2.5 biological membranes

Question 1

state the role of membranes

Answer 1

partially permeable barriers between the cell and its environment, between organelles and
the cytoplasm and within organelles
sites of chemical reactions
sites of cell communication (receptors, cell signalling, cell reconition).

Question 2

what is the fluid mosaic model

Answer 2

Phospholipid bilayer
Hydrophobic tails , hydrophilic heads
Proteins scattered
proteins and phospholipids are free to move
model that shows arrangement of biological membranes

Question 3

name the components in the fluid mosaic model

Answer 3

phospholipid
intrinsic proteins(carrier,channel)
extrinsic proteins
glycoproteins
glycolipids
cholesterol

Question 4

what is a micelle

Answer 4

one layer of phospholipids, creates sphere shape

Question 5

whats a bilayer

Answer 5

two layers of phospholipids

Question 6

describe channel proteins

Answer 6

have pores that act as channels to allow ions to pass through

Question 7

describe carrier proteins

Answer 7

change shape using ATP to carry specific molecules across membrane

Question 8

describe extrinsic proteins

Answer 8

found on the surface
provides mechanical support and act as cell receptors for hormones etc.

Question 9

describe glycolipids

Answer 9

carbohydrate chain attached to phosholipid
role in cell recognition and act as cell markers or antigens

Question 10

describe glycoproteins

Answer 10

carbohydrate chain attached to protein molecule
receptors for chemical signals/hormones/toxins
role in cell adhesion

Question 11

describe cholesterol

Answer 11

4 carbon based rings in fatty acid tail layer
provides mechanical stability and flexibility
restricts movement of membrane etc

Question 12

how does cholesterol affect membrane permeability

Answer 12

buffers the effect of lower temperature by preventing phospholipids getting too close = prevents reduction in fluidity

Question 13

what is simple diffusion

Answer 13

the net movement of particles down a concentration gradient from an area of higher conc. to lower conc.

Question 14

what molecules does simple diffusion allow to cross membranes

Answer 14

small polar or non polar

Question 15

what is facilitated diffusion

Answer 15

diffusion using proteins (carrier or channel)

Question 16

what molecules does facilitated diffusion allow to cross membranes

Answer 16

large or polar molecules

Question 17

what factors affect the rate of simple diffusion (+facilitated diffusion)

Answer 17

conc. gradient
temperature
surface area
diffusion distance
+more intrinsic proteins

Question 18

what is passive transport

Answer 18

no energy needed from ATP

Question 19

how do molecules move down/up concentration gradients

Answer 19

kinetic energy

Question 20

what do active transport require

Answer 20

energy needed from ATP

Question 21

what is active transport

Answer 21

movement of substances against their concentration gradient using ATP and carrier proteins

Question 22

what is bulk transport and name two examples

Answer 22

transport of large molecules too large to pass through membrane
endo and exocytosis

Question 23

what is endocytosis

Answer 23

bulk transport of molecules into the cell
segment of membrane surrounds and encloses particle into a vesicle

Question 24

name the different ways of endocytosis and what they move

Answer 24

phagocytosis - solids
phinocytosis - liquids

Question 25

what is osmosis

Answer 25

net movement of water molecules down their water potential gradient across a partially permeable membrane

Question 26

what is water potential

Answer 26

the tendency of water molecules to diffuse/move from one region to another

Question 27

what is the highest water potential

Answer 27

pure water 0kPa

Question 28

what is osmotic concentration

Answer 28

the amount of dissolved solutes in a solution

Question 29

what do a higher and lower osmotic concentration do to the water potential

Answer 29

higher osmotic conc= lower water potential = concentrated solution lower osmotic conc= higher water potential = dilute solution

Question 30

what is a hypertonic solution

Answer 30

has a higher osmotic conc. to the inside of cell so water moves out of cell and shrinks

Question 31

what is an isotonic solution

Answer 31

an equal osmitic/ water potential conc. inside and outside of cell

Question 32

what is a hypotonic solution

Answer 32

has a lower osmotic concentration to inside the cell so water moves in and cells expand

Question 33

what factors affect membrane structure and permeability

Answer 33

temperature solvents

Question 34

how does increasing temperature affect membranes

Answer 34

increased temp = more kinetic energy = molecules move faster = permeability/ fluidity increases

Question 35

how does a drop in temperature affect membranes

Answer 35

saturated fatty acids become compressed= unsaturated fatty acids with kinks = maintain fluidity

Question 36

how does temperature below freezing pint affect membranes

Answer 36

water freezes = expands = pierces/ forces apart closely packaged rigid layer = permeability increases

Question 37

what determines membrane fluidity at cold temperatures

Answer 37

proportions of unsaturated and saturated fatty acids

Question 38

how does a solvent affect membranes

Answer 38

organic solvents (acetone, ethanol) will damage membranes = dissolve lipids

Question 39

how does increasing temperature affect proteins in membranes and permeability

Answer 39

vibrates more= breaks hydrogen and ionic bonds = tertiary structure changes/ denatures = more permeable