Lecture 2: Mediated Transport & Osmosis

Question 0

diffusion of dissolved solutes is a __________ process.

Answer 0

random

Question 1

mediated transport is saturable. true or false?

Answer 1

true

Question 2

in a preparation for surgery, you place an intravenous line in your patient, but inadvertently use lactated ringer’s 5% dextrose hypertonic by ~2 fold instead of the isotonic dextrose. What process would occur?

Answer 2

water will move from the intracellular fluid compartment to the extracellular fluid compartment.

Question 3

a major contributor to passive segregation of ions across the cell membrane is _______________.

Answer 3

intracellular protein

Question 4

secondary active transport works by:

Answer 4

coupling transport through concentration gradients established by primary active transport.

Question 5

a patient is asked about the possible link between mild dehydration & dental disease. You explain the total body water weight is in the?

Answer 5

intracellular fluid

Question 6

the molecular mechanism of protein-mediated transport across the cell membrane is ____________________________________________.

Answer 6

integral membrane protein carries a substance across the cell membrane, causing a conformational change in the protein (such as folding) allowing the bound substance to have access to both sides.

Question 7

why is protein mediated transport faster than diffusion?

Answer 7

the energy barrier of the hydrophobic bilayer is lowered

channels>transporters

Question 8

properties of protein-mediated transport consist of:

Answer 8

1. specificity
2. saturable, due to finite # of transporters
3. faster than diffusion
4. competitive inhibition by similar substances
5. inhibitable by drugs & like substances that decrease permeability coefficient

Question 9

the determinants of flux magnitude include:

Answer 9

1. # of transporters
2. saturation of transporters
3. rate of conformational change of the transporter

Question 10

facilitated diffusion is dependent of membrane permeability. true or false?

Answer 10

FALSE

Question 11

facilitated diffusion is maintained by ________________.

Answer 11

disposal (metabolic) of transported substance

Question 12

primary active transport, seen in Na/K ATPase, maintains the electrochemical gradient & charge by ______________________________.

Answer 12

storing energy in the charge segregation.

Question 13

what type of transport indirectly depends on the expenditure of energy from primary active transport? How does it work? List an example.

Answer 13

Secondary active transport; couples transport of one item down the concentration gradient, while the other moves up the gradient.
symport or antiport/co-transporter
example: SGLUT1 transports glucose up the gradient, while Na moves down its gradient (symport). glucose transporter is consuming the concentration gradient.

Question 14

indicate direction of water movement across a cell membrane for a given extracellular fluid tonicity.
isotonic = ?
hypotonic = ?
hypertonic = ?

Answer 14

isotonic: water inside = water outside
hypertonic: #impermeable substances insidecell SHRINKS
hypotonic: #impermeable substances inside>#impermeable substances outside—->cell GROWS

Question 15

penetrating solutes are ___________ that can ___________________.

Answer 15

permeable; equilibrate across the membrane, affecting the water concentration equally on both sides
example: urea

Question 16

non-penetrating solutes ___________________ & affect water concentration by __________________________________________.

Answer 16

can’t cross the membrane; concentrating only on one side of the membrane, where they are trapped

Question 17

Osmolarity = ?

Answer 17

of ALL particles dissolved in solution

Question 18

tonicity = ?

Answer 18

of impermeable particles (OSMOTICALLY active particles) dissolved in a solution

Question 19

living cell is 300 mOsm/1 total K+, protein, & Cl- inside that is bathing in a solution of 150 mM/l NaCl—>?

Answer 19

300 mOsm/l bc the Na+ and Cl- will dissolve

now, bc the Na+ and Cl- are impermeable, the solution is isotonic.

Question 21

tonicity doesn’t always = osmolarity. true or false.

Answer 21

true.
example: 7% sucrose solution is isotonic & isoosmotic. add 10% ethanol to the solution (FYI ethanol is permeable)—->solution is now hyperosmolar (more permeable to substances outside), but still isotonic (# of impermeable substances has not changed).

Question 22

Some secreted digestion fluids are hypotonic with calcium concentrations near extracellular fluid (ECF) levels (in contrast to the low levels in cells). Because calcium does not pass across the tight junctions of epithelial cells in these locations, calcium in these fluids most probably came from:

a. facilitated transport on both sides of the epithelial cell
b. facilitated transport on the basolateral side (ECF side) of the epithelial cells and primary active transport on the apical (luminal side)
c. primary active transport on the basolateral side (ECF side) of the epithelial cells and secondary active transport on the apical (luminal side)
d. primary active transport on the basolateral side (ECF side) of the epithelial cells and facilitated transport on the apical (luminal side)
e. secondary active transport on the basolateral side (ECF side) of the epithelial cells and facilitated transport on the apical (luminal side)

Answer 22

b. facilitated transport on the basolateral side (ECF side) of the epithelial cells and primary active transport on the apical (luminal side)

the hypotonic condition means that water is not transferring with the Ca ions. So since ECF [Ca] is high facilitated diffusion will take the Ca ions from the ECF through the cell and then active transport is needed to take it from the low conc within the cell into the lumen.