Forces acting across membranes

Question 1

What is the basic structure of the membrane

Answer 1

1. Double layer of phospholipids
2. Embedded with proteins (aquaporin)

Question 2

What are the characteristics of a membrane

Answer 2

1. Selective barrier
2. Permeability can vary
3. Dynamic
4. Very thin bilayer
5. Very flexible because of fatty acids
6. Insulators against ion movement

Question 3

What is the function of the membrane

Answer 3

Selectively permeable barrier between ICF and ECF
Provide binding sites for chemical signals
Differences in membrane proteins responsible for varied charteristics

Question 4

What are the different types of membrane proteins

Answer 4

1. Integral - Span hydrophobic core of phopholipid bilayer
2. Periphrial - interact only with phosphates of bilayer and do not penetrate hydrophobic region

Question 5

What are the functions of membrane proteins

Answer 5

1. Receptors
2. Transport
3. Enzymes
4. Maintenence of cell structure
5. Communication

Question 6

What are the concentrations of ions in cellular fluid

Answer 6

Question 7

What are the differences in membrane protein content

Answer 7

Myelin - low protein content 18%, high lipid content good insulator
Plasma membrane - protein content 50%
Membranes for energy transduction - high protein content 75%

Question 8

What is the elctrochemical gradient

Answer 8

Combination of chemical gradient and electrical gradient

Question 9

What are the mechanisms of movement across membranes

Answer 9

1. Diffusion
2. Active transport
3. Osmosis
4. Filtration

Question 10

What is Endocytosis

Answer 10

Invagination of cell membrane to form a vesicle which disintegrates on inisde, releasing contents that migrate to destination
Common mechanism to terminate signals from extracellular ligands

Question 11

What is exocytosis

Answer 11

Vesicles merge with plasma membrane on inside and release contents outside of cell
Many proteins synthesized inside cell are released this way

Question 12

What is diffusion across membranes

Answer 12

Molecules move from high concentraition to low concentration down concentration gradient

Question 13

What types of diffusion is there

Answer 13

1. Passive
2. Facilitated

Question 14

Describe passive diffusion

Answer 14

Substances move directly through lipid bilayer
Molecules need to be: small, uncharged and Lipophilic

Question 15

Describe facilitated diffusion

Answer 15

Substances require assistance from membrane proteins to cross lipid bilayer
Membrane proteins can be channels or mediated transport proteins

Question 16

What type of channels proteins are there

Answer 16

Voltage gated - electric potential
Ligand gated - ligand binding

Question 17

Describe Transporters

Answer 17

Open to one side of ECF or ICF at a time

Question 18

What is active transport

Answer 18

Movement of molecules against concentraition gradient with energy

Question 19

Describe the Na+/K+ pump

Answer 19

1.Maintains high Na+ outside cell and high K+ concentration inside
2.Pumps 3 Na+ out and 2 K+ inside
3.Net movement of positive charge out cell = electrogenic pump
4.40% of resting energy is used by pump

Question 20

What is osmosis

Answer 20

Net movement of H2O from high concentrations to low concentrations of water

Question 21

What is the difference between osmosis and diffusion

Answer 21

Osmosis - Net movement of water form high concentration to low
Diffusion - Net movemet of solutes from high solute concentration to low

Question 22

Describe osmosis

Answer 22

Membranes permiable to only water will have equal concentrations on both sides of membrane but different volumes

Question 23

Describe diffusion

Answer 23

Membranes permiable to water and a solute will have equal concentrations on both sides and equal volume

Question 24

What is osmolarity

Answer 24

Total number of solute particles in solution (after they dissociate), not nature of particles

Question 25

What is Tonicity

Answer 25

Total number of non-penatrating particles in solution (particles unable to cross membrane)

Question 26

What is the importance of tonicity

Answer 26

If a solute cannot cross a membrane, a change in its concentration will cause osmotic flux and change volume of cell

Question 27

Describe an isosmotic solution

Answer 27

Question 28

Describe an isotonic solution

Answer 28

Question 29

Give examples of penetrating and non-penetrating particles

Answer 29

Penetrating - water, urea Non-penetrating - ions

Question 30

What is the Osmolarity of human plasma

Answer 30

285mosmol/l, same as osmolarity of cells

Question 31

What happens to cells in hypotonic and hypertonic solutions

Answer 31

Hypotonic - swell because water enters cell down conc. gradient Hypertonic - shrink because water leaves down a chemical gradient

Question 32

Why is osmosis important when prescribing fluids

Answer 32

Cause cells to burst Lysed cells introduce proteins to ISF, uncontrolled increase of ECF tonicity Fluids must have the appropriate tonicity Brain is most sensative to change in tonicity