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Biology > 2.1.5 - Biological membranes > Flashcards

2.1.5 - Biological membranes Flashcards

1
Q

What is compartmentalisation ?

A

Compartmentalisation is the formation of separate membrane bound areas in a cell

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2
Q

Why is compartmentalisation useful in cells ?

A
  • Protects cell components
  • Allows reaction conditions to be maintained
  • Isolates reactions making them more efficient
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3
Q

State 4 functions of plasma membranes

A
  • Recognition of other cells
  • Cell communication
  • Separates cell contents from extracellular space
  • Controls the passage of materials in and out of the cells
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4
Q

State 4 functions of membranes inside cells

A
  • Isolates DNA
  • Compartmentalises reactions
  • Form vesicles
  • Acts as an intracellular transport system
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5
Q

Describe the membrane structure

A

Membranes are formed from a phospholipid bilayer with intrinsic and extrinsic proteins

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6
Q

What is the phospholipid bilayer ?

A
  • It is the arrangement of phospholipids found in cell membranes
  • Hydrophilic phosphate heads on the outside
  • Hydrophobic fatty acid tails on the inside
  • It has a hydrophobic core
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7
Q

Why are membranes referred to as having a fluid mosaic structure ?

A
  • They are called fluid as they are able to move freely relative to each other. It gives the membrane flexibility
  • They are referred to as mosaic structures due to the fact that they have different proteins embedded in the bilayer which vary in shape size and position
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8
Q

What is a phospholipid ?

A

A phospholipid is a lipid made of glycerol, two fatty acid tails and a phosphate head

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9
Q

What is the function of a phospholipid ?

A

Phospholipids create a selectively permeable barrier to the movement of ions and molecules important for cellular function

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10
Q

What are extrinsic proteins ?

A
  • They are present in one side of the bilayer
  • They normally have hydrophilic R - groups on their outer surfaces and interact with the polar heads of the phospholipids or with the intrinsic proteins
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11
Q

What are the functions of extrinsic proteins in cell surface membranes ?

A

Can attach to the cytoskeleton

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12
Q

What are intrinsic proteins ?

A
  • Intrinsic proteins are transmembrane proteins that are embedded through both layers of the membrane
  • They have amino acids with hydrophobic R-groups on their external surfaces, which interact with the hydrophobic core of the membrane, keeping them in place
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13
Q

What are channel proteins ?

A

They are intrinsic proteins which are held in position by interactions between the hydrophobic core of the membrane and the hydrophilic R - groups on the outside of the proteins

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14
Q

What is the function of a channel proteins ?

A

They provide a hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient through membranes

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15
Q

What are carrier proteins ?

A

Carrier proteins are intrinsic proteins whose shape can change during active transport

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16
Q

What is the function of a carrier protein ?

A
  • They have an important role in both passive and active transport into the cell
  • It often involves the shape of the protein changing
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17
Q

What is a glycoprotein ?

A
  • Glycoproteins are extrinsic proteins with attached carbohydrate chains
  • They are embedded in the cell surface membrane
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18
Q

What is the function of a glycoprotein ?

A
  • Receptors for chemical signals

- Cell adhesion

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19
Q

What is chemical signalling ?

A
  • When a chemical binds to the receptor, it elicits a response from the cell. This may cause a direct response or set off a cascade of events inside the cell.
  • Used for intracellular communication
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20
Q

What is cell adhesion ?

A
  • When cells join together and move as one piece
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21
Q

What is a glycolipid ?

A
  • They are lipids with attached carbohydrate chains.

- These molecules are called cell markers or antigens.

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22
Q

What is the function of a glycolipid ?

A
  • They can recognise cells of the immune system as self or non self
  • Acts as an antigen that can be recognised by the immune system
  • Can form hydrogen bonds with water molecules to stabilise membrane
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23
Q

What is cholesterol ?

A
  • A lipid with a hydrophilic and hydrophobic end. The hydrophilic end interacts with the heads and the hydrophobic end interacts with the tails.
  • It is made up of four carbon rings with a hydroxyl groups
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24
Q

What are the functions of cholesterol ?

A
  • Regulates fluidity of membranes
  • Adds stability
  • Prevents membrane becoming too solid by stopping phospholipids from crystallising
  • Pull phospholipids together
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25
Q

What do membranes control ?

A
  • The passage of substances in and out of cells

- If membranes lose their structure, cell processes will be disrupted

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26
Q

What 3 factors affect membrane structure?

A
  • Temperature
  • Solvents
  • Cholesterol
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27
Q

How does an increase in temperature affect cell membranes ?

A
  • Increases membrane fluidity
  • Increases membrane permeability
  • Membrane loses its structure
  • Carrier and channel proteins are denatured at higher temperatures
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28
Q

Why does an increase in temperature increase membrane fluidity?

A
  • The phospholipids will have more kinetic energy and will move more
  • Increases fluidity and it begins to lose its structure
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29
Q

Why does an increase in temperature increase membrane permeability?

