Lecture 15: membrane proteins and transport

Question 1

oligosaccharides are (inside/ outside) the membrane

Answer 1

outside

Question 2

hydrophobic resides span the membrane =

Answer 2

much more favorable than np residues because of VDW interactions and hydrophobic effect

Question 3

α-helical spanning membrane is ____ residues

Answer 3

20-25 residues

Question 4

all proteins initiate with what residue?

Answer 4

methionine

Question 5

synthesis of IMP’s and secreted proteins occur at ___

Answer 5

RER

Question 6

signal hypothesis: signal sequence is

Answer 6

hydrophobic [unfavorable]

Question 7

signal hypothesis: SRP is made of ___ and does what?

Answer 7

• protein and RNA
• has hydrophobic groove that binds to hydrophobic stretch of AA’s within signal sequence
• stops protein translation
• takes entire assembly to ER membrane via interactions with SRP receptors

Question 8

signal hypothesis: driving force behind first step of SRP

Answer 8

HYDROPHOBIC EFFECT!

Question 9

signal hypothesis: what opens the translocon and releases the SRP?

Answer 9

thermodynamic coupling of GDP to GTP provides energy to open translocon and release SRP

Question 10

signal hypothesis: what happens when SRP leaves?

Answer 10

translation continues and protein grows into lumen of RER

Question 11

signal hypothesis: what cleaves the protein and where?

Answer 11

signal peptidase cleaves protein at signal sequence and removes it = N-term of mature protein continues to be produced

Question 12

4 forces that drive protein folding

Answer 12

• hydrophobic effect
• H-bonding interactions
• electrostatic interactions
• VDW interactions

Question 13

where do carbs [saccharides on N-terminal] get added/ modified?

Answer 13

golgi complex

Question 14

lumen of RER topologically (equivalent/ different) from extracellular space

Answer 14

equivalent

Question 15

larger C2 and smaller C1 means what for ΔG, energy and gradient?

Answer 15

• ΔG > 0 = not fwd rxn
• energy required
• down gradient [H - L] = thermodynamically favorable

Question 16

passive transport [direction, kinetics, molecules]

Answer 16

• down gradient [high to low] [favorable]
• linear kinetics [favorable]
• none/ carrier

Question 17

facilitated transport [direction, kinetics, molecules]

Answer 17

• up or down gradient
• hyperbolic kinetics [protein-ligand interactions]
• carrier

Question 18

active transport [direction, kinetics, molecules]

Answer 18

• up gradient [always requires energy]
• hyperbolic kinetics [needs help from carrier protein]
• enzyme

Question 19

difference between primary and secondary active transport

Answer 19

• both always needs input of energy somehow
• primary = directly uses ATP [thermodynamic coupling]
• secondary = coupled to another energy source

Question 20

linear transport kinetics

Answer 20

• no protein interactions necessary

Question 21

simple passive transport [linear] occurs (up/ down) gradient and is energy (in/ dependent)

Answer 21

down gradient; energy independent

Question 22

hyperbolic transport kinetics

Answer 22

• need help from a protein

Question 23

facilitated transfer [hyperbolic] involves a ____ and is (passive/ active)

Answer 23

involves a carrier; can be passive or active

Question 24

when does a hyperbolic curve level out?

Answer 24

when all carrier proteins are saturated

Question 25

antiport

Answer 25

uses energy of favorable [down gradient] transfer for unfavorable transfer [up gradient]