4/07/2017

JNU BIOTECH COACHING

Q25. Which of the following statements regarding membrane transport is FALSE?
1. Polar and charged solutes will not cross cell membranes effectively without specific protein carriers.
2. Each protein carrier will only bind and transport one (or a few very similar) type of solute.
3. Sugars such as glucose are always transported by active transport rather than by facilitated diffusion carriers.
4. lons are typically transported by special proteins that from membrane channels.

Ans (3) We all are aware that membranes have hydrophobic interior as it is rich in fatty acid tails of phospholipids, so it is only hydrophobic solutes which have no charge and are small, can pass through membranes by simple diffusion.........others (e.g. Ions, Large size solutes) need aid of transport proteins, which are integral membrane proteins............and transport proteins can be categorized into Carrier proteins, Channel proteins and Pumps

So choice 1 & 4 are nearly same and they are correct, as polar solutes or ions need special membrane proteins.

Some Carriers e.g. Glucose transporter i.e. GLUT......can recognize not only glucose but similar sugars such as galactose and mannose can also be transported, so choice 2 is also correct. 

Choice 3 says that glucose is transported by active transport, which is a wrong choice as glucose transport requires Carriers, i.e. Facilitated diffusion........and glucose is transported down the concentration gradient.

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