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Biochem > Ch. 8: Biological Membranes > Flashcards

Ch. 8: Biological Membranes Flashcards

1
Q

char: cell (plasma) membrane

A

a semipermeable phospholipid bilayer

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2
Q

why is “a semipermeable phospholipid bilayer” such an apt description of the cell/plasma membrane? + diagram

A

this describes both the FUNCTION and STRUCTURE of the cell membrane: as a semipermeable barrier, it chooses which particles can enter and leave the cell at any point in time

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3
Q

what is the selectivity of the cell membrane mediated by? (2)

A
  1. the various channels and carriers that poke holes in the membrane
  2. the membrane itself
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4
Q

what type of compounds enter the cell membrane easily? what type of a harder time? why?

A

cross easily: fat-soluble compounds

alternative entry: larger and water-soluble compounds

bc it is composed primarily of 2 layers of phospholipids

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5
Q

defn: fluid mosaic model

A

the theory that underlies the structure and function of the cell membrane

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6
Q

what other compounds compose the phospholipid bilayer?

A
  1. proteins
  2. distinct signaling areas within lipid rafts
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7
Q

what is a glycoprotein coat composed of?

A

carbohydrates associated with membrane-bound proteins

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8
Q

do the cell walls of plants, bacteria, and fungi contain higher or lower levels of carbohydrates?

A

higher

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9
Q

func (5): cell membrane

A
  1. to protect the interior of the cell from the external environment
  2. selectively regulate traffic into and out of the cell
  3. involved in both intracellular and intercellular communication and transport
  4. contain proteins embedded within the lipid bilayer that act as cellular receptors during signal transduction and play an important role in regulating and maintaining overall cellular activity
  5. a stable semisolid barrier between the cytoplasm and the environment, but is in a constant state of flux molecularly
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10
Q

how do phospholipids act in the cell membrane?

A

move rapidly in the plane of the membrane through simple diffusion

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11
Q

defn: lipid rafts

A

collections of similar lipids with or without associated proteins that serve as attachment points for other biomolecules and often serve roles in signaling

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12
Q

how do lipid rafts and proteins move within the cell membrane? (2)

A
  1. can both travel within the plane of the membrane, but more slowly than phospholipids
  2. lipids can move between the membrane layers, but is energetically unfavorable because the polar head group of the phospholipid must be forced through the nonpolar tail region in the membrane interior
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13
Q

defn + func: flippases

A

specialized enzymes

assist in the transition or “flip” between layers

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14
Q

how is the concentration of various membrane proteins mediated? (3)

how is the number of specific cellular receptors on the surface mediated? (1)

A

membrane proteins:
1. gene regulation
2. endocytotic activity
3. protein insertion

cellular receptors:
1. many cell, esp. those involved in biosignaling processes

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15
Q

what is the primary component of the cell membrane?

A

lipids!

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16
Q

what 4 types of lipids are involved in the cell membrane?

A
  1. a large number of phospholipids
  2. very few free fatty acids
  3. steroid molecules and cholesterol
  4. waxes
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17
Q

what is the main function of steroid molecules and cholesterol and waxes in the cell membrane? (together and individual)

A

help to maintain the structural integrity of the cell

steroid molecules and cholesterol: lend fluidity to the membrane

waxes: provide membrane stability

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18
Q

defn: fatty acids

A

carboxylic acids that contain a hydrocarbon chain and terminal carboxyl group

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19
Q

defn + aka + struct: triacylglycerols

A

aka: triglycerides

storage lipids involved in human metabolic processes

structure: contain 3 fatty acid chains esterified

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20
Q

char (3) + impact of char on plasma membrane: unsaturated fatty acids

A
  1. “healthier”
  2. tend to have one or more double bonds
  3. exist in liquid form at room temperature

impart fluidity to the plasma membrane

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21
Q

do humans make unsaturated fatty acids? do they come from food?

A

humans can only synthesize a few

the rest come from essential fatty acids in the diet that are transported as triacylglycerols from the intestine inside chylomicrons

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22
Q

what are the two important essential fatty acids for humans?

