QTTA

Question 1

What evidence is there that supports a “fluid mosaic” model of membrane structure?

Answer 1

• The cholesterol in the bilayer, electron microscopy

Question 2

Would you expect that plants that live in very cold climates have more or less unsaturated fatty acids in their cell membrane than plants that live in the tropics? Explain.

Answer 2

• Plants in warm would have more saturated to fill gaps to be colder. Plants in the cold would have more unsaturated fats to be warmer.

Question 3

Which parts of a transmembrane protein are hydrophilic? Hydrophobic?

Answer 3

• The core of the protein generally is hydrophobic, permitting passage of water-soluble molecules
• The surfaces are hydrophilic, permitting interaction with the interior of the lipid bilayer.

Question 4

Describe the pathway a cell would take to make a transmembrane protein the RER and ending up being inserted into the cell membrane.

Answer 4

• RER to the Golgi to the cell membrane

Question 5

Give an example of a specific protein from each of the six key classes of membrane proteins.

Answer 5

Transporter - Hemoglobin
Enzyme - Amylase
Cell surface receptor - Insulin
Cell-surface identity marker - T Cell
Cell-to-cell adhesion - E-cadherin
Attachments to the cytoskeleton - Vimentin

Question 6

What are the relative concentrations of sodium, potassium, and calcium inside and outside of the cell? (Like we did in class….high vs low across the membrane).

Answer 6

Outside - -Na+K+Ca^2+
Inside - K-higher in cell

Question 7

What is the difference between the passive and the active glucose symporter?

Answer 7

Passive symporters - Operate without energy input and facilitate glucose movement down the gradient

Active symporters - Use energy to transport glucose against the gradient

Question 8

What is the difference between a symporter and an antiporter. Give an example of both types of active
transporters.

Answer 8

Symporter - Molecules move in same direction glucose/Na+

Antiporter - Molecules bond to opposite sides of protein moved in different directions - H+/Ca^2

Question 9

What are aquaporins?

Answer 9

• Channel proteins that form pores in the membrane of biological cells

Question 10

Describe how might the protein plasma cell membrane composition of a neuron differs from a liver cell?

Answer 10

• Plasma membrane composition of a neuron is specialized for rapid electrical signaling

Question 11

Consider the sodium -potassium pump (Na/K ATP-ase) (figure 5.14). Can you explain how this pump works? Why is it considered an active transporter protein? What provides the energy to run this pump?

Answer 11

• Pumps K+ in and Na out
• Maintains concentration gradient
• 3 sodium bind
• ATP phosphorylation protein with bound sodium

Question 12

What do red blood cells do when placed in a hypertonic solution? How about in a hypotonic solution?

Answer 12

Hypertonic - Shrivel up

Hypotonic - Cells swell, eventually burst

Question 13

What is receptor-mediated endocytosis?

Answer 13

• A process by which cells take in specific molecules by forming vesicles from the plasma membrane

Question 14

What human genetic disease results from a mutation in the LDL receptor?

Answer 14

• Familial hypercholesterolemia

Question 15

How does this affect endocytosis of cholesterol into the cell?

Answer 15

• The low pH in the endosome causes a conformational change that releases the LDL particles