plasma membrane
boundary that separates the living cell from its surroundings
selective permeability
allows some substances to cross the plasma membrane easier than others
Transport proteins
often responsible for controlling passage across cellular membranes
Phospholipids
most abundant lipid in the plasma membrane
amphipathic
phospholipids are ________ molecules containing hydrophobic and hydrophilic regions
fluid mosaic
in the _____ model, the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids
are not
Proteins _______ randomly distributed in the membrane
phospholipids
form the main fabric of the membrane
proteins
determine most of the membranes functions
peripheral proteins
protein bounded to the surface of the membrane
integral proteins
protein that penetrates the hydrophobic core
transmembrane protein
integral proteins that span the membrane called
- non polar amino acids
- alpha helices
hydrophobic regions of an integral protein consists of on or more stretches of ___________, often coiled into ________
- transport
- enzymatic activity
- signal transduction
- cell-cell recognition
- intercelullar joining
- attachment to the cytoskeleton and extracellular matrix
functions of cell surface membranes
by binding to other molecules (often containing
How do cells recognize each other
glycolipids
membrane carbs covalently bonded to lipids form
glycoproteins
membrane carbs covalently bonded to proteins form
plasma membrane
a cell exchanging materials with its surroundings, this process is controlled by the
selectively permeable
plasma membranes are ______ __________, regulating the cells molecular traffic
hydrocarbons
what is a hydrophobic (non-polar) molecule
hydrophobic
________ molecules can dissolve in the lipid bilayer and pass through the membrane rapidly
ions and polar molecules
types of hydrophilic molecules
hydrophilic
molecules that don't cross the membrane easily
transport
proteins built into the membrane play key roles in regulating
transport proteins
allow passage of hydrophilic substances across the membrane
channel proteins
type of transport protein with a hydrophilic channel that certain molecules or ions can use as a tunnel
aquaporins
type of channel protein that greatly facilitate the passage of water molecules
carrier proteins
type of transport proteins that bind to molecules and change shape to shuttle them across the membrane
transport
_________ protein is specific for the substance it moves
diffusion
tendency for molecules to spread out evenly into the available space
dynamic equilibrium
At _____________ ________________ as many molecules cross the membrane in one direction as in the other
concentration gradient
substances diffuse down their ________ __________, the region along which the density of a chemical substance increases or decreases
no
____ work must be done to move substances down the concentration gradient
passive transport
diffusion of a substance across a biological membrane is _______ _________ because no energy is expended by the cell to make it happen
osmosis
diffusion of water across a selectively permeable membrane
- Lower solute concentration
- higher solute concentration
- equal
in osmosis, water diffuses across a membrane from a region of ________ _________ ________ to the region of _____ _______ _______ until the solute concentration is _________ on both sides
Tonicity
the ability of a surrounding solution to cause a cell to gain or lose weight
Tonicity
the ________ of a solution depends on its concentration of solutes that cannot cross the membrane relative to that inside the cell
Isotonic solution
type of solution where the solute concentration is the same as that inside the cell, no net water movement across the plasma membrane
Hypertonic Solution
type of solution where the solute concentration is greater than that inside the cell; cell loses water
Hypotonic Solution
type of solution where the solute concentration is less than that inside the cell; cell gains water
- shrivel
- burst
cells without cell walls will ________ in a hypertonic solution and _______ in a hypotonic solution
facilitated diffusion
In ___________, transport proteins speed the passive movement of molecules across the plasma membrane
- channel proteins
- carrier proteins
transport proteins include
channel
type of protein that provide corridors that allow a specific molecule or ion to cross the membrane
aquaporins
facilitate the diffusion of water
Ion Channels
facilitate the transport of ions
gated channels
ion channels that open or close in response to a stimulus
carrier proteins
_____ undergo a subtle change in shape that translocates the solute binding site across the membrane
the binding and release of the transported molecule
change in shape of a carrier protein can be triggered by
passive
facilitated diffusion is _________ because it requires no energy
some transport proteins
________ can move solutes against their concentration gradients
Active transport
_______ requires energy, to move substances across their concentration gradient
carrier proteins
All proteins involved in active transport are
concentration gradients
Active transports allow cells to maintain _____________ that differ from their surroundings (look at example!!!!!!!!! 39-46)
cotransport
occurs when active transport of a solute indirectly drives transport of other substances (look at what it does pg. 48)
- lipid bilayer
- transport proteins
small molecules and water enter or leave the cell through the ______ or via ________
vesicles
Large molecules such as polysaccharides and proteins cross the membrane in bulk via
energy
Bulk transport requires
exocytosis
transport vesicles migrate to the membrane, fuse with it, and release their contents outside of the cell
secretory
many _____ cells use exocytosis to export their products
endocytosis
the cell takes in macromolecules by forming vesicles from the plasma membrane
Endocytosis
reversal of exocytosis, involving different proteins
- phagocytosis (cellular eating)
- pinocytosis (cellular drinking)
- receptor-mediated endocytosis
three types of endocytosis
vacuole
in phagocytosis, a cell engulfs a particle in the _____
lysosome
the vacuole fuses with a ________ to digest the particle
pinocytosis
in _______, molecules dissolved in droplets are taken up when extracellular fluid is gulped into tiny vesicles