“Cell membrane “
Definition:
“Cell membrane is an envelope which separates the intracellular environment from the
extracellular environment.”
Example;
In animal cells it is present just outside the cytoplasm and in plant cells it is present
below the cell wall.
Functions of cell membrane:
1. Cell membrane provide structural support to the cell
2. It protects the cells from outside.
3. It allows the materials to move in and outside the cell (Alberts,2017).
4. It works as a selectively permeable membrane.
5. It also helps cells in movement.
6. It involves the process of endocytosis, exocytosis.
7. It involves the process of osmosis.
8. It defines cell boundaries.
It produce and transmit signals i.e in nerve cells.
9. Plasma membrane also contain proteins which act as sensors of external signals .
10. Inside eukaryotic cells some organelles are also bounded by cell membrane for
example Golgi bodies, mitochondria,nucleus etc.
Chemical Composition of cell membrane:
Chemical Composition of cell membrane is given below
1.Cell contains proteins from 60-80%
2.Three classes of lipids are found in plasma membrane
● Phosphoglycerides
● Sphingolipids
● Steroids
3.Carbohydrates are present in small quantity in plasma membrane.
Models for structure of plasma membrane:
1.Sandwich model :
This was old model . According to this lipids are sandwiched between two layers of proteins.
2. Fluid mosaic model:
According to this a membrane is a bilayer of proteins and phospholipids.The phospholipids form
a sea and protein float in it like an iceberg.
Definition:
“Cell membrane is an envelope which separates the intracellular environment from the
extracellular environment.”
Example;
In animal cells it is present just outside the cytoplasm and in plant cells it is present
below the cell wall.
Functions of cell membrane:
1. Cell membrane provide structural support to the cell
2. It protects the cells from outside.
3. It allows the materials to move in and outside the cell (Alberts,2017).
4. It works as a selectively permeable membrane.
5. It also helps cells in movement.
6. It involves the process of endocytosis, exocytosis.
7. It involves the process of osmosis.
8. It defines cell boundaries.
It produce and transmit signals i.e in nerve cells.
9. Plasma membrane also contain proteins which act as sensors of external signals .
10. Inside eukaryotic cells some organelles are also bounded by cell membrane for
example Golgi bodies, mitochondria,nucleus etc.
Chemical Composition of cell membrane:
Chemical Composition of cell membrane is given below
1.Cell contains proteins from 60-80%
2.Three classes of lipids are found in plasma membrane
● Phosphoglycerides
● Sphingolipids
● Steroids
3.Carbohydrates are present in small quantity in plasma membrane.
Models for structure of plasma membrane:
1.Sandwich model :
This was old model . According to this lipids are sandwiched between two layers of proteins.
2. Fluid mosaic model:
According to this a membrane is a bilayer of proteins and phospholipids.The phospholipids form
a sea and protein float in it like an iceberg.
