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Cell Membrane > Lecture 21: Membrane Structure And Function > Flashcards

Lecture 21: Membrane Structure And Function Flashcards

1
Q

What is the function of the cell membrane?

A

To act as a barrier, isolating cells from their external environment

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2
Q

What is a cell?

A

The functional unit of specialised function in living systems

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3
Q

What is the general structure of a membrane like?

A

Not static, but should be viewed as a two dimensional fluid

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4
Q

Why should the membrane be viewed as a two dimensional fluid?

A

Because lipids and proteins are therefore able to move in the plane of the membrane

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5
Q

What is a lipid?

A

Any class of organic compound that are fatty acids (or their derivatives) and are insoluble in water (but soluble in organic solvents)

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6
Q

What is the model of the membrane called?

A

The mosaic model

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7
Q

How thin is the cell membrane?

A

8nm (8x10^9)

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8
Q

What are there main constituents of the cell membrane?

A

50% lipids (phospholipids)

50% protein

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9
Q

What holds the two main components of the membrane together?

A

Hydrogen bonds

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10
Q

What does the lipid aspect of the membrane do?

A

It’s the barrier to entry or exit of polar substances

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11
Q

What are the function of the proteins?

A

They’re the gate keepers (ie they regulate traffic) -if they can’t pass through lipids, they gave to go through a protein

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12
Q

What is a lipid bilayer?

A

Two back to back layers of three types of lipid molecule

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13
Q

What are the three types of lipid molecule in the lipid bilayer?

A

Cholesterol and glycolipids are scattered among a double row of phospholipid molecules

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14
Q

What is the phospholipid bilayer’s association with water?

A

In water, most phospholipids tend to form a lipid bilayer or structure with polar head group at the surface in contact with water and the fatty acid chain in the core screened from water contact

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15
Q

The phospholipid bilayer comprises what number of lipids?

A

75%

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16
Q

What is the phospholipid bilayer?

A

Two parallel layers of molecule

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17
Q

What is amphipathic?

A

The molecule has both a polar and non polar region- this is a phospholipid

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18
Q

Describe phospholipids in water

A

In water, most phospholipids tend to form a lipid bilayer or structure with the polar head group at the surface in context with water and the fatty acid chain in the core (screened from water contact)

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19
Q

What part of the lipid bilayer is charged?

A

The hydrophilic surface (ie by the head)

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20
Q

Which part of the lipid bilayer is polar?

A

The head

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21
Q

Which part of the lipid bilayer is non-polar?

A

The tail (hydrophobic core)

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22
Q

What provides a highly impermeable barrier to the passage of ions?

A

The hydrophobic core

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23
Q

Why do we describe membranes as fluid?

A

Because lipids can move around within the membrane leaflet

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24
Q

Why can the compositions of leaflets be as symmetrical?

A

Because lipids rarely flip flop between membrane leaflets (therefore, different compositions of cholesterol, channel ion receptors, polysaturated fatty acid etc)

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25
Q

What three things determine the fluidity of the membrane?

A
  1. Lipid tail length
  2. Number of double bonds
  3. Amount of cholesterol
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26
Q

How does the lipid tail length affect fluidity?

A

The longer the tail, the less fluid the membrane

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27
Q

How does the number of double bonds affect the fluidity?

A

More double bonds increases fluidity

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28
Q

How does the amount of cholesterol affect fluidity?

A

More decreases fluidity (think restricted arteries)

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29
Q

Which two aspects primarily determine fluidity?

A

The number of double bonds and the amount of cholesterol

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30
Q

What does the fact that the cell membrane controls the passage of substances into cells allow for?

A
  1. The concentration gradient to be maintained
  2. The spatial organisation of chemical and physical processes within the cell
  3. The controlled uptake of nutrients and discharge of waste products and the secretion of molecules
  4. The development of a membrane potential
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31
Q

What are the two types of membrane proteins?

A
  1. Integral proteins

2. Peripheral proteins

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32
Q

What integral proteins?

