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AGRC1041 > membrane transport 1,2&3 > Flashcards

membrane transport 1,2&3 Flashcards

1
Q

plasma membrane is a semi fluid

A

phospholipid bilayer

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2
Q

in plasma membrane describe the middle and then the inner/ outer surfaces

A
  • hydrophilic heads at the inner and outer surfaces
  • hydrophobic tails in the middle
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3
Q

integral proteins

peripheral proteins

A

embedded in the bilayer

bound to inner or outer membrane surface

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4
Q

functions of proteins of the plasma membrane

A
  • transport across the membrane
  • receptors involved in cell signalling
  • enzymes that catalyze reactions
  • anchoring of cells to each other and substrates
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5
Q

is the lipid bilayer miscible with the extracellular fluid or intracellular fluid (cytoplasm)

A

no; acts as a barrier against movement of water and water-soluble substances between the extracellular environment and the cytoplasm of the cell

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6
Q

what substances are able to diffuse directly across the lipid bilayer

A

lipid-soluble substances

examples:
- gases: O2, N2, CO2
- small, uncharged polar molecules: alcohol

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7
Q

plasma membrane is ____ permeable

A

selectively

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8
Q

channel proteins

A

water filled tunnel through the protein, allow free movement of water, some ions and molecules

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9
Q

carrier proteins

A

bind with ions or molecules, conformational change in protein moves ion/molecule to other side of membrane

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10
Q

diffusion and facilitated diffusion are examples of _____ transport

A

passive

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11
Q

what causes molecules and ions to diffuse

A

random motion; termed heat aka brownian motion

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12
Q

random motion will cause molecule and ions to diffuse across membrane until

A

equilibrium is reached

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13
Q

in drug delivery, what is important in diffusion in a particular direction

A

the net rate

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14
Q

what factors affect the net rate of diffusion

A

Fick’s law of diffusion:
- concentration gradient
- permeability of membrane to substance
- surface area of membrane
- molecular weight of substance
- distance across which diffusion must occur

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15
Q

concentration gradient

A

chemical driving force

ex rate at which Na+ diffuses into the cell is proportional to concentration of Na+ outside of cell

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16
Q

permeability of membrane

A
  • phospholipid bilayer
  • the more lipid soluble the molecule (fewer polar or ionized groups) the more easily it will traverse the membrane
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17
Q

surface area of membrane: the greater the SA of membrane the

A

greater the number of molecules that are able to hit the membrane and pass through

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18
Q

why is SA a limiting factor of cell size

A

as animals/ cells get larger, their SA:V ratio gets smaller

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19
Q

do larger or smaller molecules move slower

A

larger move slower

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20
Q

do larger or smaller molecules find it harder to pass through membrane protein channels

A

larger

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21
Q

an _____ exists across a membrane when one side is relatively more pos and one more neg

A

electrical potential

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22
Q

membrane electrical potential

A

electrical driving force

charged ions will move across membrane to achieve state of equilibrium

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23
Q

equilibrium potential

A

state of balance between movement of ions due to chemical driving force and electrical driving force: so when the electrical force is equal to but opposite the direction of chemical force

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24
Q

the electrical potential difference that will balance a given concentration difference of univalent ions can be determined by the

A

nernst equation

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25
Q

pressure different across a membrane

A

can also cause the movement of molecules from one side of a membrane to another

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26
Q

pressure

A

is the sum of all the forces of the different molecules striking a membrane

generally, the pressure is greatest on the side with the greater number of molecules

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27
Q

pressure gradient force

A

greater energy available to cause net movement of
molecules from side of high pressure to low pressure

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28
Q

osmosis: if two aqueous solutions are separated by a membrane that allows only water molecules to pass
water will move into the

A

most concentrated solution

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29
Q

tonicity

A

refers to the strength of a solution in relationship
to osmosis

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30
Q

Isotonic solution

A

solute concentrations are the same on both sides of the cell membrane

cells stay same size

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31
Q

hypotonic solution

A

solution has a lower concentration of solute (more water) than the cell

water enters the cell

the cell swells (turgor) & may burst (lysis)

