Membrane transport: Passive transport

Question 1

Define passive transport

Answer 1

If a cell can move particles across its membrane without the need for energy, passive transport is shown

Question 2

Define Diffusion

Answer 2

The process of moving particles from their high concentrations to an area with a lower concentration

For water in a cell, it will move to make an equal concentration on either side of the membrane

Question 3

Define Osmosis

Answer 3

When water is diffused over a selective permeable membrane

Question 4

What is a membrane made up of?

Answer 4

Phospholipid bilayer made up of phospholipid molecules which is a bipolar molecule

Question 5

What is a bipolar molecule made up of?

Answer 5

Made up of fatty acid side which is hydrophobic which points inwards because it is hydrophobic/non-polar

a phosphoric side which is hydrophilic, making it point outwards

Question 6

What properties are needed for a molecule to pass through the membrane?

Answer 6

It must be non-polar or polar but uncharged

Question 7

What is the membrane-permeable too?

Answer 7

H2O, polar, neutral, Gases: O2 CO2 and N2.

Lipids and small, polar neutral molecules, amino acids, glucose and larger

Question 8

What is the membrane-less or impermeable to?

Answer 8

Small, polar- charged molecules (ions), large uncharged molecules, amino acids, glucose and larger

Question 9

Define Delta G

Answer 9

Change in free energy occurs when a molecule or ion is moved up or down the concentration gradient

Delta G is negative when moving down because energy is released, however when going up the energy is confused so Delta G is positive

Question 10

Define Facilitated Diffusion

Answer 10

Passive transport of a molecule across the membrane by the use of a transport protein

Passive diffusion that goes down concentration gradient meaning energy is made and released

Question 11

What is a pore channel?

Answer 11

A hole through the membrane which allows impermeable and not so very impermeable molecules/ions to pass through

Question 12

Types of pore channels

Answer 12

Potassion channel
Aquaporin water channel
Voltage gated sodium channel
Gramicidin

Question 13

What are carriers?

Answer 13

Small molecule which can carry across membrane-impermeable molecules when the substrate is bonded it causes the transport protein to change shape

Question 14

Define an ionophore

Answer 14

Group of molecules which are used for facilitating ion movements (carriers of channels).

Can be small antibiotics and synthetics

Question 15

Valionomycin is an example of a Carrier Ionophore: break down the structural name Cyclododecadepespipeptide

Answer 15

Cyclo meaning cyclic
Dodeca meaning twelve units
Depespi meaning Alkyl
Peptide amino acid
A threefold circular repeat of: L-lactate, L-valine, D-a-hydroxyisovalerate, D-valine

Question 16

What are the features of Valinomycin

Answer 16

Alternating ester and ether peptide bonds
Alternating inward and outward carbonyls (C=O)
Unchanged non-polar (This allows for it to exist in the membrane)

Question 17

What does the features of Valinomycin cause?

Answer 17

Freely membrane-permeable
6 inward-facing carbonyls co-ordinate K+ ion octahedrally
When K+ is bound the structure will change from an open circle to 3-point crown
When the structure is changed, the ion is a shield from a bilayer
Permeability =Rb+ > K+ >H+»Na»Mg2+
Carriers 10^4 ions/sec

Question 18

What is an example of a pore-forming ionophore?

Answer 18

Gramicidin A

Question 19

What are the structural features of Gramicidin A?

Answer 19

Pentadecapeptide
Formly-Va-Gly-Ala-Leu-Ala^5-Val-Val-Val-Trp-leu^10-Trp-Leu-Trp-Leu-Trp^15-CO
Most amino acids = non-polar
The N-terminal is hydrphobic because of the process of formylation

Question 20

What are the results of the features of Gramicidin A?

Answer 20

The N-terminal is moved into the membrane inwards

Folding gives a Beta-Helix which has a 5.7 amino acids/turn

Two momomers are associated with the formation of transmembrane pore