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)
Transporters may be __________or active based on solute concentration and energy usage
passive (May be bidirectional and transport multiple ligands per cycle, Classified by mechanism of operation: uniport, symport or antiport)
_________ uses concentration gradient and equilibrates solute in/out(related to transporters)
Passive
____________requires energy to move against concentration gradient or charge (related to transporters)
Active
Describe glucse transport into erythrocytes by GLUT1
- Glucose in blood plasma binds to a stereospecific site on T1
this lowers the activation energy for - A conformational change from glucose out?
T1 to glucose in T2 effecting the transmembrane passage of the glucose. - Glucose is released from T2
into the cytoplasm, and
4 . the transporter returns
to the T1 conformation, ready to transport another glucose molecule. Between
the forms T1 and T2there is an intermediate form (not shown here) in which glucose is sequestered within the transporter, with access to neither side
The amount of energy needed for the transport of a solute against a gradient can be calculated from the initial concentration gradient can be found with what formula?
Delta G= delta G’ + RT ln ([P]/[S]) (S is substrate & P is product, R is 8.315J/mol *K)
When the “reaction” is simply transport of a solute from a region where its concentration is C1
to a region where its concentration is C2, no bonds are made or broken and ΔG′°
is zero. The free-energy change for transport, ΔGt, is then what?
Delta G (subscript t) = RT ln (C2/C1)
When the solute is an ion, its movement without an accompanying counterion results in the endergonic separation of positive and negative
charges, producing an electrical potential; such a transport process is said to be ___________
electrogenic
The energetic cost of moving an ion depends on the electrochemical potential, the sum of the chemical and electrical gradients:
Delta G (subscript t)= RN ln (C2/C1) + ZF delta phi (Z is the charge on the ion, F is the constant 96,480 J/V *mol), delta phi is the transmembrane potential (in volts)
Spontaneous movement across the lipid membrane depends on what?
Depends on solute concentration & charge: Electrochemical gradient
- Chemical Potential: movement from high to low concentration
- Electrical Gradient: ions move to opposite charge; negative cell interior (-40 to -
80 mV) add term for charged molecules (zFdelta phi)
(-z = ionic charge (+1 for Na+, -1 for Cl-, +2 for Ca2+
– F = Faraday constant (charge on mole of electrons) = 96,485 C/mol)
– D = membrane potential in V (Range up to -100 mV) 1 V = 1 J/C)
______________ moves substances against the electrochemical gradient
Active transport
Active transport
Substances transported against a concentration gradient – Endergonic
What are the two types of active transport?
- Primary active transport
- Secondary active transport
Primary active transport
ATP hydrolysis creates ion or molecule concentration gradient
Secondary active transport
Existing electrochemical gradient powers a transport process
What are some examples of cellular transport scheme?
- Na+ out using ATP (primary active transport)
- Na+ returns through transporter down conc. gradient
- Glucose transport powered symport by Na+ traveling down its conc. gradient back
into cell (Secondary Active Transport)
__________ transport via symport with Na+ (secondary active) Driven by primary active transport of sodium & potassium
Na+-K+ pump maintains a low cellular [Na+]
Glucose
Eicosanoids
Derived from arachidonic acid; oxygenated variations
Isoprenoids
non-steroid derivatives; several vitamins A,K, E, retinoL
______________ often derived from arachidonic acid (C20)
Eicosanoids (Signal molecules: bind to enzymes or proteins for response)
__________ inhibits enyzme for prostaglandin synthesis: Analgesic and antipyretic
Aspirin
Steroids are derived from____________
isoprene: isoprenoids (Four fused ring system: rigid and near planar3-six-membered rings (A,B,C) + 5-carbon D ring Squalene precursor)
____________ is a precursor of steroid
hormone and bile salts (lipid digestion)
Cholesterol
__________ has cellular membrane component & precursor
Cholesterol
______________ link fatty acid to the hydroxyl group for transport/ storage & binding
to lipoproteins
Cholesterol Esters (Excess nonpolar cholesterol accumulates on blood vessel walls)
