Membrane Function and Structure Flashcards
Cellular membranes are ______ made from ______ and ______
fluid mosaics, lipids and proteins
the membrane structure results in it being
selectively permeable
what is passive transport
diffusion of a substance across the membrane
what transport does not need energy
passive transport
active transport
moves solutes against their gradients
most common lipid in the membrane
phsopolipids
what does selective permeability mean
certain molecules can pas
what transport needs energy
active transport
how do bulk transports move across the membrane
exocytosis and endocytosis
what is the boundary that separates a living cell from its surroundings
plasma membrane
why are membranes important for life
a cell must be able to separate itself from the outside environment
why must the cell be separate from the outside environment
- must keep its DNA and RNA from dissipating away
- must keep out foreign molecules that damages or destroys the cell
Charles Overton
Found that membranes were made of lipids
Irving Langmuir
made an artificial membrane
Gorter and Grendel
the phospholipid bilayer has two molecules that stick
Davson and Danielli
made the sandwich model
what is the sandwich model
sandwiched the phospholipid bilayer between two protein layers
Singer and Nicolson
Made the fluid mosaic model
Fluid Mosaic model
Sandwich Model
Fluid mosaic model
disperses the proteins
puts them in the phospholipid bilayer
present working model of the membrane
fluid mosaic membrane
in the fluid mosaic membrane, the proteins are
embedded in the phospholipid bilayer not forming a solid coat on the surface
what results in a stable membrane structure
hydrophilic portions of proteins and phospholipids are exposed to water
where are hydrophobic portions in the membrane
in the nonaqueous environment inside the bilayer
what does the membrane fence inside the cell
organically produced chemicals
the most common molecule in the plasma membrane
phospolipid
amphipathic molecules
have both a hydrophobic and hydrophilic region
phospholipids are considered ______ molecules
amphiphatic
protein movement in the membrane
laterally
phospholipid movement in the membrane
lateral and flip-flop
what is not randomly distributed in the membrane
proteins
how are membranes held together
weak hydrophobic interactions between the tails
what marks the difference in human and mouse cells
proteins
as temperatures cool what happens to the membrane fluidity
membranes go from a fluid state to a solid state
what does the temp for solidifying membranes depend on
types of lipids
what must membranes be to work properly
fluid
what is a membrane-like with more unsaturated fatty acids
more fluid than with saturated fatty acids
what is the primary reason we want unsaturated fatty acids
allows for a more efficient flow of molecules
impact of cholesterol on the membrane at warm temps
restrains movement of phospholipids and prevents the membrane from being too fluid
impact of cholesterol on the membrane at cool temps
maintains the fluidity by preventing tight packing
what has allowed organisms to live in temps that change
the ability to change lipid composition as temp changes
what determines most of membrane’s specific function
proteins
types of proteins in the membrane
peripheral proteins
integral proteins
peripheral proteins
bound to the surface of the membrane
integral proteins
penetrate the hydrophobic core and are embedded in the membrane
what are integral proteins that span the membrane called
transmembrane proteins
what does the hydrophobic region of an integral protein made from
stretches of nonpolar amino acids called alpha helices
what must molecules go through in the integral proteins
the alpha helices
six major functions of membrane proteins
- transport
- enzymatic activity
- signal transduction
- cell-cell recognition
- intercellular joining
- attachments to the cytoskeleton and extracellular matrix
six major functions of membrane proteins
- transport
- enzymatic activity
- signal transduction
- cell-cell recognition
- intercellular joining
- attachments to the cytoskeleton and extracellular matrix
transport
a protein that either shuttles a substance from one side to another by changing shape or a protein that provides a hydrophilic channel that is selective for a solute
enzymatic activity
protein built into the membrane that acts as a docking space and can change the reaction rate
signal transduction
a protein that acts as the receptor with a binding site for a molecule which can cause it to change shape to send signal into the cell
cell-cell recognition
cells that attach and build a layer for a specific purpose
intercellular joining
proteins that hook and join into junctions for physical barriers
attachments to the cytoskeleton and extracellular matrix
allows for more structure and stabilizes the location of certain membrane proteins
what membrane protein is more long-lasting
intercellular joining
what membrane protein is more short-lasting
cell-cell recognization
HIV example of cell surfaces being important in medicine
- HIV must bind to the surface protein CD4 and the co-receptor CCR5 to infect a cell
- HIV cannot enter the cell without the CCR5 receptor
- When the CCR5 receptor is blocked, HIV cannot enter
how do cells recognize each other
by binding to extracellular surface molecules
what do extracellular surface molecules often have
carbohydrates
what can membrane carbohydrates be covalently bonded to
glycolipids and glycoproteins
without the membrane carbohydrates or proteins
won’t be able to tell the different membranes apart
when do the _______ parts of the plasma membrane determine
asymmetrical
when its built by the ER and Golgi
the process of exchanging materials to the surroundings is controlled by
plasma membrane
