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Membranes & Receptors > Session 2 - Membrane Permeability > Flashcards

Session 2 - Membrane Permeability Flashcards

1
Q

Define facilitated transport

A

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

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2
Q

Define active transport

A

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

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3
Q

What is secondary active transport?

A

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

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4
Q

What is uniport?

A

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

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5
Q

What is symport?

A

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

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6
Q

What is antiport?

A

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

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7
Q

What are cotransporters?

A

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

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8
Q

What is the Gibbs free energy change in passive transport?

A

Negative as it is spontaneous

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9
Q

What is the Gibbs free energy change in active transport?

A

Positive, the transport requires energy input

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10
Q

How can protein channels used in facilitated diffusion be gated?

A

Ligand gated, voltage gated or gap junctions

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11
Q

How do carrier molecules operate in facilitated diffusion?

A

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

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12
Q

What is the normal concentration of potassium inside a cell?

A

155mM

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13
Q

What is the normal concentration of potassium outside a cell?

A

4mM

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14
Q

What is the normal concentration of calcium inside a cell?

A

10^-7M

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15
Q

What is he normal concentration of calcium outside a cell?

A

1.5mM

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16
Q

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

A

4.2mM

17
Q

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

A

123mM

18
Q

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

A

12mM

19
Q

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

A

145mM

20
Q

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

A

Forms sodium and potassium gradients

Drives many secondary active transport processes

21
Q

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

A

PMCA, SERCA

22
Q

What are the characteristics of the PMCA transporter?

A

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

23
Q

What are the main features of the SERCA pump?

A

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

24
Q

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

A

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

25
Q

What are the features of the NCX transporter?

A

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

26
Q

What are the features of mitochondrial calcium uniports?

A

Operate at high calcium concentrations

Act to buffer damaging calcium concentrations

27
Q

How can the NCX transporter contribute to ischaemia?

A
  • 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
28
Q

How is acidification opposed in cells?

A

Expelling hydrogen ions or inward movement of bicarbonate ions

29
Q

How can alkalisation be opposed in cells?

A

Expelling bicarbonate ions via the anion exchanger

30
Q

What mechanisms are commonly employed by cells to regulate pH?

A

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

31
Q

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

A

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

32
Q

How do cells resist cell swelling?

A

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

33
Q

How do cells resist shrinking?

A

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

34
Q

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

A
  • 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
35
Q

How can oedema or hypertension be treated?

A

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

36
Q

Define passive diffusion

A

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

Membranes & Receptors (2 decks)

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