8/19 Membrane transport

Question 1

Describe the components of the typical plasma membrane

Answer 1

1. Lipids: phospholipids, cholesterol, and glycolipids (this is responsible for he high permeability of the cell to lipid soluble substances such as carbon dioxide, oxygen, gatty acids, and steroid hormones. This is also why water, ions, glucose, and amino acids don’t come through well.
2. Proteins: this is the transporters, enzymes, hormone receptors, and cell sruface antigens, and ion and water channels.
   “fluid mosaic”
   Remember: water loves sugar, charge, and most amino acids!

Question 2

Diagram the distribution of total body water and major electrolytes inside and outside of cells

Answer 2

Inside the cell: no table salt or milk, but there is pot!
inside the cell: low sodium, calcium, and cloride ions; High potassium
Outside the cell: high sodium, calcium and cloride and low potasium
Water: most in the intracellular, then interstitual, then the plasma. seperated by permiable membranes between each!

Question 3

what is simple diffusion

Answer 3

The movement of molecules across a membrane due to passive forces such as a concentration gradient or a chemical gradient. smaller and more hydrophobic, the faster/easier it will move across the membrane. The rate of diffusion is directly proportional to the diving force and the permiability of the membrane (think ohlms law!)

Question 4

give examples of simple diffusion, facilitatied diffusion, ion channels, primary active transport and secondary active transport.

Answer 4

Simple diffusion: non-polar, hydrophobic molecules.
Facilitated: glucose in muscle (insulin stimulated)
ion channels: Na+, Ca2+, K+, Cl- and H+
Primary active:Na-K pump, PMCA (plasma membrane Ca ATPase).
secondary active: Symporters and Antiporters such as Na-Glucose and Na-amino acid (symporters); and Na-H and HCO3–Cl- , (antiporters) These control acid and heart calcium in the heart respectfully

Question 5

Describe the factors that determine the rate of transport of molecules across a cell membrane.

Answer 5

Rate of transport is dependent on the concentration gradient or driving force, the permiability of the membrane and the area of the membrane (ficks law of diffusion)

Question 6

What does electrochemical gradient mean?

Answer 6

The concentration gradient + the electrical gradient

Question 7

Diagram the passive forces acting on ion movement through a membrane

Answer 7

The total passive force would be the vector sum of the electrical gradient on the ion accross the membrane and the concentration gradient for the ion accross the membrane

Question 8

what is a symporter

Answer 8

a secondary active transporter that transports a molecule down its electrochemical gradient inorder to actively move another molecule in the same direction but up its electrochemical gradient.

Question 9

What is an anti-porter

Answer 9

a secondary active transporter that transports a molecule down its electrochemical gradient inorder to actively move another molecule in the opposite direction but up its electrochemical gradient.

Question 10

what is an example of a symporter

Answer 10

Na-Glucose and Na-amino acid transporters in luminal membranes of epithelial cells in intestine and kidney

Question 11

what is an example of an anti-porter

Answer 11

Na+-H+ exhange and HCO3-Cl- exchange (pH control). Na+-Ca2+ exhange (helps control intracellular calcium in hear cells) and this is why a potassium bolus will stop a heart! (Ca dependent on Na gradient that is dependent on the potassium gradeint!).

Question 12

what is the difference between the rates of simple diffusion and carrier mediated transport (kinetics of it).

Answer 12

Simple diffusion has a linear relationship between the concentration and the membrane flux (as conc up => flux up proportionally). As the concentration goes up for transporters and channels they can be saturated and the flux will platue (non-linear relationship)

Question 13

what is osmosis

Answer 13

Membrane transport of water due to a difference in solute concentration (osmotic pressure). Very clinically realavant: water moves toward the higher solute concentration. mainly due to acquaporins

Question 14

what is osmotic pressure

Answer 14

Water conc. is reduced by adding in solutes (propotional to the number of particles added), therefore water wants to move down its conc. gradient. The amount of pressure pressing the water accross the membrane is equal to the osmotic pressure. this is also thought of as the amount of pressure to hold the water at an equilibrium. Directly proportional to the osmolarity of the solution!

Question 15

how will the cell volume change in response to osmolarity changes outside of the cell

Answer 15

The cell is fragile and can swell or shrink! and can rupture

Question 16

what is the difference between hypotonic, isotonic and hypertonic

Answer 16

hypotonic means a low osmolarity, isotonic means the same osmolarity as another space and hypertonic means a high osmolarity. A cell in a hypotonic solution will swell and possibly burst as water moves from the low osmolarity to the higher osmolarity!

Question 17

what is facilitated diffusion

Answer 17

Diffusion through a transporter. No energy required, but the transporter simply allows the molocule to move down its electrochemical gradient (increases the permeability of the membrane to increase the diffusion rate)

Question 18

what are ion channels

Answer 18

Channels through the plasma membrane that allow the passage of ions down there electro chemical gradient: makes the membrane permiable to the ions that usually cannot diffuse accross the membrane.

Question 19

what are primary active transport and secondary active transport

Answer 19

Pumps and sym/anti-porters!

Question 20

what are intigral proteins?

Answer 20

Strongly embedded in the membrane, can span the entire membrane. pumps, channels, receptors etc.

Question 21

what are peripheral proteins

Answer 21

not embedded in the membrane and loosley attached. many connected to carbohydrates. modulate activity and interface with the ECM etc.

Question 22

what is osmolarity

Answer 22

the number of particles per molecule when the molecule is in solution (remember ionic bonds will break) X the concentration

Question 23

what are the four basic types of transmembrane flux?

Answer 23

simple diffusion; channel-mediated; passive transporter-mediated; active transporter.

Question 24

Name 5 ways of increasing the rate of simple diffusion

Answer 24

1. Increase surface area
2. Increase conc. gradient
3. Increase Temp.
4. Decrease distance
5. Decrease molecular weight

Question 25

how does Cystic fibrosis make it harder to breathe

Answer 25

by decreasing the rate of simple diffusion of gasses in the lungs; by decreasing surface area and increasing distance to difuse through accumulation of mucus. [pulmonary edema would do the same thing with water]

Question 26

What channel is selective gated, saturable and sensitive to the relative ion concentration (membrane polarization)

Answer 26

The Voltage gated channels

Question 27

How does a small Ca2+ flux amplify in the cardiac muscles

Answer 27

through a intracellular ligand-gated ion channel being activated by a voltage gated ion channel opening to let Ca+2 travel down the gradient created by Na+ gradient created by K-Na pump!

Question 28

What is a channelopathy?

Answer 28

a disease or condition created by the mutation of a channel. such as long Q-T and K channels or cyctic fibrosis