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BIOSCI 107 - Cell Processes > CP - Structure and Function of the Cell Membrane > Flashcards

CP - Structure and Function of the Cell Membrane Flashcards

1
Q

What are the main constituents of the cell membrane?

A

Phospholipids and proteins

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2
Q

The term to describe the membrane structure

A

Fluid Mosaic Model

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3
Q

What is the membrane structure?

A

A thin, flexible and sturdy barrier that surrounds the cytoplasm of a cell

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4
Q

What is the membrane held by?

A

Hydrogen bonds

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5
Q

What is the lipid bilayer of the cell membrane?

A

2 back-to-back (parallel) layers of 3 types of lipid molecules

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6
Q

In water, what do most phospholipids tend to form?

A

A lipid bilayer structure with the polar head groups at the surface in contact with water and the fatty acid chains in the core screened from water contact

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7
Q

What are scattered among a double row of phospholipid molecules?

A

Cholesterol and glycolipids

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8
Q

Each phospholipid molecule is _____

A

amphipathic

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9
Q

What are the features of phospholipids?

A

Hydrophobic core (non-polar tails) and charged hydrophilic surface (polar heads)

hydrophobic non-polar tails and hydrophilic polar heads

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10
Q

What is an important feature of the hydrophobic core?

A

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

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11
Q

Membranes are ____ ____ and ____ that can move around within the ____ of the ____ ____

A

fluid structures, lipids

plane, membrane leaflet

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12
Q

What do lipids rarely do? What happens to the lipid composition of the leaflets because of this?

A

Lipids rarely flip flop between membrane leaflets so the lipid composition of the leaflets can be asymmetric

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13
Q

What is the fluidity of the membrane determined by (3 factors)?

A
  1. Lipid tail length (longer the tail, less fluid the membrane)
  2. No. of double bonds (more increases fluidity)
  3. Amount of cholesterol (more decreases fluidity)
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14
Q

What are integral membrane proteins?

A

They extend into or completely across the cell membrane (transmembrane protein)

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15
Q

What is a feature of integral membrane proteins?

A

They are amphipathic, hydrophobic regions span the hydrophobic core of the lipid bilayer, which usually consists of non-polar (hydrophobic) amino acids coiled into helices and hydrophilic ends of the proteins interact with the aqueous solution

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16
Q

What are peripheral proteins? what are they easily removed by

A

They are attached to either the inner or outer surface of the cell membrane and are easily removed from it by changes in ionic strength (increasing ionic strength breaks ionic bond)

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17
Q

Membrane proteins can act as:

A

Receptors; Cell Identity Markers; Linkers; Enzymes; Ion Channels; Transporter Proteins

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18
Q

What is the selective permeability of the cell membrane? and what is it governed by?

A

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

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19
Q

What is the permeability of a molecule dependent on?

A

Its size, charge and lipid solubility

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20
Q

What is the lipid bilayer permeable to?

A
  • Non-polar, uncharged molecules, e.g. O2, N2, benzene
  • Lipid soluble molecules, e.g. steroids, fatty acids, some vitamins
  • Small, uncharged polar molecules, e.g. water, urea, glycerol, CO2
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21
Q

What is the lipid bilayer impermeable to?

A
  • Large uncharged polar molecules, e.g. glucose, amino acids

- Ions, e.g. Na+, K+, Cl-, Ca2+, H+

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22
Q

What do membrane proteins do?

A

They mediate the transport of substances across the membrane that can’t permeate the hydrophobic core of the lipid bilayer

23
Q

What is diffusion?

A

The random mixing of particles in a solution as a result of the particle’s kinetic energy, where more molecules move away from a high conc. area to a low conc. area

24
Q

What factors affect the rate of diffusion?

A
  • Conc. (greater the difference in conc. between the 2 sides of the membrane, faster the rate of diffusion)
  • Temp. (higher the temp., faster the rate of diffusion)
  • Size (larger the size of diffusing substance, slower the rate of diffusion)
  • Surface area (increase in surface area, increases rate of diffusion)
  • Diffusion distance (increase in diffusion distance slows rate of diffusion)
  • Membrane thickness (thicker the membrane, slower the diffusion)
25
Q

What is the limit on the size of cells for the rate of diffusion?

