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APHY 201 Module 02 Membrane Transport Ivy Tech
Terms in this set (56)
a phospholipid bilayer that creates a barrier between the inside of a cell (intracellular fluid) and the exterior (extracellular fluid); acts in transporting substances into or out of the cell; externally facing proteins acts as receptors, transport proteins, and in cell-to-cell recognition
fluid mosaic model of plasma membrane
Polar, hydrophilic heads and nonpolar, hydrophobic tails of phospholipids arrange with
embedded proteins and cholesterol into a
phospholipid bilayer to form the plasma
membrane of the cell. Phospholipids and membrane proteins can move laterally within the membrane unless held by the cytoskeleton.
functions of plasma membrane proteins (6)
transport, receptors for signal transduction, attachment to the cytoskeleton and extracellular matrix, enzymatic activity, intercellular joining, cell-to-cell recognition
binds cells into communities; tight junctions, desmosomes, gap junctions
adjacent integral proteins fuse to form impermeable junction encircling cell; requires substances to be absorbed through cells and prevents fluids and most molecules from moving between cells
"Rivets" or "spot-welds" that anchor cells together at plaques (thickenings on plasma membrane); reduces possibility of tearing
transmembrane proteins form pores (connexons) that allow small molecules to pass from cell to cell; for spread of ions, simple sugars, and other small molecules between cardiac or smooth muscle cells
a solution that bathes tissue cells; it is the main component of extracellular fluid; it is found in the interstitial spaces (spaces between cells); contains thousands of substances, e.g., amino acids, sugars, fatty acids, vitamins, hormones, salts, waste products
some molecules pass through easily; some do not (impermable); selectivity due to polarity, molecular size, and gates/channels/carriers
active membrane transport
energy (ATP) required; occurs only in living cell membranes; substance moves up or against its concentration or pressure gradient; utilizes pumps and vesicular transport
passive membrane transport
no cellular energy (ATP) required; substance moves down its concentration or pressure gradient
types of passive transport
diffusion (includes simple diffusion, carrier- and channel-mediated facilitated diffusion, osmosis) and filtration, dialysis
molecules using membrane transport
Ability to pass through membrane determined by lipid solubility, solute size and shape, and electrical charge. Uncharged particles preferred to cations (+) preferred to anions (-). Large, non-lipid soluble, and negatively charged (anions) least likely to diffuse into cells.
simple diffusion (equilibrium)
Substances diffuse using continual random movement of particles among one another in a liquid or gas. Uniform spreading out of molecules due to their random intermingling and molecular motion. E.g., oxygen, carbon dioxide, vitamins.
Measurable difference of particles from an area of greater concentration to an area of lesser concentration. Occurs until the concentration of the diffusing substance is uniform (diffusion equilibrium), then net diffusion ceases and simple diffusion continues. Collisions cause molecules to move down or with their concentration gradient.
certain hydrophilic molecules (e.g., glucose, amino acids, and ions) transported passively using specific membrane proteins - carriers or channels.
protein carrier specific for one chemical; binding of substrate causes transport protein to change
carrier mediated transport characteristics
Each solute requires a specific carrier. Does not require energy. Faster than non-carrier mediated diffusion. Reaches a maximum rate when all the sites are full (saturated).
Occurs when all carriers are engaged (transport maximum). Rate of diffusion based on number of binding sites available for transport. More carriers = faster transport
membrane protein with a pore for substrates to pass through; mostly ions selected on basis of size and charge. Leakage channels (always open); Gated channels (controlled by chemical or electrical signals).
How is selective permeability of a cell determined?
By number and types of carriers and channels available.
If the cell wants more/less of a substance, then the cell produces more/less of the specific proteins (carriers or channels) to move it into or out of the cell.
Difference in the concentration of solutes in solution across the membrane. ECF Na+ = 136-145 mmol/L, ICF Na+ = 12 mmol/L
Tendency of an electrically charged solute, such as K+, to move across the membrane arises from three factors:
the difference in the concentration of the solute
the charge of the solute molecule
the difference in voltage between the two sides of the membrane
Additional factors that affect rates of diffusion
molecular configuration (shape), ability of diffusing substance to dissolve in lipids, and molecular charge (if present) on the diffusing solute. Large, non-lipid soluble, and negatively charged least likely to diffuse.
