Cell Membrane Overview

Question 1

what intermolecular force drives the formation when phospholipids are added to water?

Answer 1

driven by an increase in entropy. lipids cause water to arrange into an ordered, unfavorable cage-like structure (called a Cathrate cage). forcing lipids into a bilayer reduces this effect

Question 2

phospholipids, cholesterol, and temperature

Answer 2

closer they pack, less fluid.

at low temperatures, they are packed closely together. cholesterol inserts in the hydrophobic region, seperating lipids and decreasing the strength of VDW forces (increasing fluidity)

at high temperatures, cholesterol forces lipids to become closer to each other, decreasing fluidity

Question 3

paw of a polar bear contains saturated/unsaturated phospholipids

Answer 3

something that increases fluidity

unsaturated, because they must remain fluid to be functional at low temperatures

Question 4

high temperatures require what kind of bilayer?

Answer 4

something that decreases fluidity

• saturated lipids have more VDW interaction and decrease fluidity
• longer tails have more VDW and decrease fluidity

Question 5

how does glucose enter the cell?

Answer 5

facilitated diffusion through a carrier protein

Question 6

facilitated diffusion

Answer 6

does not require ATP, limited by the number of proteins on the surface of the cell

Question 7

which type of membrane protein is most likely a hormone?

Answer 7

peripheral protein (which include peptide hormones)

steroid is not a membrane protein

integral protein cannot leave the cell membrane and would be a terrible signaling protein

lipid-bound proteins remain in the phospholipid bilayer by the fatty acid tails, so they would also be terrible signal proteins

peptide hormones interact with the integral proteins in cell receptors.

Question 8

peptide hormones include…

Answer 8

insulin. growth hormone.

Question 9

rate of osmosis across a cell membrane depends on…`

Answer 9

1. presence of aquaporins
2. intracellular and extracellular solute concentrations

does NOT depend on polarity or molecular weight of solutes

osmotic pressure is a colligative property (dependent on the ratio of solute to solvent, not the identity of the solute or solvent)

Question 10

aquaporins

Answer 10

channel proteins that allow water to flow through a cell membrane

Question 11

what is the purpose of K+ and Na+ pumps across a channel? (in a nerve cell)

Answer 11

to store electrical and chemical energy (which can be used in action potentials)

Question 12

during action potential

Answer 12

Na+ and K+ move across the membrane through sodium and potassium channels (NOT pumps)

action potential = channel

Question 13

sodium-potassium pumps

Answer 13

increase Na+ outside the cell, and K+ inside the cell

Na outside (Na, I'm outside)
K inside (special K cereal is inside the house)

Question 14

cell membranes defined by

Answer 14

semi-permeability

Question 15

phospholipids (parts)

Answer 15

1. phosphate head
2. glycerol backbone (hold it together)
3. fatty acid tails

is both hydrophilic and phobic (amphiphathic)

Question 16

passive diffusion

Answer 16

small, nonpolar molecules (like gases)

small polar molecules (water, ethanol) move slowly
large non-polar molecules move slowly

Question 17

glucose is/is not polar

Answer 17

is polar (see the OH groups)

Question 18

the diversity of phospholipids

Answer 18

serine, choline, ethanolamine, inositol, and glycerol bonded to the phosphate by phosphoester bond

Question 19

what makes up the cell membrane?

Answer 19

phospholipids, cholesterol, proteins

Question 20

cholesterol

Answer 20

4 rings, rather stable structure. maintain the fluidity of a cell membrane (keeps it fluid in low and high temperatures)

Question 21

proteins in cell membrane

Answer 21

integral (transmembrane) protein

act as receptors and transportation

Question 22

glycoproteins

Answer 22

carbohydrates bound to proteins (or glycolipids) which play a big role in communication (allows cells to recognize other cells), can be found in any proteins

Question 23

fluid mosaic model

Answer 23

a fluid membrane (discovered in 1972)

Question 24

two types of integral proteins

Answer 24

channel protein (hole inside) lets Na+ pass, or flow, through (won’t on its own), from high to low concentration (does not require energy)

carrier protein: carries a substance (like a glove) and can act against a concentratin gradient

Question 25

types of proteins found in membrane

Answer 25

peripheral, integral, lipid-bound, channel, carrier

“PLICC” membrane

Question 26

membrane fluidity affected by…

Answer 26

1. temperature
2. cholesterol
3. saturated/unsaturated

Question 27

low temperatures

Answer 27

form a crystalized state, lower fluidity

Question 28

high temperatures

Answer 28

more fluidity, increased distance between PL

Question 29

cholesterol on fluidity (very interesting)

Answer 29

increases distance between PL at low temperature

decreases distance between PL at high temperature

Question 30

saturation on fluidity

Answer 30

high saturation, reduced fluidity

the bent, unsaturated are more fluid