A

They are proteins that extend into or completely across the membrane (transmembrane)

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33
Q

What are the properties of integral proteins?

A

They’re amphipathic (is have hydrophobic regions that span hydrophobic core of lipid layer)

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34
Q

Describe the common form of integral proteins?

A

Usually hydrophobic regions consist of non-polar amino acids coiled into helices and the hydrophilic end of protein interact with aqueous solution

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35
Q

What are peripheral proteins?

A

Proteins attaches to either inner or outer surface of cell membrane and are easily removed from it

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36
Q

What can membrane proteins act as?

A
  1. Receptors (of signal)
  2. Cell identity markers
  3. Linkers
  4. Enzymes (eg glucose is broken down often at membrane surface)
  5. Channels
  6. Transporters
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37
Q

What is permeability?

A

The ability of a particular molecule to cross a cell membrane is known as its permeability and is governed by the laws of diffusion

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38
Q

What is the cell membranes permeability?

A

Semipermeable (ie, the membrane allows some substances to cross, but excludes others)

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39
Q

What determines the permeability of a molecule?

A

Size, charge and lipid solubility

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40
Q

What suggests there is more than one mechanism of permeation acting on the cell membrane?

A

The wide range of membrane permeability

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41
Q

What is the cell membrane permeable to?

A
  1. Non polar uncharged molecules
  2. Lipid soluble molecules
  3. Small uncharged polar molecules
42
Q

What are examples of non polar, uncharged molecules?

A

Oxygen, N2, benzene

43
Q

What are examples of lipid soluble molecules?

A

Steroids, fatty acids, some vitamins

44
Q

What are examples of small, uncharged polar molecules?

A

Water, glycerol, urea, CO2

45
Q

What is the cell membrane impermeable to?

A
  1. Large, uncharged polar molecules

2. Ions

46
Q

What are examples of large uncharged polar molecules?

A

Glucose, amino acids

47
Q

What are examples of ions impermeable to the cell membrane?

A

NA+, K+, Cl-, Ca2+, H+

48
Q

What is diffusion?

A

The random mixing of particles in a solution as a result of the particle’s kinetic energy

49
Q

Where do molecules move during diffusion?

A

They move away from an area of high concentration to an area of low concentration

50
Q

What increases the rate of diffusion?

A
  1. The greater the difference in concentration between the two sides of the membrane
  2. The higher the temperature
  3. Increase in surface area
51
Q

What do membrane proteins mediate?

A

The transport of substances across the membrane that cannot permeate the hydrophobic core of the lipid bilayer

52
Q

What enables a difference in concentration, or concentration gradient, across the membrane to be established?

A

Selective permeability

53
Q

What establishes an electrical gradient or membrane potential?

A

How cells maintain a difference in charged ions between the cytosol side and extra cellular side of membrane

54
Q

What decreases the rate of diffusion?

A
  1. The larger the size of the diffusing substance = slower

2. Increase of diffusion distance

55
Q

Is diffusion faster over small or larger distances?

A

Small distances

56
Q

What is the rate of diffusion size limit of a cell?

A

20 um

57
Q

What can a cell do to increase diffusion?

A

A cell can increase the membrane area available for exchange (diffusion) of a substance

58
Q

What is a concentration gradient?

A

Non-charged molecules will diffuse down their concentration gradient

59
Q

What is an electrical gradient?

A

Ions will be influenced by membrane potential in addition to their concentration gradient (ie, movement of ions will be influenced by their electrochemical gradient)

60
Q

What percentage of resting energy do cells use to maintain a concentration and electrical gradient?

A

30%

61
Q

What do gradients represent?

A

Stored energy

62
Q

What is the net movement of ions across a membrane influenced by?

A

The electrochemical gradient

63
Q

What is the electrochemical gradient?

A

The effect of both chemical and electrical gradients

64
Q

What do membranes mimic and how is it similar?

A

Mini capacitors, in the sense that they can separate and store energy

65
Q

How does Na flow?

A

High on extra cellular side to low inner cellular

66
Q

How does K+ flow?

