Cellular Interactions and Cell Membrane Transport Flashcards
define the extracellular matrix (ECM)
cells that make up tissues/organs are embedded in extracellular material
what is the ECM made of
protein fibres, ground substance, and integrins
how are cells able to communicate with each other
by secreting chemical regulators into the extracellular environment
how can it be said that cells have a give-and-take relationship with their extracellular environment
cells receive nourishment from it, and they release wastes to it
what are fluid-filled compartments separated by
epithelial membranes
where is transport occurring between intracellular and extracellular environments
across the plasma membrane
why are membranes important for transport
acts as a regulator for the passage of fluid b/w compartments (most made up of water)
why is water an important solvent?
it can interact with large (proteins) and small (inorganic ions, sugars, amino acids), molecules
draw a flowchart of the body fluid compartments
total body water splits into intracellular (67%) and extracellular fluids; extracellular fluid splits into interstitial fluid (80%) and blood plasma
compare intracellular and extracellular fluids
intra: fluid inside cells; protein and K+ rich
extra: fluid outside cells; few proteins and Na+ rich
compare interstitial fluid and blood plasma
ISF: fluid that surrounds cells except blood cells in circulatory system; few proteins
blood plasma: fluid that surrounds blood cells in circulatory system; protein rich
why is compartmentalization important
each cell can make exchanges b/w internal and external cellular environments; body systems can transfer material which helps with maintaining homeostasis
what is total body water
total volume of fluid in all compartments
what type of permeability does the plasma membrane have
selective
Why is the plasma membrane permeable to small, uncharged polar molecules even though the interior of the membrane is hydrophobic?
- they move between gaps that perform between fatty acid tails of membrane (dynamic structure with constant ‘moving’)
- kinetic barrier is not great enough to prevent diffusion from occurring on a time scale relevant to that of living systems
Is the plasma membrane permeable to nucleic acids, proteins and structural molecules?
- no
- large in size
- DNA has - charge
moving substances across the plasma membrane can be categorized in different ways. list them
carrier-protein requiring: carrier-meditated transport, non-carrier-meditated transport
energy requiring: active, passive, bulk transport
describe passive transport
spontaneous, no cell energy needed, “downhill” transport along conc gradient
what are the types of passive transport
osmosis, simple diffusion, facilitated diffusion (channel or carrier mediated)
explain the process of simple diffusion; what is the net movement
random ‘mixing’ of particles from one location to another (physical separation not necessarily needed); net movement is from higher solute concentration to lower solute concentration
define mean diffusion time
the average time it takes for a solute to diffuse
what can transport through simple diffusion through the plasma membrane. provide some examples
- small, uncharged (non-polar) lipid soluble molecules pass easily like O2, CO2, steroid hormones, ethanol, urea
- charged ions can pass through using ion channels
explain gas exchange in simple diffusion
net diffusion of O2 into cells and CO2 out of cells due to concentration gradients
what are the factors affecting rates of diffusion
magnitude of driving force, membrane surface area, membrane permeability, temperature
what do we mean by the magnitude of driving force
how large the concentration gradient is
what is one way membrane surface area can be increased
thru microvilli
explain the process of osmosis
passage of water through plasma membrane by aquaporins from low to high solute concentration
what are aquaporins and where are they found
water membrane channels; found in kidneys, eyes, lungs, salivary glands, brain
what are the requirements for osmosis
- solute concentration difference on either side of a membrane permeable to water
- membrane must be impermeable to solute, otherwise concentration difference won’t be maintained
what are osmotically active solutes
those that cannot cross the membrane but can permit osmosis
describe the net movement of water for osmosis
from more dilute (low solute) to less dilute (high solute)
describe the movement of water if aquaporins were not present
extremely slow
describe channel-mediated transport
- needs transmembrane protein that functions like a passageway or pore
- substance-specific
- some channels always open, some are gated
- most membrane channels are ion channels
what does a transmembrane protein refer to
protein embedded into membrane and spans it
describe gated ion channels
can open based on conformational shape change due to physiological stimuli (e.g. chemical regulator binding), otherwise remains closed
compare aquaporins and ion channels
aq: highly selective (water only), gated, have different classes
ion chan: have leak channels and gated channels
what are ion leak channels
channels that are open all the time (non-gated)
explain the process of carrier mediated transport
- passive transport (no ATP)
- high to low conc
- needs specific carrier-mediated proteins for each transported material
- conformational shape change with binding to “swing” material to low conc. side
what is the name(s) of the specific glucose carriers in central nervous system
GLUT1 and 3
where is carrier GLUT 2 typically found
pancreatic beta cells, hepatocytes (liver cells)
where is carrier GLUT 4 typically found
fat tissue, skeletal muscle
what are the properties of carrier-mediated transport
specificity, competition, saturation
what do we mean by competition in carrier-mediated transport
some molecules with compete with each other for the binding sites on a carrier since they are so similar (EX amino acids)
what do we mean by saturation in carrier-mediated transport
a limit to the rate of transport (to a point)
describe the transport maximum
the plateau region of saturation effects on carrier mediated transport, in which any factors above this will not make any difference to the rate of transportation
explain the process of active transport
- movement of ions and molecules against their concentration gradient
- nonspontaneous (needs energy)
- movement is uphill and needs a “pump”
what are the types of active transport
primary and secondary
explain the primary active transport process using the Ca +2 pump example
- Ca+2 inside cells binds to carrier protein site facing inside cell
- ATP hydrolyzed into ADP + P which bind to pump
- release of ADP causes conformational shape change releasing Ca+2 to extracellular side
- P releases from pump to trigger carrier to change back into original shape and let Ca+2 bind again
- this continues as long as there is ATP
how many Na+ and K+ are moving into and out of the cell in 1 primary active transport cycle; what enzyme does this
ATPase enzyme pumps 3 Na+ out of the cell and 2 K+ into the cell
What are the 3 functions of the sodium/potassium pump
1) Provides energy for coupled transport of other molecules
2) Produces electrochemical impulses in neurons and muscle cells
3) Maintains osmolality of cells
explain the process of secondary active transport
- uses energy from an electrochemical gradient or concentration gradient previously created by primary active transport
- Involves two molecules or ions
describe cotransport
both substances move in same direction
describe countertransport
both molecules move in opposite directions
how is the SGLT pump able to transport glucose against its concentration gradient
via energy from sodium movement along its concentration gradient
the small intestine has what type of sodium coupled glucose transporter; the ratio of sodium:glucose
SGLT 1; 2:1
the kidneys have what type of sodium coupled glucose transporter; the ratio of sodium:glucose
SGLT 2; 1:1
ICF/ECF composition differs, but ICF composition remains relatively steady. Why don’t intracellular concentrations change?
due to leak channels allowing for passive transport of materials back in to their originating spots (e.g. K passively diffuses back out despite normally being pumped in)
define exocytosis; what is it used for; energy?
- fusion of a vesicle with the plasma membrane, needs ATP
- used for large molecule secretion, like proteins, hormones, and neurotransmitters
define endocytosis; what is it used for
cells engulf large substances like cholesterol into a vesicle (usually triggered by plasma membrane protein and transport protein interacting) and bring it inwards
explain how a molecule moves in facilitated diffusion
down (along) its concentration gradient with the assistance of a protein carrier molecule, and no energy is required
