Session 2 - Membrane Permeability

Question 1

Define facilitated transport

Answer 1

Diffusion of a molecule across a membrane by utilising specific proteins to increase permeability. It does not require energy expenditure

Question 2

Define active transport

Answer 2

Movement of a molecule across a membrane against an electrochemical gradient. It requires energy which is obtained by coupling to a thermodynamically favourable reaction

Question 3

What is secondary active transport?

Answer 3

Active transport where the energy for the movement is obtained by moving another molecule across the membrane down a concentration gradient through a co-tansporter

Question 4

What is uniport?

Answer 4

Transport of one solute molecule species from one side of a membrane to the other

Question 5

What is symport?

Answer 5

Transport of two or more molecules across a membrane where all of the molecules travel in the same direction across the membrane

Question 6

What is antiport?

Answer 6

Transport of two or more molecules across a membrane where the molecules move in opposite directions across the membrane

Question 7

What are cotransporters?

Answer 7

Transporters in cell membranes which transport more than one molecule across the membrane

Question 8

What is the Gibbs free energy change in passive transport?

Answer 8

Negative as it is spontaneous

Question 9

What is the Gibbs free energy change in active transport?

Answer 9

Positive, the transport requires energy input

Question 10

How can protein channels used in facilitated diffusion be gated?

Answer 10

Ligand gated, voltage gated or gap junctions

Question 11

How do carrier molecules operate in facilitated diffusion?

Answer 11

Substrate binding indices a conformational change which causes substrate movement across the membrane

Question 12

What is the normal concentration of potassium inside a cell?

Answer 12

155mM

Question 13

What is the normal concentration of potassium outside a cell?

Answer 13

4mM

Question 14

What is the normal concentration of calcium inside a cell?

Answer 14

10^-7M

Question 15

What is he normal concentration of calcium outside a cell?

Answer 15

1.5mM

Question 16

What is the normal concentration of chloride ions inside a cell?

Answer 16

4.2mM

Question 17

What is the normal concentration of chloride ions outside a cell?

Answer 17

123mM

Question 18

What is the normal concentration of sodium ions inside a cell?

Answer 18

12mM

Question 19

What is the normal concentration of sodium ions outside a cell?

Answer 19

145mM

Question 20

What are the main functions of Na-K-ATPase?

Answer 20

Forms sodium and potassium gradients

Drives many secondary active transport processes

Question 21

Which primary active transporters are involved in control of resting calcium levels?

Answer 21

PMCA, SERCA

Question 22

What are the characteristics of the PMCA transporter?

Answer 22

Expels one molecule of calcium for every molecule of hydrogen brought into the cell
High affinity and low capacity so removes residual Ca

Question 23

What are the main features of the SERCA pump?

Answer 23

Accumulates calcium into the SR/ER
One molecule of calcium brought into the SR/ER for every molecule of hydrogen that is removed from the SR/ER
High affinity and low capacity so removes residual calcium

Question 24

What secondary active transporters are involved in control of resting calcium levels?

Answer 24

Na-Ca-exchanger (NCX), mitochondrial calcium uniports

Question 25

What are the features of the NCX transporter?

Answer 25

Removes one calcium ion from the cell for every 3 sodium ions moved into the cell Activity is membrane potential dependent: depolarisation reverses the mode of operation Low affinity and high capacity so removes most calcium from cell

Question 26

What are the features of mitochondrial calcium uniports?

Answer 26

Operate at high calcium concentrations | Act to buffer damaging calcium concentrations

Question 27

How can the NCX transporter contribute to ischaemia?

Answer 27

- ATP depletion inhibits the Na-K pump - Na accumulates inside the cell so the cell depolarises - Depolarisation reverses the NCX - Calcium is moved into the cell - High calcium levels are toxic to the cell

Question 28

How is acidification opposed in cells?

Answer 28

Expelling hydrogen ions or inward movement of bicarbonate ions

Question 29

How can alkalisation be opposed in cells?

Answer 29

Expelling bicarbonate ions via the anion exchanger

Question 30

What mechanisms are commonly employed by cells to regulate pH?

Answer 30

Na-K-ATPase, Na-H exchange, Band 3 anion exchange

Question 31

What is the function of Na-K-ATPase in cellular pH regulation?

Answer 31

To provide a gradient to provide energy for all transporters except the anion exchange

Question 32

How do cells resist cell swelling?

Answer 32

Osmotically active ions are extruded from the cell which causes water to leave via osmosis E.g. Conductive systems extruding potassium and chloride via uniport Extruded ions are overall electroneutral to avoid depolarising the cell

Question 33

How do cells resist shrinking?

Answer 33

Via influx of osmotically active, electroneutral ions to cause water to move into the cell via osmosis E.g. Conductive system where sodium and calcium are transported into the cell via symport

Question 34

How is sodium taken up in the proximal tubules of the kidney?

Answer 34

- NkCC2 moves 1 sodium, 1 potassium and 2 chloride ions into the cells from the tubule ROMK moves potassium from the cells into the tubule Na-K-ATPase moves sodium into the blood and potassium from the blood into the cells CIC-Kb moves chloride from the cells into the blood KCICT moves chloride and potassium from the cells into the blood via symport

Question 35

How can oedema or hypertension be treated?

Answer 35

By blocking one or more of the sodium reabsorption mechanisms using diuretics Na excretion is increased so hyperosmotic urine is produced and more water is excreted

Question 36

Define passive diffusion

Answer 36

Spontaneous diffusion of a molecule across a membrane along an electrochemical gradient without expending any energy