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A Level Biology > Module 2 Section 5 - Biological Membranes > Flashcards

Module 2 Section 5 - Biological Membranes Flashcards

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1
Q

Give three functions of cell surface membranes.

A
  • partially permeable barriers between and within cells & organelles (this allows compartments where substances are held for chemical reactions) and can control the exchange of substances passing through them
  • sites of chemical reactions (e.g. respiration)
  • sites of cell communication (cell signalling, messenger molecules bind to receptors which can lead to changes in a cell)
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2
Q

What are cell membranes made of?

A
  • Lipids (mainly phospholipids)
  • Proteins
  • Carbohydrates (which are usually attached to the two above)
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3
Q

fluid mosaic model

A

A model that describes the fluid and flexible nature of the cell membrane and the components it is made from.

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4
Q

Describe the fluid mosaic model.

A
  • Phospholipids form a bilayer
    -> this is fluid as they are constantly on the move
  • Proteins are scattered throughout the bilayer (like a mosaic/plum pudding)
  • Glycoproteins/glycolipids are bonded to these
  • Some cholesterol molecules are also in the bilayer
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5
Q

Why does the fluid mosaic model describe membranes as ‘fluid’?

A
  • The phospholipids & proteins can move around via diffusion
  • The phospholipids mostly move sideways, within their own layers
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6
Q

Why does the fluid mosaic model describe membranes as a ‘mosaic’?

A

The different types of proteins scattered throughout the bilayer move/float within it (although some may be fixed in position)
OR
The plasma membrane is made of lots of different molecules

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7
Q

Is the phospholipid tail hydrophobic or hydrophilic?

A

Hydrophobic

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8
Q

Role of phospholipids in the fluid mosaic model of cell membranes

A

Centre of bilayer is hydrophobic, so it acts as a barrier to stop water soluble substances (e.g. ions/polar substances) from diffusing through

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9
Q

Why can water diffuse through the cell membrane?

A

It’s polar, however it’s small enough to diffuse through

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10
Q

What can pass through the phospholipid bilayer (only through the phospholipids)?

A

Fat/lipid soluble substances (but not water soluble ones like ions/polar molecules).

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11
Q

Role of cholesterol in the fluid mosaic model of cell membranes

A

They give the membrane stability, as at high temperatures, they bind to the phospholids’ hydrophobic tails, causing them to pack more closely together. This makes the membrane less fluid and more rigid.

Some parts of cholesterol are hydrophobic, so it can create a further barrier to water soluble substances to stop them from moving through the membrane - cholesterol affects the permeability of the membrane.

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12
Q

What does cholesterol do when it’s cold?

A

Cholesterol prevents the phospholipids from packing too closely together, making the membrane more fluid and less rigid.

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13
Q

Role of proteins in the fluid mosaic model of cell membranes

A
  • Control the movement of substances into and out of the cell
  • Some form protein channels (pores) which allow small charged molecules through
  • Some are carrier proteins which help transport bigger molecules and charged particles across the membrane (by active transport and facilitated diffusion).
  • Some act as receptors for molecules (e.g. hormones) triggering a chemical reaction for cell signalling
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14
Q

glycolipid vs. glycoprotein

A

glyco = sweet (sugar)
glycolipid - carbohydrate bonded to a lipid
glycoprotein - carbohydrate bonded to a protein

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15
Q

Role of glycolipids & glycoproteins in the fluid mosaic model of cell membranes

A
  • Form hydrogen bonds with surrounding water molecules
  • Act as receptors for messenger molecules in cell signalling
  • Are antigens (which are involved with self-recognition)
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16
Q

Two factors that affect membrane permability

A
  • Solvent
  • Temperature
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17
Q

Explain how the type of solvent affects membrane permeability.

A
  • Membrane is more soluble in the solvent
  • Lipids dissolve in the cell membrane -> membrane loses its structure
  • Increases membrane permeability
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18
Q

Explain how low temperatures affects membrane permeability.

