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z:2017 - Biosci 107 2/2 > Structure and function of cell membrane > Flashcards

Structure and function of cell membrane Flashcards

1
Q

What is the function of a cell membrane? What does this allow?

A

Acts as a barrier isolating cells from their external environment Allows concentration gradients to be maintained, spatial organisation of chemical and physical processess within the cell

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2
Q

How should a cell membrane be viewed?

A

As a two dimensional fluid

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3
Q

What are the main constituents of a cell membrane?

A

Phospholipids and proteins

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4
Q

What do phospholipids tend to form in water? Explain the organisation

A

A bilayer structure with the polar head groups at the surface in contact with water and fatty acid chains in the cor separated from water contact

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5
Q

What is an important features ate hydrophobic core?

A

It provides a highly impermeable barrier to the passage of charged ions

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6
Q

Phospholipids have two regions on them, what are they? What does this make it?

A

Has both polar and non polar regions Makes it amphipathic

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7
Q

What is the model used to describe the structure of the cell membrane?

A

Fluid mosaic model

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8
Q

What is selective permeability?

A

Not all molecules are equal in terms of how they cross cell membranes

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9
Q

What affects the permeability of a molecules across a cell membrane?

A

Properties of molecules, interactions with cell membrane and transport proteins that are used

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10
Q

What does selective permeability allow between cells? What does this create?

A

Fluid compartments Dividing one side from the other stores different fluid gradients therefore stores energy

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11
Q

Describe the cell membrane in general structural terms

A

A sea of lipids which membrane proteins are imbedded

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12
Q

What happens, due to the integral membrane proteins, when the lipid bilayer is pulled apart ?

A

The membrane proteins stay in one of the lipid bilayers and it leaves a hole in the other one that it did not attach to

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13
Q

What is the thickness of the cell membrane?

A

8nm

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14
Q

Describe the cell membrane in general behavioural terms. What does it cover?

A

A thin flexible and study barrier the surrounding the cytoplasm of a cell

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15
Q

What is the compositional percentage of lipids and proteins in the cell membrane?

A

50/50

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16
Q

How is the lipid layer held together?

A

By hydrogen bonds

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17
Q

What is the lipid controlling?

A

The entry and exit of polar substances

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18
Q

What are the three general classes of lipids in the phospholipid bilayer?

A

Cholesterol, glycolipids and phospholipids

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19
Q

Where are cholesterol and glycolipids located relative to phospholipid? How are the phospholipids arranged?

A

They are scattered among the double row of phospholipids molecules Glycolipids are imbedded in and protrude from the lipid bilayer Cholesterols are imbedded within the fatty acid tails

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20
Q

What do phospholipids do within the cell membrane?

A

Make up the back bone of the cell membrane, the lipid bilayer

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21
Q

What is the structure of the glycolipid?

A

A lipid tail with a sugar coating

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22
Q

What can cholesterol do to the phospholipid backbone?

A

it can modify it’s properties

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23
Q

What can impact the phospholipids fluidity? How does increasing amounts affect fluidity?

A

-Cholesterol, more decreases fluidity -Number of double bonds between the bilayers, more double bonds make it more fluid as there are less kinks in the fatty acid chains to decreases mobility -Lipid tail length, the longer the tail the less fluid the membrane

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24
Q

How much of the total lipids in a cell is used in the cell membrane?

A

75% of all lipids used in cell membrane

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25
Q

Can the composition of the lipid leaflets in the phospholipid bilayer be asymmetrical? Why

A

Yes it can be because the lipids don’t ‘flip flop’ between membranes

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26
Q

How is a phospholipid bilayer formed? Why does it form this arrangement?

A

It is formed automatically as the hydrophilic head are attracted to the polar charged water which they are immersed in and the hydrophobic tails orientate themselves to exclude the water It is the lowest energy state

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27
Q

What are the types of membrane proteins?

A

Integral membrane proteins and peripheral membrane proteins

28
Q

How are integral membrane proteins connected to the cell membrane?

A

Extend into or completely across the cell membrane

29
Q

What type of membrane protein is a transmembrane protein?

A

A integral membrane protein that extends across the entire cell membrane

30
Q

How do you get integral membrane proteins out of the bilayer? What does this indicate about the layers relationship with the cell membrane? How do you get integral membrane proteins out?

A

You have to break down the bilayer Shows they have a strong interaction with the bilayer You have to use a detergent (it breaks down the phospholipid bilayer by interacting with the hydrophobic layer FYI)

31
Q

Where are peripheral membrane proteins attached to the cell membrane?

A

Either the inside or outer surface of the cell membrane

32
Q

How are peripheral membrane proteins attached to the cell membrane?

A

Attached to an integral membrane protein and other membrane proteins

33
Q

Which is harder to remove, peripheral or integral membrane proteins? Why?

A

Integral because they are imbedded in the phospholipid bilayer and have a strong interaction, peripheral are only attached onto other proteins no the lipid bilayer, so are easily removed

34
Q

What kind of bonds are used by peripheral membrane proteins to hold onto integral membrane proteins? What can break these bonds?

A

Ionic Changes in salt concentration

35
Q

What property do integral membrane proteins require to be able to imbed themselves into the cell membrane?