A
  1. alpha-linolenic acid
  2. linoleic acid
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23
Q

char (4) + impact on membrane: saturated fatty acids

A
  1. the main components of animal fats
  2. tend to exist as solids at room temperature
  3. found in processed foods
  4. less healthy

decrease overall membrane fluidity

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24
Q

how is a glycerophospholipid formed + aka?

A

aka: phospholipid

formed by substituting one of the fatty acid chains of triacylglycerol with a phosphate group, a polar head group joins the nonpolar tails

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25
Q

what do phospholipids spontaneously assemble into and why? (2) + defn for these 2 things

A
  1. micelles (small monolayer vesicles)
  2. liposomes (bilayered vesicles)

due to hydrophobic interactions

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26
Q

func (4): glycerophospholipid

A
  1. used for membrane synthesis
  2. can produce a hydrophilic surface layer on lipoproteins such as very-low-density lipoprotein (VLDL), a lipid transporter
  3. primary component of cell membranes
  4. second messengers in signal transduction
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27
Q

func: phosphate group of a phospholipid + ex (2)

A

provides an attachment point for water-soluble groups

ex:
choline (aka phosphatidylcholine aka lecithin)

inositol (phosphatidylinositol)

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28
Q

diagram: triacylglycerol vs. glycerophospholipid

A
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29
Q

char (3) + func: sphingolipids

A

func: important constituents of cell membranes

char: 1. do not contain glycerol
2. similar in structure to glycerophospholipids
3. contain a hydrophilic region and two fatty acid-derived hydrophobic tails

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30
Q

how are various classes of sphingolipids differentiated? + diagram

A

mostly in the identify of their hydrophilic regions

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31
Q

4 classes of sphingolipids and their hydrophilic groups

A
  1. ceramide
  2. sphingomyelins
  3. cerebrosides
  4. gangliosides
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32
Q

func (2): cholesterol

A
  1. regulates membrane fluidity
  2. necessary in the synthesis of all steroids
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33
Q

char (1): cholesterol

A

similar structure to that of phospholipids bc it contains a hydrophilic and a hydrophobic region

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34
Q

func (3): cholesterol

A
  1. stabilizes adjacent phospholipids in the membrane (due to interactions with the hydrophilic and hydrophobic regions of the phospholipid bilayer)
  2. occupies space between adjacent phospholipids(preventing formation of crystal structures in the membrane, and increasing fluidity at lower temps)
  3. at high temps: limits movement of phospholipids within the bilayer, thus decreasing fluidity and hold the membrane intact
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35
Q

ratio of cholesterol to phospholipid + effect

A

by mass: cholesterol composes about 20% of the cell membrane

by mole fraction: cholesterol is about half of the cell membrane

this large ratio of cholesterol to phospholipid ensures that the membrane remains fluid

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36
Q

defn + char (4): waxes

A

a class of lipids

  1. extremely hydrophobic
  2. rarely found in the cell membranes of animals, sometimes found in plant cell membranes
  3. composed of a long-chain fatty acid and a long-chain alcohol
  4. high melting point
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37
Q

func (2): waxes

A
  1. provide stability and rigidity within the nonpolar tail region (when present in the cell membrane)
  2. extracellular function in protection or waterproofing
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38
Q

what are the 3 types of membrane proteins that the fluid mosaic model accounts for? + diagram

A
  1. transmembrane proteins
  2. embedded proteins
  3. membrane-associated (peripheral) proteins
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39
Q

relationship to membrane: transmembrane proteins

A

pass completely through the lipid bilayer

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40
Q

relationship to membrane: embedded proteins

A

associated with only the interior (cytoplasmic) or exterior (extracellular) surface of the cell membrane

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41
Q

defn + reason for name: integral proteins

A

transmembrane membrane proteins and embedded proteins together

called this because of their association with the interior of the plasma membrane

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42
Q

what assists the integral proteins?

A

one or more membrane-associated domains that are partially hydrophobic

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43
Q

relationship to membrane: membrane-associated peripheral proteins

A

bound through electrostatic interactions with the lipid bilayer, especially at lipid rafts, or to other transmembrane or embedded proteins, like the G proteins found in G protein-coupled recetors

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44
Q

what 3 things are typically considered transmembrane proteins?

