Biological and Membrane Transport

What is bulk flow?

-applies to fluid and gases and is the most general form of biological transport

-requires a PRESENT GRADIENT that moves fluid from regions of HIGHER pressure to regions of LOWER pressure

-as fluid moves, all the components (solute) move with it

-molecules move along a FARTHER distance

-defined as AMOUNT moving per unit TIME

What some examples of bulk flow?

-blood moving through the circulatory system (5 L-min aka cardiac output)

-air flow in the lungs (pull air in like nitrogen, oxygen, and some CO2)

-solute flow (moles/s, g/s, etc)

-fluid flow (volume per time)

-charge flow (electrical current)

What is diffusion?

-the movement of molecules from an area of HIGHER concentration (of molecules) to an area of LOWER concentration (of molecules)

-occurs through very NARROW spaces over SMALL distances

What are the elements of diffusion?

1. Passive - no energy needed

2. Relies on a concentration gradient

3. Net movement occurs until concentration is EQUAL everywhere

4. Rapid over short distances and slowe over longer distances

5. Directly related to temperature (temperature moves particles)

6. INVERSELY related to molecular weight and size

7. Takes place in an open system or across a partition (a partition is a PHYSICAL barrier and is common)

What is diffusion relevant?

allows for the movement of solutes acorss a membrane, aiding in the...

1. delivery of nutrients (ex. glucose, amino acids, etc.)

2. delivery/removal of gases (oxygen and carbon dioxide)

3. removal of waste products

What is considered a unidirectional diffusion?

flow

How do you calculate FLOW?

A x P x C

What does the A stand for in the flow calculation?

membrane area (cm2)

What does the P stand for in the flow calculation?

permeability (cm/s)

What does the C stand for in the flow calculation?

solute concentration

What are the units for the flow calculation?

moles/seconds

How do you calculate NET FLOW?

A x P x (C1 - C2)

What does C1-C2 mean?

concentration gradient

What does the driving force for net flow reflect?

the concentration difference across the membrane

How do you calculate SPEED OR DISTANCE of diffusion?

einstein's relationship

x^2 = 2Dt

What does the x stand for in the speed or distance of diffusion calculation?

distance (cm)

What does the D stand for in the speed or distance of diffusion calculation?

diffusion constant (cm^2/s)

What does the diffusion constant depend on?

the size of the molecule

What does the t stand for in the speed or distance of diffusion calculation?

times (s)

A diffusion constant is ____ ____ to a molecule's size

INVERSELY proportional

How do you calculate a diffusion constant?

1 / molecule size

What is an example of a diffusion constant?

Small molecules (glucose, amino acids, ions)

D = 10^-5 cm2/s

Smaller molecules have _____ diffusion constants and diffuse _____ than _____ molecules with _______ diffusion constants

large, faster, larger, smaller

Time is proportional to the...

square of the distance

t = x^2

Diffusion is better at ______ distances

shorter

What examples is diffusion best utilized?

across cell membranes and cellular compartments (< 10 micrometers)

-glucose moving into a cell through a protein transporter

-rapid exchange of RBC contents with plasma

across capillaries (< 10 micrometers)

-oxygen and carbon dioxide diffuse across pulmonary capillaries

-ions and small molecules diffuse across peripheral capillaries into tissues

When diffusion is ineffective consider the alternative which is...

bulk flow

Diffusion delivered over short distances chart

Fick's Law of Diffusion

Diffusion rate = Membrane area x D x Concentration gradient / Membrane thickness

D = Solubility / Square root of M x W

The more thick the membrane, diffusion rate.....

decreases

Movement across a membrane depends on...

-properties of cell membrane (protein, lipid distribution)

-properties of substance moving (size and lipid solubility)

What does it mean the membranes are SELECTIVELY permeable?

-permeable to a substance that can freely move across

-impermeable to a substance that cannot freely move across

Hydrophobic and high B (beta) value means the molecule has a...

better opportunity to move at a faster rate across the membrane

High B (beta) value means...

the molecule wants to go inside the membrane more

What is the MEMBRANE PERMEABILITY calculation?

P = D x B (beta) / l

What does D in the MEMBRANE PERMEABILITY calculation stand for?

diffusion constant

What does l in the MEMBRANE PERMEABILITY calculation stand for?

membrane thickness

What does B (beta) in the MEMBRANE PERMEABILITY calculation stand for?

partition coefficent

What are the units of PERMEABILITY?

cm/sec

What are the different types of transport across a membrane?

-simple diffusion (non-saturable; no channel required)

-facilitated diffusion

-primary active transport (ATP required)

-secondary active transport

-water transport

What is simple diffusion?

hydrophobic molecules move free across the membrane

What molecules are involved in simple diffusion?

lipids (ex. steroid --> lead to roid rage), alcohols, CO2 and O2

these molecules have unregulated play against the membrane

Does simple diffusion REQUIRE ATP?

No!

Different types of transport across a membrane chart

What are the requirements for facilitated diffusion?

-protein on the membrane to facilitate movement

-concentration gradient favoring movement

-passive process

-goes from HIGH concentration to LOW concentration

-NO ATP required

What is a transport maximum?

-when there is an equilibrium of molecules between the outside and inside of the cells

-no more proteins are available to do any more work

-the cell is SATURABLE

Competitive inhibition of transporter with galactose results in...

reduced glucose rate because they BOTH use the same transporter

Passive diffusion is limited only by the...

solute concentration gradient, NOT by the number of transport proteins available on the membrane

Facilitated diffusion is limited by BOTH

the solute concentration gradient and the number of transport proteins available on the membrane

What are the requirements for primary active transport?

-saturable kinetics

-moves solutes from area of LOW concentration to HIGH concentration

-requires protein on membrane

-REQUIRES ENERGY (ATP)

How does CYANIDE inhibit primary active transport?

-poisons the electron transport chain, so no ATP is created

-can go undetected on a toxicology exam

How does OUABAIN and DIGITALIS inhibit primary active transport?

inhibits the Na+/K+ pump

Na+/K+ pump during primary active transport

What are some ADDITIONAL examples of primary active transport?

-calcium pumps = maintain low intracellular calcium concentrations

-proton pumps = eliminate H+ from the kidney to achieve pH balance

-H+/K+ exchange pumps = secrete gastric acid in stomach

What are the requirements for secondary active transport?

-saturable kinetics

-move solute from area of LOW concetration to HIGH concentration

-requires protein on membrane

-DEPENDENT on ANOTHER solute moving down its concentration gradient

-ATP is NOT used

Examples of secondary active transport

hitchhiking a ride from a friend

-friend has a car and gas money but you both need to go to the same place

oral rehydration solution to help sugar, water, and electrolytes re-enter the body using secondary active transport

What are the requirements for water transport through aquaporins?

-water moves via osmosis

-expressed on NEARLY EVERY CELL membrane to allow for a HIGH permeability to water

-water transport is linked to solute transport

Example of water transport

aquaporin-1 changes the permeability of the nephron to water, allowing urine to be come concentrated and for water to be conserved by the body

When you are hydrating, you turn _____ the aquaporins

OFF

When you are dehydrated/NOT hydrating, you turn ____ the aquaporins (occurs during sleeping)

ON