W2: Lesson 2.1 Flashcards
What energy is used to move materials across a membrane in simple/passive diffusion?
- uses (charge difference across membrane) concentration gradient/electrochemical gradient to move materials across membrane. High con’t. flows to low concentration.
- b/c it is following concentration gradient it does not require any energy to perform. No ATP
Characterize Na+, Ca++, and K+, H+ ion concentrations within and outside a typical cell.
Na+: higher outside a cell than inside (10-30x higher)
Ca++: extremely low inside cells (10-20 fold lower exist inside than outside cell)
K+: Higher inside the cell than it is outside the cell.
H+: higher inside the cell than outside = pH of cell is lower than that of the environment
What energy source is used to move glucose into cells, and what protein is required?
- coupled transport using active carrier protein
- high extracellular concentration of Na+ is used by cells to transport glucose into the cell (even though glucose concentrations are already higher w/in the cell than outside)
- facilitated diffusion for Na+ and active transport for glucose
Would you expect the membrane permeability of glucose, CO2, H2O, and Ca++ to be high or low
Glucose: large, uncharged, polar, molecule = less likely to move across than CO2 and H20
CO2: small, uncharged, non polar, hydrophobic molecule = highest permeability
H2O: polar, uncharged molecules w/no net charge, hydrophilic = can move across membrane
Ca++: charged ions = impermeable
Organize in order of low permeability to high permeability:
sucrose(large polar), glycerol(small polar), O2, Mg2+
Mg2+ < sucrose < glycerol < O2
Organize in order of high permeability to low permeability:
large uncharged polar molecules, ions, hydrophobic molecules, small uncharged polar molecules
hydrophobic molecules > small uncharged polar molecules > large uncharged polar molecules > ions (w/charge)
What is an electrochemical gradient?
combination of charge and concentration gradient
If there’s a (+) ion outside the membrane and the membrane is uncharged, what will determine the movement of the ion?
-the concentration difference of the ion alone
If the interior of the membrane is (-), and the ion outside the cell is a (+) ion will this attract or repel the ion?
-attracting the positive ion and transfer of the positive ion across the membrane will be enhanced
If external membrane is negative charged, and interior is positive, will this attract the + ion inside and across the membrane?
Will be less likely to transport or will be inhibited
what three states can a membrane channel be in?
open
closed
inactivated
what are the two proteins in facilitated diffusion?
- channel forming protein
- carrier protein
What are the differences between channel forming proteins and carrier proteins?
Channel: simple pores, formed by beta barrel integral membrane proteins. Porin allows small molecules to travel through. Some always open but can be closed or inactive
Carrier: these proteins actually change their shape between two or more states in a way that allows the movement of molecules through them. Others will rotate or move from one face of the lipid bilayer to the other
Discuss the ability of different transport mechanisms to be saturated. What is the mechanistic basis for whether a transport mechanisms is or is not saturable?
if transport depends on the # of transport proteins to transport then there is a maximal transport rate (Vmax) and it is said to be saturated.
Saturation vs. Unsaturation depends on the relationship between concentration gradient and movements of solute.
In simple diffusion: there’s a linear relationship between the con’t gradient and the rate of molecule movements across membrane. The greater the con’t gradient the faster solutes will move across membrane usually w/no limit. this relationship is said to be non saturable
in facilitated diffusion: con’t gradient provides energy needed to make facilitated diffusion to work, however, the solute molecules have to wait around unit a membrane protein becomes available in order for it to traverse the membrane. Increasing the amount of solute on one side of the membrane doesn’t change the # of transmembrane proteins and therefore there’s an upper limit to how fast a protein can perform it’s function. Speed of movement across membrane has a curve that flattens out, as the concentration difference goes up, past some limit. this is said to be saturable
Describe in detail an example of a coupled transport, providing components of the system and what they do
when carrier proteins move two different types of solutes across the membrane together this is know as coupled transport. If both solutes are going in the same direction this is known as symport. If two solutes are moving in opposite directions this is know as antiport.
an example of coupled transport would be Na+/Glucose symporter. Cells use the high extracellular concentration of sodium to transport glucose into the cell (which glucose con’t are aleady higher inside than outside; moving from low to high against it’s concentration gradient). This symport will undergo a change from state A to B if both sodium and glucose are bound to it, and it only goes back from state B to A if neither are attached to it. Otherwise the protein would simply act as a sodium uniport.
