Chapter 10 pt 2 Flashcards
Transbilayer Movement of Lipids Requires _____________
Catalysis
Proteins called _________ , floppases, and scramblases facilitate the transbilayer movement (translocation) of individual lipid molecules, providing a path that is energetically more favorable and much faster than the uncatalyzed movement
flippases
________________ moves PE & PS from outer membrane to to interior cytosolic leaflet (interior membrane)
Flippase
__________ moves phospholipids from cytosolic to outer leaflet
Floppase
___________ moves lipids in either direction toward equilibrium
Scramblase
______________ movement from one leaflet to the other is very slow, but (b) lateral diffusion
within the leaflet is very rapid, requiring no catalysis. (c) Three types of phospholipid translocators in the plasma membrane. PE is
phosphatidylethanolamine; PS is phosphatidylserine.
Uncatalyzed
_____________ and Cholesterol Cluster Together in
Membrane Rafts
Sphingolipids
Membrane microdomains
Stable associations of sphingolipids and cholesterol in the outer leaflet produce a microdomain, slightly thicker than other membrane regions, that is enriched with specific types of membrane proteins.
__________ proteins are prominent in the outer leaflet of these rafts, and proteins with one or several covalently attached long-chain acyl groups are common in the inner leaflet. Inwardly curved rafts called caveolae are especially enriched in proteins called caveolins
GPI-anchored
Proteins with attached ___________ groups tend to be
excluded from rafts.
prenyl
__________________ moves substances across the semi- permeable barrier down or up the electrochemical gradient
Membrane Transport
Summary of transporter types
Some types (ionophores, ion channels, and passive transporters) simply speed transmembrane movement of solutes down their electrochemical gradients, whereas others (active transporters) can pump solutes against a gradient, using ATP or a gradient of a second solute to provide the energy.
Transport May Be __________or Active
Passive
Simple diffusion
Solutes moving from a region of higher concentration to a region of lower concentration
Transporters
Membrane proteins that act by increasing the rate of solute movement across membranes
Passive transporter
Simply facilitate movement down a
concentration gradient, increasing the transport rate. This process is called passive transport or facilitated diffusion
Active transporters (pumps)
Move substrates across a membrane against a
concentration gradient or an electrical potential, a process called active transport
Primary active transporters
Use energy provided directly by a chemical reaction
Secondary active transporter
Couple uphill transport of
one substrate with downhill transport of another
Ion channel
Speed the passage of inorganic ions across membranes by a mechanism different from that of transporters. They provide an aqueous path
across the membrane through which inorganic ions can diffuse at very high rates. Most ion channels have a “gate” regulated by a biological signal. When the gate is open, ions move across the membrane, through the channel, in the direction dictated by the ion’s charge and the electrochemical gradient. (Transporter have alternating gates)
Describe the energy changes accompanying the passage of a hydrophilic solute through the lipid bilayer of a biological membrane
- In simple diffusion, the removal of the hydration shell is highly endergonic, and the energy
of activation (ΔG‡) for diffusion through the bilayer is very high. - A transporter protein reduces the ΔG‡
for transmembrane diffusion of the solute.
It does this by forming noncovalent interactions with the dehydrated solute to replace the hydrogen bonding with water and by providing a hydrophilic transmembrane pathway.
Spontaneous movement across the lipid membrane requires _______
Delta G
_______________ provides transmembrane passage for ions and polar molecules
Facilitated Diffusion
Pore/Channel & Transporters
- No additional energy - Solutes diffuse
down their electrochemical gradient
- Selectivity and transport rate mediated by
protein structural properties or charge - Pores & channels often non-saturable
- Transporters bind ligands and change
shape; can be saturated like enzymes - Can be gated or voltage dependent
- Ion-channel defects cause diseases
(Cystic fibrosis (box 11-2), CTFR – Cl- channel)