how does the plasma membrane regulate the cell’s molecular traffic
by being selectively permeable
______ can dissolve in the lipid bilayer and pass through _____
hydrophobic (nonpolar) and rapidly
______ molecules do not cross the membrane easily
polar (hydrophilic)
______ allows the hydrophilic substances to pass across the membrane
transport proteins
channel proteins
transport proteins that have a hydrophilic channel that the molecules can use to pass through the membrane
aquaporins
facilitates the passage of water
Carrier proteins
transport proteins that hold their passengers and change shape in a way that shuttles them across the membrane
types of transport proteins
carrier and channel
Diffusion
tendency of molecules to spread evenly into available space
in diffusion, each molecule moves _______
randomly
Dynamic equilibrium
as many molecules cross the membrane in one direction as the other
substances diffuse down their
concentration gradients
diffusion is a ___________ process
spontaneous
what is an example of passive transport
diffusion
diffusion of molecules is from ____ to ___ concentration
high to low
osmosis
diffusion of water across a selectively permeable membrane
water diffuses across the membrane from ____ to the _____ solute concentration
lower solute concentration to the higher
what is the goal of osmosis
for the solute concentrations to be equal
tonicity
the ability of a surrounding solution to cause cells to gain or lose water
examples of tonicity
- isotonic
- hypertonic
- hypotonic
isotonic solution
the solute is the same as that inside the cell
what do isotonic solutions do to the plasma membrane
there is no water movement across the membrane
hypotonic solutions
the solute concentration is less than that inside the cell
as a result of the hypotonic solution,
cell gains water
hypertonic solution
the solute concentration is greater than inside the cell
as a result of the hypertonic solution,
the cell loses water
the direction of osmosis is determined by the
difference in total solute concentration
osmotic concentration
total solute concentration of a solution
if the two solutions have different concentrations and are separated by a selectively permeable membrane that allows water but not solute to pass,
the water would travel from the hypoosmotic solution to the hyperosmotic
what determines how a living cell will react to changes in solute concentrations of their environment
whether they have a cell wall
osmoregulation
the control of solute concentrations and water balance
Too fluid membranes and they cannot
support the protein function
Seen as a “Fluidity Buffer”
cholesterol
Cell-cell recognition is important
Sorting cells into tissues and organs in animal embryo
The basis for the rejection of foreign cells by the immune system
Supramolecular structure
many molecules ordered into a higher level of organization that have emergent properties beyond the individual molecules
This is the best environment for ANIMAL CELLS
isotonic solutions
what happens to animal cells in hypertonic solutions
The cell will lose water because the environment has more nonpenetrating solutes
Will shrivel up and die
what happens to animal cells in hypotonic solutions
Water will enter the cell faster than it leaves, and the cell will burst
This is the best environment for PLANT CELLS
hypotonic solutions
Turgor pressure
the limit to how much the cell wall can expand before putting pressure on the cell and opposes any more water uptake
When the turgor pressure is reached, the cell becomes
turgid (firm)
what happens to plant cells in isotonic solutions
no net tendency for water to enter and the cell becomes flaccid (limp)
the plant wilts
what happens to plant cells in Hypertonic solutions
b. Plant cell will lose water to its surroundings and shrink
PLASMOLYSIS
the plasma membrane will pull away from the plant cell as it shrinks in hypertonic solutions
What solution is 1
Hypotonic Solution
What solution is 2
Isotonic Solution
What solution is 3
Hypertonic Solution
facilitated diffusion
transport proteins aid the passive movement of molecules across the plasma membrane
is facilitated diffusion passive or active
passive transport
what kinds of transport proteins are there
channel proteins and carrier proteins
what do channel proteins provide
corridors that allow a specific molecule or ion to cross
what kinds of channel proteins are there
aquaporins and ion channels
aquaporins channels are
the diffusion of water
ion channels are
the diffusion of ions
gated channels are ______ that _____ or ____ with a _____
ion channels, open or close, stimulus
what does a gated channel use to pass ions
the charge
carrier proteins
undergo a subtle change in shape to transport solute-binding site across the membrane
what triggers a carrier protein’s change in shape
the binding and release of transport molecule
is the carrier proteins still diffusion
YES
how do solutes move in facilitated diffusion
downs its concentration gradient from high to low
does facilitated diffusion need energy
NO
some transport proteins can do what
move solutes against their concentration gradients
active transport
moves substances against their concentration gradients
what does moving against concentration gradient mean
moves towards HIGHER concentration
what transport needs energy and in what form
active transport needs energy in form of ATP
how is active transport done
by specific proteins embedded in membranes
what does active transport allow cell to do
maintain concentration gradients that differ from their surroundings
one example of an active transport system
sodium-potassium pump
where is most energy going to
the sodium-potassium pump,
how many sodium ions are pumped by the sodium-potassium pump
3 sodium ions out of the cell
