lecture 21 - structure and function of the cell membrane

Question 1

thickness of membrane

Answer 1

8nm

Question 2

lipid bilayer structure described as? constitutes?

Answer 2

fluid mosaic. 50% lipids, 50% proteins (“floating in lipid sea”)

Question 3

what holds proteins and lipids together?

Answer 3

hydrogen bonds

Question 4

3 types of lipids in the bilayer

Answer 4

cholesterol and glycolipids scattered amongst double layer phospholipids (75%)

Question 5

amphipathic

Answer 5

phospholipids have both a polar and a non-polar region

Question 6

tails of phospholipids form?

Answer 6

hydrophobic core

Question 7

lipids can move around in their respective __________ _________

Answer 7

membrane leaflet

Question 8

do lipids flip flop between leaflets or nah?

Answer 8

very rarely (basically no) this allows leaflets to be assymetric in what they constitute.

Question 9

longer lipid tail length =

Answer 9

less fluid membrane

Question 10

more double bonds =

Answer 10

more fluid membrane (more space between lipids)

Question 11

more cholesterol =

Answer 11

less fluid membrane

Question 12

integral proteins

Answer 12

extend INTO or completely ACROSS the membrane (transmembrane protein)

Question 13

peripheral proteins

Answer 13

associated with but NOT EMBEDDED into the membrane. Only on the surface. may be bonded to integral proteins. e.g. cytoskeleton proteins

Question 14

how do integral membranes stay anchored in membrane?

Answer 14

hydrophobic regions span the hydrophobic core (non-polar amino acids coiled into alpha helices). the hydrophilic regions interact with the aqueous solution.

Question 15

how is the maintenance of concentration gradients allowed?

Answer 15

by the cell membrane controlling what comes in and what doesn’t

Question 16

functions of membrane proteins?

Answer 16

• receptors
• cell identity markers
• linkers
• enzymes
• channels
• transporters

Question 17

organisation of of molecules in the membrane determines?

Answer 17

selective permeability

Question 18

3 things lipid bilayer permeable to (alone)…

Answer 18

• non-polar, uncharged molecules (e.g. oxygen, nitrogen, benzene)
• lipid soluble molecules (e.g. steroids, vitamins)
• small, uncharged polar molecules (e.g. water, urea)

Question 19

2 things lipid bilayer impermeable too… (due to hydrophobic core

Answer 19

• large uncharged polar molecules (e.g. glucose)

- Ions Na+, K+, Cl-, Ca2+, H+

Question 20

diffusion

Answer 20

high to low areas of concentration. down concentration gradient. due to particles KE

Question 21

ways to decrease rate of diffusion

Answer 21

lower temperature, larger molecule, smaller concentration difference, less surface area, larger distance

Question 22

rate of diffusion limits cell size to…

Answer 22

20μm

Question 23

how is O2 gradient maintained?

Answer 23

used up as quickly as it is provided

Question 24

movement of ions influenced by…

Answer 24

electrochemical gradient = both concentration gradient and electrical gradient together

Question 25

difference in concentrations across membrane enabled by?

Answer 25

selective permeability

Question 26

membrane potential =

Answer 26

differences in charged ions across membrane forming electrical gradient. acts as a ‘capacitor’

Question 27

how much energy is required to maintain electrical and chemical gradients?

Answer 27

~30% of resting potential

Question 28

what do these electrical and chemical gradients represent?

Answer 28

stored energy

Question 29

osmosis =

Answer 29

net diffusion of water across a selectively permeable membrane, from a region of high water conc. to lower water conc.

Question 30

can osmosis still occur if membrane is more permeable to other CERTAIN solutes?

Answer 30

NO e.g. more permeable to Na+/K+ in neurons than water.. no osmosis

Question 31

osmotic pressure =

Answer 31

opposing, hydrostatic force, preventing osmosis from equilibrating the osmotic gradient

Question 32

permeability to water (Pw) =

Answer 32

permeability through lipid bilayer (Pd) + permeability through water channel (Pf)

Question 33

what causes cells to have different permeability to water?

Answer 33

different aquaporin isoforms

Question 34

permeability through lipid bilayer (Pd) is…

Answer 34

• small
• mercury insensitive
• temp. dependent (fluidity)

Question 35

permeability through water channel (Pf)

Answer 35

• large
• sensitive to Mercury
• temp. dependent
• mediated by aquaporins

Question 36

how many isoforms of aquaporins?

Answer 36

9

Question 37

osmolarity of blood =

Answer 37

280 mOsmol (isosmotic with interstitial fluid)

Question 38

same osmolarity =

Answer 38

isosmotic

Question 39

solution has higher osmolarity =

Answer 39

hyperosmotic

Question 40

solution has lower osmolarity =

Answer 40

hyposmotic

Question 41

Tonicity is?

Answer 41

effect a solution has on cell volume. Dependent on permeability of membrane to solute

Question 42

are osmolarity and tonicity the same thing?

Answer 42

NO! (remember blood lab g)

Question 43

isotonic =

Answer 43

no change in cell volume

Question 44

hypotonic solution =

Answer 44

higher concentration inside cell. cell swells and lyses (bursts)

Question 45

hypertonic solution =

Answer 45

higher concentraion outside cell. cell shrinks = CRENATION

Question 46

osmotic pressure can be opposed by?

Answer 46

hydrostatic pressure