Structure of Plasma Membrane

3.1

Structure of Plasma Membrane

Tne Necessity of Movement of Substances Across Plasma Membrane

Living cells require substances from the external environment to carry out living processes.
At the same time, the metabolic processes in cells produce waste that need to be disposed of from the cells.
Cells must allow some substances to move into and out of the cells to maintain the living processes.
The movement of substances into and out of the cell is regulated by the plasma membrane.

Structure of Plasma Membrane

The structure of the plasma membrane follows the fluid mosaic model.
This model consists of protein molecules float within the phospholipid bilayer, forming a mosaic pattern that changes frequently.
Each phospholipid molecule consists of a polar head which is hydrophilic (attracted to water) and a nonpolar tail which is hydrophobic (repels water).
The heads of the phospholipid molecule in the outer layer face the extracellular fluid, whereas the phospholipid heads in the inner layer face the cytoplasm.
The tails of the phospholipid molecule of the two layers face each other.
There are various types of protein molecules embedded partially or fully within the membrane.
The protein molecules are widely dispersed between the phospholipid bilayer.
The protein molecules with channels or canals are known as channel proteins, whereas the protein molecules that function as carriers are called carrier proteins.
Some proteins and lipids have carbohydrate chains attached to them, known as glycoprotein and glycolipid respectively.
Glycoprotein and glycolipid act as receptors to hormones such as insulin, stabilise the membrane by forming hydrogen bonds with water and act as antigens for cell identification.
There are also cholesterol molecules found between the phospholipid molecules.
Cholesterols make the phospholipid bilayer stronger, more flexible and less permeable to water-soluble substances such as ions.
The phospholipid bilayer, proteins and cholesterols are not static but form a dynamic and flexible structure.
This contributes to the characteristic of the plasma membrane and makes the plasma membrane more flexible.

The diagram shows the structure of the plasma membrane which consists of a bilayer of phospholipids, glycoproteins, glycolipids, pore proteins, carrier proteins and cholesterol. The diagram also shows the position of molecules at the outside of the cell and at the inside of the cell.

The diagram shows the types of molecules on the plasma membrane which are 1. glycolipids - a combination of lipids and polysaccharides that help cell recognition. 2. carrier proteins - transport large molecules such as glucose, amino acids, and vitamin C across the plasma membrane. 3. Cholesterol - strengthens the plasma membrane - makes the plasma membrane more flexible but less permeable to water-soluble molecules. 4. Glycoprotein - a combination of proteins and polysaccharides that help cell recognition. 5. pore proteins - allow small and water-soluble molecules such as ions to cross the plasma membrane by passive transport

Permeability of Plasma Membrane

The plasma membrane is semi-permeable because it only allows certain molecules or ions to pass through it by simple diffusion.

Structure of Plasma Membrane

3.1

Structure of Plasma Membrane

Tne Necessity of Movement of Substances Across Plasma Membrane

Living cells require substances from the external environment to carry out living processes.
At the same time, the metabolic processes in cells produce waste that need to be disposed of from the cells.
Cells must allow some substances to move into and out of the cells to maintain the living processes.
The movement of substances into and out of the cell is regulated by the plasma membrane.

Structure of Plasma Membrane

The structure of the plasma membrane follows the fluid mosaic model.
This model consists of protein molecules float within the phospholipid bilayer, forming a mosaic pattern that changes frequently.
Each phospholipid molecule consists of a polar head which is hydrophilic (attracted to water) and a nonpolar tail which is hydrophobic (repels water).
The heads of the phospholipid molecule in the outer layer face the extracellular fluid, whereas the phospholipid heads in the inner layer face the cytoplasm.
The tails of the phospholipid molecule of the two layers face each other.
There are various types of protein molecules embedded partially or fully within the membrane.
The protein molecules are widely dispersed between the phospholipid bilayer.
The protein molecules with channels or canals are known as channel proteins, whereas the protein molecules that function as carriers are called carrier proteins.
Some proteins and lipids have carbohydrate chains attached to them, known as glycoprotein and glycolipid respectively.
Glycoprotein and glycolipid act as receptors to hormones such as insulin, stabilise the membrane by forming hydrogen bonds with water and act as antigens for cell identification.
There are also cholesterol molecules found between the phospholipid molecules.
Cholesterols make the phospholipid bilayer stronger, more flexible and less permeable to water-soluble substances such as ions.
The phospholipid bilayer, proteins and cholesterols are not static but form a dynamic and flexible structure.
This contributes to the characteristic of the plasma membrane and makes the plasma membrane more flexible.

Permeability of Plasma Membrane

The plasma membrane is semi-permeable because it only allows certain molecules or ions to pass through it by simple diffusion.

Structure of Plasma Membrane

Structure of Plasma Membrane

Chapter : Movement of Substances Across Plasma Membrane

Topic : Structure of Plasma Membrane

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