the ability of phospholipids to form ____ is inherent in their molecular structure
membranes
membranes are not ___ sheets of molecules locked rigidly in place
static
a membrane is held together primarily by ________ (much weaker than covalent)
hydrophobic interactions
the ______ of phospholipids within the membrane is rapid
lateral movement
the membrane remains ______ to a lower temp if it is rich in phospholipids w unsaturated hydrocarbon tails
fluid
_____ helps membranes resist changes in fluidity when the temp changes
cholesterol
the ability to change the _____ of cell membranes in response to changing temps has evolve in organisms that live where temps vary
lipid composition
two major populations of membrane proteins
integral and peripheral
majority of integral proteins are _______
transmembrane proteins
cell's recognize other cells by binding to ____, often contain carbs on the extracellular surface of the plasma membrane
molecules
____ molecules can dissolve easily in the lipid bilayer of the membrane without aid of membrane proteins
hydrophobic
_____ built into the membrane play key roles in regulating transport
proteins
cell membranes are permeable to specific ____ and a variety of _______
ions, polar molecules
some transport proteins, called _______, function by having a hydrophilic change that certain molecules or atomic ions use as a tunnel thru the membrane
channel proteins
other transport proteins, _____, hold onto their passengers and change shape in a way that shuttles them across the membrane
carrier proteins
molecules have a type of energy called _____, which is associated with their constant motion
thermal energy
much of the traffic across cell membranes occurs by ____
diffusion
cells ____ in a hypertonic environment
shrivel
the relatively inelastic wall will only expand so much before it exerts backs a pressure on the cell, called _____
turgor pressure
healthy state for most plant cells
turgid
a wall is of no advantage if the cell is immersed in a ____ environment
hypertonic
for some gated channels, the stimulus is _____
electrical
carrier proteins and ion channels are examples of ______
passive transport
one way atp can power active transport is by transferring its __________ directly to the transport protein
terminal phosphate group
all cells have ____ across their plasma membranes
voltages
voltage is __ _____ __- a separation of opp charges
electrical potential energy
membrane potential ranges from ____
-50- -200 millivolts
two forces that drive the diffusion of ions across a membrane; a _____ force and an ____ force
chemical, electrical
an ion diffuses down its _____ gradient
electrochemical
in cases where electrical forces due to the membrane potential oppose the simple diffusion of an ion down its concentration gradient, _____ may be necessary
active transport
some membrane proteins that actively transport ions contribute to the membrane potential-- an ex is the ________
sodium-potassion pump
with each "crank: of the pump, there is a net transfer of one pos charge from the cytoplasm to the extracellular fluid, a process that stores energy as ______
voltage
the ________ appears the be the major electrogenic pump of animal cells
sodium-potassion pump
large molecules generally cross the membrane in bulk by mechanisms that involve packing in _______
vesicles
many secretory cells use _____ to export products
exocytosis
endocytosis and exocytosis also provide mechanisms for rejuvenating or remodeling the ________
plasma membrane
3 types of endocytosis:
phagocytosis, pinocytosis, receptor-mediated endocytosis
one class of local regulators in animals, ____, consists of compounds that stimulate nearby target cells to grow and divide
growth factors
numerous cells can simultaneous receive and respond to the molecules of growth factor produced by a nearby cell called _____
paracrine signaling
a more specialized type of local signaling called _____ occurs in the animal nervous system
synaptic signaling
animals and plants use chemicals called ____ for long distance communication
hormones
our current understanding of how chem messengers act on cells had its origins in the pioneering work of the american ____
sutherland
cell-to-cell message can be divided into three stages:
reception, transduction, response
the ______ helps ensure that crucial activities like these occur in the right cells, at the right time, and in proper coordination with the activities of other cells in the organism
cell-signaling process
a molecule that specifically binds to another molecule
ligand
_______ generally causes a receptor protein to undergo a change in shape
ligand binding
most signal receptor are ____ ____ _____
plasma membrane proteins
we cans see how transmembrane receptors work by looking at 2 major types:
g protein coupled-receptors and ligand-gated ion channels
the nearly 1000 ____ examined to date make up the largest family of cell-surface receptors in mammals
GCPRs
when a signaling molecule binds as a ligand to the receptor protein, the gate opens or closes, allowing or blocking the diffusion of ________, through a channel in the protein.
specific ions
_______ are very important in the nervous system
ligand-gated channels
intracellular receptors proteins are found in either the ____ or ____ of the target cell
cytoplasm, nucleus
special proteins called _____ control which genes are turned on
transcription factors
when receptors fro signaling molecules are plasma membrane proteins , transaction stage of cell signaling is usually a ________ _______
multistep pathway
one benefit of multiple steps is the possibility of greatly _____ the signal
amplifying
widespread cellular mechanism for regulating protein activity
phosphorylation and dephosphorylation
the addition of _____ often changes the form of a protein from inactive to active
phosphate groups
_____ regulate a large proportion of the thousands of proteins in a cell
protein kinases
the immediate effect of cAMP s usually the activation of ______
protein kinase A
the activation of protein kinase A then ______ other protein
phosphorylates
ultimately, a signal transduction pathway leads to the regulation of one or more ______
cellular activities