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What is selective permeability?
The ability to allow certain substances to pass through an object more easily than others.
What is an amphipatic molecule?
A molecule that has both a hydrophilic and hydrophobic region.
What holds a membrane together?
Hydrophobic interactions.
Are hydrophobic interactions stronger or weaker than covalent bonding?  Is the difference large or small?
Hydrophobic interactions are much weaker than covalent bonds.
What property of cholestorol allow it to be a temperature buffer in animal cells?

  • Making the membrane less fluid at relatively higher temperatures.

  • Hinders the close packing of phospholipids thus lowering the temperature required for the membrane to solidify.

What is an integral protein?
Proteins that penetrate the hydrophobic core of the lipid bilayer.
What is a peripheral protein?
Proteins which are not embedded in the lipid layer, but instead are loosely bound to the surface of the bilayer.
What is cell-cell recognition?
The ability for a cell to determine one type of neighboring cell from another.
What does -glyco refer to?
The presence of a carbohydrate.
What is a glycolipid?
A short, branched chain of fewer than 15 sugar units covalently bonded to a lipid.
What is a glycoprotein?
A short, branched chain of fewer than 15 sugar units covalently bonded to a protein.
What does a transport protein do in relation to the membrane of a cell?
A transport protein allows hydrophilic substances to avoid contact with the lipid bilayer of the membrane.
What is a channel protein?
A specific kind of transport protein which forms a hydrophilic channel which allows certain molecules or atomic ions to pass through the membrane.
What is an aquaporin?
A specific kind of channel protein which allow the passage of water through a cellular membrane.
What is the rate of water molecules through an aquaporin?
Three billion water molecules per second.
What is a carrier protein?
A specific type of transport protein that holds onto its passangers and changes shape in a way that shuttles them across the membrane.
What is diffusion?
The movement of molecules of any substance so that they spread out evenly into the available space.
In the abscence of other forces, a substance will diffuse...
...from where it is more concentrated to where it is less concentrated.
What is a concentration gradient?
The region along which the density of a chemical substance decreases.
Diffusion is a _____ process, needing no input of ______.
sponteneous; energy
How does most of the traffic across the cell membrane occur?
Through diffusion.
What is passive transport?
The diffusion of a substance across a biological membrane, because no energy is necessary for this process to occur.
What is osmosis?
The diffusion of water across selectively permeable membranes.
What is tonicity?
The ability of a solution to cause a cell to gain or lose water.
What are the two factors which are taken into account when considering tonicity?
  • Solute concentration
  • Membrane permeability
If there is a higher concentration of nonpentrating solutes in the surrounding solution...
...water will tend to leave the cell.
If there is a higher concentration of nonpentrating solutes in the cell...
...water will tend to leave the surrounding solution.
What is an isotonic environment in relation to a cell?
An environment that has the same tonicity as the cell.
When a cell is placed in an isotonic solution what will be the effect of water in the solution?
There will be no net movement of water across the plasma membrane.  Water flows across the membrane, but the movement in both directions is equal.
What is an hypertonic environment in relation to a cell?
An environment that has a higher rate of tonicity than the cell.
What happens to a cell in a hypertonic solution?
The cell will lose water to its environment, shrivel, and probably die.
What is an hypertonic environment in relation to a cell?
An environment that has a lower level of tonicity than the cell.
What happens to a cell in a hypotonic solution?
Water will enter the cell faster than it leaves and the cell will swell an lyse (burst).
Can a cell with a wall better tolerate an execessive loss or uptake of water?
What is osmoregulation?
The control of water balance.
What is a cell when it is turgid?
Very firm.
What is a cell when it becomes flaccid?
It becomes limp.
Is a cell wall an advantage in a hyptonic environment?
What is plasmolysis?
When a cell with a cell wall shrivels and the plasma membrane pulls away from the cell wall.
What is facilitated diffusion?
The passive diffusion of of polar molecules and ions through transport proteins through the membrane.
What is a gated channel?
A channel protein that can open or close in response to a stimulus.
What is an ion channel?
A transmembrane protein channel that allows a specific ion to flow across the membrane down its concentration gradient.
What are the two types of stimulus activate a gated channel?

  • Chemical

  • Electrical

What is active transport?
The movement of substances through a membrane that require energy.
What forms of protein does active transport utilize and which do they not utilize?  Why?
Active transport utilizes carrier proteins and not channel proteins.  Because the latter only opens up a channel to allow substances to flow through, which requires the substance to act of its own accord.
What does active transport allow a cell to do internally?
It allows a cell to maintain internal concentrations of small solutes that differ from concentrations in its environment.
What is one way in which ATP can power active transport?
Transfering its terminal phosphate group directly to the transport protein, inducing the protein to change its shape to translocate the substance across the membrane.
What is a sodium-potassium pump?
A transport system which exchanges sodium for potassium across the plasma membrane of animal cells using the exchange of terminal phosphate groups.
What is membrane potential?
The voltage across the membrane.
What is the range of membrane potential?
-50 to -200 milivolts.
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