Membrane Transport Flashcards
Energetic of transport across a membrane equation
ΔG = RTln([X]b/[X]a) + ZFΔψ
Membranes are permeable to:
Hydrophobic, small molecules, and some small uncharged, polar molecules.
Membranes are highly impermeable to:
Large uncharged polar molecules and ions
Carrier molecules
Form a hydrophobic shield around polar molecules, often ions.
Valinomycin
Hydrophobic exterior and hydrophilic interior that associated with the charge of the ions.
Methods of facilitated transport
Pores/channels, transporters
Pores are made of
beta sheets
Channels are made of
Alpha helices
Characteristics of pores/channels
Non-stoichiometric, no conformational change, PASSIVE, selective, may be gated (ligand or voltage).
Characteristics of transporters
Stoichiometric, undergo conformational changes, active or passive, specific molecules, may be regulated.
Glucose is transported by a:
Uniporter, that may operate in both directions based on the concentration gradient
Purple bacteria as an example of active transport
Bacteriorhodopsin is a transporter that undergoes conformational changes to move H+ ions across the membrane against their gradient for processes such as ATP synthesis.
Rhodopsin ground state
All-trans retinal
Rhodopsin intermediate states
L = 13-cis protonated, M = 13-cis neutral, N = 13-cis protonated. Cycle allows hydrogen ions to be passed down the asparagine residues on the opposite side of the channels
Human rhodopsin uses rhodopsin for:
Absorption of wavelength facilitates cell signalling and neural transmissions through a GPCR.
GPCRs
Span the membrane 7 times, alpha helices. Many ligands bind to cause physiological responses.
GPCRs comprise —% of all known drug targets
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Na,K-ATPase
Transporter that moves 3 Na+ with its gradient, whilst anti-porting 2 K+ against its gradient.
Na+ leaves the cell, K+ enters the cell.
A third of total energy at rest is spent by the:
Na+/K+ ATPase
Glucose transport in the intestinal epithelial cell (IEC)
Glucose and Na+ are symported into the cell (secondary active) so that glucose can then (passively) diffuse out the other side and Na+ is rebalanced through the Na+/K+-ATPase (active).