how many potassium ions are pumped by the sodium-potassium pump
2 potassium ions into the cell
what gives the membrane a charge
the movement of Na and K ions
step 1 of the potassium-sodium pump
sodium in the cytoplasm binds to the pump
when is the sodium affinity high with the sodium-potassium pump
when the protein has the original shape
Step 2 of the sodium-potassium pump
the binding of sodium stimulates the phosphorylation by ATP
Step 3 of the sodium-potassium pump
the phosphorylation leads to a change in protein shape
when is the sodium affinity low with the sodium-potassium pump
when the protein changes shape with the addition of energy
why is sodium released to the outside of cell
the reduced affinity releases it to the outside
step 4 of the sodium-potassium pump
potassium binds onto the extracellular side of the pump
what triggers the release of the phosphate group from the pump
when potassium from outside binds to the pump
when is the potassium affinity high with the sodium-potassium pump
after the release of sodium and is still in the new shape
what happens when the phosphate group is removed from the pump
restores the protein’s original shape
when is the potassium affinity low with the sodium-potassium pump
when the protein’s shape is restored with the removal of the phosphate
why is the potassium released from the sodium-potassium pump
the lower affinity causes it to be released inside the cell
what kind of pump is the sodium-potassium pump
uniport
membrane potential
the voltage difference across a membrane
how is the voltage created across the membrane
the differences in the distribution of positively and negatively charged ions
what two forces drive the diffusion of ions across a membrane
chemical and electrical force
what are the two forces that drive the diffusion of ions across a membrane called
electrochemical gradient
the chemical force in the electrochemical gradient
the ion’s concentration gradient
the electrical force in the electrochemical gradient
effect of membrane potential on ion’s movement
electrogenic pump
transport protein that generates voltage across a membrane
what is the major electrogenic pump in ANIMALS
sodium-potassium pump
what is the major electrogenic pump in PLANTS, FUNGI and BACTERIA
proton pump
what does the proton pump do
helps store energy that can be used for cellular work
what does the proton pump pump
hydrogen ions
how is the proton pump used in the mitochondrion
it couples the chemical and electrical process to make ATP
cotransport
active transport of a solute indirectly drives transport of other solutes
how is cotransport often used in plants
hydrogen ion gradients to drive active transport of nutrients into the cell
uniport
transports one molecule at a time
antiport protein
two molecules are moved in opposite directions across the bilayer
symport protein
two molecules are moved in the same direction across the membrane are
how do small molecules and water enter or leave the cell
through the lipid bilayer or by transport proteins
how do large molecules (polysaccharides and proteins) move across a membrane
through vesicles called Bulk Transport
does bulk transport need energy
YES
types of bulk transports
endocytosis and eocytosis
exocytosis
transport vesicles migrate to the membrane, fuse with it and release their contents to the outside of the cell
what is an example of exocytosis
secretory cells that export their products
endocytosis
cell takes in macromolecules by forming vesicles with the plasma membrane
how is endocytosis different from exocytosis
its the reversal and uses different proteins
types of endocytosis
- phagocytosis
- pinocytosis
- receptor-mediated endocytosis
phagocytosis and pinocytosis have no what
receptor mediation
phagocytosis
engulfs a particle in a vacuole
the vacuole fuses with lysosomes to digest particles
pinocytosis
extracellular fluid is “gulped” into tiny vessicles
receptor-mediated endocytosis
binding of ligands to receptors that triggers vesicle formation
receptor-mediated endocytosis is only possible when
ligands can bind which means only select cells can do it
where does receptor-mediated endocytosis function the most
in the immune system
how do human cells use receptor-mediated endocytosis
to take in cholesterol for synthesis of membranes and other steroids
how is cholesterol carrier
carried by the blood by the low density lipoproteins (LDLs)
where is cholesterol carried to
to the LDL binding sites and entering cells by endocytosis
hypercholesterolemia
missing or defective LDL receptor proteins which means there is a high level of lipids in the blood
how does SARS-Cov-2 enter the body
through the olfactory bulb
uniport
symport
Antiport
how are gated channels stimulated
electrical stimulus or when a specific substance binds to the channel
ATP hydrolysis
Supplies the energy for most active transport
The cytoplasmic side of the membrane is
negative
the cytoplasmic side of the membrane favors
the passive transport of cations into the cell
The extracellular side of the membrane is
positive
the extracellular side of the membrane favours
the passive transport of anions out of the cell
The benefit of electronic pumps
Help store energy that can be tapped for cellular work
Water and solutes enter and leave the cell by diffusing through
a. the lipid bilayer of the plasma membrane
b. Being pumped across the membrane by transport proteins
Receptor-mediated endocytosis is a specialized form of
pinocytosis
Endocytosis or exocytosis
exocytosis
Endocytosis or exocytosis
Endocytosis
Pinocytosis or phagocytosis or receptor-mediated endocytosis
pinocytosis
Pinocytosis or phagocytosis or receptor-mediated endocytosis
phagocytosis
Pinocytosis or phagocytosis or receptor-mediated endocytosis
receptor-mediated endocytosis
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