Membrane Transport

Question 1

Define Isotonic? (Healthy size cell)

Answer 1

Solute concentration(osmotic pressure) is the same inside and outside the cell.

Question 2

Define Hypotonic.(Very swollen cell)

Answer 2

Solute concentration (osmotic pressure) is greater inside the cell than outside the cell.

Question 3

Define hypertonic.(“Dehydrated” looking cell)

Answer 3

Solute concentration(osmotic pressure) is lower in the cell than outside the cell.

Question 4

What energy drives diffusion? (No barriers)

Answer 4

Diffusion occurs due to the inherent, kinetic energy of molecules and the potential energy stored in a concentration gradient.

Question 5

Is osmosis diffusion of water? (P Bio 375)

Answer 5

NO!

Question 6

Define osmosis.

Answer 6

The flow of water across a water permeable membrane toward a region of higher solute concentration.

Question 7

What differs diffusion from osmosis?

Answer 7

Diffusion depends upon a concentration gradient. Osmosis depends on osmotic pressure; the number of solute particles. (Neither their size, charge state, nor hydrophilicity have effect of the osmotic pressure of the system.)

Question 8

Define Aquaporins.

Answer 8

Transmembrane proteins that form water channels.

Question 9

Define osmolarity and osmolality.

Answer 9

Osmolarity: Number of particles of solute per liter of water.
Osmolality: Number of particles of solute per kilogram of water.

Question 10

Osmotic flow of water is through 1.__________. Water flows 2.____ an osmotic gradient.

Answer 10

1. Aquaporins
2. Up

Question 11

Define osmotic pressure.

Answer 11

A colligative property: it depends on the number of particles of solute, but not the nature of the particles.
The pressure that must be applied to oppose osmosis.

Question 12

Why is osmotic pressure important for hydrostatic pressure?

Answer 12

Osmotic pressure counteracts hydrostatic pressure to prevent fluid from leaving the capillaries.

Question 13

Define colloid osmotic pressure (π)

Answer 13

Is the osmotic pressure due to the plasma proteins within the capillary, pulls fluid into the capillary.

Question 14

Define hydrostatic pressure. (Pʜ)

Answer 14

Pressure that forces fluid out of the capillary.

Question 15

Which pressure has more strength generally? Hydrostatic pressure (Pʜ) or Colloid osmotic pressure (pi)

Answer 15

Hydrostatic pressure.
This means about 3L of fluid per day leaves the capillaries.
This is returned to the circulatory system as lymph.

Question 16

Define tonicity.

Answer 16

The relative level of non-penetrating solutes in a fluid in which cells are being bathed.(in Lec)
Or
The capability of a solution to modify the volume of cells by altering their water content .(Google)
The ability of extracellular solution to make water move into or out of a cell by osmosis . (Google)

Question 17

Define channel. What are common types?

Answer 17

A water filled hole, transmembrane protein(s). Aquaporins, and ion channels, both gated and ungated,

Question 18

What are the two main properties of ion channels. Name all ions important for this class(4). Name the types of gated channels(5).

Answer 18

1. Selectivity: What type of ion does through.
   Ex. Na+, K+, Ca++, Cl-
2. Gating: What opens or closes the channel.
   Ex. Ungated channel = Leak channel, voltage gated-channel, ligand gated = chemically gated, mechanically gated channel, temperature gated channel.

Question 19

What’s the difference between passive and active transport.

Answer 19

Active requires ATP (directly or indirectly).
Passive requires only a gradient (being gated doesn’t mean it needs ATP!)

Question 20

Define what a Carrier Protein is.

Answer 20

Carrier proteins have two confirmations that expose the binding site to either the extracellular fluid or the intracellular fluid. They are NOT a continuous pore like a channel. (Also called transporter/symporter)

Question 21

What is the GLUT protein responsible for?

Answer 21

It is a glucose transporter(carrier protein!) that is responsible for the facilitated diffusion of glucose. (Uses facilitated diffusion)

Question 22

Define facilitated diffusion.

