Cell Membrane Structure and Composition

Questions and Answers

To serve as receptors for hormones

To synthesize proteins

To determine the fluidity of the membrane (correct)

To provide a barrier for water-soluble substances

Integral proteins extend through the whole thickness of the membrane, while peripheral proteins are attached to one side (correct)

Integral proteins are attached to the outer surface of the membrane, while peripheral proteins are embedded in the membrane

Integral proteins are found in the lipid bilayer, while peripheral proteins are found in the cytoplasm

Integral proteins are small, while peripheral proteins are large

To determine the fluidity of the membrane

To serve as receptors for hormones

To provide a barrier for water-soluble substances (correct)

To synthesize proteins

To serve as receptors and attachment sites Signup and view all the answers

Phospholipids Signup and view all the answers

All of the above Signup and view all the answers

To serve as receptors, ion channels, and carriers Signup and view all the answers

55% Signup and view all the answers

To provide a barrier for water-soluble substances Signup and view all the answers

Providing a barrier for water-soluble substances Signup and view all the answers

Study Notes

The cell membrane is composed of lipid bilayer (42%), proteins (55%), and carbohydrates (3%).
The lipid bilayer is continuous over the entire surface, providing a barrier that prevents the movement of water-soluble (lipid-insoluble) substances.

The lipid bilayer is made up of phospholipid (the major lipid in the cell membrane) and cholesterol.
Phospholipid molecules are 2 molecules in thickness, with each molecule having:
- A head containing the phosphate radical, which is relatively water-soluble (hydrophilic) and exposed to water inside or outside the cell.
- Tails containing the fatty acid radical, which is relatively water-insoluble (hydrophobic) and present in the water-poor interior of the membrane.
Cholesterol is lipophilic and dissolves in the phospholipid bilayer, helping to determine the permeability of the lipid layer to water-soluble substances and the fluidity of the membrane.

Proteins do not form a continuous layer in the cell membrane, instead existing as globular masses floating in the lipid bilayer.
There are two types of proteins:
- Integral proteins, which extend through the whole thickness of the membrane and have functions such as:
  - Receptors for hormone action.
  - Ion channels for ion passage.
  - Carriers for transporting substances like glucose and amino acids.
  - Enzymes.
- Peripheral proteins, which are attached to the cell membrane from outside or inside and do not extend through the whole thickness of the membrane, often acting as enzymes.

Carbohydrates are present on the outer surface of the cell membrane, forming a loose coat called glycolcalyx.
They may be combined with proteins (glycoproteins) or lipids (glycolipids).
Functions of carbohydrates include:
- Receptors.
- Attaching cells to each other.
- Immune response.
- Providing an overall negative surface charge to most cells.