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Transport Across Selectively Permeable Cell Membranes

Terms in this set (19)

active transport
Ions or molecules moving across a cell membrane against a concentration difference - requires ATP energy! The Na+/K+ ATPase pump is a famous example of active transport.
passive transport
the movement of ions or molecules across a cell membrane without the use of energy by the cell. Water and gases move passively across membranes in the human body.
diffusion
Movement of molecules from an area of higher concentration to an area of lower concentration.
osmosis
diffusion of water
faciliated transport (diffusion)
passive transfer of a substance into or out of a cell along a concentration gradient by a process that requires a carrier; a great example of this is the glucose channel that allows glucose to flow down its concentration gradient.
aquaporins
water channel proteins - water may flow either direction through a membrane, but always down its concentration gradient.
Voltage-gated Na+ channels
When this channel opens, Na+ flows passively INTO the cell. It only opens when the membrane potential is a little less negative than normal. It allows the cell to be "depolarized" since Na+ makes the interior of the cell briefly positive.
Voltage-gated K+ channels
When this channel opens, K+ flows passively OUT of the cell. This causes the cell to "repolarize" after it has depolarized, since so many positive ions are leaving the cell.
Glucose Channel
Membrane channel that only opens when insulin is bound to a peripheral receptor. When it opens, glucose flows passively into the cell.
isotonic solution
A solution with the same concentration of water and solutes as inside a cell, resulting in the cell retaining its normal shape because there is no net movement of water.
hypertonic solution
A solution in which the concentration of solutes is greater than that of the cell -- water can flow freely, so it will flow OUT of the cell (via osmosis) to balance out the concentrations since ions can't flow freely. Cells, especially brain cells and red blood cells, shrink (called crenation) under these conditions.
hypotonic solution
A solution in which the concentration of solutes is less than that of the cell -- water can flow freely, so it will flow INTO of the cell (via osmosis) to balance out the concentrations since ions can't flow freely. Cells, especially brain cells and red blood cells, swell under these conditions. RBCs may even burst!
What is the concentration of Na+ in human blood?
135-145mEq/L
How do oxygen and carbon dioxide go through cell membranes?
These small molecules diffuse through cell membranes according to their concentration gradient. This means oxygen enters the blood in the lungs, and carbon dioxide enters the lungs from the blood.
Use the root words to define intracellular, extracellular, and intercellular. How about intermolecular forces?
intracellular = "inside the cell" extracellular = "outside the cell". Intercellular = between cells
Intermolecular forces are those "between" molecules.
Compare the concentrations of Na+ ions and K+ ions inside the cell and in the blood.
Na+ is concentrated outside of cells, particularly in the blood. K+ is concentrated inside of cells. This difference is maintained by the Na+/K+ATPase pump.
Na+/K+ ATPase pump
transports 3 Na+ out of cytoplasm for every 2 K+ moved in. This accomplishes two important things #1 - Na+ is always more concentrated in the blood than in cells (and K+ always more concentrated inside of cells)
#2 - the inside of the cell at rest is negative relative to the large amount of Na+ ions outside the cell.
Endocytosis
A process in which a cell engulfs extracellular material through an inward folding of its plasma membrane - active transport
Phagocytosis
A type of endocytosis in which a cell engulfs large particles or whole cells
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