A

20μm - don’t need to know this bc we don’t need to know any numbers hehe (from perla)

26
Q

What is the conc. gradient?

A

The selective permeability of the membrane enables a difference in conc. across the membrane to be established

27
Q

What will diffuse down their conc. gradients?

A

Non-charged molecules

28
Q

What is the electrical gradient?

A

Cells can maintain a difference in charged ions between the inside and outside of membrane, establishing an electrical gradient or membrane potential

29
Q

What will be influenced by membrane potential in addition to their conc. gradient?

A

Ions

30
Q

What will be influenced by the electrochemical gradient (which effects both conc. and electrical gradient)?

A

Net movement of ions

31
Q

Membranes ___ ____ and can ____ and ____ ____

A

mimic capacitors, separate, store charge

32
Q

How much ~% of resting energy do cells use to maintain conc. and electrical gradients?

A

~30% (dont needa know this one either xoxoxox)

33
Q

What does the resting energy that cells use to maintain conc. and electrical gradients represent?

A

Stored energy

34
Q

What is osmosis?

A

The net diffusion of water across a semi-permeable membrane (which is more permeable to water than to solutes) from a high water conc. area to a low water conc. area

35
Q

What happens when solutions of different solute conc. are separated by a semi-permeable membrane?

A

There is tendency for water to move from the solution for lesser solute conc. to the solution of greater solute conc.

36
Q

What happens when an osmotic gradient exists?

A

Water will want to move to eliminate it

37
Q

What can osmotic water movement be prevented by?

A

An opposing force

38
Q

What is defined as the osmotic pressure of the solution?

A

The hydrostatic pressure applied to oppose osmosis (prevent the inward flow of water across a semi-permeable membrane)

39
Q

What property is osmotic pressure and why?

A

Colligative property, because it only depends on the numbers and not the types of particles in solution

40
Q

What is the equation of membrane permeability to water (Pw)?

A

Pw = Pd (through lipid bilayer) + Pf (through water channel), where Pf > Pd

41
Q

What are the properties of permeability through lipid bilayer (Pd)?

A
  • Small (not a lot of water flow through the bilayer but there is a large amount of water)
  • Mercury insensitive (tends to not be blocked by mercury)
  • Temp. dependent (higher the temp., the more permeability through the lipid bilayer, can change lipid fluidity)
42
Q

What are the properties of permeability through water channel (Pf)?

A
  • Large
  • Mercury sensitive (mercury can block the channel)
  • Temp. independent
43
Q

What is Pf mediated by? (+ what are these?)

A

Aquaporins which are channels that allow only water to flow through them without any ions (9 isoforms)

44
Q

Why do cells have different Pw?

A

They express different aquaporin isoforms, and you can change Pw of a membrane by changing what aquaporin channels are put into that membrane

45
Q

How would you calculate the osmolarity of 0.5 NaCl + H2O?

A

0.5M Na+ + 0.5M Cl - = 1 Osmol

46
Q

If the solution has the same osmolarity, it is ____

A

isosmotic

47
Q

If the solution has a lower osmolarity, it is _____

A

hyposmotic

48
Q

If the solution has a higher osmolarity, it is _____

A

hyperosmotic

49
Q

If osmosis occurs, what happens?

A

A change in cell volume

50
Q

What is tonicity?

A

The effect a solution has on cell volume

51
Q

What is tonicity dependent on?

A

The membrane permeability of the solute so the osmolarity of the solution doesn’t always indicate the effect it will have on cell volume

52
Q

What occurs in an isotonic solution?

A

No change in cell volume

53
Q

What occurs in a hypotonic solution?

A

Cell swelling and eventually, cell lysis (haemolysis)

54
Q

What occurs in a hypertonic solution?

A

Cell shrinkage (crenation)

BIOSCI 107 - Cell Processes (4 decks)

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