A
  1. transporters
  2. channels
  3. receptors
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45
Q

char (2): carbohydrates

A
  1. generally attached to protein molecules on the extracellular surface of cells
  2. generally hydrophilic
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46
Q

what is the impact of carbohydrates hydrophilicity?

A

interactions between glycoproteins and water can form a coat around the cell

47
Q

func(1): carbohydrates

A

can act as signaling and recognition molecules

48
Q

how are membrane carbohydrates and membrane proteins taken advantage of?

A

our immune systems and some pathogens do this to target particular cells

49
Q

func (2) + char (2): membrane receptors

A

char: 1. tend to be transmembrane proteins
2. there are some that are carbohydrates or lipids, especially in viruses

func: 1. activate or deactivate some of the transported for facilitated diffusion and active transport
2. biosignaling

50
Q

why are cell-cell junctions formed? what are they typically formed of? what is the function of these?

A

cells within tissues can form a cohesive layer via intercellular junctions

generally comprised of cell adhesion molecules (CAM)

func: provide direct pathways of communication between neighboring cells or between cells and the extracellular matrix

51
Q

defn: cell adhesion molecules (CAM)

A

proteins that allow cells to recognize each other and contribute to proper cell differentiation and development

52
Q

what are the 3 types of cell-cell junctions?

A
  1. gap junctions
  2. tight junctions
  3. desmosomes
53
Q

func + char + aka + diagram: gap junctions

A

func: 1. allow for direct cell-cell communication
2. permit movement of water and some solutes directly between cells
3. do not generally transfer proteins

aka: connexons

  1. often found in small bunches together
  2. formed by the alignment and interaction of pores composed of 6 molecules of connexin
54
Q

func (2) + char (2): tight junctions

A

func: 1. prevent solutes from leaking into the space between cells via a paracellular route
2. a physical link between the cells as they form a single layer of tissue

char: 1. found in epithelial cells
2. must form a continuous band around the cell

55
Q

what happens when tight junctions limit permeability significantly enough?

A

to create a transepithelial voltage difference based on differing concentrations of ions on either side of the epithelium

56
Q

why must tight junctions form a continuous band around the cell?

A

this is necessary for them to be effective, else fluid could leak through spaces between tight junctions

57
Q

func + how are they formed + where are they found: desmosomes

A

func: bind adjacent cells by anchoring to their cytoskeletons

formed by interactions between transmembrane proteins associated with intermediate filaments inside adjacent cells

primarily found at the interface between two layers of epithelial tissue

58
Q

func: hemidesmosomes

A

similar function to desmosomes but their main function is to attach epithelial cells to underlying structures, especially the basement membrane

59
Q

summary: selectivity of different substances into and out of the cell via the cell membrane

A

transport of small nonpolar molecules –> rapid through cell membrane via diffusion

ions and larger molecules –> more specialized transport processes

60
Q

summary of different membrane traffic processes differ (2)

A
  1. active or passive
  2. driven by concentration gradients or intracellular energy stores
61
Q

what is ALL transmembrane movement driven by? what does this tell us?

A

concentration gradients

the gradient will tell us whether this process will be passive or active

62
Q

what are transport processes classified as active or passive depending on?

A

their thermodynamics

63
Q

char (thermodynamics): passive vs. active transport

A

PASSIVE = spontaneous process that do not require energy

ACTIVE = nonspontaneous and require energy

64
Q

how are passive and active transport affected by temperature?

A

PASSIVE = generally increase in rate as temperature increases

ACTIVE = may or may not be affected by temperature, depending on the enthalpy of the process

65
Q

what is the primary thermodynamic motivator in most passive transport?

