cell membrane transport

Question 1

what type of transport is passive

Answer 1

-simple diffusion and facilitated diffusion

Question 2

what are the two types of active transport

Answer 2

-primary (direct)
-secondary (indirect)

Question 3

what does the electrochemical gradient do

Answer 3

-drives passive processes
-involves and based on both the electrical and chemical properties
-no additional energy input
-always depends on the concentration gradient of the solute
-for charged molecules also depends on any difference in voltage between the ECF and ICF
-if Na+ was trying to move past a +ve membrane, more force would be needed as the charges repel

Question 4

what are hydrophobic solutes

Answer 4

-solutes that can move through the membrane, in other words, they like fatty acids
-can move through the membrane by simple diffusion

Question 5

what’s the equation for Jx

Answer 5

Jx= Px ([X]o-[X]i)
Jx= flux
Px= permeability coefficient
difference in [X] between ECF and ICF

Question 6

what are transmembrane proteins

Answer 6

-classed as integral membranes (embedded within membrane)
-composed of membrane-spanning alpha-helical domains (protein structure)
-can be single or multi pass

Question 7

what is a protein’s membrane topology

Answer 7

how proteins move in and out of the membrane

Question 8

what are the different types of transmembrane proteins

Answer 8

-pore (non-gated channel)
-channel (gated pore)
-carrier
-pump

Question 9

why are there different types of transmembrane proteins

Answer 9

-solutes require specific types of transmembrane proteins
-all transmembrane proteins have multiple transmembrane segments surrounding a solute pathway

Question 10

why do transmembrane proteins create hydrophilic permeation pathways through the membrane

Answer 10

-amino acids have different properties which determine whether the protein is hydrophobic or hydrophilic
-amphipathic helices- alternating hydrophobic and hydrophilic amino acids
-hydrophobic surfaces face lipid molecules
-hydrophilic surfaces create a central pore
*if confused look at slide, page 10

Question 11

how do pores allow facilitated diffusion

Answer 11

-driving force for movement is electrochemical gradient
-always open as pores are conduits
-multiple subunits
-e.g. aquaporins

Question 12

how do channels allow facilitated diffusion

Answer 12

-driving force for movement is the electrochemical gradient
-gated ion channels
-multiple subunits
-e.g. potassium channel

Question 13

what are the different types of channels

Answer 13

-voltage gated
-ligand gated (ECF and ICF ligands)
-mechanical-gated

Question 14

what do each type of channel have

Answer 14

-a moveable gate (determined by Amino Acids)
-a sensor : voltage (charge) , ligand (molecules which bind) or mechanical (stretch physically)
-a selectivity filter
-an open channel pore

Question 15

how do carriers allow facilitated diffusion

Answer 15

-driving force for movement is the electrochemical gradient
-never had continuous transmembrane path
-e.g. GLUT

Question 16

is carrier mediated facilitated diffusion faster or slow than a channel and a pore

Answer 16

slower

Question 17

process of carrier mediated facilitated diffusion

Answer 17

-carrier is open to outside
-X enters from outside and binds at a binding site
-the outer gate closes and X becomes occluded, still attached to its binding site
-the inner gate opens with X still bound
-X exits and enters the inside of cell
-the inner gate closes occluding an empty binding site
-cycle can also follow in reversed order

Question 18

how can carriers mediate active transport

Answer 18

-through pumps, co-transporters and exchangers

Question 19

which way does active transport move a solute to

Answer 19

-against the electrochemical gradient
-AT needs metabolic energy (ATP)

Question 20

what does primary active transport use

Answer 20

-pumps
-a chemical reaction e.g. ATP hydrolysis
-pumps depends on the hydrolysis of ATP to turn ATP-> ADP +Pi which releases energy
-primary AT needed for secondary AT

Question 21

what does secondary AT use

Answer 21

-co-transporters and exchangers
-use the chemical gradient from the primary reaction to drive the movement of ions

Question 22

what does saturation of pumps mean

Answer 22

-when all the pumps are fully saturated, this means there is a finite amount that they can transport

Question 23

how can co-transporters move both solutes in the same direction

Answer 23

-when things move in the same directions (in or out)
-requires a driving force whose electrochemical gradient provides the ender - often inward Na+ electrochemical gradient
-e.g. Na+/glucose transporter
-also called symporters

Question 24

exchangers can move solutes in opposite directions

Answer 24

-requires a driving solutes whose electrochemical gradient provides the energy
-often the inward Na+ electrochemical gradient
-e.g. Na+/Ca2+ exchanger
-called antiporters