A
  • Phospholipids have little energy -> don’t move around lots -> low permeability
  • Channel & carrier proteins denature -> increases permeability
  • Ice can penetrate the membrane, leaving big pores when it melts -> increases permeability
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19
Q

Explain how temperatures between 0 and 45°C affects membrane permeability.

A

0-45°C:
* Phospholipids aren’t too closely packed together and so can move around
* Increasing temp increases kinetic energy -> permeability increases

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20
Q

Explain how high temperatures affects membrane permeability.

A
  • Above 45°C, phospholipid bilayer melts -> membrane becomes more permeable
  • Water expands, putting pressure on the membrane
  • Channel and carrier proteins denature -> don’t control the transfer of substances -> permeability increases
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21
Q

Graph of alcohol concentration on membrane permeability

A

https://cdn.discordapp.com/attachments/1293960808828506224/1295071505683582996/image.png?ex=670d50d4&is=670bff54&hm=66ac284f71797a5cfc32b8104882a56e876736e025b575bf9698fe08d5685211&

pg 127 of CGP textbook

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22
Q

Graph of temperature on membrane permeability

A

https://cdn.discordapp.com/attachments/1293960808828506224/1295071805337239654/image.png?ex=670d511b&is=670bff9b&hm=18e48c8e45d3aae7be247ce1f2705dbf84b708f2d247170e16a29310c6b8c602&

pg 127 of CGP textbook

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23
Q

diffusion

A

The passive, net movement of molecules from an area of high concentration to an area of low concentration, down the concentration gradient, until equilibrium is reached. No external energy is required.

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24
Q

Simple diffusion

A

Where particles simply diffuse through the membrane.

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25
Q

Where can diffusion occur?

A

In solutions or gases

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26
Q

osmosis

A

The net movement of water molecules from a high water potential to a lower water potential, across a partially permeable membrane down the water potential gradient.

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27
Q

water potential (general definition)

A

The likelihood of water molecules to diffuse into or out of a solution.

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28
Q

water potential (pressure definition)

A

Pressure exerted by free water molecules on a membrane.

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29
Q

What is water potential measured in?

A

kPa

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30
Q

What is the water potential of:
a) distilled water?
b) a solution of glucose?

A

a) 0
b) negative

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31
Q

The more –ve the water potential, the ____ the concentration of the solutes.

A

stronger

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32
Q

hypotonic solution

A

A more dilute solution than the cells - has less concentrated solutes

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33
Q

hypertonic solution

A

A more concentrated solution than the cells - has more concentrated solutes

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34
Q

isotonic solution

A

The same concentration of solutes as the cell

35
Q

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

A

The solution has a higher water potential than the cell, so the net water movement is into the cell through the partially permeable plasma membrane down the water potential gradient via osmosis.

Animals cells swell and eventually burst, while plant cells’ vacuoles & cytoplasms swell and push against the cell wall. The cell becomes turgid.

36
Q

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

A

The solution has a lower water potential than the cell, so the net water movement is out of the cell through the partially permeable plasma membrane down the water potential gradient via osmosis.

Animals cells shrink, while plant cells become flaccid as the cytoplasm & plasma membrane pull away from the cell wall (plasmolysis).

37
Q

plasmolysis

A

When a plant cell is placed in a hypertonic solution, the cytoplasm & plasma membrane pull away from the cell wall

38
Q

ψ meaning

A

Greek letter psi
symbol for water potential

39
Q

Explain why the potato cylinders are each blotted dry before reweighing (RP). [2]

A

Water will affect the mass, and the amount of water on each cylinder will differ.

40
Q

model for how animal cells react to different water potentials of solutions

A

chickens’ eggs that have had their shells dissolved

41
Q

How can you investigate how animal cells are affected by water potential?

