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1. Biology A-level > 3. Cell Membranes and Transport > Flashcards

3. Cell Membranes and Transport Flashcards

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1
Q

phospholipid

A
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2
Q

describe phospholipid head

A

charged

hydrophillic

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3
Q

micelle

A
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4
Q

how are phospholipids held together in bilayers

A

weak hydrophobic interactions between the hydrocarbon tails allowing some membrane fluidity

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5
Q

Fluid Mosaic Model of Membrane Structure

A

Singer and Nicholson - 1972

-fluid, components of the membrane, particularly phospholipids can move between the two layers of membrane

-mosaic, looked at freeze fracture electron microscopy
-cell membrane is fractured along the line of least resistance – the centre of the bilayer. The images produced have a speckled effect caused by the proteins exposed, looked like a mosaic

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6
Q

why is it called the fluid mosaic model 2 marks

A

mosaic of protein molecules, randomly arranged

lipid layer is fluid - can move

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7
Q

fluid mosaic model membrane diagram

A
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8
Q

two types of membrane proteins

A

extrinsic

intrinsic

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9
Q

extrinsic proteins

A

on or in one side of the bilayer

eg receptors

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10
Q

intrinsic proteins

A

runs through both sides of the bilayer

eg transport proteins

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11
Q

eg of intrinsic protein and where it is found

A

ATP synthase

embedded on cristae of mitochondria

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12
Q

diagram of intrinsic and extrinsic proteins

A
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13
Q

characteristics of intrinsic proteins

A

hydrophilic and hydrophobic parts

span the membrane

some are channel proteins

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14
Q

channel protein

A

have hydrophilic R groups lining the space down the middle of the protein. These channels are specific to particular charged or polar particles and allow them to diffuse across the membrane in facilitated diffusion.

have hydrophilic groups lining the pore

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15
Q

protein carriers

A

involved in active transport and facilitated diffusion across the membrane; these are specific to the polar or charged molecules carrier

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16
Q

channel and carrier

A
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17
Q

cell membranes

A

selectively permeable

hydrophobic layer in middle of bilayer is impermeable to polar and charged particles

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18
Q

function of cell membrane

A

Taking up nutrients/other requirements/reference to selective permeability;
phagocytosis/secreting chemicals; cell recognition;
adhesion; receptor sites.

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19
Q

How do non polar molecules get through cell membrane

A

Non-polar molecules like oxygen, carbon dioxide and fat-soluble vitamins (A, D, E and K) dissolve in the hydrophobic layer and can cross the membrane by simple diffusion.

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20
Q

glycoprotein

A

These are proteins with carbohydrate chains attached

These carbohydrate chains also project out into whatever fluid is surrounding the cell (they are found on the outer phospholipid monolayer)

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21
Q

glycolipid

A

These are lipids with carbohydrate chains attached

These carbohydrate chains project out into whatever fluid is surrounding the cell (they are found on the outer phospholipid monolayer)

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22
Q

glycocalyx

A

All of the carbohydrates projecting outside of the cell

glycocalyx is mainly involved in cell to cell recognition

only found on the side of the bilayer that faces out of the cell

act as antigens in cell recognition

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23
Q

cell membrane - carbohydrates

A

act as specific antigens.

-An individual’s specific antigens are unique to themselves
- are involved in cell recognition and signaling, playing a critical role in immune responses
-If the carbohydrate structures on a cell are recognized as foreign, they trigger an immune response.

providing energy needed by the cell to survive

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24
Q

cell membrane - hydrophobic region, molecules of cholesterol

A

regulate the fluidity of the membrane and are found between fatty acid tails.

If there is not enough cholesterol, the membrane becomes too fluid

if there is too much cholesterol, the membrane becomes too rigid.

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25
Q

label

A

A - Hydrophilic heads

B - Hydrophobic tail

C - Intrinsic protein

D - Oligosaccharide/ glycoprotein

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26
Q

explain at temp below 40 degrees celcius effect on pigment in cell

A

the increased kinetic energy of the phospholipids and proteins in the membrane causes them to move more. This creates gaps between the phospholipids. The pigment will also have more kinetic energy so will move more and diffuse out of the cell into the water through these gaps.

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27
Q

explain at temp above 40 degrees celcius effect on pigment in cell

A

protein components of the membrane begin to denature, forming pores through which the pigment can diffuse out more easily. The graph will level off as all proteins denature and the cell membrane becomes fully permeable to the pigment.

28
Q

is diffusion active or passive

A

passive

29
Q

what does passive mean?

A

ATP/energy from respiration is not required

Respiratory inhibitors that inhibit ATP production do not affect passive transport methods.

In passive transport, movement is from high concentration to low concentration.

30
Q

diffusion

A

passive

the random movement of particles from a region of their high concentration to a region of their low concentration

vis phospholipid bilayer

transports -
small, non-polar or lipid-soluble molecules

31
Q

factors affecting rate of diffusion

A
  1. surface area of the membrane
  2. length of diffusion pathway
  3. steepness of concentration gradient
  4. temperature
  5. membrane permeability
32
Q

diffusion -
surface area of the membrane

A

A higher surface area gives more places over which diffusion can happen and increases the rate of diffusion. Folds in the cell membrane increase the surface area.

