topic 9 - osmosis + diffusion

why does selective permeability happen in cell membranes?

due to the amphipathic nature of the bilayer & specificity of transport proteins

what are some things that can pass through easily?

1. hydrocarbons (lipids)

2. nonpolar steroids; ex. testosterone, estradiol

3. small, uncharged, nonpolar things; ex. CO₂, O₂

what are some things that cannot pass through easily?

1. large, charged, polar molecules; ex. sugars

2. ions

what do sugars require to get through the cell membrane?

they require a transport protein

passive transport

requires no additional energy (ATP) for transportation

active transport

requires E (ATP)

diffusion

a type of passive transport in cells in which molecules move from areas where there are more of them to areas where there are fewer of them.

it is a slow process, and it is spontaneous

what do all molecules have and then what do they do?

thermal (kinetic E) and they spread out into open areas

do the molecules move randomly or directionally?

molecules independently move randomly & bounce off one another; however, together, they move directionally

rule of diffusion

in the absence of other forces, a substance will diffuse from where it is more concentrated to where it is less concentrated. the substance moves down its concentration gradient (the gradient drives diffusion)

Concentration Gradient

A difference in the concentration of a substance across a distance. requires two "places" - one with a high concentration & one with a low concentration

spontaneous

(of a process) requiring no energy

what are things that affect the rate of diffusion?

1. permeability of membrane

2. concentration difference

3. temperature

osmosis

still diffusion, just specific to water

solute

A substance that is dissolved in a solution.

solvent

the substance in which the solute dissolves

solution

A homogeneous mixture of two or more substances

hypertonic

having a higher concentration of solute than; "more solute"

hypotonic

having a lower concentration of solute than; "less solute"

hyper/hypotonic "to"

hyper/hypotonic is a relative comparison comparing 2 solutions, so we have to use "to" after the word

isotonic

when 2 solutions have the same tonicity (molar concentration). the solutions do not have to be the same solute. for ex. a solution with 0.1 M NaCl and a solution with 0.1 M glucose have the same tonicity.

tonicity

the ability of a solution to make water move in or out of a cell by osmosis

what happens if a membrane is impermeable to solutes?

if solutes can't move, the water will. water has to move through aquaporins

aquaporins

transport channel proteins that move water in/out of the cell

Ψ = Ψs + Ψp

water potential equations where:

Ψ = water potential

Ψs = solute potential

Ψp = pressure potential

Ψs = -iCRT

solute potential equations where:

i = ionization constant

C = concentration (the thing that changes)

R = pressure constant

T = temperature

what does distilled water have that is separate?

Ψs = 0 MPa

MPa stands for megapascals (a unit)

surroundings hypertonic to animal cell

the cell loses water so it shrivels up & dies

surroundings hypotonic to animal cell

the cell gains water leading to it bursting (lysis)

lysis

the disintegration of a cell by rupture of the cell wall or membrane

surroundings isotonic to animal cell

no net movement of water; ideal

surroundings hypertonic to cell w/ cell wall

plasmolysis will occur; the cell membrane will go away due to shriveling up & dying but a cell wall is left behind

plasmolysis

contraction of the protoplast of a plant cell as a result of loss of water from the cell

surroundings hypotonic to cell w/ cell wall

cell becomes turgid which is ideal b/c the cell wall exerts turgor pressure

turgor pressure

the force within the cell that pushes the plasma membrane against the cell wall (+Ψp - positive pressure)

surroundings isotonic to cell w/ cell wall

cell will be flaccid (flimsy); if all cells are like this, a plant will wilt

what are transport proteins similar to?

enzymes

why are transport proteins similar to enzymes?

1. they can be saturated

2. specific for a molecule

3. can become inhibited

what does it mean to be saturated?

to have a limited rate of transport

what does it mean if something is inhibited?

a shape change will prevent it from working

which is quicker: facilitated or regular diffusion?

facilitated diffusion; it's much quicker than regular diffusion

facilitated diffusion

diffusion of polar molecules

still diffusion

when polar molecules move down their concentration gradient; ex. water, glucose

where does facilitation come from?

transmembrane proteins, specifically carrier proteins and channel proteins. both types of proteins are specific though, they carry only 1 thing.

how does facilitation come from carrier proteins?

the substances to be transported binds to the carrier protein. this causes the carrier to change its shape & pull the substance to the other side. this could also be used in active transport.

how does facilitation come from channel proteins?

channel proteins provide a hydrophilic passage for molecules to sink into. they could be gifted, for example,

aquaporins for osmosis. these proteins are more likely to be involved in facilitated diffusion.

which type of protein (carrier or channel) is more likely to be involved in facilitated diffusion?

channel proteins