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Biology > Biological Membranes > Flashcards

Biological Membranes Flashcards

1
Q

what is a plasma membrane?

A

a membrane at the cell surface

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2
Q

what is the function of a plasma membrane?

A
  • they create a barrier between the cell and its environment
  • they control which substances enter and leave the cell by being partially permeable (only letting some molecules through)
  • they allow substances to move across via diffusion, osmosis or active transport
  • they allow recognition by other cells and cell communication/signaling
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3
Q

what is an intracellular membrane?

A

internal membranes within cells

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4
Q

what is the function of an intracellular membranes?

A
  • they divide the cell into different compartments
  • they act as a barrier between the organelle and the cytoplasm
  • they can form vesicles to transport substances (e.g. proteins) between different areas of the cell
  • they control which substances enter and leave the organelle by being partially permeable
  • they can be the sight of chemical reactions
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5
Q

what is an advantage of intracellular membranes dividing cells into different compartments?

A

it makes different functions of the cell more efficient (e.g. the substances needed for respiration, like enzymes, are kept inside mitochondria by its outer membrane)

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6
Q

what feature of an intracellular membrane can make chemical reactions more efficient?

A

if it is folded - this increases its surface area, increasing the efficiency of chemical reactions
(e.g. the inner membrane of a mitochondria is folded to make respiration more efficient)

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7
Q

what is the function of membranes within organelles?

A

they act as barriers between the membrane contents and the rest of the organelle
(e.g. thylakoid membranes within chloroplasts keep the components needed for photosynthesis together)

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8
Q

what is model used to describe the arrangement of molecules in a membrane?

A

fluid mosaic model of membranes

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9
Q

why is it called the fluid mosaic model?

A
  • ‘fluid’ - the phospholipids are constantly moving (mainly sideways within their own layer)
  • ‘mosaic’ - the scattered proteins through the bilayer are like tiles in a mosaic
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10
Q

what is the structure of the fluid mosaic model?

A
  • it is a continuous double layer (bilayer) of phospholipid molecules
  • some proteins have a carbohydrate attached (glycoproteins)
  • some lipids have a carbohydrate attached (glycolipids)
  • cholesterol molecules are also present within the bilayer
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11
Q

draw a diagram of the fluid mosaic model

A

p117

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12
Q

draw a diagram of the phospholipid bilayer

A

(include head and tail of phospholipid)

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13
Q

what are the 5 main components of most membranes?

A
  • phospholipids
  • cholesterol
  • proteins
  • glycolipids
  • glycoproteins
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14
Q

what is the structure of a phospholipid?

A

each phospholipid is made up of a:
- non-polar, hydrophobic tail that faces inwards
- polar, hydrophilic head that faces outwards
therefore, they automatically arrange themselves into a bilayer

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15
Q

what does hydrophobic mean?

A

repels water

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16
Q

what does hydrophilic mean?

A

attracts water

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17
Q

what is the role of a phospholipid?

A
  • they form a barrier to dissolved (water-soluble) substances due to the hydrophobic tails preventing polar molecules or ions from passing across the membrane
  • this ensures water soluble molecules (e.g. sugars, amino acids, proteins) cannot leak of the cell
  • it allows fat-soluble substances (e.g. fat-soluble vitamins) to dissolve in the bilayer and pass directly through the membrane
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18
Q

what is cholesterol?

A

a type of lipid that is present in all cell membranes (expect bacteria’s)

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19
Q

where is cholesterol within the phospholipid bilayer?

A
  • cholesterol molecules fit between the phospholipids
  • they do this by binding to their hydrophobic tails
  • this causes them to pack more closely
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20
Q

what is the role of cholesterol?

A
  • it gives the membrane stability
  • it can create a further barrier to polar substances moving through the membrane due to it having hydrophobic regions
  • it helps the cells survive through temperature changes by adjusting how fluid/rigid the membrane is by altering how closely packed together the phospholipids are (fluidity increases at lower temperatures)
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21
Q

how does cholesterol give the membrane stability?

A
  • cholesterol molecules fit between the phospholipids by binding to their hydrophobic tails
  • this causes them to pack more closely, making the membrane less fluid and more rigid
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22
Q

what is the role of a protein?

A
  • they control what enters and leaves the cell
  • they act as receptors for molecules (e.g. hormones) in cell signaling (when a molecule binds to the protein, a chemical reaction is triggered inside the cell)
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23
Q

what are the 2 types of proteins within membranes?

