Cell membranes

Question 1

function of membrane proteins

Answer 1

Signaling, protection, structure and movement, transport and general homeostasis

Question 2

3 components of a lipid (glycerophosholipids)

Answer 2

1. fatty acid tail
   - ~16-18 carbon (even #), unbranched, saturated or unsaturated
2. glycerol backbone
   - ester linkage to fatty acid tails
3. phosphate head
   -“R” is linked (ester) to another molecule
   -choline, ethanol amine, glycerol, inositol, serine

i.e. phosphatidylcholine (PC) and phosphatidylethanolamine (PE)

Question 3

what is cholesterol? where is it found? what does it do to cell membranes?

Answer 3

-type of steroid
-intercalates between phospholipid with the OH- closest to the aqueous interface
-small amounts = decrease fluidity, “Stiff”
-large amounts= increase fluidity, interfere with interactions between lipid tails

Question 4

sphingolipids; components; cellular function, what structure it contributes to

Answer 4

-sphingosine backbone, NOT glycerol like other lipids therefore membrane fluidity is decreased
-sugar residues with many functions
–> cellular functioning: form lipid rafts and myelin
–> contribute to glycocalyx which signal to other cells

“Sphingosine is formed by an amino alcohol head group, with two hydroxyls, and one amino group attached to a long unsaturated hydrocarbon chain of typically 18 carbon atoms”

in sphingolipids the glycerol component is replaced by a long-chain amino alcohol known as sphingosine, which is amide-linked to a fatty acid and phosphate group

Question 5

types of sphingolipids

Answer 5

ceramide
sphingomyelin
cerebroside
ganglioside

Question 6

what is the bond between a fatty acid tail and the glycerol backbone

Answer 6

ester linkage

Question 7

what can sphingolipids form?

Answer 7

lipid rafts and myelin

Question 8

what is a glycocalyx

Answer 8

-glycocalyx signal to other cells
-they are proteins (glycoproteins) and lipids that are bound to carbohydrates that vary in size
-outer leaflet of the cell; protect structure and singaling functions
-sphingolipids contribute to them

Question 9

membrane lipids characteristics

Answer 9

-amphipathic- micelle or phospholipid bilayer
–> both thermodynamically favourable (i.e. hydrophilic head in aqueous environment on outside)
-increase [ ] of phospholipids then bilayer formation more favourable then micelles

Question 10

what membrane lipids inside the cell dont need to do

Answer 10

-membrane lipids inside the cell dont need to:
-signal to other cells
-protect cells from harsh environments or microbes
-form a glyocalyx
–> therefore dont need sphingolipids
-less cholesterol in membrane of organelles
–> Golgi or smooth ER might have more cholesterol and sphingolipids because they are made or modified there

Question 11

diffusion

Answer 11

diffusion: high to low [ ], spread out molecules; spontaneous (Gibbs)

Question 12

osmosis

Answer 12

osmosis: water diffuses through semi-permeable membrane (allows water to pass through, but is impermeable to at least 1 solute)

i.e. if add sugar to a semipermeable system then water will go to where sugar [ ] is higher to balance it out

Question 13

what are membrane lipids a barrier to?

Answer 13

-charged and polar molecules
-medium and large non polar molecules

Question 14

integrity of membrane via membrane lipids

Answer 14

-ionic and fluid homeostasis, cell movement, and shape
-less integrity = threaten cell survival

Question 15

membrane permeability and concentration gradients and osmosis

Answer 15

-cell membranes are semi-permeable
-aquaporins in plasma membrane –> high water conductance
-membranes impermeable to larger solutes
-interior of cell has high [ ] of large solutes therefore must expend energy to regulate solute concentration and cell volume
–> concentration gradients