Transport through cell membranes

Question 1

Cell membranes are:

Answer 1

-composed of phospholipids and proteins
-selectively permeable

Question 2

Two ways of moving across membrane:

Answer 2

1. passive transport
   -down a concentration gradient ([high]->[low])
   -does not require cellular energy
   -may or may not use membrane proteins
2. active transport
   -up a concentration gradient ([low]->[high])
   -requires cellular energy (ATP)
   -uses membrane proteins

Question 3

Diffusion

Answer 3

the passive movement of molecules
-molecules move from areas of high concentration to areas of low concentration

Question 4

Simple vs facilitated diffusion

Answer 4

-Simple:
–movement through intermolecular spaces or membrane openings
–no interaction with carrier proteins

-Facilitated:
–interaction with carrier proteins

Question 5

Simple diffusion (intramolecular spaces):

Answer 5

-movement through spaces between phospholipids
-molecules must be lipid soluble
-ex: diffusion of O2, nitrogen, CO2, and alcohols

Question 6

Simple diffusion (protein channels):

Answer 6

-movement through tubular proteins that span entire membrane
-selective: size and electrical charges
-may be gated
-ex: aquaporins
allow passage of water through cell membranes

Question 7

Gated channels:
Voltage-gated
and
Chemical (ligand) gated

Answer 7

Voltage-gated:
-open/close in response to changes in electrical potential across cell membrane
ex: Na+ and K+ channels

Chemical (ligand) gated:
-open/close in response to binding of chemical
ex: acetylcholine channel

Question 8

Facilitated diffusion

Answer 8

-carrier mediated diffusion

-molecules infuse using carrier protein
-carrier protein changes shape during transport
-specific

-ex: transport of glucose and amino acids

Question 9

Rate of facilitated diffusion:

Answer 9

the speed at which the carrier protein can move the substance

Question 10

Diffusion rate effectors:

Answer 10

-temperature
-molecule size
-concentration gradient
-membrane electrical potential
-pressure differential

Question 11

Membrane electrical potential example:

Answer 11

-concentration of negative ions is the same on both sides of the membrane
-positive charge applied to right side, negative charge to left
—creates electrical gradient
-negatively charged ions will be attracted towards positive charge on right
–net diffusion from left to right
-this creates concentration gradient, moving ions from right to left
–the two forces: electrical and concentration gradients will eventually balance each other

Question 12

Osmosis

Answer 12

-diffusion of water through a semipermeable membrane
-uses aquaporins (channels)
-travels down concentration gradient

-movement in and out of cell is normally balanced so no net movement occurs

-net movement of water caused by a concentration difference of water

Question 13

Solvent vs solute

Answer 13

solvent: a fluid substances dissolve in
ex: water

solute: a substance dissolved in a solvent
ex: salt or sugar

Question 14

Osmosis across a ——— membrane

Answer 14

semi-permeable

water can pass through membrane, but other solutes cannot

Question 15

Osmosis with solute concentrations:

Answer 15

osmosis will move towards higher solute concentration
from [high] water to [low] water

Question 16

Osmotic pressure

Answer 16

-due to nondiffusbale solutes (can’t cross boundary)
-OP pulls fluid across boundary
pressure that develops due to osmosis, the more solutes inside a cell, the higher its osmotic pressure

Question 17

Hydrostatic pressure

Answer 17

-due to fluid pressing against boundary
-HP pushes fluid across the boundary
-pressure exerted by water against plasma membrane

Question 18

Filtration:

Answer 18

the movement (down a pressure gradient) of fluid across filtration membranes cause by hydrostatic pressure
-ex: capillaries

Question 19

Isotonic

Answer 19

-solution and cell have same solute concentration
-no net movement of water

Question 20

hypotonic

Answer 20

-solution has lower solute concentration than inside the cell
-water moves into the cell by osmosis
-leads to swelling and bursting (lysis)

Question 21

hypertonic

Answer 21

-solution has greater solute concentration than inside the cell
-water moves out of cell by osmosis
-cell shrivels and becomes crenate

Question 22

How much NaCl and glucose in isotonic, hypotonic, hypertonic

Answer 22

isotonic: 0.9% NaCl and 5% glucose

hypotonic: <0.9% and 5%

hypertonic: >0.9% and 5%

Question 23

Solution most commonly given when blood volume needs to be increased quickly

Answer 23

isotonic

Question 24

solution given to patients with edema (swelling ) to pull water back into blood, but can potentially over increase vascular volume

Answer 24

hypertonic

Question 25

solutions given with caution because they can result in dangerous lysing of red and white blood cells

Answer 25

hypotonic

Question 26

Diffusion continued until molecules reach ——

Answer 26

equilibrium

Question 27

active transport

Answer 27

-requires cellular energy
-moves against concentration gradient [low] to [high]
-uses carrier proteins
-two types: primary and secondary

Question 28

Primary active transport

Answer 28

-carrier protein uses ATP directly to move molecules against their concentration gradient
-ex: Na-K+ pump

Question 29

Na+-K+ Pump

Answer 29

-located in plasma membrane
-1 ATP powers pump to transport:
—-3 Na+ ions out of cell
—-2 K+ ions into cell
—-both against concentration gradient
-establishes negative electrical voltage inside cell
-regulates volume of cell: activated by increase in cell volume

Question 30

Na+-K+ steps:

Answer 30

1. carrier in membrane binds intracellular sodium
2. ATP phosphorylates protein with bound sodium
3. Phosphorylation causes conformational change in protein reducing its affinity for Na+. The Na+ then diffuses out
4. the conformational has higher affinity for K+. extracellular potassium binds to exposed sites
5. binding of potassium causes dephosphorylation of protein
6. dephosphorylation of protein triggers change back to original conformation, with low affinity for K+. K+ diffuses into the cell, and the cycle repeats

Question 31

Secondary active transport

Answer 31

-uses the energy from one molecule/driver moving down its concentration gradient to power movement of another molecule up its concentration gradient
-ATP used indirectly to create concentration gradient of driver

-Sympoter: transport substance in same direction as driver
-antiporter: transport substance in opposite direction of driver

-ex: sodium-glucose co-transport

Question 32

Vesicular transport

Answer 32

-one more way to move across membrane

Question 33

endocytosis:
phagocytosis
pinocytosis

Answer 33

phagocytosis: “cell-eating”
-pseudopods form and flow around SOLID particles. forms a vesicle (phagosome) which is pulled into cell

pinocytosis: “cell drinking”
-fluid phase endocytosis
-brings extracellular fluid and dissolved solutes; fuses with endoscope
uses:
-sample environment
-main way in which nutrient absorption occurs in the small intestine

Question 34

Exocytosis:

Answer 34

-process where material is ejected from cell
-substance being ejected is enclosed in secretory vesicle
-commonly exocytosed substances: hormones, neurotransmitters, mucus, cellular wastes