L8: Cell Membranes & Membrane Transport

Question 1

What barriers do biological membranes have?

Answer 1

Selective permeable

Question 2

What do the selective permeable biological membranes block?

Answer 2

Passage of almost all water soluble molecules

Question 3

What molecules can freely move through the bilayer?

Answer 3

Small, uncharged or hydrophobic molecules by simple diffusion down concentration gradients

Question 4

What do charged polar molecules require to move across the membrane?

Answer 4

Specialist proteins (pumps, transporters etc.)

Question 5

What molecules can permeate across the lipid bilayer?

Answer 5

Hydrophobic molecules, small uncharged polar molecules

Question 6

Is the concentration of Na+ ions higher on the outside or inside of cells?

Answer 6

Outside

Question 7

Is the concentration of K+ ions higher on the inside or outside of the cell?

Answer 7

Inside

Question 8

Is the concentration of Cl- higher on the inside or outside of cells?

Answer 8

Outside

Question 9

Define Simple/Passive diffusion

Answer 9

A molecule dissolves in the phospholipid bilayer, diffuses across and moves along the concentration gradient

Question 10

What does the rate of diffusion depend on?

Answer 10

Octonal/water PARTITION COEFFICIENT (Kow) of the solute

Question 11

What is Kow?

Answer 11

Equilibrium constant for partitioning of a molecule between oil (octanol) and water

Question 12

If the value of Kow is higher what does it mean in terms of lipid?

Answer 12

More lipid soluble it is

Question 13

What are transmembrane movement of ions & hydrophilic molecules mediated by?

Answer 13

Proteins

Question 14

2 ways solutes can cross biomembranes

Answer 14

1) Passive diffusion
2) Active transport

Question 15

Why are ion channels gated?

Answer 15

Enables the generation of action potential

Question 16

Why do facilitated diffusion involve a conformational change in selective carrier protein?

Answer 16

Allow molecule to pass through the membrane & be released on the other side

Question 17

Define uniport transport

Answer 17

When a particular type of molecule moves across a membrane, through carrier protein independently

Question 18

Define symport transport

Answer 18

2 kinds of molecules move in the same direction while diffusing through carrier proteins

Question 19

Define antiport transport

Answer 19

Mechanism for the couple transportation of 2 different molecules/ions passing through a membrane in opposite directions

Question 20

What is a coupled transport?

Answer 20

Transport system where 1 molecule/ion moves down an electrochemical gradient linked to another molecule in the same/opposite direction

Question 21

Which 2 transports are part of coupled transport?

Answer 21

Symport & antiport

Question 22

What is the transporter affinity for substrate given by?

Answer 22

Km

Question 23

What does primary active transport use?

Answer 23

ATP

Question 24

What does secondary active transport use?

Answer 24

An electrochemical gradient

Question 25

Define active transport

Answer 25

Movement of molecules against the concentration gradient, requiring energy

Question 26

Where does Na+/K+ ATPase function in?

Answer 26

Plasma membrane

Question 27

Where does H+ - ATPase function in?

Answer 27

Lysosomal membrane

Question 28

Where does Ca2+ - ATPase function in?

Answer 28

Plasma membrane/ ER/SR

Question 29

STEP 1 of functioning of Na+/K+ ATPase

Answer 29

1) Na+ binds to intracellular site
2) This triggers an AUTOPHOSPHORYLATION of the pump

Question 30

What does phosphorylation cause?

Answer 30

A conformational change to release Na+ to the outside & exposes a K+ binding site

Question 31

What does binding of K+ trigger?

Answer 31

A dephosphorylation of the pump

Question 32

What happens after the K+ binding site is exposed?

Answer 32

Pump returns to original conformation & K+ is discharged into the interior of the cell

Question 33

Role of Oubain

Answer 33

Inhibits the Na+/K+ ATPase by preventing K+ from binding

Question 34

Why is SGLUT 1 important?

Answer 34

Intestinal epithelial cells for absorption of dietary glucose

Question 35

Why is SGLUT 2 important?

Answer 35

Epithelial cells in proximal tubules of kidney for reabsorption of glucose from primary urine