Chapter 5: Membrane Dynamics

Question 1

Explain body fluid compartments and name the two types in regards to cells.

Answer 1

• Body fluid compartments are filled primarily with water and are separated by membranes
• Intracellular: area inside cells
• Extracellular: area outside cells

Question 2

What is passive transport?

Answer 2

Passive transport: molecules move high  low concentration without using energy

• Simple diffusion
  Lipid-soluble molecules
  Ions through nonspecific channels
• Facilitated diffusion

Question 3

What is active transport?

Answer 3

Active Transport: molecules move from low to high concentration using ATP

Question 4

What is osmosis?

Answer 4

Net movement of water across a semi-permeable membrane from side with more water to less water
Aided by channels in membrane

Question 5

WHat is used to measure the the concentration of a solution?

Answer 5

• Osmolarity (OsM) is a measure of solution concentration
  OsM = total # solute particles/L solution
• In the body solute concentrations are usually expressed in milliosmoles = mOsM
• Plasma and most cells are 300mOsM

Question 6

How is the osmolarity of blood regulated?

Answer 6

• Osmoreceptors in the hypothalamus detect increases in solutes (due to dehydration, etc)
• Concentration of particles must constantly be maintained, or cells are damaged (e.g. neurons)

Question 7

What is the difference between non penetrating and penetrating solutes?

Answer 7

• Solution: consists of a solvent (water) and a solute (molecules dissolved in water)
• Molecules in a solution are in constant motion
• If there is a concentration difference between two regions, random motion will establish equilibrium
  Solutes that can cross membrane = penetrating
  Solutes that cannot cross membrane =non penetrating

Question 8

What is tonicity? How does it work?

Answer 8

• Tonicity is the effect of a solution’s solute concentration on the osmosis of water
• Tonicity takes into account permeability of membrane to solutes
  Penetrating vs nonpenetrating solutes
• If solute crosses membrane, tonicity will change
• Solutions with a higher solute concentration than cell are hypertonic
• Water leaves cell- crenation
• Solutions with a lower solute concentration than cell arehypotonic
• Water enters cell - lysis

Question 9

Using Jerry’s shit as an example, explain the the phenomena of diffusion?

Answer 9

• Jk! XD
• Net diffusion: Due to random movement, the net direction of diffusion is from high to low

Question 10

What molecules can diffuse through the plasma membrane?

Answer 10

• Nonpolar lipid soluble molecules and small uncharged polar molecules – permeable
  Steroid hormones, water, gases
  Net O2 into cells, CO2 out of cells

Question 11

How do ions diffuse through the plasma membrane?

Answer 11

Charged ions can cross the plasma membrane by passing through ion channels

• Some channels may always be open, others gated

Question 12

Explain the various types of membrane transporters.

Answer 12

1. Channel proteins: create a water filled pore.
   Gated channels: open and close in response to signals
   Open channel: usually open (pore)
2. Carrier proteins: never form an open channel between the two sides of the membrane
   Uniport carriers: transport only one kind of substrate
   Symport carrier: move two or more substances in the same direction across the membrane
   Antiport carrier: move substrate in the opposite direction

Question 13

Explain facilitated diffusion.

Answer 13

• Most molecules too large and polar to cross
• Instead, specific carrier proteins within the membrane move these molecules across
• Random movement of molecules
  No ATP
  High to low concentration
• Transport proteins may be permanent in the plasma membrane or be inserted when needed
  Muscle cells insert carrier proteins to take in more glucose when needed as during exercise

Question 14

What is primary active transport?

Answer 14

• Move molecules from low to high concentration
• ATP hydrolysis directly provides energy
• Pump is activated by phosphorylation using a Pi from ATP
  Na+/K+ pump
  Ca2+ pump

Question 15

What is secondary active transport?

Answer 15

• Energy from an ion gradient is used to move a second solute against its concentration gradient
• Symport: 2nd molecule is moved in same direction
• Antiport: 2nd molecule is moved opposite direction

Question 16

How many transport proteins can be on a single epithelial cell?

Answer 16

• Epithelial cells may have many different types of transport proteins on a single cell

Ex: movement of glucose across the intestinal wall

Question 17

What is membrane potential?

Answer 17

• There is a difference in charge on each side of the plasma membrane due to:

Permeability of the membrane
Action of Na+/K+ pumps
Negatively charged molecules inside the cell

• Inside of cell is negative relative to outside