[Campbell Biology P.147] Refer to Figure 6.6 b , 'Structure of the plasma membrane.' Which c... | Practice Question

Refer to Figure 6.6 b , 'Structure of the plasma membrane.' Which components correspond to the 'dark bands' observed in the colorized TEM image 6.6 a , and which component corresponds to the 'gold band'?

  • A: Dark bands: Hydrophilic regions of phospholipids and proteins; Gold band: Hydrophobic regions.
  • B: Dark bands: Hydrophobic regions of phospholipids; Gold band: Hydrophilic regions.
  • C: Dark bands: Carbohydrate side chains; Gold band: Proteins.
  • D: Dark bands: Proteins; Gold band: Phospholipids.

Explanation

Figure 6.6's caption explains that the plasma membrane consists of a double layer of phospholipids with proteins. It states that 'hydrophobic parts of phospholipids and membrane proteins are found in the interior of the membrane, while the hydrophilic parts are in contact with aqueous solutions on either side.' In TEM, electron-dense hydrophilic regions appear dark, and less electron-dense hydrophobic regions appear lighter gold band . Thus, the dark bands correspond to the hydrophilic heads of phospholipids and hydrophilic regions of proteins at the surfaces, and the gold band corresponds to the hydrophobic tails of phospholipids and hydrophobic regions of proteins in the interior.