A
  • Make sodium chloride solutions of different concentrations (e.g. 0.2, 0.4, 0.6, 0.8 and 1.0M)
  • Pour an equal volume of each concentration into five different beakers
  • Take the deshelled chickens’ eggs and pat dry with a paper towel to remove any excess moisture
  • Use a mass balance to measure the mass of each egg
  • Place each egg into a different beaker, so that the sodium chloride completely covers the eggs
  • Leave all the eggs for 24 hours
  • Remove the eggs and pat each egg dry with new dry paper towels
  • Reweigh each egg
  • Percentage change in mass = (final mass - initial mass) / initial mass * 100
  • Plot a graph of percentage change in mass against sodium chloride concentration. You can use this to estimate how solutions of different water potential affect the mass of the egg
42
Q

facilitated diffusion

A

The passive movement of large or charged molecules (diffusion) through the plasma membrane via carrier proteins and channel proteins (transport proteins) from an area of high concentration to an area of low concentration, down the concentration gradient

43
Q

Why do some bigger molecules go through facilitated diffusion?

A

They would diffuse very slowly through the phospholipid bilayer

44
Q

How is facilitated diffusion triggered?

A

A chemical messenger binds to the transport protein, causing it to change shape to allow a specific substance to pass through the membrane

45
Q

Transport proteins are open all the time. T/F and why?

A

False - they open & close to only let certain molecules pass through

46
Q

Can polar molecules diffuse through membranes?

A

Yes, but only at a slow rate.

47
Q

Give examples of some molecules that diffuse through facilitated diffusion.

A
  • Glucose
  • Amino acids
  • Ions
  • Polar molecules
48
Q

How potassium ions transported across the membrane? Is this passive or active?

A

Facilitated diffusion - channel protein. Passive

Most ions are transported this way (can you give one that isn’t?)

49
Q

How are calcium ions transported across the membrane? Is this passive or active?

A

Active transport - carrier protein. Active

50
Q

How are bacteria transported across the membrane? Is this passive or active?

A

Endocytosis. Active

51
Q

How are enzymes and hormones transported across the membrane? Is this passive or active?

A

Exocytosis. Active

52
Q

The tails of phospholipids are polar/non-polar.

A

non-polar (& hydrophobic)

53
Q

Identify the type of particle that could cross the membrane using simple diffusion.

A

hydrophobic & non-polar

54
Q

Why will only uncharged particles pass through the membrane?

A

The phosphate heads are -vely charged, but the fatty acids are uncharged. Fatty acids make up most of the membrane structure, so the membrane is uncharged

55
Q

What route do particles that pass through the membrane via simple diffusion take?

A

They go through little gaps formed from the tilting of phospholipids with unstaturated fatty acids

56
Q

Look at a molecule of triglyceride. Why can’t it diffuse through a cell membrane?

A

It is too large to diffuse through the membrane by simple diffusion.

57
Q

Look at a molecule of citric acid. Why can’t it diffuse through a cell membrane?

A

It is too charged and hydrophilic to diffuse through the membrane by simple diffusion.

58
Q

Explain why glucose can’t just diffuse through the phospholipid bilater. Suggest a way that it can travel through a membrane.

A

Glucose is polar, hydrophilic (water soluble), lipophobic (not lipid soluble) and large.
Facilitated diffusion

59
Q

Look at a diagram of a fatty acid molecule. Describe its properties and how it can travel through a membrane.

A

Fatty acids are non-polar, hydrophobic (not water soluble) and lipophilic (lipid soluble).
Simple diffusion

60
Q

For simple diffusion, the rate of diffusion* is/isn’t* meaningfully affected by the presence of transport proteins.

A

isn’t

61
Q

Diffusion & osmosis need energy. T/F and why?

A

Both diffusion and osmosis rely on the random movement of particles, which requires energy. Cells don’t need extra energy to transport them though.

62
Q

Explain why a highly folded membrane may enable a higher rate of facilitated diffusion, compared to a membrane with no folds.

A
  • Increasing the number of folds increases the surface area to volume ratio.
  • This provides more space for a larger number of transport proteins on the membrane.
  • If all other factors are constant, an increase in the number of transport proteins increases the rate of facilitated diffusion.
63
Q

How do carrier proteins work?

