Pintar - Cell membranes

Question 1

Main types of phosphoglycerides (3)

Answer 1

1) Phosphatidylethanolamine: head group = CH2-CH2-NH3+ (neutral charge with P-)
2) Phosphatidylserine: P attaches to O of serine, so NH3+ and COO- (net - charge) with P-)
3) Phosphatidylcholine: CH2-CH2-N-(CH3)3+ ( neutral charge)

Question 2

Cholesterol

Answer 2

Polar OH near membrane surface, multiple ring structure adds rigidity to membrane region

Question 3

Glycolipid Structure

Answer 3

Sugar added to sphingosine backbone, sugar is external to membrane with sphingosine + FA chains inserted

Question 4

Channels, Carriers, Pumps

Answer 4

Channels open and allow ion diffusion along gradient, no energy input. Carriers transport specific molecules along concentration gradient, still no energy input directly. Pumps require energy to move against gradient.

Question 5

Uniport, Symport, Antiport

Answer 5

Uniport: one molecule one way
Symport: two molecules co-transported in the same direction
Antiport: two molecules co-transported in opposite directions

Question 6

Unitransport mechanism

Answer 6

Specific to one molecule/ion, randomly opens and closes on both sides, so ends up transporting according to diffusion gradient

Question 7

Symporter Mechanism

Answer 7

ex: Na/glucose pump, Na binding increases affinity for glucose, glucose binding causes conformational change of enzyme to release both into cell interior.

Question 8

Glucose Trancellular Transport Mechanism

Answer 8

glucose/Na symporters at apical and basal cell membranes. Following diffusion gradient, glucose enters cell at apical, and leaves cell through basal. Na/K antiport keeps intracellular [Na] low so that symport keeps taking place.

Question 9

ATP-driven active transport pumps (3)

Answer 9

P-type Pump: autophosphorylate using ATP, conformational change pumps ions
F-type (V-type) Proton Pump: Use H+ flux to drive ATP synthesis, acidify vesicles
ABC Transporter: Pumps small molecules

Question 10

P-Type Transporter Phosphorylation (I + II)

Answer 10

I - Uptakes Ca2+ from cytosol in unphosphorylated state. Phosphorylation causes Ca2+ release to SR
II - K+ released into cell and Na+ binded when unphosphorylated. ATP binding and hydrolysis causes Na/K pump to switch conformation, releasing Na to ECM and binding K. ADP + P release continues cycle

Question 11

ABC Transporter Mechanism

Answer 11

2 ATPase domains bind ATP, moving substrate to the other side of the membrane. ATP hydrolysis releases substrate
-Overactivity in tumor cells causes multidrug resistance when drug expelled from cells too quickly.

Question 12

Classes of membrane lipids (4)

Answer 12

1) Phosphoglycerides: head group, phosphate, Glycerol + 2 FA (ex: if head group is choline, phosphotidylcholine)
2) Sphingolipids: sphingosine backbone (ex: sphingomyelin)
3) Glycolipids: Sphingosine backbone, carbs on external face
4) Sterols: Cholesterol