Cell Membranes

Question 1

What is an amphipathic molecule?

Answer 1

A molecule that has both Hydrophobic and hydrophilic areas

Question 2

What is the difference between lipids and detergents?

Answer 2

• Lipids form bi-layered vesicles and membranes, and are cylindrical
• detergents form micelles, and are cone-shaped

Question 3

What determines the nature of lipid bilayer fluidity?

Answer 3

• Cholesterol

- Temperature

Question 4

Why is the contained phase of the membrane-limited organelles considered extracellular space?

Answer 4

• Compartment topology
• newly synthesized proteins for excretion, or transmembrane proteins, are contained within vesicles and when the vesicle binds to the cell membrane its contents are released into extracellular space.

Question 5

Contrast the extracellular face and the protoplasmic face of membranes?

Answer 5

Extracellular Face: -more glycolipids & glycoproteins

Intracellular Face: -more phosphatidyl-serine

Question 6

What force is involved in the Hydrophobic Effect?

Answer 6

entropy

Question 7

What is the most common lipid?

Answer 7

Phosphatidyl Choline

Question 8

What is the structure of phosphatidyl choline?

Answer 8

-Polar head group: Choline, Phosphate, Glycerol-Nonpolar Tail: Hydrocarbon tail, usually 1 that is unsaturated

Question 9

What group of lipids has an overall negative charge on their head group at physiological conditions?

Answer 9

Phosphatidyl-serine

Question 10

Why are glycolipids expressed in cell membranes?

Answer 10

for immune self-recognition

Question 11

What is the glycocalyx?

Answer 11

• a thick region of carbohydrates that is on the outside of the plasma membrane
• thought to be a protectant of the plasma membrane itself

Question 12

Phospholipid synthesis adds lipids to which side of the plasma membrane?

Answer 12

The cytosolic side

Question 13

What enzyme catalyzes the non-specific flipping of phospholipid molecules?

Answer 13

scramblase

Question 14

What enzyme is used to generate sidedness in plasma membranes?

Answer 14

Flippase

Question 15

What is the purpose of lipids organizing into localized domains/rafts?

Answer 15

allows for functions to be carried out more efficiently

Question 16

Presence of which lipid in the outer (extracellular) leaf of the plasma membrane is a signal for apoptosis?

Answer 16

phosphatidyl-serine

Question 17

What lipid molecule plays an important role in intracellular signalling?

Answer 17

Phosphatidyl-Inositol

Question 18

How is water distributed over the body fluid compartments?

Answer 18

-60% intracellular fluid-30% interstitial fluid-10% plasma

Question 19

What are the normal concentrations of ions in intracellular fluid?

Answer 19

• Low Sodium (5-15 mM)-High Potassium (140 mM)

- Low Chloride (5-15 mM)-Very low Calcium (0.0001 mM)

Question 20

What are the normal concentrations of ions in extracellular fluid?

Answer 20

• High Sodium (145 mM)-Low Potassium (5 mM)

- High Chloride (110 mM)-High Calcium (1-2 mM)

Question 21

What is the difference between active transport, diffusion, and facilitated diffusion?

Answer 21

• Active transport requires ATP
• Diffusion occurs down a chemical or electric gradient through membranes
• Facilitated Diffusion still is down electrochemical gradient, but there are channels in the membrane

Question 22

Describe how a primary active transport system works

Answer 22

Energy, usually in the form of ATP, is used to alter the conformation of a transporter protein to transport a molecule against its concentration gradient

Question 23

What drives secondary active transport?

Answer 23

ATP is used to transport a molecule against its gradient, this molecule will then re-cross the membrane along its gradient through a symporter or antiporter

Question 24

What is the basic cellular role of a P-type ATPase (ion pump)?

Answer 24

• to maintain high extracellular [Na] and high intracellular [K]
• maintains osmolarity and cell volume-generates heat

Question 25

How do cardiac glycosides (digitalis) work in heart failure?

Answer 25

-Inhibition of the Na/K ATPase leads to an increased intracellular [Na], which by decreasing the activity of the Na/Ca antiporter, leads to a greater intracellular [Ca], which strengthens the heartbeat

Question 26

How do defects in chloride channel trafficking lead to cystic fibrosis?

Answer 26

in skin, CFTR fluxes chloride in symport with Na-When CFTR is defective, NaCl stays on outside of epithelium in respiratory tract-leads to thick sticky mucous

Question 27

List types of molecules in order of their ability to cross lipid bilayers

Answer 27

Most
-Hydrophobic molecules
-Small uncharged polar molecules
-Large uncharged polar molecules
-Ions
least

Question 28

Why is it so difficult for ions to cross the cell membrane unassisted?

Answer 28

charge allows them to associate with water, it is very difficult to strip ions from water because of a strong hydration shell

Question 29

During what type of membrane crossing are saturation kinetics displayed?

Answer 29

carrier or transporter mediated

Question 30

What are the three types of Gated membrane channels?

Answer 30

• Voltage
• Ligand
• Mechanically gated

Question 31

How do cells control carrier activity? (facilitated diffusion)

Answer 31

The cell will insert or remove carriers from the plasma membrane

Question 32

What is the molecular mechanism of the Na/K ATPase?

Answer 32

1. 3 Na bind
2. ATP phosphorylates active site
3. Conformational change releases Na
4. 2 K bind
5. Mg2+ catalyzes dephosphorylation of enzyme
6. Conformational change releases K

Question 33

How is glucose transported into cells?

Answer 33

Via a sodium-glucose symporter