Textbook Problem

In the fluid mosaic model:

plasma membrane proteins orient their hydrophilic sides toward the internal bilayer.

phospholipids often flip-flop between the inner and outer layers.

the mosaic refers to proteins attached to the underlying cytoskeleton.

the fluid refers to the phospholipid bilayer.

the mosaic refers to the symmetry of the internal membrane proteins and sterols.

Summary Introduction

Introduction:

The membrane of the cell is composed of the phospholipid bilayer and proteins. The structure of the membrane is explained by the fluid-mosaic model proposed by Singer and Nicolson. The proteins are distributed unevenly in the bilayer of the lipids.

Answer to Problem 1TYK

Correct answer:

The fluid in the fluid-mosaic refers to the bilayer of phospholipids.

Explanation of Solution

Explanation for the correct answer:

Option (d) is given that thephospholipid bilayer is the fluid part of the membrane. The cellular membrane is formed of the phospholipids and proteins. The fluidity of the membrane is imparted by the phospholipid bilayer, which is amphipathic in nature. Hence, option (d) is correct.

Explanation for the incorrect answers:

Option (a) is given that the hydrophilic sides of the membrane proteins are present towards the internal layer. The proteins present in the membrane are hydrophilic in nature and are present towards the cytosolic or outer sides. They are attracted towards water and span the membrane. So, it is an incorrect option.

Option (b) is given that phospholipids often flip-flop in the layer. The phospholipid layer of the membrane is continuous and uniform. The lipid molecules move sideways rather than flip-flop movement across the inner and outer sides of the membrane. So, it is an incorrect option.

Option (c) is given that the protein attached to the cytoskeleton forms the mosaic part. The mosaic portion of the membrane is formed by the protein. Proteins span the membrane and are present on both the outer and inner sides of the membrane. The inner proteins are attached to the cytoskeleton. So, it is an incorrect option.

Option (e) is given that the mosaic is formed by the symmetry of the internal proteins and sterols. The mosaic region comprises the total proteins present in the membrane. Proteins are unevenly distributed in the membrane. So, it is an incorrect option.

Hence, options (a), (b), (c), and (e) are incorrect.

Conclusion

Therefore, it is concluded that the fluid part of the membrane is formed by the phospholipid bilayer, while the mosaic region is formed by the total protein of the membrane.