A

an increase in entropy

66
Q

defn: passive transport processes

A

those that do not require intracellular energy stores but rather utilize the concentration gradient to supply the energy for particles to move

67
Q

defn + char (3): simple diffusion

A

substrates move down their concentration gradient directly across the membrane

char: 1. the most basic of all membrane traffic processes
2. only particles that are freely permeable to the membrane are able to undergo simple diffusion
3. there is potential energy in a chemical gradient, some of which is dissipated as the gradient is utilized during simple diffusion

68
Q

analogy: energy used in simple diffusion

A

there is potential energy in the ball when it sits at the top of the hill

as the ball spontaneously rolls down the hill, and some of the energy is dissipated

69
Q

defn: osmosis

A

a specific kind of simple diffusion with water – water will move from a region of lower solute concentration to one of higher solute concentration

aka: water will move from a region of higher WATER concentration (more DILUTE solution) down a gradient to a region of LOWER water concentration (more CONCENTRATED solution)

70
Q

when is osmosis most important? + what happens in these cases?

A

when the solute itself is impermeable to the membrane

in this case: water will move to try to bring solute concentrations to equimolarity

71
Q

defn + effect: hypotonic solution

A

defn: if the concentration of solutes INSIDE the cell is HIGHER than the surrounding solution

effect: such a solution will cause a cell to swell as water rushes in, sometimes to the point of bursting (lysing)

72
Q

defn + effect: hypertonic solution

A

defn: a solution that is more concentrated than the cell

effect: water will move out of the cell

73
Q

defn + effect: isotonic solution

A

defn: if the solutions inside and outside are equimolar

effect: does not prevent movement, rather prevents the NET movement of particles

74
Q

diagram: osmosis

A
75
Q

mnemonic: hypotonic

A

water flows into a cell placed in hypOtonic solution, so imagine the cell swelling to form a giant letter O

76
Q

defn + char: osmotic pressure

A

char: one method of quantifying the driving force behind osmosis

char: 1. colligative property

77
Q

defn: colligative property

A

a physical property of solutions that is dependent on the concentration of dissolved particles but not on the chemical identity of those dissolved particles

78
Q

eqn: osmotic pressure

A

where M = molarity of the solution
R = ideal gas constant
T = absolute temperature (in kelvins)
i = the van’t Hoff factor

79
Q

defn + ex: i (van’t Hoff factor)

A

the number of particles obtained from the molecule when in solution

ex: glucose remains one intact molecule, so iglucose = 1, sodium chloride becomes 2 ions (Na+ and Cl) so inacl = 2

80
Q

does osmotic pressure depend on the identity of the particles in solution?

A

no, just the presence and number of particles in solution

81
Q

what is the relationship between osmotic pressure and the cell membrane?

A

the osmotic pressure is maintained against the cell membrane, rather than the force of gravity

if the osmotic pressure created by the solutes within a cell exceeds the pressure that the cell membrane can withstand, the cell will lyse

82
Q

analogy: osmotic pressure

A

a “sucking” pressure –> drawing water into the cell in proportion to the concentration of the solutin

83
Q

unless otherwise specified, what does a semipermeable membrane refer to?

A

a membrane governed by the same permeability rules as biological membranes: small, nonpolar, lipid-soluble particles (and water) can pass through freely, while large, polar, or charged particles cannot

84
Q

defn + char: facilitated diffusion

A

simple diffusion for molecules that are impermeable to the membrane (large, polar, or charged) because the energy barrier is too high for these molecules to cross freely

classic examples involve a carrier or channel protein

85
Q

what does facilitated diffusion require?

A

integral membrane proteins to serve as transporters or channels for these substrates

86
Q

defn + analogy: carriers

A

only open to one side of the cell membrane at any given point

analogy: similar to a revolving door because the substrate binds to the transport protein (walks in), remains in the transporter during a conformational change (spins), and then finally dissociates from the substrate-binding site of the transporter (walks out)

87
Q

defn + cause + char: occluded state

A

cause: binding of the substrate molecule to the transporter protein induces a conformational change

char: brief time

defn: the carrier is not open to either side of the phospholipid bilayer

88
Q

func: channels

A

viable transporters for facilitated diffusion

89
Q

how do channels act in open conformations? can they also be in a closed conformation?

