SFP: Cell Membranes

Question 1

name the general regions of the plasma membrane from exterior to interior

Answer 1

glycocalyx, hydrophilic region, hydrophobic region, hydrophilic region

Question 2

what are the main types of membrane lipids?

Answer 2

phosphoglycerides

Question 3

name major types of phosphoglycerides

Answer 3

1. phosphatidylcholine
2. phosphatidylethanolamine
3. phosphatidylserine
4. phosphatidylinositol
5. phosphatidic acid

Question 4

describe the basic molecular structure of cell membranes

Answer 4

membranes consist of a phospholipid bilayer with integral proteins and peripheral proteins; the composition of the membrane varies and directly determines the properties of the membrane

Question 5

Describe the 3 main types of lipids in cell membranes and explain their corresponding effects
on physical properties of membrane fluidity and rigidity

Answer 5

1. phosphoglycerides: polar head group with two fatty acid tails. kinks in unsaturated fatty acid tails increase fluidity of the membrane, as this loosens the packing of lipids
2. sphingomyelin: have an OH group on the polar head that allows them to form H bonds and a larger saturation of hydrocarbon tails that increase packing in the cell membrane. this and their high affinity for cholesterol means they increase rigidity in the membrane
3. cholesterol: increases packing of FA tails, increasing membrane rigidity

Question 6

Define asymmetry of cell membranes and explain the function of flippases

Answer 6

phospholipids are distributed unevenly within the bilayer by flippases; the outer layer contains more PC and SM.

flippases flip phospholipids in the membrane

Question 7

Describe the differences between peripheral and integral membrane proteins.

Answer 7

peripheral: associated with the membrane, but not embedded in the membrane

integral: proteins embedded into the lipid bilayer

Question 8

Specify 3 types of integral membrane proteins and the molecular basis for their insertion into the cell membrane

Answer 8

1. transmembrane proteins: hydrophobic amino acids span the hydrophobic portion of the membrane, while hydrophilic domains protrude onto the outer and inner layers. can be single or multipass
2. GPI anchored proteins: protein is connected to a GPI anchor that is linked to a polar head in the bilayer. they’re covalently bound.
3. lipid anchored proteins: anchored to the inner layer of the membrane via covalent attachment to a fatty acid

Question 9

gives examples for the three types of integral membrane proteins

Answer 9

transmembrane: receptors and transporters

GPI anchored: adhesion molecules and complementary regulatory proteins

lipid anchored proteins: RAS and signaling proteins

Question 10

name the three examples of lipid anchored proteins

Answer 10

1. myristoylation: covalent attachment of C14 fatty acid to N terminal glycine of membrane protein
2. palmitoylation: covalent attachment of C16 fatty acid to internal cysteine of membrane protein
3. farnesylation: covalent attachment of farnesyl (C15 group) to C terminal cysteine of membrane protein; anchored into the membrane (RAS)

Question 11

Describe the following basic property of cell membranes: self-assembly

Answer 11

cell membranes assemble themselves, largely via the hydrophobic effect. polar heads form H bonds with water, and water forces the hydrophobic regions inward.

Question 12

Describe the following basic property of cell membranes: fluidity

Answer 12

lipids can rotate and move laterally in the membrane. the ength of FA chains and degree of saturation can also impact fluidity of the membrane.

Question 13

Describe the following basic property of cell membranes: selective permeability

Answer 13

membranes allow certain and specific molecules into the cell freely, and allow others in through highly regulated methods. the membrane decides what comes in and out of the cell.

Question 14

Describe the following basic property of cell membranes: fluid mosaic model

Answer 14

membrane proteins can move laterally and float through the membrane

Question 15

define micelles and liposomes

Answer 15

micelles: collection of phospholipids with polar heads in contact with water and FA tails packed to form an inner core

liposomes: artificial membrane vesicle; phospholipid bilayer encapsulating an aqueous core. have uses in cell delivery of hydrophobic molecules in the membrane or hydrophilic molecules in the core

Question 16

Describe how lipid rafts are formed and their functional significance

Answer 16

formed by the interactions between sphingomyelin and cholesterol; they move freely within the bilayer and serve as a platform for organizing membrane proteins into functional compartments

Question 17

Describe the structure and function of the following membrane specialization: polarity of
cell membranes

Answer 17

membranes have an apical surface and a basolateral surface segregated by tight junctions. each surface has distinct functions and proteins.

Question 18

Describe the structure and function of the following membrane specialization: microvilli

Answer 18

protrusions of the plasma membrane on the apical surface that increase the surface area of the membrane. this can be seen in epithelial cells in the intestine

Question 19

Describe the structure and function of the following membrane specialization: glycocalyx

Answer 19

a coat formed by peripheral and integral membrane glycoproteins on the apical membranes of epithelial cells