membranes

Question 1

which parts of a phospholipid molecule is hydrophilic / hydrophobic ?

Answer 1

head is hydrophilic

tail is hydrophobic

Question 2

what is the phospholipid bilayer ?

Answer 2

double layer of phospholipid molecules, with heads facing outwards

Question 3

which type of cell membrane is cholesterol present in ?

Answer 3

all of them except bacterial cell membranes

Question 4

what does cholesterol do to the membrane and how ?

Answer 4

Fits between phospholipid molecules and binds to the hydrophobic tails, causing them to pack closer.
This makes membrane less fluid, more rigid.

Question 5

how do proteins allow substances to pass through membrane?

Answer 5

• form channels which allows small / charged particles through
• carrier proteins transport molecules / ions across membranes by active transport / facilitated diffusion

Question 6

what are the four functions glyco lipids/proteins linked with the membrane :

Answer 6

• stabilize membrane by forming H-bonds with surrounding water molecules
• sites where drugs/hormones/antibodies bind
• act as receptors for cell signalling
• act as antigens

Question 7

describe how cells communicate

Answer 7

• cell releases a messenger molecule (e.g. hormone)
• molecule travels (e.g. in blood)
• messenger molecule binds to receptor on cell membrane

Question 8

what are membrane - bound receptors ?

Answer 8

proteins in cell membrane that act as receptors for messenger molecules

Question 9

what special structure feature do receptor proteins have?

Answer 9

specific shape, which only messenger molecules with complementary shape can bind to

Question 10

what is a target cell ?

Answer 10

a cell that responds to a particular messenger molecule

Question 11

Describe membrane permeability at low temp > 0

Answer 11

• pack close, so membrane is rigid
• channel / carrier proteins deform, increasing permeability
• ice crystals may piece membrane (increase permeability)

Question 12

Describe membrane permeability at mid temp 0 - 45

Answer 12

• phospholipid have more energy, move more, not as tightly packed
• membrane is partially permeable
• increase in temp increases permeability

Question 13

Describe membrane permeability at high temp < 45

Answer 13

• bilayer breaks down, membrane becomes more permeable

- channel / carrier proteins deform (increase permeability)

Question 14

Describe the effect of a solvent on membrane permeability

Answer 14

• increases permeability due to the solvent dissolving lipids in membrane, so it loses structure
• increase in concentration will increase permeability

Question 15

define diffusion

Answer 15

the net movement of particles from an area of high concentration to an area of low concentration

Question 16

what does it mean that diffusion is a passive process ?

Answer 16

requires no energy

Question 17

what are the four factors of rate of diffusion ?

Answer 17

temp / conc gradient / thickness of exchange surface / surface area

Question 18

what color is phenolphthalein in alkaline conditions ?

Answer 18

pink

Question 19

what color is phenolphthalein in acid conditions ?

Answer 19

colourlless

Question 20

what is facilitated diffusion ?

Answer 20

diffusion of larger molecules / ions / polar molecules through carrier / channel proteins in the membrane

Question 21

how do carrier proteins carry out facilitated diffusion ?

Answer 21

• large molecule attaches to carrier protein
• protein changes shape
• molecule released on other side

Question 22

how do channel proteins carry out facilitated diffusion ?

Answer 22

• form pores in membrane for charged particles to diffuse through
  (there are diff channel proteins for diff charged particles)

Question 23

what is used in active transport ?

Answer 23

carrier proteins

Question 24

what is endocytosis ?

Answer 24

cell surrounds substance with section of plasma membrane and pinches off to form a vesicle inside cell, this uses ATP for energy

Question 25

describe exocytosis

Answer 25

- vesicle buds off from Golgi body - vesicle moves to plasma membrane - vesicle fuses with membrane - contents are released outside of cell (uses ATP)

Question 26

define osmosis

Answer 26

diffusion of water molecules across a partially permeable membrane down a water potential gradient

Question 27

what has the highest water potential ?

Answer 27

pure water

Question 28

define hypotonic solution

Answer 28

higher water potential

Question 29

define isotonic solution

Answer 29

same water potential

Question 30

define hypertonic solution

Answer 30

lower water potential

Question 31

describe plant cell in hypotonic solution

Answer 31

- water moves into cell - vacuole swells - vacuole / cytoplasm push against wall - cell becomes turgid

Question 32

describe plant cell in hypertonic solution

Answer 32

- water moves out of cell - cell becomes flaccid - cytoplasm / membrane pull away from cell wall - called plasmolysis

Question 33

why is membrane described as mosaic ?

Answer 33

arranged w/ lots of different components