Movement of solvent (e.g., water) across selectively permeable membrane; water can move through an aquaporin or plasma membrane
water specific channel; allows water to move rapidly down its osmotic gradient
When does osmosis occur?
occurs when water concentration is different on the two sides of a membrane
back pressure of water on membrane due to the force of gravity
tendency of water to move into cell by osmosis
Water moves by osmosis if there is a difference in water concentration (osmotic pressure) until?
Water moves by osmosis until hydrostatic pressure (back pressure of water on membrane) and osmotic pressure (tendency of water to move into cell by osmosis) equalize.
ability of solution to alter cell's water volume
solution with same non-penetrating solute concentration as cytosol; cell volume stays the same; equivalent to 0.9% NaCl solution
solution with higher non-penetrating solute concentration than cytosol; cell volume shrinks due to water leaving the cell by osmosis
solution with lower non-penetrating solute concentration than cytosol; cell volume increases causing cell to swell and burst as water continues to flow in by osmosis
movement of water and solute molecules across the cell membrane due to hydrostatic pressure generated by the cardiovascular system. Depending on the size of the membrane pores, only solutes of a certain size and charge may pass through it.
Utilizes diffusion and ultrafiltration of a fluid across a semipermeable membrane. Removes wastes and excess water from the blood. The blood flows in one direction and the dialysis solution flows in the opposite direction.
types active transport processes
two types of active processes (active transport and vesicular transport); both require ATP to move solutes across a living plasma membrane because solute too large for channels or not lipid soluble or not able to move down concentration gradient
primary active transport
energy from hydrolysis of ATP causes shape change in transport protein that "pumps" solutes (ions) across membrane; Na-K pump
maintains the resting membrane potential of cells; Moves 3 Na out and 2 K into the cell while utilizing 1 ATP with each pump.
secondary active transport
cotransport driven by the concentration gradient created by primary active transport; indirectly requires ATP; only functions when Na-K pump is also functioning
integral membrane protein that is involved in the transport of many differing types of molecules across the cell membrane; a type of cotransporter Ex: symporter works in the plasma membrane and molecules like glucose are transported across the cell membrane at the same time as sodium (Na)
active transport of large particles, macromolecules, and fluids across membrane in membranous sacs called vesicles; requires cellular energy (e.g., ATP)
Membranous sac of large particles, macromolecules, and fluids formed by a portion of membrane pinching off from organelles or cell membrane
cellular process where cells eject waste products or chemical transmitters (such as hormones) from the interior of the cell
membrane bound bubbles that carry chemical substances like lipids and proteins to the cell membrane where they are released or secreted from the cell
transport into cell; includes phagocytosis, pinocytosis, receptor-mediated endocytosis
type of endocytosis; cell eating; process in which extensions of cytoplasm surround and engulf large particles and take them into the cell; requires ATP
type of endocytosis; cell drinking; process by which a cell takes in liquid (ECF) from the surrounding environment; requires ATP
type of endocytosis; allows specific endocytosis and transcytosis; cells use to concentrate materials in limited supply; uptake of enzymes, low-density lipoproteins, iron, insulin, and, unfortunately, viruses, diphtheria, and cholera toxins
cell-environment interactions involve plasma membrane
lipid bilayer so the polar parts (phosphate heads) of the phospholipids are face the inner and outer surfaces, and nonpolar parts (tails) are in the middle - limits molecular movements. Charged because inside is lined with negative charges and outer surface lined with positive charges (membrane potential) - creates electrical gradient. Cells interact directly or indirectly by responding to extracellular chemicals. Ex; receptor proteins found on outer surface of bilayer bind hormones or neurotransmitters. Always involves glycocalyx for cell recognition.
difference in electric potential between the interior and the exterior of a biological cell. With respect to the exterior of the cell, typical values of membrane potential range from -40 mV to -80 mV.
difference in electric potential energy between two points (for cells, opposite charged ions separated by the cell membrane)
resting membrane potential
voltage that exists across the plasma membrane during the resting state of an excitable cell
state of a plasma membrane of an unstimulated neuron or muscle cell in which the inside of the cell is relatively negative in comparison to the outside
How does the RMP come about, and how is it maintained?
diffusion of ionic imbalances that polarize the membrane, and active transport processes maintain the membrane potential
the concentration gradient of what ion contributes the most to membrane potential?
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