The association of glucose with state A isn’t common, but the carrier protein is going to wait until both glucose and sodium are attached before it changes to the state B.
what force drives water across cell membranes? and how do different types of cells deal with this.
Osmosis drives water across cell membrane. Unlike con’t grad. which moves from high to low. Water follows from a location of low solute concentration to a high con’t.
Animal cells/multicellular cells/bacteria use Na+/K+ pumps (pump 3 Na+ out of cell and 2 K+ into cell) to regulate osmolarity as this equilibrates osmotic pressure across membrane
Plant cells are prevented from swellin by their rigid walls and can tolerate osmotic differences across their plasma membranes, internal turgor pressure builds up which at equilibrium forces as much water as enters
Protozoa avoid becoming swollen with water by periodically extruding water from a special contractile vacuoles
What are ionophores?
- Ionophores are a special group of lipid soluble proteins
- involved in moving charged ions across membranes and disrupt ion gradients
- can be channel forming proteins or carrier proteins
- they are passive transporters and only facilitate the movement of ions from one are to another area in an area of high concentration to an area of low concentration.
Why is calcium so low inside cells?
-one of the reasons for very low con’t of free calcium inside cells is the use of high energy phosphate molecules, like ATP for cell energy. Higher con’t of free calcium inside cells would probably cause the formation of calcium phosphate, which crystallizes
What is the difference between symport and antiport?
Symport takes 2 solutes in same direction and antiport in opposite
What are the three mechanisms cells use to move material through their membrane?
simple passive diffusion
facilitated diffusion
active transport
What is the difference between simple and facilitated diffusion? what are the similarities?
Facilitated diffusion can be regulate simple cannot
facilitated produces channel or carrier proteins to transport material down concentration gradient and simple just use concentration gradient
Facilitated allows molecules w/very low permeability, like charged ions to cross the membrane, passive/simple does not.
facilitated is saturable and passive is not
Similarities: they both use concentration gradient
In active transport what form of energy do protein complexes need?
Pumps (ATP or light)
Is sodium higher inside or outside cell?
outside
Is potassium higher inside cell or outside cell?
inside
Is calcium higher inside or outside cell?
outside
Is hydrogen higher inside or outside cell? what does this do to the cell?
hydrogen is higher inside cell, which lowers the pH of cells
Do hydrophobic molecules have high or low permeability? give examples of these molecules.
High permeability b/c most are small, uncharged, and polar
E.g., O2, CO2 N2 and benzene
Do Small uncharged polar molecules have high or low permeability? give examples of these molecules
permeable but less easily than hydrophobic molecules
e.g., H2O, urea, glycerol
Do large uncharged polar molecules have low or high permeability? give examples of molecules
less likely to move across membrane
e.g., sucrose and glucose
Do ions have low or high membrane permeability? Give examples of these ions
not permeable
e.g., H+, Na+, HC2O3-. K+, Ca++, Cl-, Mg++
Why can ionophores be used as antibiotics?
b/c they disrupt ion gradients important to cell function and can move charged ions through lipid
How do ion channels regulate pores?
- in response to a variety of external stimuli, binding of specific ligands to receptors, voltage or ligand gated channels,
- e.g., neuromuscular systems open/close in response to ionic changes surrounding membrane signals can be stimulatory or inhibitory
e. g., channels found on skeletal muscle of cells use binding of acetylcholine
What do complex responses in cells require?
