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Biology SL > 1.4 Membrane Transport > Flashcards

1.4 Membrane Transport Flashcards

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1
Q

what two key qualities do cellular membrane? (2)

A
  • they are semi-permeable -> certain materials may freely cross (large and charged substances are typically blocked)
  • they are selective (membrane proteins may regulate the passage of material that cannot freely cross)
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2
Q

what two ways can the movement of material crossing the biological membrane be?

A

active
passive

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3
Q

what is passive transport?

A

involves the movement of material along a concentration gradient (high concentration -> low concentration)

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4
Q

why do materials not require energy expenditure (ATP hydrolysis) for passive transport?

A

because materials are moving down a concentration gradient

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5
Q

what are three main types of passive transport?

A
  • simple diffusion - movement of small or lipophilic molecules (eg. O2, CO2)
  • osmosis - movement of water molecules (dependent on solute concentration)
  • facilitated diffusion - movement of large or charged molecules via membrane proteins (eg. ions, sucrose)
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6
Q

what is active transport?

A

the movement of materials against a concentration gradient (low concentration -> high concentration)

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7
Q

why does active transport require the expenditure of energy (eg. ATP hydrolysis)?

A

materials are moving against the gradient

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8
Q

what are the 2 main types of active transport?

A
  • primary (direct) active transport - involves to direct use of metabolic energy to mediate transport
  • secondary (indirect) active transport - involves coupling the molecule with another moving along an electrochemical gradient
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9
Q

what is diffusion and what are its characteristics? (30

A
  • the net movement of molecules from a region of high concentrations to a region of low concentrations
  • the directional movement along a gradient is passive and will continue until molecules become evenly dispersed equilibrium)
  • small and non-polar (lipophilic) molecules will be able to freely diffuse across cell membranes
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10
Q

what three things can influence the rate of diffusion?

A
  • temperature (affect kinetic energy of particles in solution)
  • molecular size (larger particles are subjected to greater resistance within a fluid medium)
  • steepness of gradient (rate of diffusion will be greater with a higher concentration gradient)
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11
Q

what is osmosis?

A

the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration (until equilibrium is reached)

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12
Q

why is water considered the universal solvent?

A

it will associate with and dissolve, polar or charged molecules (solutes)

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13
Q

why are there less free water molecules in high solute concentrations?

A

as water is associated with the solute

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14
Q

what is osmolarity?

A

the measure of solute concentrations as defined by the number of osmoles of a solute per litre of solution (osmol/L)

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15
Q

what would a hypertonic solution be?

A

solutions with a relatively higher osmolarity
(high solute concentration -> gains water)

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16
Q

what would a hypotonic solution be?

A

solutions with a relatively lower osmolarity
(low solute concentration -> loses water)

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17
Q

what would an isotonic solution be?

A

solutions that have the same osmolarity
(same solute concentration -> no net water flow)

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18
Q

how can you estimate/interpolate the osmolarity of a tissue? (3 step)

A
  • tissue will lose water when placed in hypertonic solutions and gain water when placed in hypotonic solutions
  • water loss or gain may be determined by weighing samples before and after bathing in solution
  • tissue osmolarity may be inferred by identifying the concentration of solution at which there is not weight change
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19
Q

what kind of solution should tissues and organs be kept in for medical procedures to prevent cellular edssication?

A

solution must share the same osmolarity as the tissue/organ (ie. isotonic) to prevent osmosis from occurring

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20
Q

what 2 negative effects can uncontrolled osmosis have to cell viability?

A
  • in hypertonic solutions water will leave the cell causing it to shrivel (crenation)
  • in hypotonic solutions, water will enter the cell causing it to swell and potentially burst (lysis)
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21
Q

what are the effects of uncontrolled osmosis in plant tissues with the presence of an inflexible cell wall? (2)

A
  • in a hypertonic solution the cytoplasm will shrink (plasmolysis) but the cell wall will maintain a structure shape
  • in a hypotonic solution the cytoplasm will expand but be unable to rupture within the constraints of the cell wall (turgor)
22
Q

what is facilitated diffusion?

A

the passive movement of molecules across the cell membrane via the aid of a membrane protein

23
Q

what is facilitated diffusion used for?

A

used by molecules that are unable to freely cross the phospholipid bilayer (eg. large, polar molecule and ions)

24
Q

how is facilitated diffusion mediated?

A

mediated by two distinct types of transport proteins
channel proteins and carrier proteins

25
Q

how do carrier proteins work? (2)

A
  • integral glycoproteins which bind a solute and undergo a conformational change to translocate the solute across the membrane
  • carrier proteins will only bind a specific molecule via an attachment similar to an enzyme-substrate interaction
26
Q

what do carrier proteins have the ability to do?

A

carrier proteins may move molecules in the presence of ATP (ie. are sued in active transport)

27
Q

how do carrier proteins differ from channel proteins?

A

much slower rate of transport than channel proteins

28
Q

what are channel proteins and how do they work?