A
  • channel proteins
  • carrier proteins
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24
Q

what is a glycolipids?

A

a lipid with a carbohydrate attached

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25
Q

what is a glycoprotein?

A

a protein with a carbohydrate attached

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26
Q

what is the role of glycolipids and glycoproteins?

A
  • they stabilize the membrane by forming hydrogen bonds with surrounding water molecules
  • they act as receptors for messenger molecules in cell signaling
  • they are sites where drugs, hormones and antibodies bind
  • they are antigens (cell surface molecules involved in self-recognition and the immune response)
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27
Q

what are the 2 factors that affect membrane permeability?

A
  • temperature
  • solvent concentration
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28
Q

draw a graph showing membrane permeability against temperature

A

p119

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29
Q

from the graph, what happens at temperatures below 0?

A
  • the phospholipids don’t have much energy so cant move very much
  • therefore, they are packed closely and the membrane is rigid
  • channel and carrier proteins in the membrane denature, increasing the permeability of the membrane
  • ice crystals may also form, piercing the membrane, making it highly permeable when it thaws (defrosts)
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30
Q

from the graph, what happens between temperatures of 0-45?

A
  • the phospholipids can move around and aren’t packed as closely together
  • therefore, the membrane is partially permeable
  • as temperature increases between these values, the phospholipids gain more energy and move more, increasing membrane permeability
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31
Q

from the graph, what happens at temperatures above 45?

A
  • the phospholipid bilayer starts to melt and break down, increasing membrane permeability
  • water inside the cell expands, putting pressure on the membrane
  • channel and carrier proteins in the membrane denature, meaning they can no longer control what enters and leaves the cell, increasing membrane permeability
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32
Q

how does solvent concentration affect membrane permeability?

A
  • the permeability of a cell membrane depends on the solvent surrounding them
  • some solvents (e.g. ethanol) dissolve the lipids in the cell membrane, meaning it loses its structure, increasing permeability
  • some solvents (e.g. ethanol) increase membrane permeability more than others (e.g. methanol)
  • increasing the concentration of these solvents will increase membrane permeability
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33
Q

draw a graph showing membrane permeability against alcohol concentration

A

p119

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34
Q

investigating cell membrane permeability - beetroot PAG

A

p120

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35
Q

why do cells need to communicate with eachother?

A
  • to control processes inside the body
  • to respond to changes in the environment
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36
Q

what is cell signaling?

A
  • a way for cells to communicate with each other
  • it uses messenger molecules
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37
Q

summarize how cell signaling works

A
  • it starts when one cell releases a messenger molecule (e.g. a hormone)
  • this molecule travels to another cell (e.g. in the blood)
  • the messenger molecule is then detected by the cell because it binds to a receptor on its cell membrane
  • the binding then triggers a change in the cell (e.g. setting off chemical signals)
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38
Q

what is are membrane-bound receptors?

A

proteins in the cell membrane that act as receptors for messenger molecules

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39
Q

what are a feature of these receptor proteins?

A

-they have specific shapes, meaning only messenger molecules with a complementary shape can bind to them

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40
Q

what is a target cell?

A
  • different cells have different types of receptors that respond to different messenger molecules
  • the cell that responds to a particular messenger molecule is called a target cell
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41
Q

show hoe messenger molecules bind to target cells, but NOT non-target cells

A

p122

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42
Q

how do hormones work as messenger molecules?

A

they bind to receptors in cell membranes, triggering a response in the cell

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43
Q

how does the hormone glucagon work as a messenger molecule?

A
  • glucagon is released when there isn’t enough glucose in the blood
  • it binds to receptors on liver cells
  • this causes the liver cells to break down stores of glycogen to glucose
44
Q

how does the hormone FSH work as a messenger molecule?

A
  • FSH is released by the pituitary gland during the menstrual cycle
  • it bind to receptors on cells in the ovaries, causing an egg to mature ready for ovulation
45
Q

what is the role of drugs in membrane receptors?

A
  • many drugs work by binding to receptors in cell membranes
  • they either trigger a response in the cell or block the receptor and prevent it from working
46
Q

how does the drug morphine work alongside membrane receptors?

A
  • the body produces chemicals called endorphins to relieve pain
  • endorphins bind to opioid receptors in the brain and reduce the transmission of pain signals
  • morphine is used to relieve pain
  • it works by binding to the same opioid receptors, triggering the same reduction of pain signals
47
Q

how does the drug antihistamine work alongside membrane receptors?

