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Biology > 3.2.3 Transport across cell membranes > Flashcards

3.2.3 Transport across cell membranes Flashcards

1
Q

what is the name of the model of a plasma membrane structure?

A

fluid-mosaic model

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2
Q

the model of the plasma membrane is ‘fluid’ because…

A

the phospholipids are constantly moving

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3
Q

the model of the plasma membrane is ‘mosaic’ because…

A

proteins are scattered/dotted through the bilayer

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4
Q

which six structures make up a plasma membrane?

A
  • phospholipid bilayer
  • integral proteins
  • peripheral proteins
  • glycoproteins
  • glycolipids
  • cholesterol
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5
Q

why do the phospholipids arrange in a bilayer?

A

the hydrophilic heads are attracted to water and the hydrophobic tails are repelled by water

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6
Q

what is the function of the phospholipid bilayer?

A

creates a partially permeable membrane so only allows small, non-polar molecules to diffuse through

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7
Q

what is the characteristic of an integral protein?

A

they span across from one side of the bilayer to the other

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8
Q

what are the functions of integral proteins?

A

are carrier proteins or channel proteins involved in the transport of molecules across the membrane

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9
Q

what is the characteristic of a peripheral protein?

A

they do not extend completely across the membrane

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10
Q

what are the functions of peripheral proteins?

A
  • provide mechanical support
  • can act as receptors and allow the cell to detect chemical released from other cells so that they can responds
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11
Q

what is a glycoprotein?

A

a protein with a carbohydrate attached

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12
Q

what is a glycolipid?

A

a lipid with a carbohydrate attached

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13
Q

what are the functions of glycoproteins / glyolipids?

A
  • can act as antigens to facilitate cellular recognition
  • play an important role is cell signalling and communication
  • help with cell adhesion (make connections which allow cells to connect to one another to form tissues)
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14
Q

what is the function of cholesterol?

A
  • restricts the lateral movement of other molecules in the membrane which makes the membrane less flexible
  • this is useful as it makes the membrane less fluid at high temperatures and prevents water and dissolved ions leaking out
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15
Q

what is diffusion?

A

the net movement of molecules / ions from an area of high concentration to an area of low concentration

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16
Q

molecules can diffuse simply if they are…

A

lipid soluble and very small

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17
Q

molecules cannot diffuse simply if they are…

A

water soluble (polar) and large

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18
Q

what are the four factors affecting simple diffusion?

A
  • concentration gradient
  • membrane thickness
  • surface area
  • temperature
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19
Q

how and why does the concentration gradient affect simple diffusion?

A
  • the greater the concentration difference the faster the rate of diffusion
  • diffusion slows down over time as equilibrium is reached so concentration gradient must be maintained
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20
Q

how and why does the membrane thickness affect simple diffusion?

A
  • the thinner the membrane the faster the rate of diffusion
  • thin membranes reduce the distance particles have to travel
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21
Q

how and why does the surface area affect simple diffusion?

A
  • the larger the surface area the greater the rate of diffusion
  • increasing the SA (e.g., by folding) means more particles can be exchanged in the same amount of time
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22
Q

how and why does the temperature affect simple diffusion?

A
  • the higher the temperature the faster the rate of diffusion
  • at higher temperatures, particles have more kinetic energy so they will be able to move around faster
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23
Q

what is facilitated diffusion?

A

hydrophilic substances move down a concentration gradient across the cell membrane via integral membrane proteins

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24
Q

what are the two types of integral proteins involved in facilitated diffusion?

A
  • channel proteins
  • carrier proteins
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25
Q

what is a channel protein?

A

a protein with a central pore which is lined with hydrophilic amino acids and water

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26
Q

how do channel proteins facilitate diffusion?

A

hydrophilic substances can pass through the channel from one side of the membrane to the other

27
Q

what are two features of channel proteins?

A
  • channel proteins are selective for the chemical that can pass through
  • some types of channel proteins only open in response to a certain trigger whereas others are always open
28
Q

how do carrier proteins facilitate diffusion?

A
  • carrier proteins have a binding site for a specific molecule
  • when the molecule binds it causes the tertiary structure of the carrier protein to change shape
  • this change in shape enables the molecule to be released to the other side of the membrane
29
Q

what are the two factors affecting the rate of facilitated diffusion?

A
  • concentration gradient
  • number of channel/carrier proteins
30
Q

how does the concentration gradient affect the rate of facilitated diffusion?

A
  • the greater the concentration gradient the faster the rate of facilitated diffusion
  • this is true until all the proteins are in use or once equilibrium is reached
31
Q

how does the number of channel/carrier proteins affect the rate of facilitated diffusion?

A
  • the greater the number of channel/carrier proteins the faster the rate of facilitated diffusion
  • this is true until all the proteins are in use so it becomes a limiting factor
32
Q

what is osmosis?

A

the movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane

33
Q

what is water potential?

A

the pressure created by water molecules

34
Q

what unit is water potential measured in?

A

kilopascals (kPa)

35
Q

what is the water potential of pure water?

A

0 kPa

36
Q

what happens to the water potential of pure water when a solute is dissolved in it?

