Lecture 8b Flashcards
d)
what determines a substances ability to pass through the plasma membrane?
their size and polarity
how can ions, polar and/or large molecules pass through the plasma membrane?
can only cross through membrane proteins
what transports large quantities of substances in the cell?
substances that are large can be imported or removed from the cell through bulk transport via vesicles
what are the two ways molecules leave and enter the cell?
1) passive transport (no energy required)
2) active transport(energy required)
what are the three types of passive transport?
1)diffusion through membrane
2)osmosis - specific to water
3)facilitated diffusion - required integral membrane proteins
what are two types of active transport?
1) transporter pumps
2) bulk transport ( endocytosis and exocytosis )
transporter pumps = goes from low energy to high energy as it goes against the concentration gradient
bulk transport = -> endocytosis = vesicles sucking in materials into the membrane
exocytosis = vesicles that pack and secrete these materials
passive transport
what happens in diffusion?
substances move from an area of high concentration to an area of low concentration untill equilibrium is reached
molecules moving across the membrane
does not need energy
what is net movement?
movement in one direction minus the movement in the opposite direction - movement in the direction of concentration gradient
what is the net movement at equilibrium?
net movement is zero but exchange still occurs on a molecule-for-molecule basis
the molecules are always moving however same amount of molecules in both directions = equilibirum
passive transport
what is osmosis?
the diffusion of water across a selectively permeable membrane
- water diffuses across a membrane from low solute concentration to high solute concentration
driven by impermeable solutes only
water can pass through the gradient
what is the net movement of water?
the net movement of free water is from low solute concentration to high solute concentration
free water= not interacting with solute thus free to diffuse
what is osmotic pressure?
hydrostatic pressure needed to stop the net flow of water across a membrane due to osmosis.
must apply pressure to prevent water flow
high solute concentration leads to high or low osmotic pressure?
high solute concentration= high osmotic pressure
low solute concentration = low osmotic pressure
what is tonicity?
the ability of a solution to cause a cell to gain or lose water; the measure of the osmotic pressure gradient.
depends on the total concentration of impermeable solutes
what is an isotonic solution?
where the solute concentration in the solution is the same as inside the cell
- no net water movement across the plasma membrane
what is hypertonic solution?
where the solute concentraion in the solutions is larger than that inside the cell
- cell loses water
what is hypotonic solution?
where the solution concentration in the solution is smaller than that inside the cell
- cell gains water
influx of water causing the cell to burst
Tonicity in plant cells
what type of solution surrounds a plant cell that is getting fed water?
hypotonic
the water vacuole is full and provides turgor pressure on the cell wall- the cell is turgid (firm)
- turger pressure = where the cells have reached their absorption point and wont take in anymore water thus they will not burst
tonicity in plant cells
what solution surrounds a healthy plant cell?
isotonic
net movement is equal
the water vacuole does not exert enough pressure on cell wall to give proper support - the cell becomes flaccid (limp) and the plant may wilt
tonicity in plant cells
what solution surrounds a dying plant cell?
hypertonic
water seeks to exit the cell therefore the cell wall cannot help, the membrane pulls away from the wall ( plasmolysis )
what is osmolarity?
the total concentration of all solutes
measured in osmoles
what is iso-osmotic?
number of particles/solutes is the same on both sides of the membrane
what is hyper-osmotic?
number of particles/solutes is greater on one side of the membrane than the other
what is hypo-osmotic?
number of particles/solutes is lower on one side of the membrane than the other
what is osmoregulation?
controls the water balance
example: paramecium (purple )- hypertonic to the pond water it lives in therefore its cell has a contractile vacuole that acts as a pump to force water out of the cell
is 0.3M ethyl alchohol hypotonic or isotonic to mammalian cells?
hypotonic and causes an influx water which is dangerous for the animal cell
where do you find osmoregulation in plant cells?
the cell walls
they help maintain water balance
osmosis problem
Solution A contains 0.15mM of NaCl
solution B contains 0.3mM of sucrose
What is the tonicity of the solution A with respect to solution B?
osmosis problem
what is facilitated diffusion?
where transport proteins speed up the passive movement of molecules across the plasma membrane.
no energy input required
net movement down its concentration gradient ( high concentration to a low concentration )
what are channel proteins?
channel proteins found in facilitated diffusion that provide hydrophilic corridors allowing specific molecules/ions to cross the membrane.
what do aquaporins do in channel proteins?
aquaporins are for facilitated diffusion of water
what is the role of ion channels in channel proteins?
they open or close in response to a stimulus (gated channels)
why are channel proteins gated?
they are usually gated to regulate the cell over what comes in and what comes out
i.g. aquaporins
when do the carrier proteins undergo a change in shape?
they undergo a subtle change in shape when they bind to a solute that translocates the solute-binding site across the membrane
GLUT4 transports glucose inside the cell
LacY transports lactose inside the cell
what is the difference between carrier proteins and channel proteins based on speed?
carrier proteins are much slower because they must change shape
the rate of carrier proteins is dependent on the number of carriers in the membrane
what are the three terms carrier proteins are classified as?
