W1 L3 (Membrane Physiology) Flashcards
Why does water diffuse to an area of higher osmotic pressure?
Osmotic pressure simply refers to the amount of dissolved solute meaning higher osmotic pressure means water wants to go there.
Osmotic pressure
The amount of pressure needed to keep water out of an area (water wants to go to a place of high osmotic pressure)
Plasma membrane
A protein-studded lipid bilayer that encloses each cell, separating it from the extracellular fluid. It is the barrier to solute diffusion. It is also there to maintain gradients.
What are 3 of the plasma membrane’s primary objectives
- Cell’s survival
- Maintaining homeostasis
- Function cooperatively and in coordination with other cells
What parts make up the plasma membrane?
Mostly lipids, proteins, and some carbs
What 5 factors make for a high rate of diffusion?
- Steep [ ] gradient
- High permeability
- Small Particles
- Short lateral distance
- Large SA (lots of places to cross)
What determines the movement of a solute across membranes?
The type of solute and the gradient
Which particles cross the membrane freely?
Lipids (soluble) ex. steroid and fats
Gasses ex. oxygen and carbon dioxide
Small, nonpolar (hydrophobic) molecules pass freely
Which particles don’t cross the membrane freely?
Proteins, ions, sugars, amino acids
Large, charged (hydrophilic) molecules don’t pass freely
Channel
Small, water-filled passageways through the plasma membrane; formed by membrane proteins that span the membrane and provide highly selective passage for small water-soluble substances such as ions
What are the 3 functions of the lipid bilayer?
- Form structure of the membrane
- Maintain concentrations inside and outside of the cell through selective permeability
- Responsible for the fluidity of the membrane
Glycoproteins/Glycolipids
Surface proteins and lipids that are coated by sugars (carbohydrates) and protrude from the surface of the cell and function like antennae in cell-cell communication
Trilaminar appearance
2 dark hydrophilic regions and 1 lighter hydrophobic core when stained and seen under an electron microscope
Carrier protein
Membrane proteins, which, by undergoing reversible changes in shape so that specific binding sites are alternately exposed at either side of the membrane, can bind with and transfer particular substances unable to cross the plasma membrane on their own.
Channel proteins
Small water-soluble substances can pass through a water-filled pathway without interacting with the hydrophobic tails. Certain channels are selective to certain solutes.
How does water cross the membrane?
Through aquaporins
Aquaporin
A pore that allows water to cross the membrane directly
Explain the relationship between ion-channels and pores
Not all pores are ion-channels, but all ion-channels are pores
Explain how cholesterol is a bidirectional regulator of membrane fluidity.
Cholesterol is tucked between phospholipid molecules and in the cold prevents hydrocarbon chains from packing together too tightly. When it is too hot it stabilizes the membrane by raising the boiling point.
What are the hydro-affinities, polarities, and charges of the two components of the membrane?
Head-Hydrophilic, polar, and negatively charged
Tail-Hydrophobic, non-polar and uncharged
Fluid-mosaic model
A model of membrane structure where the lipid bilayer is embedded with membrane proteins and is ever-changing (fluid)
Diffusion of particles
The passive movement of solute down its concentration or electrical gradient
Osmosis (Passive)
Water moving down its concentration gradient, essentially to an area of higher solute concentration (higher osmotic pressure)
Osmotic pressure
The force required to oppose osmosis
Osmotic pressure formula
P(osm)=R x T x [Solute]
R=Gas constant
T= Temperature
[Solute] = Concentration of solute
What happens to a hypoosmotic and hyperosmotic solution
Hypoosmotic- Increase in volume due to water entry
Hyperosmotic- Decrease in volume due to water exit
In which direction does H20 move in terms of solute concentration and osmotic pressure
It goes to an area of higher solute concentration
It goes to an area of higher osmotic pressure
Docking-marker acceptors
A protein that binds lock-and-key fashion with the docking markers of secretory vesicles. The vesicle then disposes of its contents through exocytosis.
Membrane-bound enzymes
Surface-located proteins that control specific chemical reactions at either the inner or the outer cell surface. Cells are specialized in the types of enzymes embedded within their plasma membranes
Receptor site
A membrane protein that binds specific transmitters and causes the cell to alter its behavior. Transmitters can only alter a cell if the given cell has a receptor for that given transmitter.
Cell adhesion molecules (CAMs)
Proteins that stick out of the membrane and are used to link up cells when they communicate/interact.
Self-recognition
The short sugar chains that project from a cell’s outer membrane and allows cells to interact
How do cells recognize each other?
Different cells have different markers which help them to recognize each other
Why is cell to cell recognition important in embryonic development?
It is important so that cells of the same type group together to form tissues
How do cells know to not invade the others space during tissue growth, and what is an exception to this?
Cells know not to invade each others space by use of surface markers, an exception to this is during cancer when cells with abnormal cell surface carbohydrate markers spread uncontrollably and invade neighboring cell’s space.