A

Low on extra cellular side, high in intracellular side (so flows out)

67
Q

How does chloride flow?

A

High on outside, low on inside, but flows both ways

68
Q

What is osmosis?

A

The net diffusion of water across a semi permeable membrane

69
Q

What is a semipermeable membrane more permeable to- water or solutes?

A

Water

70
Q

When solutions of different solute concentrations are separated by a semipermeable membrane, what tends to happen?

A

Water tends to move from the solution of lesser solute concentration to the solution of greater solute concentration

71
Q

When does diffusion stop?

A

When a equilibrium is reached

72
Q

What prevents osmotic water movement?

A

An opposing force called “osmotic pressure of the solution”, or hydrostatic pressure

73
Q

What is colligative property?

A

Colligative properties are the physical changes that result from adding solute to a solvent.

74
Q

What is osmotic pressure?

A

A colligative property

75
Q

How is osmotic pressure and colligative property?

A

It depends on the numbers and not the type of particles in solution (CHECK)

76
Q

What do you need to know to determine a cell’s osmolarity in Osmoles?

A

The concentration of a solution and knowledge of its ionisation properties

77
Q

What is the osmolarity for 1m glucose + H20?

A

= 1m glucose

= 1 Osmol (no association)

78
Q

What does 0.5 M NaCl+ H2O equal?

A

0.5M Na+ + 0.5 M Cl-

1 Osmol

79
Q

What does 0.5M CaCl2 + H2O equal?

A

0.33 M Ca2+ + 2x (0.33 M Cl-)

= 1 Osmol

80
Q

What is the solution if it has the same osmolarity when comparing two solutions?

A

Isosmotic

81
Q

When comparing two solutions, what do we call it if the solution has lower osmolarity?

A

Hyposmotic

82
Q

When comparing two solutions, what do we call it if the solution has higher osmolarity?

A

Hyperosmotic

83
Q

What is the osmolarity of the concentration of body fluids?

A

280 mOsmol

84
Q

Why does the osmolarity of extra cellular and intracellular fluid have to be equal? (Isosmotic)

A

So that no net water flow (osmosis) occurs. If osmosis occurs, a change in cell volume will occur

85
Q

What is tonicity?

A

The effect a solution has on cell volume

86
Q

What does the tonicity of a solution depend on?

A

The membrane permeability of the solute (so the osmolarity of a solution does not always determine the effect it will have on cell volume)

87
Q

Are osmolarity and tonicity always the same thing?

A

Not always

88
Q

What do we term “no change in cell volume”?

A

Isotonic solution

89
Q

What do we term a solution that causes cell swelling and eventually cell lysis (haemolysis)?

A

Hypotonic solution

90
Q

What do we term a solution that causes cell shrinkage (crenation)?

A

Hypertonic solution

91
Q

What types of molecules diffuse down a concentration gradient?

A

Non-charged molecules

92
Q

What types of molecules are influenced by both membrane potential (electrical gradient) and their concentration gradient? (Electrochemical)

A

Ions

93
Q

What types of molecules diffuse down a concentration gradient?

A

Non-charged molecules

94
Q

What types of molecules are influenced by both membrane potential (electrical gradient) and their concentration gradient? (Electrochemical)

A

Ions

95
Q

Size of the cell membrane?

A

8nm (8x10^-9)

96
Q

What bond holds lipids and proteins together?

A

Hydrogen bonds

97
Q

Which lipid comprises 75% of lipids?

A

Phospholipids

98
Q

What is amphipathic?

A

A molecule with both polar and non polar regions

99
Q

What does the number of double bonds do to fluidity?

A

It increases it

100
Q

Describe integral proteins?

A

Amphipathic
Non-polar, hydrophobic amino acids coiled into helices spanning hydrophobic core, hydrophilic polar ends interacting with aqueous solution

101
Q

Size limit of diffusing molecule?

A

20um

102
Q

How does membrane thickness affect diffusion rate?

A

It slows it down

Cell Membrane (6 decks)

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