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AS Biology > Chapter 4: Membranes and transport > Flashcards

Chapter 4: Membranes and transport Flashcards

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1
Q

what are cell surface membranes made up of

A
  • lipids (phospholipids and cholesterol)
  • proteins
  • carbohydrates
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2
Q

what is the structure of phospholipids made up of

A
  • 1 polar hydrophillic phosphate head (faces water and forms H bonds)
  • 2 non-polar hydrophobic fatty acid tails (faces away from water towards each other)
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3
Q

what do phospholipids form

A

the phospholipid bilayer

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4
Q

what forms the basic structure of membranes

A

phospholipids

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5
Q

what are the physical properties of the phospholipid bilayer

A
  • fluid
  • molecules free to move laterally by diffusion
  • viscosity of olive oil
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6
Q

what affects the viscosity of the bilayer

A
  • depends on hydrophobic interactions of fatty acid tails
  • less hydrophobic interactions means it is more free to move and less viscous
  • double bonds and fatty acid tail length affect membrane fluidity
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7
Q

what happens to the viscosity if there are 3 saturated fatty acid tails

A
  • highly ordered packing

- less hydrophobic interactions so the membrane is more viscous

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8
Q

what happens to the viscosity if there is 1 unsaturated fatty acid tail between 2 saturated fatty acid tails

A
  • double bond at kink disrupts close packing of 2 saturated fatty acid tails
  • less hydrophobic interactions so the membrane is more fluid
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9
Q

what does a fluid membrane mean

A

phospholipid molecules are free to move laterally

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10
Q

what is meant by the fluid mosaic model of the membrane structure

A

protein molecules are scattered and float freely in the phospholipid bilayer
(like icebergs in the sea)

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11
Q

what is the function of cholesterol

A
  • maintains membrane fluidity and therefore membrane stability
  • prevents freezing at a low temperature
  • acts as a plug (blocks the passage of polar molecules through the membrane
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12
Q

what is the permeability of the membrane

A

-membrane is partially and selectively permeable

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13
Q

what does movement across membrane depend on

A
  • depends on molecular size and polarity
  • small and uncharged molecules are permeable
  • large polar molecules have restricted flow
  • ions have restricted flow
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14
Q

how are large polar molecules and ions transported across membranes

A

using carrier and channel proteins

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15
Q

what are intrinsic proteins

A

proteins that are inside the bilayer

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16
Q

what are extrinsic proteins

A

proteins that are outside but close to the membrane

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17
Q

what is the arrangement and distribution pattern of protein molecules in the phospholipid bilayer

A

asymmetrical

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18
Q

what are the two types of intrinsic proteins

A
  • partially transmembrane protein (found on one side of the phospholipid bilayer only)
  • transmembrane protein (penetrates through the phospholipid bilayer with both ends hydrophillic and a hydrophobic center)
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19
Q

why do protein molecules remain inside the membrane

A

due to hydrophobic and hydrophillic interactions

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20
Q

what is the membrane structure maintained by

A
  • hydrophillic interactions between hydrophillic phosphate heads and regions of proteins facing water
  • hydrophobic interactions between hydrophobic fatty acid tails and other fatty acid tails, cholesterol and hydrophobic regions of protein
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21
Q

what is the function of carrier proteins

A

carry large polar molecules across the membrane by changing their shape

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22
Q

what is the function of channel proteins

A

for transportation of small charged ions and small polar molecules across the membrane

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23
Q

what is the function of cell surface receptor

A
  • chemical signal (ligand) binds to the binding site of the cell surface receptor
  • e.g. insulin on a liver cell or neurotransmitter from one nerve cell to another
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24
Q

what is ligand

A

a biological molecule which binds specifically to other molecules during cell signalling

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25
Q

what is the function of enzymes in the cell surface membrane

A
  • thykaloid membrane of chloroplast for photosynthesis
  • inner membrane of mitochondria for respiration
  • microvilli of a gut epithelial cells for digestion
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26
Q

what is the electron transport chain

A
  • a series of electron carriers

- found in thylakoid membrane (chloroplast) and inner membrane of mitochondria

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27
Q

what are antigens

A
  • tell which are self or non self antigens

- identity of the cell

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28
Q

what are glycoproteins

A

carbohydrate chains that face the outside of the membrane

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29
Q

function of glycoproteins

A
  • receptor site for chemical signal

- antigen of the cells for cell-cell recognition

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30
Q

when is cell-cell recognition needed

A
  • growth and development (correct cells sticking together for forming tissues)
  • immune response (only attacks nonself antigens)
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31
Q

what are nonself antigens

A

foreign cells

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32
Q

what are self antigens

A

cells from the same body

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33
Q

function of glycolipids

A
  • stabilise membrane structure

- carbohydrate chains form hydrogen bonds with water

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34
Q

what are the uses of cell signaling

A
  • homeostasis

- control and coordination of the body

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34
Q

what are the uses of cell signaling

A
  • homeostasis

- control and coordination of the body

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35
Q

what does the cell signaling pathway involve

A

the stimulus response model (animals only)