A
  • integral lipoproteins which contain a pore via ions may cross from one side of the membrane to the other
  • channel proteins are ion-selective and may be gated to regulate the passage of ions in response to certain stimuli
  • channel proteins only move molecules along a concentration gradient (eg. not used in active transport)
29
Q

what is an example of carrier protein?

A

the axons of nerve cells, transmit electrical impulses by translocating ions to create a voltage difference across the membrane

30
Q

how do sodium-potassium pumps work in the axon? (2)

A
  • at rest, the sodium-potassium pump expels sodium ions from the nerve cell while potassium ions are accumulated
  • when neurons fires, these ions swap locations via facilitated diffusion via sodium and potassium channels
31
Q

how do potassium channels work? (3)

A
  • integral proteins w/ a hydrophilic inner pore via which potassium ions may be transported
  • the channel is compromised of four transmembrane subunits, while the inner pore contains a selectivity filter at its narrowest region that restricts passage of alternative ions
  • potassium channels are typically voltage-gated and cycle between an opened and closed confirmation depending on the transmembrane voltage
32
Q

what does active transport do?

A

uses energy to move molecules against a concentration gradient

33
Q

how can energy be generated for active transport? (2)

A
  • the direct hydrolysis of ATP (primary active transport)
  • indirectly coupling transport with another molecules that is moving along its gradient (secondary active transport)
34
Q

how do carrier proteins or protein pump work (active transport)? (3 step)

A
  • a specific solute will bind to the protein pump on one side of the membrane
  • the hydrolysis of ATP (to ADP +Pi) causes a conformational change in the protein pump
  • the solute molecule is consequently translated across the membrane (against the gradient) and released
35
Q

what does the sodium-potassium pump ion exchange result in?

A

3 sodium (moves out of cell)
2 potassium ions (move into cell)

36
Q

what is the process of ion exchange against the gradient of the sodium-potassium pump? (6)

A
  1. 3 sodium ions bind to intracellular sites on the sodium-potassium pump
  2. a phosphate group is transferred to the pump via the hydrolysis of ATP
  3. the pump undergoes a conformational change, translocating sodium across the membrane
  4. the conformational change exposes 2 potassium binding sites on the extracellular surface of the pump
  5. the phosphate group is released which causes the pump to return to its original conformation
  6. this translocated the potassium across the membrane, completing the ion exchange
37
Q

how are materials destined for secretion transported around the cell?

A

in membranous containers called vesicles

38
Q

what is the endoplasmic reticulum?

A

membranous network that is responsible for synthesising secretory materials

39
Q

what is rough ER embedded with and for what?

A

ribosomes and synthesises proteins destined for extracellular use

40
Q

what is smooth ER’s role?

A

involved in lipid synthesis and also plays a role in carbohydrate metabolism

41
Q

how are materials transported from the ER?

A

the ER membrane bulges and then buds to create a vesicle surrounding the material

42
Q

what happens to the vesicle from the ER?

A

the vesicle is transported to the golgi apparatus and fuses to the internal (cis) face of the complex

42
Q

what happens to the vesicle after it has been fused with the golgi?

A
  • materials move via vesicles from the internal cis face of the golgi to the externally oriented trans face
  • in the golgi materials may be structurally modified
43
Q

what happens to materials within the golgi after being sorted in the golgi? (2)

A
  • secreted into the extracellular fluid (constitutive secretion)
  • may be transported to the lysosome
44
Q

where will vesicles containing materials destined for extracellular use will be transported? (2)

A

transported to the plasma membrane
- the vesicle will fuse with the cell membrane and its materials will be expelled into the extracellular fluid

45
Q

what happens to materials sorted by the golgi?

A
  • released immediately into the extracellular fluid (constitutive secretion)
  • stored within an intracellular vesicle for a delayed release in response to a cellular signal (regulatory secretion)
46
Q

how is the plasma membrane held together? (2)

A
  • held together by weak hydrophobic associations between the fatty acid tails of phospholipids
  • this weak association allows for membrane fluidity and flexibility as the phospholipids can move around to some extent
47
Q

what do weak associations in the plasma membrane allow for?

A

allows for the spontaneous braking and reforming of the bilayer, allowing larger materials to enter or leave the cell without having to cross the membrane (this is an active process and requires hydrolysis)

48
Q

what is endocytosis and what is the steps?(3)

A

process by which large substances (or bulk amounts of smaller substances) enter the cell without crossing the membrane
- an invagination of the membrane forms a flask-like depression which envelopes the extracellular material
- the invagination is then sealed off to form an intracellular vesicle containing the material

49
Q

what are 2 main types of endocytosis?

A

phagocytosis - the process by which solid substances (usually to be transported to the lysosome)
pinocytosis - the process by which liquids/dissolves substances are ingested (allows faster entry than via protein channels)

50
Q

what is exocytosis? (2)

A

process by which large substances (or bulk amounts of small substances) exit the cell without crossing the membrane
- vesicles (eg. from golgi) fuse with the plasma membrane, expelling their contents into the extracellular environment

51
Q

what does exocytosis add?

A

process of exocytosis adds vesicular phospholipids to the cell membrane, replacing those lost when vesicles are formed via endocytosis

Biology SL (38 decks)

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