A
  • Higher temperature means the cell membrane loses its structure
  • This makes it easier for things to pass through as its fluidity is higher
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30
Q

What happens if the temperature of the cell membrane decreases ?

A
  • The fatty acid tails of the phospholipids move less and become more rigid, stiffening the membrane
  • This decreases the overall fluidity of the membrane, also decreasing its permeability and potentially restricting entry of important molecules into the cell
  • Low temperature can also slow cell growth by preventing the cell’s increase in size.
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31
Q

What happens in extremely low temperatures ?

A

In extreme situations, liquid in the cell can begin to freeze, forming crystals that pierce the membrane and might ultimately kill the cell

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32
Q

Outline how the effect of temperature on membrane permeability can be investigated

A
  • Beetroot cells contain betalain
  • Pieces of equal size beetroot are placed in water and heated in waterbaths at different temperatures for the same amount of time
  • The solutions are then placed in a colorimeter
  • When membranes are disrupted the red pigment is released
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33
Q

How can a colorimeter show the permeability of membranes?

A
  • The more betalain leaks out, the more permeable the membrane
  • More betalain leaking means more colour is absorbed by the colorimeter
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34
Q

Suggest 3 improvements of the design of the experiment

A
  • Cut pieces from same place in beetroot
  • Blot surface of beetroot before experiment
  • Use same volume of water
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35
Q

What causes membranes to dissolve ?

A

Organic solvents

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36
Q

Why do organic solvents cause membranes to dissolve ?

A

They are less polar than water and will therefore dissolve membranes, disrupting cells

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37
Q

How do solvents affect cell membranes ?

A
  • The membrane loses its structure

- This increases its permeability

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38
Q

Why do solvents increase membrane permeability?

A

This is because they dissolve phospholipids

39
Q

Give an example of a solvent that can dissolve phospholipids

A

Ethanol, Methanol etc.

40
Q

Define diffusion

A

The net movement of particles from a region of high concentration to a region of low concentration

41
Q

Is diffusion active or passive ?

42
Q

Define passive transport

A

Movement of substances that does not require energy

43
Q

Which 2 factors affect the rate of diffusion

A
  • Temperature

- Concentration gradient

44
Q

What effect does an increase in temperature have on the rate of diffusion ?

A
  • It increases the rate of diffusion
45
Q

Why does a higher temperature increase the rate of diffusion ?

A
  • Higher temperature means particles have more kinetic energy and move at higher speeds.
  • Therefore, they can diffuse quicker too
46
Q

What effect does a greater difference in concentration of two regions have on the rate of diffusion ?

A

It increases the rate of diffusion

47
Q

What 4 factors affect the rate of diffusion across a membrane ?

A
  • Temperature
  • Concentration gradient
  • Surface area of membrane
  • Thickness of membrane
48
Q

An increase in surface area of an exchange surface has what effect on rate of diffusion ?

A

Increases the rate of diffusion

49
Q

An increase in membrane thickness has what effect on the rate of diffusion ?

A

Decreases the rate of diffusion

50
Q

What sort of molecules can move via diffusion across a membrane ?

A
  • Small molecules
  • Lipid soluble molecules
  • Non-polar molecules
51
Q

Why can steroid hormones easily cross a membrane by simple diffusion ?

A
  • They are lipid soluble

- They are non polar

52
Q

Why is it easier for oxygen to diffuse across a membrane than water ?

A
  • Oxygen molecules are small and non-polar whereas water molecules are polar
  • Water is only partially charged so it is still able to diffuse through the membrane, though only slowly
53
Q

Define facilitated diffusion

A

Diffusion across a plasma membrane through protein channels

54
Q

Is facilitated diffusion passive or active ?

A

It is passive

55
Q

What does facilitated diffusion allow to move across a membrane ?

A
  • large molecules
  • lipid insoluble molecules
  • charged particles
56
Q

What are the 5 factors which affect the rate of facilitated diffusion ?

A
  • Temperature
  • Concentration gradient
  • Surface area
  • Membrane thickness
  • Number of channel proteins
57
Q

Why are membranes containing protein channels selectively permeable ?

A
  • Most protein channels are specific to one molecule or ion

- Therefore only these specific molecules/ions are able to move across the membrane

58
Q

How do protein channels allow charged particles to move through the membrane ?

A

They provide a hydrophilic channel for charged particles

59
Q

What happens to charged molecules when they try to cross the membrane ?

A

The hydrophobic interior of the phospholipid bilayer repels the charged molecules

60
Q

Which types of movements of particles require ATP ?

A
  • Active Transport

- Bulk Transport

61
Q

What does active transport require to occur ?

A
  • ATP

- Carrier proteins

62
Q

Why is active transport considered to be selective ?