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36
Q

what are the stages of the stimulus response model

A
  • stimulus
  • receptor
  • coordinator/regulator/control center
  • effector
  • response
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37
Q

what is stimulus

A
  • changes from the set point/norm

- external/internal changes

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38
Q

what is the receptor

A

specialised group of cells to detect stimulus and converts it into signal to be transmitted

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39
Q

what is the coordinator/regulator/control center

A

transmission by:

  • nervous system by electrical and chemical signals
  • endocrine system by chemical signals
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40
Q

what is the effector

A

muscles, glands or organs that would produce the response

41
Q

what is response

A

an action produced as the result of the stimulus to restore the set point

42
Q

what is cell signalling

A

a mechanism by which (receptor) cells detect a stimulus and send message/signal to (coordinator and then effector) cells to carry out a response to the stimulus

43
Q

what is cell signalling

A

a mechanism by which (receptor) cells detect a stimulus and send message/signal to (coordinator and then effector) cells to carry out a response to the stimulus

44
Q

why are hormones a good signal molecule

A

because they are small molecules

45
Q

how are animal hormones passed to the target cell

A

from endocrine gland cell to target cell through bloodstream

46
Q

how are plant hormones passed to target cell

A
  • from secretory cell to target cell
  • short distance: from cell to cell by diffusion
  • long distance: through phloem sap
47
Q

what is the first step in cell signalling

A

secretion- endocrine gland cells secrete small quantities of hormones to tissue fluid and then hormone diffuses into the blood

48
Q

what is the second step in cell signalling

A

transportation-hormones are carried by the blood stream throughout the body

49
Q

what is the third step in cell signalling

A

reception-hormones (1st messenger/extra cellular messenger/signal molecule) bind to the receptors on cell surface membrane/cytoplasm/nucleus of target cells

50
Q

what is the fourth step in cell signalling

A

transduction - in the target cell, 2nd messenger/intracellular messenger/signal molecule activates a series of cascading reactions to amplify the signal (increasing each reaction)

51
Q

what is the fifth step in cell signalling

A

a specific response (e.g. gene expression (CHON/enzyme synthesis), secretion, movement, metabolic change

52
Q

what are the main steps in cell signalling

A
  1. secretion
  2. transportation
  3. reception
  4. transduction
  5. response
53
Q

what are intracellular receptors

A
  • hydrophobic signal molecules can pass through the cell surface membrane and bind to the receptors in the cytoplasm or nucleus
  • e.g. steroid hormones, oestrogen, progesterone, testosterone
54
Q

what are the cell signaling types

A
  • nicotine - accepting acetyleholine receptors
  • glucagon receptor
  • oestrogen receptor in the nucleus
55
Q

what are subcellular membranes

A
  • membranes of organelles with specialised function
  • mitochondria for aerobic respiration
  • chloroplast for photosynthesis
  • lysosome for digestion within the organelle
  • endoplasmic reticulum for protein transport
  • golgi apparatus for collecting, modifying, transporting and distributing material
56
Q

what is passive movement across membrane

A
  • no cellular energy required

- movement comes from kinetic energy of particles

57
Q

which movements across the membrane are passive

A
  • simple diffusion
  • facilitated diffusion (by channel and carrier proteins)
  • osmosis
58
Q

which movements across the cell membrane are active

A
  • active transport
  • endocytosis (phagocytosis and pinocytosis)
  • exocytosis
59
Q

what is active movement across the membrane (active transport)

A

needs cellular energy (ATP)

60
Q

what is diffusion

A

the movement of molecules/ions from a region of higher concentration to a lower one down a concentration gradient until their concentration becomes even throughout the solution/equilibrium is reached

61
Q

why isnt cellular energy needed for diffusion

A

because the molecules/ions move randomly due to their kinetic energy

62
Q

what is the diffusion rate formula

A

(membrane surface area x concentration gradient across membrane)/membrane thickness or distance

63
Q

what kind of molecules can diffuse through cell membranes

A

only small uncharged molecules can diffuse through cell membranes e.g. H2O, O2 CO2

64
Q

what is facilitated diffusion

A
  • diffusion of specific small ions/polar molecules through H2O filled polar channel in channel protein/pore protiens
  • carrier proteins carrying large polar molecules through cell membrane by changing their shape
65
Q

what is the characteristic about membrane that limits transport into and out of the membrane

A

the membrane is partially and selectively permeable

66
Q

how is the membrane partially permeable

A

allows passage of substances of alpha polarity and size

67
Q

how is the membrane selectively permeable

A
  • channel proteins and carrier proteins only ‘select’ specific molecule to be transported across the membrane
  • binding site shape of carrier protein is complementary to the molecular shape
68
Q

what is osmosis

A

the net movement of water molecules from a region of high water potential to a region of lower water potential through a partially permeable membrane until the water potential becomes even on both sides of the membrane/equilibrium is reached