A

the water potential becomes negative

37
Q

the more solute dissolved in the solution, the more ____ the water potential

A

negative

38
Q

if solution A has a water potential of -50 kPa and solution B has a water potential of -250 kPa, which solution has a higher concentration of water?

A

solution A

39
Q

if solution A has a water potential of -50 kPa and solution B has a water potential of -250 kPa, what would be the direction of osmosis?

A

water will move from A to B

40
Q

what is an isotonic solution?

A

when the water potential is the same in the solution and the cell within the solution

41
Q

what happens when a cell is placed in an isotonic solution?

A

there is no net (overall) movement of water

42
Q

what is a hypotonic solution?

A

when the solution has a higher (more positive) water potential than the cell

43
Q

what happens when an animal cell is placed in a hypotonic solution?

A

water will move into the cell by osmosis causing the cell to swell up and eventually burst

44
Q

what happens when a plant cell is placed in a hypotonic solution?

A

water will move into the cell by osmosis causing the cell to become turgid (it will not burst due to the strength of the cell wall)

45
Q

what is a hypertonic solution?

A

when the solution has a lower (more negative) water potential than the cell

46
Q

what happens when an animal cell is placed in a hypertonic solution?

A

water will move out of the cell by osmosis so the cell will shrivel as it loses water from its cytoplasm

47
Q

what happens when a plant cell is placed in a hypertonic solution?

A
  • water will move out of the cell by osmosis
  • cell will not shrink due to cell wall
  • however, the cytoplasm will shrink and the cell membrane will pull away from the cell wall
  • known as plasmolysis
48
Q

what is active transport?

A
  • the movement of molecules and ions from an area of lower concentration to an area of higher concentration (against a concentration gradient)
  • using metabolic energy provided by ATP and carrier proteins
49
Q

how are molecules actively transported using carrier proteins and ATP?

A
  • molecule binds to the receptor on the carrier protein which is complementary in shape
  • ATP binds to the carrier protein from the inside of the cell and is hydrolysed into ADP + Pi
  • this causes the carrier protein to change shape and release the molecule to the other side
  • the phosphate ion is then released and the carrier protein returns to its original shape
50
Q

how does the co-transport of glucose and sodium ions in the ileum work?

A
  • sodium ions are actively transported out of the epithelial cell into the blood by the sodium-potassium (Na+/K+) pump
  • this reduces the sodium ion concentration in the epithelial cell, creating a concentration gradient
  • sodium ions then move down their concentration gradient by facilitated diffusion from the lumen into the epithelial cell
  • they do this using a co-transporter protein, so glucose also attaches and is transported into the epithelial cell against its concentration gradient
51
Q

once in the epithelial cell, how is glucose transported into the blood?

A

facilitated diffusion

52
Q

what are 5 features you would expect to find in a cell specialised for absorption?

A
  • folded membrane/microvilli so large surface area for absorption
  • large number of mitochondria so more ATP is made by respiration and to release energy for active transport
  • large number of co-transport/channel/carrier proteins so fast rate for absorption
  • membrane-bound digestive enzymes so maintains a concentration gradient for fast absorption
  • constant blood flow maintains a concentration gradient
53
Q

what is bulk transport?

A
  • the transfer of a large quantity of material across a cell
  • often molecules/particles which are too large to be transported by facilitated diffusion or active transport
  • endocytosis and exocytosis
54
Q

what is endocytosis?

A

large particles/molecules are transported into the cell

55
Q

how does endocytosis work?

A
  • cell membrane folds inwards to form a cavity around the particles (a process known as invagination)
  • membrane completely encircles the particles to form a vesicle
  • vesicle moves into the cell
56
Q

what is exocytosis?

A

large particles/molecules are transported out of the cell

57
Q

how does exocytosis work?

A
  • vesicle containing proteins, for example, moves towards the cell membrane
  • vesicle fuses with the cell membrane to secrete the protein
58
Q

what do endocytosis and exocytosis require?

A

energy provided by ATP

59
Q

what are the two factors affecting membrane permeability?

A

temperature and solvents

60
Q

how does a temperature below 0°C affect the plasma membrane permeability?

A
  • phospholipids are packed closely together and the
    membrane is rigid
  • channel and carrier proteins can denature which
    increases the permeability of the membrane
  • ice crystals can form and pierce the membrane, increasing permeability when it thaws
61
Q

how does a temperature between 0 - 45°C affect the plasma membrane permeability?

A
  • phospholipids move around freely and the membrane is partially permeable
  • as temperature increases, kinetic energy increases so the membrane becomes more permeable
62
Q

how does a temperature above 45°C affect the plasma membrane permeability?

A
  • phospholipids start to melt increasing membrane permeability
  • water inside the cell expands putting pressure on the membrane
  • channel and carrier proteins in the membrane denature increasing permeability
63
Q

how do solvents affect plasma membrane permeability?

A
  • non-polar solvents such as alcohols or acetone insert themselves into the bilayer
  • this pushes phospholipids out of their orderly placement and increases their movement
  • disruption of the membrane structure increases its permeability
  • solvent can also denature proteins by disrupting bonds

Biology (21 decks)

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