A

OPEN = channels are exposed to both sides of the cell membrane and act like a tunnel for the particles to diffuse through, thus permitting more rapid transport kinetics

can also be in a closed conformation

90
Q

result: active transport

A

results in the net movement of a solute against its concentration gradient, just like rolling a ball uphill

91
Q

does active transport require energy?

A

always, but the source varies

92
Q

how does primary active transport work?

A

uses ATP or another energy molecule to directly power the transport of molecules across a membrane

typically involves the use of a transmembrane ATPase

93
Q

how does secondary active transport work + aka

A

aka: coupled transport

uses energy to transport particles across the membrane, however there is no direct coupling to ATP hydrolysis

harnesses the energy released by one article going DOWN its electrochemical gradient to drive a different particle UP its gradient

94
Q

defn: symport vs. antiport

A

SYMPORT = when the particles flow in the same direction across the membrane

ANTIPORT = when the particles flow in opposite directions

95
Q

defn: endocytosis

A

occurs when the cell membrane invaginates and engulfs material to bring it into the cell

96
Q

why is it important that the material is encased in a vesicle in endocytosis?

A

cells will sometimes ingest toxic substances

97
Q

defn: pinocytosis

A

the endocytosis of fluids and dissolved particles

98
Q

defn: phagocytosis

A

the ingestion of large solids such as bacteria

99
Q

process: endocytosis

A
  1. substrate binding to specific receptors embedded within the plasma membrane initiates endocytosis
  2. invagination will then be initiated and carried about by vesicle-coating proteins, most notably clathrin
100
Q

defn: exocytosis

A

occurs when secretory vesicles fuse with the membrane, releasing material from inside the cell to the extracellular environment

101
Q

what 2 situations are exocytosis important in?

A
  1. the nervous system
  2. intercellular signaling
102
Q

what 2 factors lead to an electrochemical gradient between the exterior and interior of cells?

A
  1. the impermeability of the cell membrane to ions
  2. the selectivity of ion channels
103
Q

defn: membrane potential, Vm

A

the difference in electrical potential across cell membranes

104
Q

value: resting potential

A

for most cells: between -40 and -80 mV

although, the potential can rise as high as +35 mV during depolarization of the cell

105
Q

why does maintaining membrane potential require energy?

A

because ions may passively diffuse through the cell membrane over time using leak channels

106
Q

func: ion transporter or pump such as sodium-potassium pump (Na+/K+ ATPase)

A

regulates the concentration of intracellular and extracellular sodium and potassium ions

chloride ions also participate in establishing membrane potential

107
Q

func: Nernst equation

A

used to determine the membrane potential from the intra- and extracellular concentrations of the various ions

108
Q

func: Na+/K+ ATPase

A

to maintain a low concentration of sodium ions and high concentration of potassium ions intracellularly by pumping three sodium ions out for every two potassium ions pumped in

this movement of ions removes one positive charge from the intracellular space of the cell, which maintains the negative resting potential of the cell

109
Q

why are cell membranes more permeable to K+ ions than Na+ ions at rest?

A

because there are more K+ leak channels than Na+ leak channels

110
Q

how is a stable resting membrane potential maintained? (2)

A

the combination of 1. Na+/K+ ATPase activity and 2. leak channels together

111
Q

why are mitochondria referred to as the powerhouse of the cell?

A

because of their ability to produce ATP by oxidative respiration

112
Q

char (2): outer mitochondrial membrane

A
  1. highly permeable due to many large pores that allow the passage of ions and small proteins
  2. completely surrounds the inner mitochondrial membrane, with the presence of a small intermembrane space in between the two layers
113
Q

char (4): inner mitochondrial membrane

A
  1. has a much more restricted permeability compared to the outer one
  2. contains numerous infoldings (cristae) which increase the available surface area for the integral proteins associated with the membrane that are involved in the ETC and ATP synthesis
  3. encloses the mitochondrial matrix
  4. contains a high level of cardiolipin and does not contain cholesterol
114
Q

func: mitochondrial matrix

A

where the citric acid cycle produces high-energy electron carriers used in the electron transport chain

Biochem (12 decks)

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