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32
Q

Hypertonic solution:

A

solution has a higher percentage of solute (less water)
than the cell

water leaves the cell

the cell shrinks

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33
Q

red blood cells in less than 0.9% NaCl will

A

swell: hypotonic

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34
Q

red blood cells in a solution with a concentration higher
than 0.9% NaCl

A

will shrink; hypertonic

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35
Q

The movement of water from a hypotonic to a hypertonic solution causes an increase in ______ in the hypertonic compartment

eventually, this hydrostatic pressure will equal the
osmotic pressure, and the movement of water will ___

A

hydrostatic pressure
stop

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36
Q

most abundant substance to diffuse across cellular membranes

A

water

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37
Q

Typically, the cytoplasm of cells has a higher
concentration of ____ than extracellular fluid

which means it has higher _____

A

solutes

osmolarity

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38
Q

cells control their intracellular osmolarity by

A

pumping out ions

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39
Q

diffusion through cell membranes occurs via 2 processes:

A

1) simple diffusion: directly through lipid bilayer, CHANNEL proteins
2) facilitated diffusion; through specific CARRIER protein

40
Q

what molecules can use simple diffusion to cross membrane

A

lipid soluble such as CO2, O2, steroids and alcohols

or water soluble / water through hydrophilic channel proteins

41
Q

channel proteins

A
  • integral protein
  • have central canal/ pore that is hydrophilic
  • selectively permeable by diameter of pore (size), electrical charge or protein structure
  • opened or closed by gates
42
Q

aquaporins

A

type of channel protein that allows passage of water

43
Q

potassium channel (simple diffusion, channel protein)

what passes and in which direction

how many protein subunits does it consist of

what exists at the surface of the pore/ function?

what is in lined with/ function

A
  • permits passage of K+ out of the cell
  • consists of 4 protein subunits surrounding a central pore
  • at the surface of the pore are pore loops: selectivity filter
  • lined with carbonyl oxygens: interact with hydrated K+, strip water & allow K+ to pass through, Na+ too small to interact with carbonyl O2
44
Q

sodium channel (simple diffusion, channel proteins)

what are inner surfaces lined with, what is their function

what is too large to fit through

A
  • inner surfaces lined with amino acids that are strongly negatively charged, pull small Na+ away from water molecules
  • hydrated K+
    ions too large to fit through channel
45
Q

gating of protein channels controls

A

permeability of channels

46
Q

_____ of channel proteins opens or seals pore (to open or close gates)

A

conformational change

***the protein doesn’t go through conformational change like carrier proteins tho, I feel like this is confusing but this is just talking about the opening/closing of gates

47
Q

opening and closing of gates in channel proteins is controlled by what 2 mechanisms

A

voltage gating

ligand (chemical) gating

48
Q

describe voltage gating of protein channels

A
  • Molecular conformation of the gate, or its chemical bonds, responds to the electrical potential across cell membrane
  • Cells in general have a small net excess of negative ions clustered beneath the plasma membrane
  • If the cell is depolarised, differential between inside & outside of cell reduced
  • gate opens & ions enter
49
Q

examples of voltage gating

A
  • sodium & potassium channels
  • neurons & muscle cells
  • calcium channels
50
Q

describe ligand gating of protein channels

A
  • Gates are opened by the binding of another molecule
  • causes a change in conformation or chemical bonds
  • gate opens
51
Q

example of ligand gating protein channels

A

neurotransmitter channels in nerve & muscle cells

52
Q

what facilitates diffusion in facilitated diffusion

A

carrier proteins; specific for particular molecules,

still down a concentration gradient!!

