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Semester 2 - Membranes and Receptors > Session 2.1 - Role Of Membrane As Permeability Barriers > Flashcards

Session 2.1 - Role Of Membrane As Permeability Barriers Flashcards

1
Q

What is required to move a small hydrophillic molecule or ion across a semi permeable membrane?

A

A large free energy change

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2
Q

What does the difficulty involved in movement of small hydrophillic molecules across a membrane mean?

A

The transverse movement of hydrophilic molecules across a membrane is a rare event

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3
Q

How is the movement of ions and hydrophillic molecules mediated and regulated?

A

By specific membrane transport systems.

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4
Q

Give six roles of transport processes in cell membrane

A

PIE Can’t Make Gravy
pH, Ionic, Extrusion, Cell volume, metabolic fuels + building blocks, Generation of ionic gradients

  • Maintenance of pH
  • Maintenance of ionic composition
  • Regulation of cell volume
  • Concentration of metabolic fuels and building blocks
  • Extrusion of waste products of metabolism and toxic substances
  • Generation of ionic gradients necessary for the electrical excitability of nerve and muscle
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5
Q

How do hydrophobic molecules move through cell membrane?

A

easily diffuse through the lipid bilayer – including O2 and CO2

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6
Q

How do small, uncharged polar molecules move through membrane?

A

Diffuse

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7
Q

How do large, uncharged polar molecules move?

A

e.g. glucose and sucrose, are not able to diffuse through the lipid membrane – transport proteins required

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8
Q

How do ions move through membrane?

A

Not able to diffuse, require transport proteins

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9
Q

Complete the sentence

The smaller the membrane coefficient…

A

… the larger the net rate of transport

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10
Q

What is the rate of diffusion of molecules proportional to?

A

Concentration gradient

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11
Q

What is the term for the diffusion of water across a membrane up concentration of solute?

A

Osmosis

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12
Q

What is different about osmosis in cells such as those that line the kidney proximal tubule?

A

Facillitated by water channels - aquaporins

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13
Q

Define diffusion

A

Passive (i.e. spontaneous), non-energy requiring, movement of molecules across the lipid bilayer

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14
Q

Describe facilitated transport

Give an example of facilitated transport

A

Specific proteins increase the permeability for a polar substance e.g Band 3 and Cl-

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15
Q

Why can water move the lipid bilayer easily?

A

Because it is a very small molecule

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16
Q

What does the band 3 protein do in cells?

A

HCO3- out, Cl- in anion exchange. Example of facilitated diffusion

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17
Q

Why is facilitated diffusion described as a saturatable process?

A

Because each carrier can interact with a few ions at any moment, and there are a finite number of transporters in membrane.

18
Q

What is the Vmax for facilitated diffusion?

A

When all transporters are saturated

19
Q

What is not altered by facilitated transport and why?

A

Equilibrium - Speeds up the rate at which equilibrium is reached, does not modify it

20
Q

Name three types of pores in facilitated diffusion

A

Ligand gated ion channels
Voltage - gated ion channels
Gap junction

21
Q

What is a ligan gated ion channel?

A

Opens or closes in response to ligand binding to a receptor site

22
Q

What is a voltage fated ion channel?

A

Open/close in response to potential difference across the membrane

23
Q

What is a gap junction (connexin)

A

Closed when cellular calcium concentration rises above 10 micromoles or cell becomes acid

24
Q

What is the difference between passive and active transport?

A

If the transport of an ion or molecule can occur spontaneously or requires energy (active transport)

25
Q

What is the free energy change in the transport of a molecule across a membrane determined by?

A

The concentration gradient of the transported species and by the electrical potential across the membrane bilayer

26
Q

How do ions overcome unfavourable chemical or electrical gradients?

A

Movement of transported ion coupled to a thermodynamically favourable reaction

27
Q

What provides the energy for primary and secondary active transport?

A

The hydrolysis of ATP

28
Q

What proportion of a cells ATP is used on active transport?

A

30-50%

29
Q

Give an example of an active transport system

A

Na+-K+-ATPase pumps 3 Na+ out and 2 K+ in at the expense of one ATP.

30
Q

How can active transport be used to generate ATP? Give an example

A

If active transport pump runs in reverse

In mitochondria, a gradient of H+ ions is employed to drive ATP synthesis via an ATP-dependent proton transporter

31
Q

What is a cotransporter?

A

Co-transporter: transfer of one species depends on the simultaneous/sequential transfer of a second species

32
Q

Why is co-transport knownn as a secondary active transport process?

A

Hydrolysis of ATP used indirectly. Membrane transport may be drivin by many different gradients, such as sodium, phosphophenolpyruvate and protons

33
Q

Give an example of three cotransport systems

A

Na+ - Glucose transport
Na+ - Ca2+ exchange
Na+ - H+ exchange

34
Q

What is symport?

A

Transfer of second solute in same direction as first

35
Q

What in uniport?

A

One solute molecule species is transported from one side of the membrane to the other

36
Q

What is antiport?

A

Transfer of second solute in opposite direction to the first

37
Q

Describe the Na+ - Glucose transport cotransport system and give what type of cotransport it is

A

Co-transport system of the small intestine and kidney. Entry of sodium provides the energy for the entry of glucose to the cell.

Symport

38
Q

Describe the Na+ - Ca2+ exchange cotransport system and give what type of cotransport it is

A

Inward flow of sodium down its concentration gradient drives outward flow of Ca2+ up its concentration gradient.
ANTIPORT

39
Q

Describe the Na+ - H+ exchange exchange cotransport system and give what type of cotransport it is

A

Inward flow of sodium down its concentration gradient leads to cell alkalization by removing H+

40
Q

What are the two categories of co-transport?

A

Symport and Antiport

Semester 2 - Membranes and Receptors (14 decks)

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