The activation of several ion channel proteins, each in different compartments or cell organelles
Why does simple diffusion have a linear relationship between concentration and rate of molecule movement across membrane?
b/c the greater the concentration difference the faster solutes will move across the membrane (aka non-saturable)
on a graph this forms a linear relationship
Why does facilitated diffusion have a saturable condition?
-the number of molecules that transport across the membrane depend on the available proteins. The concentration gradient can be super high and this would not speed up the movement of molecules. Thus there’s an upper limit to how fast protein can perform its function = saturable relationship
What is a coupled transport?
carrier proteins that move two solutes across the membrane
can be antiport or symport
how can coupled transports be associated w/active transport?
carrier proteins can perform coupled transport where one solute is moving down its concentration gradient and the other is moving from an area of low to high concentration (against it’s con’t gradient)
example: Na+/glucose
What is an example of a symport in the body?
in epithelial cells lining the small intestines
- these cells absorb nutrients including glucose from digested food and pass them on to the bloodstream and neighboring tissue.
- At least 3 membrane transport are required to accomplish this.
1)since sodium concentration is
high outside the cell, the symport can use the energy stored in that gradient to co-transport
glucose into the cell’s interior. That occurs at the top, or apical membrane surface of the cell,
which faces the interior of the intestine
2) As a result both Na+ and glucose will rise w/in the cell. Glucose can’t cross cell membrane effecitvelly and facilitated diffusion out of the cell is accomplished using a membrane carrier protein, which acts as a uniport for glucose.
3) finally, sodium can’t leave the cell
without assistance and the influx of sodium, if unaccounted for, would eventually raise the
internal sodium concentration to the point that the transport of glucose would stop. Therefore, to
keep the internal concentration of sodium low, it is move out of the cell again, but this time
against its concentration gradient. A sodium/potassium ion exchange pump is what does this
Can sodium leave the inside of the cell w/o assistance?
No b/c outside of the cell has higher Na+ concentration so moving Na+ out of the cell would be moving it against its concentration gradient and this would require require the sodium potassium exchange pump.
If you take red blood cells and place them in a solution that has high concentration (hypertonic solution) what will happen to the water in the cell?
Water will move out of the cell to the solution, thus cell would shrink aka crenated
Describe the process of osmosis?
The movement of water. Water moves from low concentrations of solute to higher
What happens to red blood cells if placed in a solution that has very low concentration of salt (hypotonic solution)?
Water will flow into the cell and swell or burst
What is the Donnan effect in animal cells?
Osmolarity inside the cell is greater than outside the cell, aka the concentration gradient of water causes water to move into cells.
What are the ways that different cells deal with the Donnan effect?
Multicellulars animlas pump more sodium inos our of the cell than potassium ions into the cell and this equilibrtes an osmoti pressure across the membrane
Animal cells and bacteria control their intracellular osmolarity by actively pumping our inorganic ions, such as sodium, so that their cytoplasm contains a lower total concentration of inorganic ions than the extracellular fluid, thereby compensating for their excess of organic solutes
Plant cells are prevented from swelling by their rigid walls and so can tolerate an osmotic difference across plasma membranes, an internal turgor pressure is built up, which at quilibrium forces out as much water as enters
Many protozoa avoid becoming swollen w/water, despite an osmoti difference accross the plasma membrane by periodically extruding water from special contractile vacuoles
Describe carrier proteins and how they work:
Carrier proteins facilitate diffusion down the electrochemical gradient
They actively maintain concentration differences between inside and outside of cell
Actually change their shape between two or more states in a way that allows the movement of molecules through them. They can undergo large morphological change that effectively transfers solutes from one side of the membrane to the other and others will rotate or move from one face of the lipid bilayer to the other.
Can perform coupled transport
What is the permeability constant value?
Each molecule has a permeability constant for a particular compound and represents how easily it can move across the membrane
How do you determine the rate of movement of a compound across a simple biological membrane?
Multiply the area of the membrane by its permeability coefficient and the actual concentration difference across the membrane