33
Q

diffusion -
length of diffusion pathway

A

the shorter the diffusion pathway, the faster diffusion can happen. Flattened cells, thinner membranes and less layers of cells decrease diffusion pathways.

34
Q

diffusion -
steepness of concentration gradient

A

the larger the difference between the high and low concentrations, the faster diffusion happens. Circulation and ventilation increase concentration gradients.

35
Q

diffusion -
temperature

A

the higher the temperature, the more kinetic energy particles have and the faster they move. This increases the rate of diffusion.

36
Q

diffusion -
membrane permeability

A

is affected by salt concentration, presence of detergents and organic solvents.

37
Q

diffusion -
lipid solubility

A

more lipid soluble a molecule is

faster it will diffuse across a membrane

38
Q

facilitated diffusion

A

passive process

uses specific protein carriers or channels

transports - Charged particles and polar molecules, large molecules (too big to cross via simple) accross the membrane

high conce to low conc

eg glucose and protons

39
Q

co-transport

A

two different particles are transported through the same protein at the same time

via a carrier protein

40
Q

eg of co transport

A

glucose and Na+, which are transported into cells together.

41
Q

protein carriers and facilitated diffusion

A

rate of facilitated diffusion depends on number of protein carriers

42
Q

factors affecting facilitated diffusion

A

temperature

concentration gradient

number of protein carriers

43
Q

osmosis

A

net movement of water from an area of high water potential to an area of low water potential across a selectively permeable membrane

passive process (requires no energy from ATP is unaffected by ATP inhibitors)

44
Q

define water potential

A

Water potential is defined as the tendency of water to leave a system by osmosis.

The difference between the free energy of water molecules in a system and the free energy of molecules in pure water/the tendency for water molecules to leave/move out of a system.

45
Q

what does water potential depend on

A

solute concentration (solute potential)

and

the pressure exerted on the solution (pressure potential).

46
Q

highest water potential

and unit of water potential

A

0

kPa

47
Q

hypotonic solution

A

lower solute concentration and therefore a higher water potential

48
Q

red blood cell

lysis

A

lack cell wall, haemolysis occurs, red pigment released (haemoglobin), remove debris, measure with colorimeter

49
Q

isotonic solution

A

same concentration of solute and the same water potential

50
Q

hypertonic solution

A

higher concentration of solute and a lower water potential

crenation - water moves out of the cells

51
Q

hypertonic solution
effect on
pressure potential

A

The vacuole shrinks,

The cytoplasm pulls away from the cell wall (a process called plasmolysis),

The cell becomes flaccid, and the pressure potential becomes zero, as there is no internal pressure exerted on the cell wall.

52
Q

The relationship between the solute, water and pressure potentials can be expressed by the equation:

A

Ψw = Ψs + Ψp

(pressure potential is a positive number, solute and water potentials are negative)

53
Q

Incipient Plasmolysis
Water potential, solute potential and bathing soultion relationship

A
54
Q

Explain how this pressure potential is built up in cell X. [3]

A

water passes into cell by osmosis; cytoplasm expands;
cell becomes turgid;
as cytoplasm/contents push against wall;
wall inelastic/resists further expansion. (not: rigid) [3 max]

55
Q

turgid

water potential

A

is 0

solute potential and pressure potential cancel out

56
Q

plasmolysis

A

The vacuole and cytoplasm shrink because of the loss of water and the cytoplasm pulls away from the cell wall.

When cells are plasmolysed the pressure potential is 0 kPa; the water potential and solute potential of the cells are equal.

57
Q

incipient plasmolysis

A

The point where 50% of the cells are plasmolysed is taken to be the point where the water potentials of solution and tissue are equal.

Wp = 0

58
Q

crenation vs plasmolysis

A

Crenation occurs in animal cells, whereas plasmolysis occurs in plant cells.

59
Q

lysis

A

only occurs in animal cells - burst

plant cells - surrounded by a rigid cell wall that can withstand the turgor pressure of the turgid cell contents.
Turgid means cells or tissues that are swollen due to water uptake.

60
Q

Diagram of turgid and plasmolysed cells

A
61
Q

Active transport

A

moves substances from low to high concentrations (against a concentration gradient) using specific protein carriers and energy from ATP.

62
Q

factors affecting active transport

A

Respiration rate - Aerobic respiration uses oxygen. The more oxygen that is available, the faster the rate of respiration and active transport.

Temperature can also affect respiration rate - increased temperatures can result in higher rates of active transport.

Cyanide is a respiratory inhibitor - that binds to cytochrome in the electron transport chain, preventing ATP production. As a result, cyanide prevents active transport. Passive transport is unaffected by cyanide.

63
Q

bulk transport

A

movement of solids or liquids

64
Q

endocytosis

A

type of bulk transport

Two Types:
phagocytosis is the movement of solids – like cells or large proteins;
pinocytosis is the movement of liquids.

cell membrane extends around the particles being taken into the cell.

Eventually the particles are surrounded and the membrane of the cell fuses around the particle,

forming a vesicle in the cytoplasm containing the particle.

65
Q

exocytosis

A

mechanism by which large particles such as enzymes and hormones are secreted from cells.

The vesicle containing the particles migrates to the cell membrane and fuses with it,

releasing the particles to the outside of the cell.

1. Biology A-level (9 decks)

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