Terms in this set (64)
the boundary that separates a living cell from its surroundings
they allow some substances to cross more easily than others
The temperature at which a membrane solidifies depends its
Cell membranes rich in phospholipids containing unsaturated fatty acids are
_____________ than those rich in saturated fatty acids.
Membranes must be fluid to function properly - they are usually about as fluid as salad oil!
In animal cells, the steroid/sterol ___________ has different effects on membrane fluidity at different temperatures (plants produce little or no cholesterol).
Protein's determine most of a membrane's specific functions
peripheral membrane proteins
are bound to the surface of the membrane.
integral membrane proteins
penetrate the hydrophobic cores and, in many cases, span the entire cell membrane.
Integral membrane proteins that span the entire membrane are called
The __________ regions of an integral membrane protein consist of one or more stretches of _________ amino acids, often coiled into alpha helices.
Cells recognize each other by binding to surface molecules, often ___________, on the plasma membrane.
endoplasmic reticulum; golgi apparatus
The asymmetrical distribution of proteins, lipids, and associated carbohydrates in the plasma membrane is determined when the membrane is constructed by the ______________ and _____________
plasma membranes are
hydrophobic (nonpolar) molecules
such as hydrocarbons, can dissolve in the lipid bilayer and pass through the membrane rapidly.
such as ions and polar molecules, cannot diffuse through cell membranes.
an extremely small polar molecule, diffuses very slowly through cell membranes.
allow passage of hydrophilic substances across the membrane.
Some transport proteins, called ____________, have a hydrophilic channel that certain molecules or ions can use enter or leave a cell
Channel proteins called ___________ facilitate the passage of water.
Other transport proteins, called ____________, bind to molecules and change shape to shuttle them across the membrane.
is the tendency of molecules (e.g., solutes in solutions) to spread out evenly into the available space.
as many molecules cross one way as cross in the other direction
Soluble substances diffuse down their ____________ from the side with higher concentration to the side with lower concentration.
The diffusion of a substance across a biological membrane down its concentration gradient is ____________ because no energy is expended by the cell to make it happen.
is the diffusion of a solvent (e.g., water) across a selectively permeable membrane from the side with lower TOTAL solute concentration to the side with higher solute concentration.
TOTAL solute concentration
The direction of osmosis is determined only by the difference in _____________ on the two sides of the membrane.
the ability of a solution to cause a cell to gain or lose water.
In an ______________, the total solute concentration is the same as that inside the cell and there is no net movement of water across the plasma membrane.
In a _____________, the solute concentration is greater than that inside the cell and the cell loses water via osmosis.
In a _______________, the solute concentration is less than that inside the cell and the cell gains water via osmosis.
the control of solute concentrations and water
balance, is a necessary adaptation for life in such environment.
help maintain water balance in plant cells
A plant cell in a _______ solution swells until the wall
opposes uptake; the cell is now turgid (firm).
If a plant cell and its surroundings are ________, there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt.
In a __________ environment, plant cells lose water.
Eventually, the cell membrane pulls away from the wall,
a usually lethal effect called
Transport proteins allow passage of ________ substances across the membrane.
Some ____________, called channel proteins, have a hydrophilic channel that certain molecules or ions can use as a tunnel to enter the cell.
Channel proteins called a ___________ facilitate the passage of water into the cell.
Other transport proteins, called _______________, bind to molecules and then undergo a change in shape (conformation) to shuttle them across the membrane.
A transport protein is ________ for the substance it moves.
In ___________, transport proteins speed the passive movement of molecules across the plasma membrane.
provide channels/pores that allow specific molecules or ions to cross the membrane
undergo changes in shape that translocate solute-binding sites across the membrane.
moves solutes against their concentration gradient.
active transport requires energy, usually in the form of
The __________________ is one type of active transport system
is the voltage difference across a membrane.
Two combined forces, collectively called the _____________, drive the diffusion of ions across a membrane
a chemical force
the ion's concentration gradient
an electrical force
the effect of the membrane
potential on the ion's movement
an electrogenic pump
is a transport protein that generates voltage across a membrane (membrane potential).
the sodium-potassium pump
is the major electrogenic pump of animal cells.
The main electrogenic pumps of plants, fungi, and bacteria are
occurs when active transport of a solute indirectly drives transport of another solute.
bulk via vesicles
Large molecules, such as polysaccharides and proteins, cross the membrane in
In _________, a cell takes in macromolecules or, in some cases, entire cells, by forming vesicles from the plasma membrane.
a cell engulfs a particle, or even another cell, by forming a food vacuole.
molecules dissolved in the extracellular environment of a cell are taken up when extracellular fluid is engulfed into tiny vesicles
In _________________, binding of ligands to receptors triggers vesicle formation.
is any molecule that binds specifically to a receptor site of another molecule.
In _____________, transport/secretory vesicles migrate to the plasma membrane, fuse with it, and release their contents to the extracellular environment.
Many _____________ use exocytosis to export their products.