enzymes bind to sites on the channel inside the cytosol and open the arms of the channel

65
Q

How does a mechanically gated channel work

A

Two arms on the outer membrane pull apart to open the channel and allow flow to the inner cytosolic membrane

66
Q

What type of diffusion do carrier proteins mediate

A

Facilitated diffusion

67
Q

How does the facilitated diffusion of carrier proteins work

A

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
Q

In carrier proteins, do solutes move up or down the gradient

A

Down

69
Q

As solutes move down the concentration gradient in carrier proteins, what specific diffusion is mediated

A

Passive facilitated diffusion

70
Q

What is GLUT1

A

A glucose transporter in mammalian cells that will move glucose but not fructose, more specifically D-glucose but NOT L-glucose

71
Q

What are the features of membrane carrier proteins

A
  • Specificity
  • Facilitates diffusion (passive)
  • Saturable
  • Can be inhibited/blocked by substances to stop the function when needed (controllable)
72
Q

What is active transport

A

The type of transport against the gradient, that requires energy to be successfully completed

73
Q

What are examples of energy used in active transport

A

ATP hydrolysis, light absorption, movement of electrons

74
Q

What is the first pump to be discovered in mammalian cells

A

The sodium-potassium ATPase
- in nerve cells of a crab

75
Q

What is the function of sodium-potassium ATPase

A

Moves Na+ out and K+ in, with the help of ATP hydrolysis for energy (moves 3 Na+ out for every 2 K+)

76
Q

What is the signifigance of Na-K ATPase

A
  • 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
Q

What pump is found in muscle cells of animals

A

Ca2+ -ATPase

78
Q

What pump is found in parietal cells lining the stomach

A

H+/K+ ATPase (proton pump)

79
Q

What is symport

A

When two molecules move in the same direction across the membrane in facilitated diffusion

80
Q

What is antiport

A

When two molecules move in opposing directions across the membrane in facilitated diffusion

81
Q

What symport tactic is used in epithelial cells of the intestines

A

Glucose/Na+ symport

82
Q

What are the features of coupled transport

A

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
Q

Do different types of membranes (lysosomal, plasma, mitochondrial, etc.) have different types of channels and carriers

A

Yes, each membrane has its own specific set of channels and carriers based on the function required

84
Q

Transporters are proteins encoded by _____

A

Genes

85
Q

How do the transporters on membranes vary type to type

A
  • 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
Q

What is the term for ion channel diseases

A

Channelopathies

Biol 130 (5 decks)

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