A
  • cell damage causes the release of a chemical called histamine
  • histamine binds to receptors on the surface of other cells and causes inflammation
  • antihistamines work by blocking histamine receptors on cell surfaces
  • this prevents histamine from binding and stops inflammation
48
Q

what is the definition of diffusion?

A

the net movement of particles from an area of high concentration to an area of lower concentration (down a concentration gradient)

49
Q

what is classed as a particle?

A

molecules or ions

50
Q

what does net movement mean?

A

particles will move both ways but the net movement is calculated by the majority - the overall movement

51
Q

when does diffusion end?

A

when all the particles are evenly distributed throughout the liquid or gas - its reached equilibrium

52
Q

diffusion is a _______ process

A

passive - it requires no energy (particles can diffuse across as long as they can move freely)

53
Q

what are the 4 factors that affect the rate of diffusion?

A
  • concentration gradient
  • diffusion distance/thickness of exchange surface
  • surface area
  • temperature
54
Q

how does the concentration gradient affect diffusion rate?

A
  • increased concentration gradient = increased rate of diffusion
  • decreased concentration gradient = decreased rate of diffusion
55
Q

how does the diffusion distance/thickness of exchange surface affect diffusion rate?

A
  • increased diffusion distance = decreased rate of diffusion
  • decreased diffusion distance = increased rate of diffusion
56
Q

how does the surface area affect diffusion rate?

A
  • increased surface area = increased rate of diffusion
  • decreased surface area = decreased rate of diffusion
57
Q

how does the temperature affect diffusion rate?

A
  • increased temperature = increased rate of diffusion
  • decreased temperature = decreased rate of diffusion
58
Q

investigating diffusion

A

p125

59
Q

what is the definition of osmosis?

A

the net movement of water molecules from an area of high water potential to an area of lower water potential, across a partially permeable membrane (down a water potential gradient)

60
Q

what is the definition of water potential?

A

the tendency/potential of water molecules to diffuse into or out of a solution
IT IS ALWAYS A NEGATIVE VALUE

61
Q

what is the symbol of water potential?

A

Ψ

62
Q

what are the units of water potential?

A

kPa

63
Q

what is the water potential of pure water?

A

0kPa

64
Q

how do you calculate water potential?

A

pressure potential + solute potential

65
Q

how do you lower a solutions water potential?

A
  • adding solutes
  • this gives a more negative water potential
  • therefore, the more negative the value, the stronger the concentration of solutes in the solution
66
Q

what is an isotonic solution?

A
  • its when two solutions have the same water potential
  • this means the cells in an isotonic solution wont lose or gain any water due to there being no water potential gradient
67
Q

what happens to animal cells in an isotonic solution?

A

they stay the same

68
Q

what happens to plant cells in an isotonic solution?

A

they stay the same

69
Q

what is a hypotonic solution?

A
  • when the solution has a higher water potential compared to the inside of the cell
  • this means water will move into the cell by osmosis
70
Q

what happens to animal cells in a hypotonic solution?

A

they swell and could potentially burst (hemolyzed/lysis?)

71
Q

what happens to plant cells in a- hypotonic solution?

A
  • the vacuole will swell
  • the contents of the vacuole and cytoplasm will push up against the cell wall
  • this will cause the cell to become TURGID (swollen)
  • however, it wont burst as the inelastic cell wall is able to withstand the pressure increase
  • this provides support for the plant
72
Q

what is a hypertonic solution?

A
  • when the solution has a lower water potential compared to the inside of the cell
  • this means water will move out of the cell by osmosis
73
Q

what happens to animal cells in a hypertonic solution?

A

it will shrink (crenation?)

74
Q

what happens to plant cells in a hypertonic solution?

A
  • it will become FLACCID (limp)
  • the cytoplasm and plasma membrane will eventually pull away from the cell wall - this is called PLASMOLYSIS
75
Q

what is plasmolysis?

A

when the cytoplasm and plasma membrane pull away from the cell wall

76
Q

investigating the effect of water potential on plant cells

A

p128

77
Q

investigating the effect of water potential on animal cells

A

p129

78
Q

what is facilitated diffusion?

A

the diffusion of larger molecules or charged particles from an area of high concentration to an area of lower concentration through carrier proteins and channel proteins

79
Q

where does facilitated diffusion take place?

