Docsity
Docsity

Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity


Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan


Guidelines and tips
Guidelines and tips

Transport in Membranes: Ionophores, Porins, Channels, Aquaporins, Schemes and Mind Maps of Thermodynamics

An in-depth exploration of passive and active transport across membranes, focusing on ionophores, porins, ion channels, and aquaporins. It covers the thermodynamics of transport, passive-mediated transport, and active transport, as well as specific examples of ionophores, porins, and ion channels. The document also discusses the role of these transport mechanisms in maintaining osmotic balance, signal transduction, and membrane potential.

What you will learn

  • What are the classes of ATPases and how do they contribute to active transport?
  • What is the difference between passive and active transport across membranes?
  • How do ionophores increase the permeability of a target membrane for ions?
  • What is the role of ion channels in maintaining osmotic balance and membrane potential?
  • How do aquaporins permit rapid rates of water transport across the membrane?

Typology: Schemes and Mind Maps

2021/2022

Uploaded on 09/12/2022

dyanabel
dyanabel 🇺🇸

4.7

(20)

288 documents

1 / 40

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
Passive and Active Transport
1. Thermodynamics of
transport
2. Passive-mediated
transport
3. Active transport
neuron, membrane potential,
ion transport
pf3
pf4
pf5
pf8
pf9
pfa
pfd
pfe
pff
pf12
pf13
pf14
pf15
pf16
pf17
pf18
pf19
pf1a
pf1b
pf1c
pf1d
pf1e
pf1f
pf20
pf21
pf22
pf23
pf24
pf25
pf26
pf27
pf28

Partial preview of the text

Download Transport in Membranes: Ionophores, Porins, Channels, Aquaporins and more Schemes and Mind Maps Thermodynamics in PDF only on Docsity!

Passive and Active Transport

1. Thermodynamics of **transport

  1. Passive-mediated** **transport
  2. Active transport** neuron, membrane potential, ion transport

Membranes

  • Provide barrier function
    • Extracellular
    • Organelles
  • Barrier can be overcome by „transport proteins“
    • To mediate transmembrane movements of ions, Na
      • , K +
    • Nutrients, glucose, amino acids etc.
    • Water (aquaporins)

Two types of transport across a membrane: o Nonmediated transport occurs by passive diffusion, i.e., O 2

, CO

2

driven by chemical potential gradient, i.e.
cannot occur against a concentration gradient

o Mediated transport occurs by dedicated transport proteins

1. Passive-mediated transport/facilitated diffusion : [high] -> [low]

  1. Active transport : [low] -> [high] May require energy in form of ATP or in form of a membrane potential

A) Ionophores Organic molecules of divers types, often of bacterial origin => Increase the permeability of a target membrane for ions, frequently antibiotic, result in collapse of target membrane potential by ion equilibration

1. Carrier Ionophore , make ion soluble in membrane, i.e. valinomycin, 10 4 K + /sec 2. Cannel-forming ionophores , form transmembrane channels, gramicidin A, 10 7 K + /sec

Valinomycin

o One of the best characterized ionophores, binds K

ions o Cyclic peptide with D- and L-Aa o Discrimination between Na

, K

, Li

? K

(r=1.33Å), Na

(r=0.95Å)

B) Porins

o Membrane spanning proteins with β-barrel structure, with central aqueous channel, diameter ~ 7x11Å ~600 D, little substrate

selectivity, E. coli OmpF

o Maltoporin , substrate selectivity for maltodextrins, α(1->4)- linked glucose oligossaccharide degradation products of

starch, greasy slide

C) Ion Channels

o All organisms have channels for Na

, K

, and Cl

o Membrane transport of these ions is important for: o Osmotic balance o Signal transduction o Membrane potential o Mammalian cells: extracellular: 150mM Na

, 4mM K

intracellular: 12mM Na

, 140mM K

passive diffusion of K

ions through opening of **K

channels** from cytosol to extracellular space **K

-channels** have high selectivity of K

over Na

selectivity 10 4

The selectivity filter

o The ion needs to be dehydrated to pass through the most narrow opening of the channel o In the dehydration, water is replaced by hydroxyl groups from the channels amino acids o These hydroxyls will stabilize K

but not Na

, because Na

is much smaller than K

o Cavity in the middle of the channel = middle of the membrane !!! Contains water

Ion channels are gated

o Channels can be closed and opened upon signal: o Mechanosensitive channels open in response to membrane deformation: touch, sound, osmotic pressure o Ligand-gated channels open in response to extracellular chemical stimulus: neurotransmission o Signal-gated channel, open for example on intracellular binding of Ca 2+ o Voltage-gated channel: open in response to membrane potential change, transmission of nerve impulses

Time course of an action potential

Voltage gated K

V

channels o Tetramer, S5,S6 ~KcsA, T1 domain in cytosol o Gating by the motion of a protein paddle o S4 helix contains 5 positive charges, spaced by 3 Aa = acts as voltage sensor

Ion channels have two gates o One to open and one to close o T1 domain contains inactivation peptide that blocks pore entrance a few ms after V-dependent pore opening

Cl

- channel differ from cation channels o Present in all cell types. Permit transmembrane movement of chloride ions along concentration gradient: [Cl

] extracellular: 120mM; intracellular 4mM o Homodimer with each 18TMDs