Week 2 Review Flashcards
Describe the concentration of ions in the intracellular and extracellular compartments of our bodies. What permits these differences in ionic concentration to exist?
- intracellular = negative
- extracellular = positive
- selective permeability of the cell membrane permits the differences in ionic concentration to exist
- cell membrane is impermeable to K+ but it’s leaky, not perfect at keeping K+ in
- Every time a + charged potassium makes its way out, it leaves a net negative charge behind
Explain the phrase “materials move from areas of high concentrations to areas of low concentrations unless somehow prevented from doing so”
- nature of molecules is to be at equilibrium, but a mechanism such as the cell membrane has the ability to regulate molecules in/out of the cell, causing the concentrations to be unequal
- molecules will always move from high to low concentration because of thermal energy unless there is something in their way
What is a major function of the cell membrane?
- protection
- regulation of substances going in/out of the cell
What molecules easily pass through the cell membrane? What molecules do not?
- non-polar molecules (uncharged, lipid soluble, hydrophobic) move through rapidly
- polar molecules (charged, water soluble, hydrophilic) are largely refused entry
How does the anatomy of the cell membrane help this structure function in regulating the movement of solutes across it?
- ion channels on the membrane allow for and regulate movement of ions
- phospholipid bilayer allows lipid soluble molecules through
- other channels on the membrane allow movement of other substances
How might changing the properties of the cell membrane change the function of the cell?
the cell no longer has a protective layer that regulates substances going in/out
selectively permeable
allows some molecules to cross the membrane but not others
non-carrier mediated transport
molecules move through a semipermeable membrane from high concentration to low concentration
mediated transport
transporters (membrane proteins) move molecules through the membrane to the other side either up or down the concentration gradient
simple diffusion
- spontaneous net movement of particles down a concentration gradient resulting in equal distribution of the particles
- driven by thermal energy
facilitated diffusion
- passive process
- random movement of molecules, no ATP, high to low conc, and transporters can help
- Ex: glucose will move down its conc gradient without help but glucose transporters (Glut4) can pick up glucose to move them into the cell quicker
active transport
- energy requiring
- molecules can move from low to high concentration or high to low concentration
- involves ATP and specific carrier molecules
membrane channels and pores
“holes” in the membrane that can open and close to regulate movement of molecules
osmosis
movement of water molecules from areas of high water concentration to areas of low water concentration
Explain why a solute concentration gradient between 2 compartments can also influence water concentrations.
Addition of a solute to water decreases the concentration of water in that solution (water and sweet tea example).
What physical factors influence the rate of simple diffusion?
- membrane permeability
- solute concentration
- size of the molecule
- electrochemical gradient
Explain the role distance plays in the diffusion of solutes
- shorter distance = less travel for the molecule; higher saturation of molecules
- longer distance = more travel for the molecule; takes longer to diffuse; lower saturation
hydrophilic
- water loving
- heads of phospholipids that form the external and internal layers of the bilayer
- interact with charged water molecules and with proteins
hydrophobic
- water hating
- tails of phospholipids
- interact with nonpolar/uncharged molecules
In order for a drug to cross a cell membrane by simple diffusion, would it have to be a polar or non-polar molecule?
- non-polar
- the tails of the phospholipid are hydrophobic, so they like uncharged, non-polar molecules
- non-polar molecules move easier across the membrane
What is an ion channel or pore and what is its function?
- part of cell membrane that is selectively permeable to certain ions
- regulates movement of ions
- difference in charges creates an electrical gradient
What is an electrochemical gradient? What is its role in ion movement?
- used for an ion that can move across the membrane (pulls + ions in, pushes - ions out)
- chemical gradient = difference in solute conc across the membrane
- electrical gradient = difference in charges across the membrane
What is a resting membrane potential (RMP) and what causes it?
- when cell is at rest and there is no net movement (-60-75 mV)
- generated by the “leaking” of K from inside to outside, creating a - charge in the intracellular
- no net movement = no conc is changing even though there is slight movement of a few ions (leakiness)
Explain the general purpose and mechanisms of mediated transport.
- occurs when more of a molecule is needed faster than normal (i.e. cannot just rely on simple diffusion)
- passage of molecules through a membrane is mediated by a transporter
- can move from low to high conc OR high to low conc
- Ex: Glut4 transporter with glucose
What happens when a transporter moves a molecule from low to high concentration?
- Requires expenditure of energy
- Solute binds to a specific site on the transporter
- Conformational change occurs in transporter
- Transporter & solute move through the membrane
- Dissociation of solute from the transporter then occurs, depositing solute either inside or outside the cell
- Transporter can then pick up a molecule and move it to another compartment or go back to its starting point
What factors determine the magnitude of solute movement that can occur by mediated transport?
- Number of transporters available
- Speed at which transporter undergoes conformational change to move the molecule
- Extent to which binding sites are saturated
What is a limitation of facilitated diffusion?
movement is still driven by concentration gradients, so can’t go from low to high
What are the characteristics of active transport?
- requires energy in the form of ATP
- can move up or down conc gradient
- specific carrier molecules and/or biological pumps
- have to bind, better bind = more effective carrier molecule
- using energy to move molecules down the conc gradient speeds up the facilitated diffusion process
endocytosis
- process by which a piece of the cell membrane engulfs an organism, molecule, etc.
- The resulting vesicle then enters the cell and is degraded
- Ex: WBCs protecting our body from invasions
exocytosis
- vesicle is formed inside the cell and fuses with the membrane, releasing the contents into the extracellular space
- Ex: insulin; excretion of proteins into the extracellular matrix
epithelial transport
- movement of substances across the apical (luminal) and basolateral (serosal) membranes via the paracellular or transcellular pathway of epithelium
- Ex: absorption of material in the GI tract into the blood, movement of substances between the kidney tubules
paracellular pathway of epithelial transport
substance diffuses between the adjacent cells of the epithelium
transcellular pathway of epithelial transport
substance moves into the epithelial cell across the apical or basolateral membrane, diffuses through the cytosol and exits across the opposite membrane
osmosis
the movement of water across a concentration gradient
osmotically active
- solutes that cannot cross a membrane and promote osmosis
- play important role in movement of water in capillaries
- role in edema formation
hypotonic
higher water concentration outside the cell, so the water moves into the cell and causes it to swell
isotonic
solute concentrations are equal, cell will not change shape
hypertonic
lower water concentration outside the cell, so water moves out of the cell and causes it to shrink
osmotic pressure
amount of pressure required to stop the movement of water
Explain the role that non-diffusible large molecules (proteins) play in defining the tonicity of a cell in driving osmosis
- larger molecules determine flow of osmosis
- the side with more large molecules (less water) will require more water coming into the cell, making it a hypotonic solution
Explain why active transport but not an ion channel is needed to facilitate the movement of potassium into a cell.
- Because the movement of K and Na is forced, it requires ATP
- Ion channels do not require energy
- High concentration of K inside cell, so it has to go against concentration gradient to get into the cell
Explain why an ion channel is sufficient to facilitate the inward movement of Cl ion into a neuron.
[Cl] is higher outside the cell, lower inside. Since ions move from high to low conc, energy isn’t required for Cl to move in. Since energy isn’t required, ion channel can move it.
What barriers to movement are created by an epithelial layer?
it is harder for molecules to move through since the epithelial layer can be thick
vs. a simple squamous epithelium layer which is just one layer of cells and thinner