A

in the cell membrane

80
Q

why do we need facilitated diffusion?

A
  • large molecules would be extremely slow at diffusing through the phospholipid bilayer due to their size
  • charged particles would also diffuse slowly due to them being water soluble and the phospholipid bilayer being hydrophobic
81
Q

what are some examples of large molecules that need to use facilitated diffusion?

A
  • amino acids
  • glucose
82
Q

what are some examples of charged particles that need to use facilitated diffusion?

A
  • polar molecules
  • ions (e.g. sodium, chloride)
83
Q

facilitated diffusion is a _______ process

A

passive - requires no energy

84
Q

what is the key difference between diffusion and facilitated diffusion?

A

facilitated diffusion uses membrane proteins - carrier and channel

85
Q

what is the role of carrier proteins?

A
  • they move large or charged molecules into or out of a cell, down a concentration gradient
  • different carrier proteins facilitate the diffusion of different molecules
86
Q

what is an example of a carrier protein?

A

GLUT1 found in all animal cells to transport glucose across the plasma membrane

87
Q

how do carrier proteins work?

A
  1. a large molecule attaches to a carrier protein in the membrane
  2. the protein changes shape
  3. this releases the molecule on the opposite side of the membrane
    SEE DIAGRAM P131
88
Q

what is the role of a channel protein?

A
  • they form (water filled?) pores in the membrane for smaller charged particles (ions and polar molecules) to diffuse through, down a concentration gradient
  • these pores are gated (can open and close)
  • different channel proteins facilitate the diffusion of different charged particles
89
Q

how do channel proteins work?

A
  • they form a pore
    SEE DIAGRAM P132
90
Q

what is a key difference between carrier and channel proteins?

A
  • carrier proteins can switch between 2 shapes
  • channel proteins are a fixed shape
91
Q

what is the definition of active transport?

A

the movement of molecules and ions across a plasma membrane from a region of low concentration to an area of higher concentration (against/up a concentration gradient) through carrier proteins and using ATP
SEE DIAGRAM P132

92
Q

how are carrier proteins used in active transport?

A

in the same way as facilitated diffusion!
1. a molecule attaches to a carrier protein in the membrane
2. the protein changes shape
3. this releases the molecule on the opposite side of the membrane
SEE DIAGRAM P131

93
Q

active transport is an _____ process

A

active - it uses the ATP from respiration to move the solute against its concentration gradient

94
Q

what is the difference between active transport and facilitated diffusion?

A
  • active transport is and active process (uses energy)
  • facilitated diffusion is a passive process (does not)
95
Q

what is endocytosis?

A

the movement of large molecules or objects INTO the cell

96
Q

why do we need endocytosis?

A
  • some molecules are too large to be taken into a cell by carrier proteins
  • therefore, in order to travel across the plasma membrane, it needs to be taken in by endocytosis
97
Q

what are some examples of molecules that are taken in by endocytosis?

A
  • proteins
  • lipids
  • some carbohydrates

some cells (e.g. white blood cells - mainly phagocytes) take in much larger objects (e.g. micro organisms and dead cells) through endocytosis in order to destroy them

98
Q

what is the process of taking a cell in by endocytosis?

A
  • a cell surrounds a substance with a section of its plasma membrane
  • the membrane then pinches off to form a vesicle inside the cell containing the ingested substance
  • this substance has now been taken in by endocytosis
    SEE DIAGRAM P132
99
Q

endocytosis is an ______ process

A

active - it requires ATP for energy

100
Q

what is exocytosis?

A

the movement of molecules OUT OF the cell

101
Q

why do we need exocytosis?

A
  • some substances produced by the cell need to be released from it
  • therefore, this is done through exocytosis
102
Q

what are some examples of substances released by exocytosis?

A
  • digestive enzymes
  • hormones
  • lipids
103
Q

what is the process of exocytosis?

A
  • vesicles containing the substances pinch off from the sacs of the golgi apparatus
  • they then move towards the plasma membrane
  • the vesicles fuse with the plasma membrane and release their contents outside of the cell
  • however, some substances (e.g. membrane proteins) are inserted straight into the plasma membrane instead
    SEE DIAGRAM P133
104
Q

endocytosis is an _____ process

A

active - it requires ATP for energy

105
Q

summary of transport mechanisms

A

p134
(all info already in flashcards)

Biology (11 decks)

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