A

They need to be amphipathic

36
Q

Describe the distribution of an integral membrane protein’s charge, where are they located relative to the cell membrane?

A

Has non-polar regions that span the hydrophobic core of the bilayer (this makes these regions hydrophobic as well) and hydrophilic ends (polar regions) which interact with the aqueous solution outside of the bilayer

37
Q

What is the structure of the hydrophobic region of the integral membrane proteins? What kind of molecule are they?

A

Tend to be non-polar amino acids that are coiled into a helix

38
Q

What are the hydrophilic regions of the integral membrane proteins made of?

A

Polar amino acids

39
Q

What can membrane proteins do? Briefly outline what each of these functions do inside a cell

A

Receptor proteins (receive neurotransmitter and hormones and transduce into the cell)

cell identify markers (prevents immune response from killing cell)

linkers (link onto other cell membranes/cytoskeletal elements)

enzymes (allow chemical reactions to occur on cell membrane)

ion channels (allow ion movement into and out of cell)

transporters (move molecules in and out of cell)

40
Q

What is about a membrane that creates selective permeability?

A

The molecular organisation of the membrane

41
Q

Label the diagram

A
42
Q

Label the diagram

A
43
Q

What do protein channels do to allow impermeable molecules through the cell membrane?

A

Mediate substances across the hydrophobic core of the bilayer

44
Q

In the lipid bilayer, what kind of molecules are permeable? What makes them permeable through this bilayer?

A

Small molecules (both non-polar and slightly polar) (e.g. O2, CO2 , H2O, N2) - can easily dissolve into the bilayer Non-polar uncharged molecules and lipid soluble molecules - can pass through fatty acid tails

45
Q

In the lipid bilayer, what kind of molecules are impermeable? What makes them impermeable through this bilayer?

A

Large molecules (e.g. glucose, amino acids) - too large to move through gaps of membrane Highly charge ions (Na+, K+, Cl-, Ca2+ etc.) - can’t move across due to electrical gradients across membranes

46
Q

How do molecules that are impermeable through the cell membrane get into the cell membrane?

A

Through protein channels (ion channel or transporter)

47
Q

What process allows permeable molecules to come into the cell?

A

Diffusion

48
Q

What is diffusion?

A

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

49
Q

What factors increase the rate of diffusion?

A

The rate of diffusion is increased by: the greater the difference in concentration between the two side of the membrane, the higher the temperatures, the smaller the size of the diffusing substance, the larger the surface area, the smaller the distances needed to travel

50
Q

What happens once the concentration of substance is equally distributed?

A

There is no net movement, solution reaches equilibrium

51
Q

Because cells depend on diffusion, what are the physical consequences of this on the cells?

A

-The rate of diffusion sets a limit on the size of the cell to 20µm -cells require a high surface area -the membrane must be thin as thicker membrane slow diffusion

52
Q

How is the electrical gradient established?

A

A cell has a charge of -80µV and 0V outside so positive ions are electrically attracted into the cell and negative ion are repelled from the cell

53
Q

How will a molecule such a O2 be attracted to a cell differently from Na+?

A

O2 is uncharged so it will only be attracted to the cell by the concentration gradient, however Na+ will be affected by a combination of the concentration gradient and electrical gradient

54
Q

Are concentration and electrical gradients working in the same direction?

A

Sometimes, depends on the condition in the cell

55
Q

What is the movement of ions influenced by? What is this a combination of?

A

The electrochemical gradient Combination of the affects of the concentration and electrical gradient

56
Q

What kind of electrical device do cells mimic? Why is this?

A

Capacitors They can seperate and store charge

57
Q

How much of a cells resting energy is used to maintain concentration and electrical gradients?

A

30%

58
Q

What do the concentration and electrical gradients represent?

A

Stored energy

59
Q

What are the relative concentrations of Na+, K+ and Cl- inside the cell?

A

Low Na+, high K+, low Cl-

60
Q

What is the movement of Na+, K+ and Cl- across the cell membrane? Explain

A

Na+ want to go into the cell with the electrical gradient (going into (-) cell environment) and with its concentration gradient (from high outside cell to low inside cell) K+ wants to leave cell due to concentration gradient (high inside, low outside), however electrical gradient pulls K+ back, however in this case the concentration gradient is stronger than the electrical gradient Cl- can be considered at electrochemical equilibrium as concentration gradient takes it into the cell (high outside, low inside) but electrical gradient takes it out of the cell (- charge inside repels).

61
Q

What is osmosis?

A

The net diffusion of water across a semi-permeable membrane

62
Q

What is more permeable through a semi-permeable membrane, water or solutes?

A

Water

63
Q

What causes osmosis? What direction does the water flow?

A

When solutions of different solute concentrations are separated by a semi-permeable membrane The water flows from the solution of less solute (and more water) to the solution of more solutes and (less water)

64
Q

What can prevent osmosis from occurring between a semi-permeable membrane? What is this defined as?

A

A hydrostatic pressure Defined as the osmotic pressure of the solution

65
Q

What is the osmotic pressure determined by?

A

It depends on the number of particles in solution (not the type of particles FYI)

z:2017 - Biosci 107 2/2 (16 decks)

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