Question

Which of the following factors would tend to increase membrane fluidity?

A) A greater proportion of unsaturated phospholipids

B) A greater proportion of saturated phospholipids

C) A lower temperature

D) A relatively high protein content in the membrane

E) A greater proportion of relatively large glycolipids compared with lipids having smaller molecular masses

Which state correctly describes bound ribosomes? Choose all correct states.

A) Bound ribosomes are enclosed in a membrane.

B) Bound and free ribosomes are structurally different.

C) Bound ribosomes are most commonly found on the surface of the endoplasmic reticulum.

D) Bound ribosomes generally synthesize membrane proteins secretory proteins

E) Bound ribosomes produce alpha- and beta-tubulins.

Answer 1

As long as the membrane is 'overcrowded' with lipids, it stays flexible. With high levels of saturated fatty acids the membrane loses its flexibility/fluidity. So, greater proportion of unsaturated phospholipids will tend to increase membrane fluidity. The correct answer is thus option A.

Ribosomes do not have membranes and are different from other cell organelles. So, the Bound ribosomes are not enclosed in a membrane. Both bound and free ribosomes have the same structure and characteristics, the only difference is in their location and function. Bound and free ribosomes are not structurally different. The products from the bound ribosomes are secreted or exported out of the cell, whereas the products from the free ribosomes are used inside the cell. The bound ribosomes are found on the surface of the endoplasmic reticulum.  Bound ribosomes generally synthesize membrane proteins secretory proteins. The tubulins are present in the microtubes which are already in the cell, so they are produced along with the subunits by the free ribosomes. Thus the correct answers are options C and D.