A

Specific substances are transported by specific carrier proteins

63
Q

Describe how active transport occurs with aid of a carrier protein

A
  • Molecules or ions bind to receptors in the channel of the carrier protein
  • ATP binds to the opposite side of the carrier protein
  • ATP is hydrolysed to form ADP and phosphate
  • The phosphate molecule binds to the carrier protein which causes the protein to change shape
  • The carrier protein opens and allows the molecules through
  • Phosphate molecule is released and recombines with ADP to form ATP
  • The carrier protein returns to its original shape
64
Q

Define endocytosis

A

The bulk transport of materials into cells

65
Q

Outline how endocytosis occurs

A
  • In endocytosis, the cell takes in biological molecules by forming new vesicles from the plasma membrane
  • A small area of the plasma membrane invaginates (sinks inwards) to form a pocket
  • As the pocket deepens, it pinches inwards forming a vesicle containing substances that had been outside the cell
66
Q

Define pinocytosis

A

The bulk transport of liquids into cells

67
Q

Outline how pinocytosis occurs

A
  • In pinocytosis, a cell gulps droplets of extracellular fluid into tiny vesicles, encapsulating molecules dissolved in the fluid
  • Pinocytosis is non specific, any and all included solutes are taken into the cell
68
Q

Define phagocytosis

A
  • The bulk transport of solids into cells
  • Cellular eating
  • Most commonly the process by which white blood cells engulf pathogens
69
Q

Outline how phagocytosis occurs

A
  • The cell surface membrane invaginates when it comes into contact with a bacterium
  • The membrane then enfolds around the bacterium forming a vesicle
  • The vesicle then pinches off and moves into the cytoplasm towards lysosomes
70
Q

Define receptor-mediated endocytosis

A

It enables cells to acquire bulk quantities of specific substances from the extracellular fluid

71
Q

Outline how receptor-mediated endocytosis occurs

A
  • Receptor proteins in the membrane bind to specific substances (ligands), then cluster to form coated pits.
  • Coated pits then form a vesicle that contains ligand molecules and is coated in proteins
72
Q

Define exocytosis

A

The bulk transport of materials out of a cell

73
Q

Outline how exocytosis occurs

A
  • Vesicles are usually formed by the golgi apparatus
  • Vesicles move towards and fuse with the cell surface membrane
  • Contents of the vesicle are then released outside of a cell and the vesicle membrane becomes part of the cell membrane
74
Q

Name an example of exocytosis

75
Q

Does bulk transport require ATP ?

76
Q

Why would a molecule be moved by bulk transport ?

A

It is too big for channel or carrier proteins

77
Q

Name 3 things which are moved by bulk transport

A
  • Enzymes
  • Hormones
  • Bacteria
78
Q

What is osmosis ?

A

Osmosis is the diffusion water molecules, across a partially permeable membrane, from an area of high water potential to an area of low water potential ?

79
Q

What type of process is osmosis ?

A

Osmosis is a passive process

80
Q

What is water potential ?

A
  • Osmosis refers to the concentration of free water molecules
  • It is the pressure exerted by water molecules as they collide with a membrane or container
81
Q

What are the units for water potential ?

82
Q

What is the water potential of pure water ?

83
Q

Why does water potential decrease as solute is added ?

A
  • When a substance is dissolved in water the kinetic energy of the water is lowered
  • Because water molecules cluster around the solute
  • Movement of water molecules is partially impeded
  • So a lower pressure is exerted
84
Q

What is a hypertonic solution ?

A
  • Having a higher concentration of solute relative to another solution
  • Low water potential
85
Q

What is an isotonic solution ?

A

Having the same concentration of solute relative to another solution

86
Q

What is a hypotonic solution ?

A
  • Having a lower concentration of solute relative to another solution
  • High water potential
87
Q

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

A
  • Water will move into the cell by osmosis, increasing the hydrostatic pressure inside the cell
  • Causes the cell to burst
  • Cytolysis
88
Q

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

A
  • Water will be lost to the solution by osmosis, down the water potential gradient
  • This reduces the volume of the cell
  • Crenation
89
Q

What would be the effect of placing a red blood cell in a hypotonic solution?

A
  • Net movement of water into the cell
  • Cell swells and bursts
  • Causing Haemolysis
  • Cell contents lost, haemoglobin released
90
Q

What would be the effect of placing a red blood cell in a hypertonic solution?

A
  • Net movement of water out of the cell
  • Cell shrinks and shrivels
  • Becomes darker in colour as haemoglobin is more concentrated
  • Crenation
91
Q

What would be the effect of placing a plant cell in a hypotonic solution?

A
  • Net movement of water into cell
  • Protoplast pushed against cell wall
  • Cell becomes turgid
92
Q

Why do plant cell walls not burst from osmosis?

A
  • They have strong cellulose cell walls

- Cell walls are able to resist the hydrostatic pressure

93
Q

What would be the effect of placing a plant cell in a hypertonic solution?

A
  • Net movement of water out of cell
  • Contents shrink
  • Protoplast completely pulled away
  • Plasmolysis occurs

Biology (30 decks)

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