What is cystic fibrosis, what is the cause, and how is it treated?
It is a disease where there is a production of extremely thick mucus in the respiratory tract and pancreas. It can lead to breathing complications.
A mutation in the CFTR pump leading to accumulation of chloride ions due to membrane impermeability.
It is treated with therapy and drugs, however, most people don’t make it past 30. However, with knowledge of the genetic linkage to the unfinished pumps, there is hope for those with the disease.
What types of transporters are symporters and antiporters?
They are co-transporters who work by secondary-active transport.
Permeable
Allowing a given substance to pass the cell membrane
Impermeable
Not allowing a given substance to pass the cell membrane
Selective permeability
Allows some particles to pass while excluding others
What are the two properties that influence whether or not a particle can penetrate a membrane without assistance?
- The relative solubility of the particle in lipids
2. The size of the particle
Passive forces
Don’t require an energy input
Active forces
Require an energy input
Unassisted membrane transport
Molecules that can penetrate the membrane without any assistance
What are the 2 types of unassisted membrane transport
The 2 kinds are
- Diffusion down a concentration gradient
- Movement along an electrical gradient
Diffusion (Passive)
Random collisions and intermingling of molecules as a result of their continuous thermally induced random motion
Concentration gradient
A difference of a given solute concentration between two adjacent areas
Chemical gradient
A passive process in which ions move down electrochemical gradient through open channels (from high to low concentration and attraction of ion to area of opposite charge)
Steady state
Dynamic equilibrium
What two factors affect molecules in solution reaching a steady state
- Temp- Temp is proportional to speed
- Molecular size- Size is inversely proportional to speed
Molecular speed is proportional to speed to reach steady state
Explain how diffusion plays a major role in oxygen and gas exchange.
Deoxygenated blood in vessels comes to the lungs and diffusion of oxygen into the blood occurs before it is sent to the rest of the body.
Passive transport
Carrier proteins aid in facilitating diffusion down a concentration gradient, this an extremely slow process.
How many molecules pass through with passive transport
100-10000 particles/second
Electric gradient
A difference in charges between two adjacent areas
What are the types of passive transport
- Osmosis
- Diffusion
- Facilitated diffusion
Electrochemical gradient
A gradient that exists with concentration and ions for a certain particle
Facilitated diffusion (Passive)
The passing of the membrane of a given substance through a selective protein (channel protein)
How many water molecules can pass through an aquaporin at once?
One billion
What happens when a membrane separates pure water from a solution of a nonpenetrating solute (All solute in one side and all water in the other, only water can pass)
The water is the only thing that can move meaning that it should technically all go to the other area. However, hydrostatic pressure (the pressure downwards on the solute side keeps a small amount of water in the other one).
This ensures that the osmotic pressure of the water going to solute equals the pressure downwards on the solute container.
Tonicity
The effect that a solution has on a cell
Isotonic Solution
There is no net movement of water as the concentration of solute is the same inside and out.
Hypertonic Solution
There is a net movement of water out of the cell as the concentration of solute outside is greater than the concentration inside; this causes the cell to shrivel.
Hypotonic Solution
There is net movement of water into the cell as the concentration of solute inside the cell is greater than the concentration outside; this causes the cell to swell or burst.
Types of active transport
- Exocytosis
- Endocytosis
- Sodium-Potassium pump
Carrier-mediated transport
Transport of a substance across the plasma membrane facilitated by a carrier molecule. There are 2 types:
- Facilitated diffusion
- Active transport
Facilitated diffusion (Passive)
- Carrier protein takes conformation of high solute concentration
- Solute binds protein
- Binding leads to a change and the solute is released on the other side of the membrane
- Carrier protein returns to original conformation
3 factors that determine the amount of carrier-mediated transport that takes place
- Selectivity-Each carrier protein is specified for a specific particle.
- Saturation-Only so many particles can be transported per unit time which is why a saturation point or maximum possible efficiency may be reached
- Competition-If two types of similar particles can bind a protein then they may compete to be transported
Active Transport
A transport of particles requiring an energy input to transport particles against their concentration gradient
Explain how glucose is brought into the cells.
Facilitated diffusion. Glucose is polar and non-lipid soluble which makes it difficult for it to cross the membrane. High concentrations of glucose in the bloodstream means that it needs to diffuse into the cells. A glucose carrier protein is required to bring it into the cells.
What is the limiting factor in simple and facilitated diffusion respectively?
Simple- There are no limiting factors and the rate is simply proportionate to the concentration of solute outside the cell.
Facilitated- The limiting factor is the saturation of binding sites.
How does the binding site in facilitated diffusion differ from that in active transport?
The facilitated diffusion binding site does not change while the active transport binding site does.
What role does ATP play in active transport?
It alters the binding site depending on which side of the membrane the binding site is facing; this changes the affinity for different molecules.