69
Q

what is water potential

A

a measurement of the tendency of water molecules to move and is proportionate to the number of free water molecules

70
Q

what is the water potential of pure water

A

0 kPa at atmospheric pressure (P atm)

71
Q

what is the water potential of a solution

A

less than 0 kPa at Patm

72
Q

what is the formula for water potential

A

water potential = solute potential + pressure potential

73
Q

what is solute potential

A

the extent by which the solute lowers the water potential

74
Q

why does adding solutes to water lower the water potential

A

the solute dissolves, attracting water molecules around it to form hydration shells, lowering the number of free water molecules

75
Q

what is the correlation between water potential and solute potential

A
  • water potential is proportional to solute potential
  • when the water potential drops the solute potential drops
  • when the solute increases, the solute potential decreases
76
Q

what is pressure potential

A

a measure of the hydrostatic pressure that tends to move water from one place to another
-it is the contribution of pressure to H2O potential

77
Q

what is the pressure potential at atmospheric pressure

A

pressure potential = 0 kPa at Patm

78
Q

what happens to pressure potential when the pressure is more or less than atmospheric pressure

A
  • when P> Patm,, pressure potential >0kPa (+)

- when P< Patm,, pressure potential <0kPa (-)

79
Q

what is the correlation between water potential and pressure potential

A
  • water potential is proportional to pressure potential
  • positive pressure creates a pushing force that increases water potential
  • negative pressure creates a suction force that decreases water potential
80
Q

what is the path of net water movement out of the cell

A

vacuole -> tonoplast -> cytoplasm -> partially permeable cell surface membrane -> external environment
all through osmosis

81
Q

what is the path of net water movement out of the cell

A

vacuole -> tonoplast -> cytoplasm -> partially permeable cell surface membrane -> external environment
all through osmosis

82
Q

what is incipient plasmolysis

A
  • when the water potential keeps dropping until 0kPa (when the cell surface membrane stops not pushing against the cell wall in plant cells)
  • the starting part of plasmolysis
82
Q

what is incipient plasmolysis

A
  • when the water potential keeps dropping until 0kPa (when the cell surface membrane stops not pushing against the cell wall in plant cells)
  • the starting part of plasmolysis
83
Q

what is plasmolysis

A
  • cell surface membrane shrinks away from the cell wall

- becomes flaccid

84
Q

what is the Na+ - K+ pump

A

transport of specific molecules/ions by specific carrier proteins against their concentration gradient/uphill using ATP through a partially permeable membrane where a potential difference (charge difference) is built up across the membrane

85
Q

what is the importance of the Na+-k+ pump

A
  • nerve impulse transmission
  • kidney function for selective reabsorption of glucose, amino acids, vitamins and hormones
  • osmo regulation
  • raw material for CHON synthesis, glycolysis, protein synthesis etc.
86
Q

properties of carrier proteins

A

-globular protein
-specificity for particles transported
opening on one side of the membrane only
-not gated
-thousands/millions particles transported per time
-can be a pump
-transports in same and different direction (symporter/cotransporter and antiporter)

87
Q

properties of channel protein

A
  • globular protein
  • specificity for particles transported
  • opening on both sides of membrane
  • gated by pores
  • one to a few particles transported at a time
  • cannot be a pump
  • cannot be a symporter/cotransporter or antiporter
88
Q

what is endocytosis

A

bulk transport of materials into the cell with the expenditive of ATP (due to change in shape of cell surface membrane

89
Q

what are the two types of endocytosis

A
  • phagocytosis

- pinocytosis

90
Q

what is phagocytosis

A
  • ‘cell eating’ process
  • takes in solid particles by engulfing and forms phagocytic vacuole/phagosome
  • e.g. white blood cell engulfing bacteria or amoeba engulfing food
91
Q

what is phagocytosis

A
  • ‘cell eating’ process
  • takes in solid particles by engulfing and forms phagocytic vacuole/phagosome
  • e.g. white blood cell engulfing bacteria or amoeba engulfing food
92
Q

what is pinocytosis

A
  • ‘cell drinking’ process

- takes in fluid

93
Q

which is bigger vacuole or vesicle

A

vacuole

94
Q

first step of exocytosis

A

vesicle carrying useful material to be secreted or waste to be excreted out of the cell

95
Q

second step of exocytosis

A

membrane of vesicle fuses with cell surface membrane

96
Q

third step of exocytosis

A

materials are released out of the cell

97
Q

fourth step of exocytosis

A

membrane of vesicle becomes part of the cell surface membrane

98
Q

when is active transport used

A
  • specific ions/molecule

- across membrane by carrier proteins

99
Q

which transport processes need a membrane

A
  • facilitated diffusion
  • osmosis
  • active transport
100
Q

problems caused by large sized organisms (related to surface area) and how r they solved

A
  • the bigger the size (mass), the smaller the surface area:volume ratio -solved by increasing surface area e.g. alveoli
  • distance increases from site of exchange- solved by transport system

AS Biology (11 decks)

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