53
Q

how many glucose carrier proteins are identified

A

5

54
Q

glucose transporter 4 is a type of glucose carrier protein, what is it activated by

A

insulin

increases rate of diffusion by 10-20x

55
Q

in simple diffusion the rate is proportional to the concentration gradient

in facilitated diffusion, it is different in 2 key ways; the rate is proportional to:

A

1) the number of carrier proteins available (saturation of carrier proteins= vmax)

2) similar molecules can compete for binding w the carrier protein

56
Q

facilitated diffusion uses _____ proteins

A

CARRIER!!!!

not channel (thats simple diffusion)

57
Q

active transport

A

when molecules or ions moving against concentration gradient

requires energy

58
Q

active transport: where do K+ and Na+ have high concentrations

A
  • K+: high concentrations intracellularly
  • Na+: high concentrations extracellularly
59
Q

active transport requires ____ proteins

A

carrier

60
Q

two types of active transport

A

1) primary: energy derived from breakdown of ATP,

2) energy that stored as ionic concentration gradient derived originally from primary active transport

61
Q

describe ex of primary and secondary active transport in regards to NA+-K+ pump

A
  • Na+-K+ pump uses ATP to drive Na+ out of the cell (primary)
  • Creates a strong chemical driving force
    to move Na+ back into the cell
  • As Na+ moves down its concentration
    gradient, it may take another molecule
    with it (the amino acid glutamine) (secondary)
62
Q

primary active transport; sodium potassium pump

what direction does it pump

A

pumps Na+ out of the cell & simultaneously pumps K+
into the cell, both against their concentration gradients

63
Q

what is sodium-potassium pump responsible for

A
  • responsible for maintaining concentration gradients & so also negative electrical voltage inside the cell
  • also responsible for transmitting nerve impulses
64
Q

sodium potassium pump: what part of the carrier protein has receptor sites for binding Na+, and how many does it have

A

inside of the cell
has 3 receptor sites for binding Na+

65
Q

sodium potassium pump: what part of the carrier protein has receptor sites for binding K+, and how many does it have

A

outside of the cell
has 2 receptor sites for binding K+

66
Q

sodium potassium pump: when Na+ binds intracellularly, what happens

A
  • ATPase enzyme cleaves
    adenosine triphosphate (ATP)
  • generates adenosine diphosphate (ADP) & a single
    phosphate group, releasing energy
  • released energy causes conformational change
  • Na+ released extracellularly
67
Q

sodium- potassium pump: what happens after Na+ is released extracellularly

A
  • extracellular K+ then binds
  • triggers the release of the phosphate group
  • causes conformational change
  • K+ released intracellularly
68
Q

all the steps of sodium potassium pump

A
  • Na+ binds intracellularly
  • ATPase enzyme cleaves
    adenosine triphosphate (ATP)
  • generates adenosine diphosphate (ADP) & a single
    phosphate group, releasing energy
  • released energy causes conformational change
  • Na+ released extracellularly
  • extracellular K+ then binds
  • triggers the release of the phosphate group
  • causes conformational change
  • K+ released intracellularly
69
Q

in nerve cells ___% of cells energy is used to drive sodium potassium pump

A

70

70
Q

sodium potassium pump has important role in controlling cell _____

how

A

volume

  • inside the cell are proteins & molecules that cannot
    leave
  • most are negatively charged
  • attract large numbers of positive ions
  • causes osmosis of water into cell
  • 3 Na+ expelled for every 2 K+ gained
  • equals a net loss of ions
  • osmosis of water out of the cell
71
Q

sodium potassium pump:

___ Na+ expelled for every ___ K+ gained

A

3
2

72
Q

sodium potassium pump also plays important role in transmission of ______

A

nerve impulses

3 Na+ expelled for every 2 K+ gained; deficit of positive ions inside the cell –> electrical potential

73
Q

primary active transport: calcium pump

A
  • calcium uniport
  • Ca2+ extremely low intracellularly
  • pumps Ca2+
  • out of the cell
  • into sarcoplasmic reticulum of muscle cells
  • into mitochondria
74
Q

how does Na+ facilitate secondary active transport

A
  • When Na+ transported out of the cell by primary active transport a large concentration gradient develops
  • equates to a large energy store!
  • Na+ trying to diffuse down its chemical gradient into
    the cell
  • allows other molecules to be pulled through with Na+
  • co-transport
    Involves a carrier protein that can bind Na+ & the molecule to be co-transported
  • once they are both attached, Na+ gradient causes both Na+ & other molecule to be transported into cell
75
Q

symport (secondary active transport)