A

Large/polar molecule binds to carrier protein
Carrier proteins changes shape to be complementary to the molecule
This moves and releases the molecule to the other side of the membrane

64
Q

Carrier proteins do not require an external source of energy to function. T/F and why?

A

False - they can act in passive (facilitated diffusion) and active (active transport) methods of transport.

For active transport, carrier proteins require energy in the form of ATP to change shape, in order to move the solute against the concentration gradient.

65
Q

Proteins are hydro____ and polar/nonpolar.

A

hydrophilic and polar - think of the OH and NH2 groups

66
Q

How do really big molecules enter cells?

A

Endocytosis

67
Q

Give three examples of molecules that enter cells through bulk transport.

A
  • Some carbohydrates
  • Lipids
  • Proteins
  • Microogranisms & dead cells can also be taken in by phagocytes.
68
Q

Describe how endocytosis occurs.

A
  • Cell surrounds a substance with a bit of its membrane
  • The membrane (bends inwards and) pinches off to form a vesicle
  • The vesicle moves into the cytoplasm for further processing of the substance
69
Q

Describe how exocytosis occurs.

A
  • Vesicles containing substances are formed by the Golgi apparatus
  • The vesicles move to and fuse with the plasma membrane (which then bends inwards)
  • The vesicles then release their contents out of the cell (or sometimes into the membrane e.g. membrane proteins)
70
Q

Does bulk transport need an external energy source?

A

Yes - ATP.

71
Q

Describe how cell signalling works.

A
  • A cell releases a messenger molecule
  • Messenger molecule travels (e.g. in the blood) to another cell
  • This cell has got the complementary membrane-bound receptor, so the molecule binds to the receptor
  • This triggers a change in the cell
72
Q

How do antihistamine drugs work to relieve pain?

A
  • Antihistamines are a complementary shape to the membrane-bound receptors that bind to histamines, so they bind to them
  • This means the messenger molecules (histamines) can no longer bind to their complementary receptors as they’ve been blocked
  • This means the histamines can’t trigger a change or response in the cells
73
Q

Give three examples of membrane-bound receptors.

Don’t necessarily need to know

A
  • Proteins
  • Glycoproteins
  • Glycolipids
74
Q

How is ATP broken down?

A

ATP is hydrolysed to form ADP and 1 phosphate (separated from the others)

75
Q

The energy for direct active transport is provided by the ATP molecule, stored in the bond between…

A

two phosphates

76
Q

active co-transport

A

The coupled movement of substances across a cell membrane via a carrier protein

77
Q

How does active co-transport work?

A
  • the transport protein binds to the first particle and one phosphate in ATP
  • it hydrolyses ATP into ADP and one phosphate ion
  • this opens up the transport protein; the transport protein changes shape
  • this transfers the first particle across the membrane and reveals a second binding site
  • the specific desired second particle binds to the second binding site in the transport protein
  • this causes the phosphate ion to be released, triggering the transport protein to revert back to its original shape and releasing the second particle through the membrane

Don’t think you need to know this

78
Q

two ways active co transport can get its energy

A

hydrolysis of ATP
moving a particle down its concentration gradient

79
Q

indirect active transport

A

The movement of one type of particle uses energy, and this movement maintains the concentration gradient needed for transportation of a different particle(s)

80
Q

indirect active transport process

A
  • one particle moves against its concentration gradient by active transport with a carrier protein
  • this means the concentration gradient is in the right direction for both particles
  • another transport protein moves the two particles down their concentration gradient via facilitated diffusion
81
Q

intrinsic protein (+ examples)

A

a protein embedded in both layers of the membrane with their arrangement determined by their hydrophilic and hydrophobic regions (they are more hydrophobic)
e.g. carrier/channel proteins

Don’t know if you need to know this

82
Q

extrinsic protein (+ examples)

A

a hydrophilic protein found on the surface (outer or inner) of the plasma membrane
e.g. enzymes, glycoprotein

Don’t know if you need to know this

83
Q

What are extrinsic proteins also called?

A

peripheral proteins

Don’t know if you need to know this

A Level Biology (4 decks)

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