Lecture 14: membrane structure and function

Question 1

structure of micelle

Answer 1

spherical shell of lipids with single FA tail

Question 2

critical micellar concentration [CMC]

Answer 2

concentration of lipid when addition of more monomers to solution doesn’t increase the monomer concentration

Question 3

micelle formation entropically driven by ____

Answer 3

hydrophobic effect; hydrocarbon tails driven towards each other to form micelles

Question 4

what determines CMC value for different lipids?

Answer 4

chemical composition of lipid

Question 5

structure of triacylglycerols

Answer 5

• glycerol backbone + 3 fatty acids [ester linkages]
• nonpolar NOT AMPHIPATHIC
• NO POLAR HEAD GROUP = NO CMC = CANT FORM MICELLES

Question 6

polar head groups of triacylglycerols

Answer 6

NO POLAR HEAD GROUP

Question 7

role of pancreatic lipase

Answer 7

cleaves fatty acid tails from glycerol backbone = produces free fatty acid chains that can go on to form their own micelles [now amphipathic because no longer attached to triacylglycerol]

Question 8

transition of triacylglycerols to free fatty acid chain requires (2)

Answer 8

• formation of bile salt micelles

- activity of pancreatic lipase

Question 9

each hydrocarbon tail is a source of energy but ___

Answer 9

but needs to be cleaved off glycerol backbone

Question 10

structure of lipid bilayer in gel phase

Answer 10

• head groups tightly packed
• regular tails
• thicker membrane

Question 11

structure of lipid bilayer in liquid crystal phase

Answer 11

• head groups loosely packed
• tails disordered = more movement
• thinner membrane

Question 12

Tm

Answer 12

temp required to transition from gel into liquid crystal; midpoint of melting curve

Question 13

lower Tm vs higher Tm

Answer 13

• lower Tm = more fluid membrane

- higher Tm = less fluid membrane

Question 14

why does Tm dec with inc head size?

Answer 14

smaller heads mean tails can be closer to each other = more VDW interactions so bigger heads means less interactions = increased fluidity

Question 15

why does Tm inc with inc fatty acid tail length?

Answer 15

inc # of VDW interactions = more energy required to reach a fluid state; more C on tail = less fluid

Question 16

why does Tm dec with inc # of double bonds

Answer 16

limits the # of packing interactions that can occur

Question 17

increased cholesterol content causes Tm to ____ because

Answer 17

broadens transition between different states [ensures a fluid membrane]

Question 18

how does cholesterol change Tm?

Answer 18

DOES NOT change Tm

Question 19

lateral diffusion vs transverse diffusion

Answer 19

• lateral = within one leaflet; 100x faster in liquid crystal phase
• transverse = exchange between monolayers; much slower than lateral [big energy barrier = needs an enzyme]

Question 20

integral/ intrinsic vs peripheral/ extrinsic membrane proteins

Answer 20

• integral = significantly interact with one bilayer; NOT easily removed
• peripheral = weakly associated with bilayer; easily removed

Question 21

sizes of head groups

Answer 21

PL~PC > PS~PE

Question 22

composition of lipid/ protein in myelin

Answer 22

80/20

Question 23

composition of lipid/ protein in RBC plasma membrane

Answer 23

25/75

Question 24

composition of lipid/ protein in mitochondrial inner membrane

Answer 24

25/75

Question 25

more specialized cell membranes usually have (lower/ higher) protein content

Answer 25

higher