Membrane Transport and Lipid Bilayer Quiz

Na+/K+-ATPase changes conformation as it exchanges Na+ for K+

If 3 Na+ ions out for every 2 K+ ions in, what does this do to net charge on each side of the membrane

As the pump operates, it makes the cell interior more

Na+/K+-ATPase Pump is unidirectional; pumps Na+ ions out & K+ ions in phosphorylation-induced shape change alters ion

The purpose of ship’s pump is not to keep the ocean full of water, but to keep the ship

Humans have hundreds of different transporters that use this Na+ gradient to move specific

Glucose-Na+ symport protein uses the electrochemical Na+ gradient to drive the import of

Cotransport: Coupling active transport to existing ion

Movement of 2 moles of Na+ ions into a cell can generate a glucose conc. that is 30,000 times higher

Two types of glucose transporters allow gut epithelial cells to transport glucose from intestine to

The lipid bilayer is ideally suited to prevent loss of charged & polar solutes (ions, sugars, AA). Must allow movement of nutrients, respiratory gases, hormones, wastes, etc.

Membranes are a billion times more permeable to water than to small ions.

Approximately equal quantities of +/- charges inside and outside of cell. Tiny excesses of + or - charges do occur near PM and have imp. electrical effects.

Each cell membrane has its own characteristic set of carrier proteins.

Transporters and channels move inorganic ions and small, polar molecules cross membrane — facilitated diffusion.

Membranes are a selectively permeable barrier - two means for movement both of which lead to net flux of ions/compounds (influx - into cell; efflux out of cell).

1. Passively by diffusion 2. Actively by energy-coupled transport process.

______ substance moves from region of high conc. to region of low conc.; eventually eliminating conc. difference driven by random thermal motion leading to increase in entropy electrochemical gradient --chemical - compartment concentration difference -- electrical - compartment charge difference.

An electrochemical gradient has two components Width of green arrow -- magnitude of gradient.

Different processes by which substances move across membranes.

______ through membranes must be concentration difference must be membrane permeable directly through lipid -- partition coefficient - measure of polarity; ratio of solubility in nonpolar solvent/water -- molecule size (smaller is faster) Size of letter denotes concentration

Different processes by which substances move across membranes 1. Simple diffusion through lipid bilayer 2. Facilitated transport through aqueous, protein-lined channel; “channels” 3. ______; “transporters” 4. Active transport; “pumps”

Diffusion of ions through membrane channels transport is passive and proceeds down the concentration gradient of the ion being transported Usually 107 - 108 ions/s gated -- open/close with the proper stimulus bidirectional -- depending on the gradient, channels may transport ions in either/both of the two possible directions. Figure 12-20 Ions in solution are “hydrated” by water molecules ______ has a selectivity filter for ion specificity Figure 12-19 ______ Unsolvated = water removed

Major categories of gated ion channels 1. Voltage-gated channels -- opens due to change in voltage difference 2. Ligand-gated channels -- opens due to ligand binding; usually not the transported species 3. Stress (mechanically) gated -- opens due to mechanical stimulation Figure 12-27 1. Voltage gated 2. Ligand gated Neurotransmitter receptor -- a ligand gated ion channel Fig. 1 2 -4 2 Neurotransmitter receptor -- a ligand gated ion channel Fig. 1 2 -4 3 3. ______ Stretch-activated Piezo channels respond to light touch Ion-conducting pore Channels in skin allow us to respond to light touch Channels in bladder cells detect when the bladder is full Mechanically-activated ion channels allow us to hear Fig. 1 2 -2 8 Stress-gated ion channels allow us to hear

Different processes by which substances move across membranes 1. Simple diffusion through lipid bilayer 2. Facilitate transport through aqueous, protein-lined channel; “channels” 3. Facilitated transporters; “transporters” 4. ______; “pumps”

3. Facilitated transporters binds to membrane-spanning protein that changes its shape; facilitative transporter passive -- doesn’t require energy bidirectional -- depends on conc. 102 - 104 molecules/s molecule-specific; (AA, sugars) activity regulatable ______ Solute binding on one side of membrane may or may not be required to change protein shape, exposing solute to other surface (Example) Glucose transporter -- facilitated diffusion of glucose Outward open Inward open Changes shape randomly even without glucose; glucose binding induces shape change Side of membrane with highest glc conc. will tend to bind most glc If glc higher outside, will move glc inward and vice versa Fig. 1 2 -9 (Example) Glucose transporter -- facilitated diffusion of glucose into muscle cell down concentration gradient (High --> Low) 14 related transporters (isoforms; GLUT 1-14) in humans Glucose in cell then phosphorylated to glc6-phosphate, which cannot bind the transporter and stays in the cell See Fig. 1 2 -9

Example of regulation of a transporter á glucose levels triggers insulin secretion by pancreas á glucose uptake into various cells (e.g., skeletal muscle and fat cells) Absence of insulin ~5% transporters on PM Presence of insulin ~50% transporters on PM

Different processes by which substances move across membranes 1. ______ through lipid bilayer 2. Facilitate transport through aqueous, protein-lined channel; “channels” 3. Facilitated transporters; “transporters” 4. Active transport: “pumps”

Active transport uses energy to move molecules “up” conc. gradient (Low --> High) energy source may be ______, light absorbance or electron transfer, etc.

Facilitated transport through aqueous, protein-lined channel