Membrane Structure and Transport of Small Molecules

Question 1

Lipid protein interactions

Answer 1

Noncovelent-can move in bilayer

Question 2

Phosphoglycerides strucutre (3 names too)

Answer 2

Two fatty acid chains attached to to of three carbons of glycerol backbone

• one chain is nonsaturated-leading to kink-increases fluidity
• remaining hydroxyl attaches to phosphate, then to one of three head groups
• Usually no charge, unless serine is the head protein

phosphatidyl ehanoloamine, serine (negative), chline

Question 3

Sphingolipds

Answer 3

Sphingosine backbone

• sphingomyelin
• fatty acid tail and phophocholine head group

Question 4

Glyoclipids

Answer 4

Derived from sphingoseine with sugars added rather than phosphate

• asymmetric-sugar on external face of PM
• entry point for cholera toxin
• can be charged

Question 5

Sterols

Answer 5

Polar OH-locaed near membrane surfaces (both leaflets)

• rigid sterol ring stiffens regions of membrane
• strengthens PM

Question 6

Lipid hydropathy?

Answer 6

Amphipathic

• allows to form into a bilayer
• assuemble spontaneously
• micelle, or bilayer-keeping hydrophobic dry
• Try to keep as genetically favorable as possible

Question 7

Lipid compostion

Answer 7

Depends on membrane type and cell type

• cholesterol and SM sit outside PM
• phoshphochoine/phosphotidylethanoloamine d structures are in intracellular membranes
• glycolipids in PM and inriched in myelin-little in internal membranes

Question 8

Lipid movement

Answer 8

Diffuse between inner and outer layers but no flipping, also rotation occurs
-flipping creates and maintains assymetries

Question 9

Assymetric distribution of leaflets

Answer 9

Innner-phosphodylethanolamineand phosho serine (negative)

Outer-sphingolipds, glycolipids, phospho choine

Cholestrol-roughly equal between leaflets

Question 10

Lipid rats

Answer 10

Areas of non-random lipid distribution

• enricehd in cholesterol and sphingomyelin-thick structure that causes long SM chains
• sequesters subsets of membrane proteins

Question 11

PI

Answer 11

Phosphotidlinositol-major role in cell signaling

• PIP3-serves as dock for downstream signaling molecules when they are soluble-precursor to IP3
• PIP3 can be cleaved and be active in cell signalling

Question 12

Integral vs peripheral membrane proteins

Answer 12

Integral-incorporated into membrane with stretches of hydrophobic AA, either alpha helix of 15-20 aa or barrel with hydrophilic aa buried
-integral proteins have lipid covalently attached that can reversibly interact with membrane

Periperhal-associate with membrane via charge

Question 13

Post translations that mediate association with membrane

Answer 13

Amide linkage, thioester linkage

Covalent attachment but is reversible and can be regulated

Question 14

Cytoskeleotn and membrane proteins

Answer 14

Membrane proteins can diffuse within membrane-but are anchored to internal cytoskeleton

Question 15

Small molecules/ions crossing PM rate

Answer 15

Hydrophobic easily go across
Small/large uncharged+polar go through very slowly
Ions never go through

Question 16

Passive Transports

Answer 16

Channel mediated/Transporter mediated

• channlels are ion specific pores that open and close in regulated manner
• carriers-enzyme-like proteins that mediate passive transport down concentration gradient without chemical change

Question 17

Active transport

Answer 17

Puumps-need energy, move against concentration gradient, ATP

Question 18

Multiple of the same concentration gradients

Answer 18

Additive-potential can promote or oppose ion movements driven by concentration gradients-produce electrochemical gradient

Question 19

Ion channels are critical to… by means of

Answer 19

muscle and nerve function

thousands of K+, N+, and Ca2+ channels

Question 20

Types of carrier type transporters

Answer 20

Uniport-passive, transport down concentration gradient

symport/anticoupled

• sym-cotransported ion
• anti-something out, makes free for other to go in

Question 21

Carrier uniporters transport

Answer 21

Oscillate between which side is open-whether or not solute bound

• solutes bind when oscillation occurs go in
• move down concentration gradient at higher rate than by diffusion

Question 22

Na glucose symporter

Answer 22

Coupled carrier transport
Sodium binds, results in increase affinity for glusce, when both bind increase open and close rate
-both sites need to be occupied for conforation switch to occur
-allows transport of glucose against concentration gradient without direct energy expenditure

Question 23

Polarity determination

Answer 23

By which receptor proteins are on top vs bottom

-nonrandom distribution of membrane proteins!

Question 24

Transceullular glocose transport

Answer 24

1. na down gradient dragging glucose inside-symporter-versus gradient
2. Glucose down gradient through different transporter
   Moves from digestive system, to epithelial, then out-down gradient-uniporter

Na/K pop towards EC-keep Na low in epithelial cell so system can work

Question 25

Three classes of ATP driven pumps

Answer 25

Active transpot

Ptype=multpass TM domains

• autophosphorylate themselves with P from ATP
• Conformatinal change
• Pumps Ions

ABC transporter
-pumps small molecules (rather than ions)

Question 26

Ca2+ ATPase

Answer 26

90% membrane protein in muscle cell

takes calcium from cyto-sequeesters in membrane space

• kinases bind ATP and can have specific AA phosphorylated=conformatinal change
• Ca enters bidning site-comes in , released into cell
• energy is from hydrolysis of ATP that leads to conformational change

Question 27

Na+/K+ ATPase

Answer 27

Both transported against concentration gradient

1/3 of cellular energy used to maintain this pump

Na+ inside cell binds, phosphorylation, conformational change, Na+ transproted and released

K+ binds outide cell binds-dephosphorylation-induces another conformational change, K+ then enters cytoplasm and released

Question 28

ABC transporters

Answer 28

ATP binding casettes

Two ATPase domains

• small molecule (ions) bonds to non-ATP bound state
• When ATP is bound, two ATPase binding domains can dimerize to produce conformation change that exposes substrate to opposite side of membrane for release
• ATP hydrolysis releases substrate, then prepares transporter for another round-conformational change when both ATP send the ion through

Question 29

High levels of one type of ABC transporter

Answer 29

Multiple drug resistance
-allows more of hydrophobi drug to be cleared from cytoplasm

Chlorquine resistance (amiplifed transporter from malaria genome pumping drugs out)

ATP binding CFTR -drives opening and closing of Cl- channel-so an function as channel as well as transporter