1) uniporters=a single solute moves in one direction,recognizes only one substrate
2) symporters=two solutes move in the same direction, recognizes two different substrates in the same direction
3) antiporters=two solutes moving in opposite directions, recognizes two different substrates in opposite directions
what is the main function that occurs in active transport?
moves substances against their concentration gradient therefore requires energy ( ATP )
what are the two types of active transport?
1) Primary active transport = carrier mediated and energy is provided by the ATP
2) Secondary active transport = co-transport, ATP required, ion gradient as a mean of transport (takes advantage of the gradient and hops on another molecule using downward movement)
What are the main differences between passive transport and active transport?
passive:
- net movement from high to low concentration untill equilibrium is reached
- no energy is required as its going with the gradient
- passive transport through a channel or transporter that is by facilitated diffiusion
active:
- requires ATP as the net movement is going against the concentration gradient
- large or small transported molecules
- requires a carrier/transporter protein
- allows the cell to maintain different internal and external environments
what is primary active transport?
- requires energy (ATP)
- donating a phosphate group by ATP to a carrier protein leads to a conformational change of shape
- allows the passage of substances across the membrane
- transports substances from low to high concentrations (against the concentration gradient)
what type of transport is the sodium-potassium pump?
primary active transport
Describe the process of Na/K ATPase
1) three cytoplasmic Na+ binds to the sodium potassium pump. (high affinity when the protein has this shape) -
2) the binding of Na+ stimulates phosphorylation by ATP
3) phosphorylation leads to a change in protein shape, reducing its affinity for Na+ (released outside)
4) This new shape has a high affinity for two K+, therefore the two K+ bind on the extracellular side which triggers the release of the phosphate group.
5) loss of the phosphate group restores the protein’s original shape ( has a lower affinity for K+)
6) the K+ is released, Na+ affinity is high and the cycle repeats
what do ion pumps have the ability to do?
have the ability to generate membrane potential
- they are electrogenic pumps/transport proteins that generate a voltage across a membrane
gives an uneven overall net charge across membrane
membrane potential= voltage difference across a membrane
how is voltage created?
think of ion pumps
voltage is created by differences in the distribution of positive and negative ions across a plasma membrane
if sodium potassium pump sends three Na+ out and two K+ in, what relative charge, positive or negative, does it create inside the cell versus the exterior?
creates a negatively charged interior relative to a positively charged exterior.
extracting positive ions from the inside of the cell would create a net charge across the membrane (more positive outside than in)
what is the main electrogenic pump of animal cells?
the Na+/K+ ATPase
especially important for neurons
what is the result of membrane potential?
favors the passive transport of cations into the cell and anions out of the cell via ion channels
what two types of gradients does the active transport create?
1) an electrical gradient = different net charge inside and outside the cell
2) a concentration gradient = more Na+ outside the cell causes the ions to diffuse down the concentration gradient
Both the electrical and concentration gradients together create what?
these two forces create a different type of net gradient= an electrochemical gradient which drives processes like cellular respiration, transmission of nerve impulses and muscle contraction.
what does secondary active transport do?
- secondary active transport pumps can produce electrochemical gradients that store energy for cellular work
- *use of an existing gradient to drive the active transport of a solute *
blocking any pump would result in no facilitated transport
what is bulk transport?
- large molecules that cannot cross the membrane by aforementioned mechanisms
- therefore these large molecules must cross the plasma membrane in bulk transport via vesicles
requires energy
large molecules such polysaccharides, proteins, viruses, bacteria
how do large molecules undergoing bulk transport leave and enter the cell?
leave a cell by exocytosis
enter a cell by endocytosis
bulk transport
what happens in exocytosis?
- vesicle fuses with the plasma membrane and releases contents into extracellular space
- membrane proteins and phospholipids are incorporated into plasma membrane by exocytosis
- can be regulated or constitutive
what are the three types of processes of endocytosis?
1) phagocytosis= large particles engulfed into vacuole which fuses with the lysosome
2) Pinocytosis= nonspecific uptake of extracellular fluid
3) receptor-mediated endocytosis= triggered by binding of ligand to surface receptor.
what happens in receptor-mediated endocytosis?
a vesical is formed through recruitment of a coated pit when specific molecules attach to their respective surface receptors on the membrane
- unlike pinocytosis, this is a specific mechanism in that it takes in specific molecules
- once in the molecules exit the vesicle, the receptors are returned to the cell surface for reuse.
- most blood cholesterol travels in lipoprotein particles
- LDL contains cholesterol destines for uptake by cells
- cells take in LDLs via receptor-mediated endocytosis (LDLs bind to specific surface receptors)
