Question

Integral cell membrane proteins
(a)Are partially embedded in lipid bilayers
(b)Are completely embedded in lipid bilayers
(c)Show lateral but not vertical movements within the lipid bilayer
(d)All of these

Answer 1

Hint: An integral membrane protein is a type of membrane protein that is permanently attached to the biological membrane. Intrinsic proteins usually float and freely move about within the lipid matrix. Integral cell membrane proteins are capable of lateral movements.

Complete answer:
Membrane proteins are mostly globular, without orderly or symmetrical arrangements they are randomly dispersed and discontinuous. They remain partially or completely inside or outside the lipid bilayer. Those proteins which are completely outside the lipid bilayer are known as extrinsic or peripheral proteins, and those which penetrate the lipid bilayer are called intrinsic or integral proteins. Integral proteins amount to 70-80% of the membrane proteins. Some integral proteins span the entire lipid bilayer. They are called transmembrane proteins. They are α-helix proteins. They form pores through the membrane and also transmit signals from one surface of the membrane to the other. Intrinsic proteins usually float and freely move about within the lipid matrix, just as icebergs float and drift in the open sea. Their lateral movements often result in the aggregation of functional proteins. The dispersed distribution of proteins forms the mosaic pattern of the fluid-mosaic model. Integral cell membrane proteins are capable of lateral movements while certain other transmembrane proteins show vertical movements for transport purposes.

Additional Information: -Membrane proteins are structural as well as functional molecules. Most of them have a functional role, while some serve as structural constituents.
-Functional proteins serve as enzymes, Permeases, receptor molecules, antigens, etc.
-Enzymes determine the functional properties of the membrane and mediate its chemical operations in an orderly manner.
So, the correct option is ‘All of these’.

Note: - Permeases serve as gatekeepers, channels, and carriers in the selective transport of substances across the membrane.
- Receptors and antigens play an important role in cell recognition, cell interaction, and cell to cell adhesion.
- In general, proteins of the plasma membrane constitute its structural framework and also help it in cell recognition, cellular adhesion, transport of materials, perception, and transmission of signals, etc.