B2.1 Membranes and Membrane Transport

Question 1

Phospholipids are amphipathic. Explain what this means

Answer 1

they have a hydrophilic head and and hydrophobic tail

Question 2

Name another amphipathic lipid

Answer 2

cholesterol

Question 3

what happens when phospholipids are placed in water

Answer 3

the hydrophilic phosphate heads orient towards the water and hydrophobic hydrophobic tails orient away from the water forming a PHOSPHOLIPID MONOLAYER

Question 4

what are the 2 regions of a phospholipid bilayer

Answer 4

a hydrophobic core and a hydrophilic outer layer

Question 5

what cannot pass through the hydrophobic region of the lipid bilayer barrier and why

Answer 5

• large molecules because the hydrophobic region is tightly packed and has low permeability for them
  -polar molecules and ions as they are hydrophilic so will not interact

Question 6

integral proteins

Answer 6

partially hydrophobic and embedded in phospholipid bilayer

Question 7

peripheral proteins

Answer 7

hydrophilic and are attached to surface of integral proteins or to membrane with a a hydrocarbon chain

Question 8

2 types of transport proteins

Answer 8

channel and carrier

Question 9

what are channel proteins

Answer 9

form holes or pores where molecules travel through eg ions
some are gated

Question 10

what do carrier proteins do

Answer 10

change shape to transport substance across the membrane

Question 11

glycoproteins

Answer 11

act as cell markers/antigens for cell to cell recognition

Question 12

what is simple diffusion

Answer 12

the net movement, due to random motion of molecules or ions, of a substance from a region of higher concentration to a region of lower concentration

Question 13

molecules that move by simple diffusion

Answer 13

oxygen- diffuses into cells from capillaries surrounding- conc gradient by respiration
carbon dioxide- diffuses out of cells into surrounding capillaries

Question 14

what does the rate of diffusion depend on

Answer 14

steepness of conc gradient
temperature
surface area
properties of molecules or ions

Question 15

the higher the difference in conc across membrane…

Answer 15

higher the rate of diffusion

Question 16

the higher the temperature

Answer 16

the higher the rate of diffusion because molecules have more kinetic energy so random movement of molecules is faster

Question 17

the greater the surface area

Answer 17

the higher the rate of diffusion

Question 18

the larger the molecule

Answer 18

the slower it diffuses because they require more energy to move

Question 19

what can diffuse quickly

Answer 19

uncharged molecules - oxygen- as they can move directly across phospholipid bilayer
non polar molecules because they are soluble in the bilayer
smaller polar molecules- urea

Question 20

what is osmosis

Answer 20

the diffusion of water molecules from a region of lower solute concentration to a region of higher solute concentration, across a partially permeable membrane

Question 21

what channel proteins allow water to pass through membrane easily

Answer 21

aquaporins

Question 22

when does facilitated diffusion occur

Answer 22

when substances cross phospholipid bilayer with the help of channel and carrier proteins- passive and down a con gradient

Question 23

how does a carrier protein work

Answer 23

the substance that needs transporting attaches to binding site and the shape of the protein changes so it opens up to the other side of the membrane

Question 24

what is active transport

Answer 24

the movement of molecules and ions across a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration

Question 25

what does active transport require

Answer 25

carrier proteins- pumps which require energy from ATP from respiration to change shape

Question 26

how does the atp release energy

Answer 26

it is hydrolised

Question 27

what is selective permeability

Answer 27

ability of the membrane to differentiate between different types of molecules, only allowing some molecules through while blocking others

Question 28

what are glycoproteins

Answer 28

cell membrane proteins that have a carbohydrate chain attached on the extracellular side

Question 29

what are glycolipids

Answer 29

lipids with carbohydrate chains attached on the outer surface of cell membranes

Question 30

what does the carbohydrate chain allow for

Answer 30

enables them to act as receptor molecules so they can bind with substances at the surface

Question 31

label in fluid mosaic model

Answer 31

phospholipid bilayer integral proteins peripheral glycoproteins cholesterol

Question 31

receptor types

Answer 31

signalling- bind to hormones and neurotransmitters involved in endocytosis involved in cell adhesion so cells can attach to each other forming tissues act as antigens for cell identification

Question 32

saturated fatty acids

Answer 32

they are straight so can pack closely together so have high mp- maintain stability

Question 33

unsaturated fatty acids

Answer 33

contain 1 or more double bonds they have bends in the chain so cant pack together tightly so have lower mp and allow membranes to be fluid and flexible

Question 34

cholesterol importance

Answer 34

maintains membrane fluidity at low temp because it disrupts close packaging of phospholipids increases membrane stability at high temp as it holds fatty acid tails together acts as barrier

Question 35

what is the term for bulk transport into cells

Answer 35

endocytosis

Question 36

what is the term for bulk transport out of cells

Answer 36

exocytosis

Question 37

what does bulk transport require

Answer 37

energy and vesicles

Question 38

what happens during endocytosis

Answer 38

transports materials into cells and plasma membrane engulfs material forming a sac around it eg, phagocytosis

Question 39

what happens during exocytosis

Answer 39

materials transported out of cells- releases and packaged into secretory vesicles that travel to surface and fuse with membrane and release contents outside cell

Question 40

what do sodium potassium pumps do

Answer 40

they move 3 sodium ions out of cells and 2 potassium ions into cell using 1 ATP molecule by moving ions against conc gradient via active transport

Question 41

what are sodium potassium pumps

Answer 41

integral proteins that generate an electrochemical gradient between the inside and outside of a nerve cell

Question 42

steps of sodium potassium pumps

Answer 42

3 sodium ions inside of axon bind to pump and ATP attaches so the pump opens to outside of axon 3 sodium ions released out, 2 potassium ions enter and bind to their sites phosphate released so pump changes shape again

Question 43

what is cotransport

Answer 43

the coupled movement of substances across a cell membrane via a carrier protein -facilitated diffusion and active transport

Question 44

example of cotransport

Answer 44

Reabsorption of glucose back into the blood is under the control of sodium-dependent glucose cotransporter proteins

Question 45

what are cams

Answer 45

cell adhesion molecules are integral proteins that protrude into extracellular environment

Question 46

why does cell adhesion need cams

Answer 46

involves the binding of CAMs to other cells or to the extra-cellular matrix