A

both moving in same direction, co-transport

76
Q

antiport (secondary active transport)

A

moving in different directions, counter-transport

77
Q

uniport (primary active transport or facilitated diffusion)

A

specific to one molecule

78
Q

uniport, symport or antiport:

calcium

A

uniport

79
Q

uniport, symport or antiport:

Na-glucose

A

symport

80
Q

uniport, symport or antiport:

Na-K

A

antiport

81
Q

uniport, symport or antiport:

Na-Ca

A

antiport

82
Q

describe sodium-glucose symport

A
  • 2 binding sites:
  • one for Na+
  • one for glucose
  • The conformational change necessary to allow Na+ to enter
    the cell can only occur if glucose also binds
  • both Na+ & glucose move in same direction
  • co-transport
  • Important in renal & intestinal cells
83
Q

describe how Na+ facilitates counter-transport

(different directions)

A
  • Na+ again tries to move down its concentration gradient
    into the cell
  • molecule to be transported needs to move out of the
    cell
  • Na+ binds to a binding site on the extracellular portion
    of the carrier protein
  • counter-transported molecule binds to its binding site
    intracellularly
  • once both have bound, a conformational change occurs &
    energy released from Na+ moving down its concentration
    gradient transports the other molecule out of the cell
84
Q

sodium-calcium antiport (secondary active transport)

which direction do they move

which cells does it occur in

A
  • Na+ moves intracellularly
  • Ca2+ moves extracellularly

occurs in all cells

85
Q

what are the two vesicular transport mechanisms

A

1) endocytosis; into cell
* phagocytosis
* pinocytosis
* receptor-mediated

2) exocytosis; out of cell
* constitutive
* regulated

86
Q

endocytosis is for

A

molecules that are too large to enter via carrier proteins

87
Q

endocytosis has key roles in

A
  • cell signaling: endocytosis of hormone-receptor
    complexes terminates signaling
  • cellular defense: ingestion of pathogens to be degraded by lysosomes, ingested products follow different pathways
  • degraded (lysosomes)
  • recycled
  • stored
88
Q

phagocytosis (endocytosis)

A
  • ‘cell eating’
  • large particles
  • only a few, specialised cells perform phagocytosis
  • phagocytes
  • includes macrophages & neutrophils
  • phagocytose pathogens, damaged & apoptotic cells or debris
89
Q

pinocytosis (endocytosis)

A
  • ‘cell drinking’
  • extracellular fluid & solutes; large proteins
  • occurs continually in most cells
  • rate varies between cells
90
Q

receptor mediated endocytosis

A
  • highly specific as to which molecules endocytosed
  • allows for ingestion of minor components of
    extracellular fluid, without large volumes of ECF
  • specific receptors on membrane surface
91
Q

direction of movement exocytosis

A

trans face of the Golgi apparatus to the cell membrane

92
Q

in exocytosis vesicles contain

A

synthesised proteins & waste products

93
Q

in exocytosis vesicles formed by

A

membrane proteins & lipids from Golgi

replenish those lost from the cell membrane during
endocytosis

94
Q

2 forms of exocytosis

A

1) Constitutive Exocytosis
* occurs in all cells
* components of the extracellular matrix
* waste products
* initial packaging in endoplasmic reticulum
* modified & repackaged in Golgi
* replenishes lipids & proteins of cell membrane

2) Regulated Exocytosis
* products stored for release at specified time
* hormones, digestive enzymes, neurotransmitters
* vesicle membrane does not replenish cell membrane

95
Q

Solutes are pumped into the _____

A

extracellular/interstitial fluid

96
Q

water drawn into interstitial fluid by ____

returned to vascular system via _____

A

osmosis

lymphatic system

AGRC1041 (20 decks)

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