Answer 22

A passive process that depends only on the concentration gradient. Requires aid of membrane protein to carry out the diffusion. (Ex. H2O & Aquaporins, Glucose and GLUT protein.)

Question 23

Define primary active transport. (Carrier protein still)

Answer 23

Utilizing ATP energy in order to change the conformation of the carrier protein.
Ex. Na+/K+-ATPase!

Question 24

What are 3 common examples of Primary active transport ATP-ases?

Answer 24

1. Na+/K+-ATPase (sodium potassium pump): uses ATP hydrolysis to pump 3 Na+ ions out of the cell and 2 K+ ions into the cell for each round of transport.
2. Ca++-ATPase: pumps Ca++ out of cytosol.
3. H+/K+-ATPase: proton pump involved in acid secretion in the stomach.

Question 25

Notable concentration gradients of ions in ICF vs ECF. Note things about Na+, K+, and Cl-. Why are these gradients notable?(2 reasons)

Answer 25

Na+ generally has a higher concentration outside of the cell. K+ generally has a **lower** concentration outside the cell. Cl- generally has a higher concentration outside of the cell. The gradients are key for 1. Membrane potential and 2. Secondary active transport.

Question 26

Define secondary active transport and a common example. What are the two types of secondary active transport?

Answer 26

The use of energy from one gradient to power transport of another gradient (often unfavorable/going against a gradient). Ex. **Na+-glucose cotransporter. SGLT protein** Two types: 1. Transport molecules in the same direction (cotransporter, or symporter). 2. Transport molecules in the opposite direction (countertransporter, or exchanger.)

Question 27

What is required for the SGLT protien (sodium-glucose cotransporter) to work? How is it used?

Answer 27

Requires both Na+ and glucose to be binded to the carrier protien for transport to occur. This protien is involved in the key first step in the absorption of glucose from the digestive tract.

Question 28

Define saturation of carrier proteins. Can channels be saturated?

Answer 28

The transport rate reaches a maximum at high concentrations when all carrier binding sites are occupied. No channels can not.

Question 29

Define competitive inhibition of carrier proteins. Can channels have competitive inhibition?

Answer 29

A molecule that competes with the transported substance for the binding site will lower the rate of transport. No channels do not have competitive inhibition.

Question 30

Define competitive inhibition of carrier proteins. Can channels have competitive inhibition?

Answer 30

A molecule that competes with the transported substance for the binding site will lower the rate of transport. No channels do not have competitive inhibition.

Question 31

Optional: what is SGLT2?

Answer 31

Sodium-glucose cotransporter in the kidney tubules.

Question 32

Define Epithelia

Answer 32

Tissues, that form a barrier between the external environment and the internal environment of the body.

Question 33

What are the two sides(membranes) of a epithelium? What do they face respectively? What separates them?

Answer 33

The Apical membrane/side faces the lumen. (Kinda spikey) The Basolateral membrane/side faces the underlying tissue. (Smoother) These membranes are linked by tight junctions between adjacent cells.

Question 34

Define what a lumen is.

Answer 34

The space within the tubes, tracts, cavities, and cells of the body. Air, blood, fluids, food, and other substances move through the lumen.

Question 35

Why is it beneficial that the epithelium has two separate membrane layers?

Answer 35

Different transport proteins are localized on the apical vs basolateral surfaces of epithelial cells to enable transport in one direction across both membranes of the epithelium. Transport can be more selective in direction.

Question 36

Define secretion of the epithelium.

Answer 36

Transport from ECF to lumen.

Question 37

Define absorption in the epithelium.

Answer 37

Transport from lumen to ECF(body).

Question 38

Fluid secretion happens why? (Secretion of Epithelium)

Answer 38

Happens because of osmosis, as ions(solutes) move into lumen, creates a higher degree of **osmolairty** inside the lumen and water follows by osmosis. Ions move in between the membranes through(only ECF ->basolateral membrane): 1. Na+/K+-ATPase 2. Cotransporter that moves Na+,K+,and Cl- (symporter) Ions move from between membrane to lumen through (apical membrane -> Lumen): 1. CFTR (a chloride channel)