Primary active transport
A carrier-mediated transport system in which energy is directly required to operate the carrier and move the transported substance against its concentration gradient
Can primary transport also be considered symport or antiport? For example, can’t the Na/K-pump be considered antiport, since the Na and K are transported in opposite directions?
Co-transport, exchange, symport, or antiport are not primary active transport (immediate energy expenditure). These processes are secondary active transport (energy is expended later to move back the
molecule that went down its gradient). Moreover, the Na/K ATPase is not an antiporter; rather, it is a pump. An antiporter moves at least one substance against its gradient and at least one other substance
with its gradient but in the opposite direction. The pump hydrolyzes ATP to directly overcome the energy barriers that contest the opposite movement of the two ions against their gradients.
Does Na/K ATPase move these particles with or against their chemical and electrical gradients?
Sodium is moved out of the cell up against its concentration gradient and also up its electrical gradient as the inside of the cell is negatively charged.
Potassium is moved into the cell against its concentration gradient and down its electrical gradient as the inside of the cell is negatively charged.
What does phosphorylation do to binding sites?
It changes their shape and affinity for different molecules
Pump
An active transport mechanism in living cells by which specific ions are moved through the cell membrane against a concentration or electrochemical gradients
Describe the 3 roles of the sodium-potassium pump
- Establishes a gradient essential for signal functioning
- Helps regulate cell volume by controlling solute concentrations
- The energy used for the pump is used later on in secondary-transport (cotransport) of glucose molecules
Explain the steps of the sodium-potassium pump
- The pump is facing the ICF and has 3 high-affinity spots for sodium molecules and 2 low-affinity spots for potassium molecules.
- 3 sodium ions bind inducing ATP to bind and split into phosphate and ADP.
- Phosphorylation leads to a conformational change in the shape of the pump and for the 3 sodium ions to be released into the ECF due to low affinity and for 2 potassium ions to bind due to high affinity
- When 2 sodium molecules bind the phosphate group attached releases and dephosphorylation of the pump causes the sodium molecules to be released and the pump to revert to its original conformation
Phosphorylation
The attaching of a phosphate group, typically donated by an ATP molecule
Dephosphorylation
The detachment of a phosphate group
Electrogenic movement
Unequal movement of charges, for example, Na-K ATPase
ATP hydrolysis
The releasing of a high-energy phosphate group by an ATP molecule
Is ATP hydrolysis exergonic or endergonic?
It is exergonic; energy is released to be used by the cell
Co-transport
Moving 2 molecules, one down its gradient and one up its gradient.
Co-transport carriers
Carriers, such as the luminal carriers in intestinal and kidney cells are cotransport carriers that have two binding sites, each of which interacts with a different molecule to be transported; for example, the sodium and nutrient cotransporters or the Na–K ATPase
How is glucose brought into the cell?
The sodium-potassium pump created a high sodium concentration outside that wants to come back in and can be coupled with a glucose molecule to enter the cell without any ATP as the work has already been done. This is a type of secondary active transport.
Secondary active transport
A transport mechanism in which a carrier molecule for glucose or an amino acid is driven by a concentration gradient established by the energy-dependent pump to transfer the glucose or amino acid uphill without directly expending energy to operate the carrier
Name 2 types of primary active transport pumps
- Na (OUT) - K (IN)
2. Ca (OUT) (ATP is used)
Name 4 types of co-transporters (secondary active transport)
- Na (IN) Choline (IN)
- Na (IN) Glutamate (IN)
- K (OUT) Cl (OUT)
- NA (IN) Ca (OUT)
Gated ion channel
Water-lined protein pores that are: selective, very fast (10^6 ions/sec), current from ions (charges) moving, diffuse down [ ] or ion gradient. The gate opens or closes for given molecules.
Passive ion channel
A gate constantly opens and closes that can be influenced to affect permeability. They let sodium, potassium, and chlorine ions pass. Their function is to set net permeability for resting state.
Ligand-gated channel
An ionotropic receptor that opens by a ligand binding to the gate (ex.glutamate, GABA, acetylcholine). They function in synaptic transmission (ie. the motor neuron sends these transmitters)
Ionotropic receptor
A channel and receptor
Selective Antagonist
A type of receptor, ligand, or drug that blocks or dampens a biological response by binding to a receptor rather than provoking the response like an agonist.
TTX
Blocks the voltage-gated Na channel and functions as pufferfish toxin
Procaine
Blocks the voltage-gated Na channel and functions as a local anesthetic to prevent the nerve system from feeling pain
Curare
Blocks the acetylcholine-gated channel and functions as a plant defense that is also used in blow-darts
Ketamine
Blocks the glutamate-gated channel and is used a vet-anesthetic
Conus toxin (from cone snail)
Blocks the voltage-gated calcium channel and is used by snails to hunt fish
Why is the cone snail also called the cigarette snail?
Because after injection one has just enough time to smoke a cigarette before dying
Voltage-gated ion channel
A channel that drives action potentials and synaptic transmission to try to restore or build membrane potential
