CELL
CELL MEMBRANE
• Named plasma membrane by Nageli and Cramer
• It is categorised as a bio membrane
Model for structure of cell membrane
Fluid Mosaic Model:
• • Proposed by Singer and Nicholson
• • Said that bio-membranes have quasi-fluid structure as lipids and intrinsic proteins are
able to make movement within bilayer. The lipids and proteins are held in position by their non –
covalent bonds.
• • Formed of phospholipid bilayer with protein on either side
• Lipids:
• Forms bilayer and is the structural framework of the cell
• ✓ Formed of amphipathic phospholipid molecules
• ✓ The Hydrophobic nonpolar tail ends of two layers adjoin each other while the Hydrophilic
polar heads are directed outwards.
• ✓ Hydrophilic heads are associated with proteins
• ✓ This arrangement forms a water-resistant membrane but allows passage of lipid soluble
substances
• ✓ Lipids form a fluid crystalline bilayer and provide flexibility to the Membrane
• Proteins:
• Globular proteins form a layer on either face and occur in two forms:
• a) Extrinsic or peripheral proteins: loosely bound to intrinsic proteins or the polar heads of
lipids. They are soluble and can dissociate from the membrane. Eg: Spectrin of RBC membrane
• b) intrinsic or Integral proteins: penetrate the lipid layer and tightly held there by
hydrophilic or hydrophobic Interaction
• ✓ Large Globular Integral proteins extending beyond lipid layer called Channel proteins.
Provide passage for water soluble substances in and out of the cell.
•
, • Small integral protein partially penetrates the bilayer and exposed on the surface only. As
they provide stability to the bilayer so called structural proteins.
• ✓ Glycoproteins : these are oligosaccharides attached to the outer surface to integral proteins.
Oligosaccharides attached to lipids form glycolipids.
• Glycoproteins and glycolipids form Glycocalyx whose function is:
• a) Cell recognition : recognise cells of own types which helps in blood grouping and immune
response
• b) Receptor proteins on the surface of cell membrane
• ✓ Carrier proteins: helps in transport of substances in and out of the cell against concentration
gradients Eg : Permease
✓ Membrane proteins also act as Enzymes
Importance of fluid nature of cell membrane:/ Function:
a) allows transitional movement of intrinsic proteins and lipid molecules
b) helps renewal and repair of cell membrane
c) permits cell movement and changes in cell shape
d) selectively permeable and thus allows only useful substances to enter and maintains homeostatsis
of cell.
E) its receptors help in binding hormones drugs and neurotransmitter.
f) Glycocalyx helps in cell recognition and cell adhesion
CELL MEMBRANE
• Named plasma membrane by Nageli and Cramer
• It is categorised as a bio membrane
Model for structure of cell membrane
Fluid Mosaic Model:
• • Proposed by Singer and Nicholson
• • Said that bio-membranes have quasi-fluid structure as lipids and intrinsic proteins are
able to make movement within bilayer. The lipids and proteins are held in position by their non –
covalent bonds.
• • Formed of phospholipid bilayer with protein on either side
• Lipids:
• Forms bilayer and is the structural framework of the cell
• ✓ Formed of amphipathic phospholipid molecules
• ✓ The Hydrophobic nonpolar tail ends of two layers adjoin each other while the Hydrophilic
polar heads are directed outwards.
• ✓ Hydrophilic heads are associated with proteins
• ✓ This arrangement forms a water-resistant membrane but allows passage of lipid soluble
substances
• ✓ Lipids form a fluid crystalline bilayer and provide flexibility to the Membrane
• Proteins:
• Globular proteins form a layer on either face and occur in two forms:
• a) Extrinsic or peripheral proteins: loosely bound to intrinsic proteins or the polar heads of
lipids. They are soluble and can dissociate from the membrane. Eg: Spectrin of RBC membrane
• b) intrinsic or Integral proteins: penetrate the lipid layer and tightly held there by
hydrophilic or hydrophobic Interaction
• ✓ Large Globular Integral proteins extending beyond lipid layer called Channel proteins.
Provide passage for water soluble substances in and out of the cell.
•
, • Small integral protein partially penetrates the bilayer and exposed on the surface only. As
they provide stability to the bilayer so called structural proteins.
• ✓ Glycoproteins : these are oligosaccharides attached to the outer surface to integral proteins.
Oligosaccharides attached to lipids form glycolipids.
• Glycoproteins and glycolipids form Glycocalyx whose function is:
• a) Cell recognition : recognise cells of own types which helps in blood grouping and immune
response
• b) Receptor proteins on the surface of cell membrane
• ✓ Carrier proteins: helps in transport of substances in and out of the cell against concentration
gradients Eg : Permease
✓ Membrane proteins also act as Enzymes
Importance of fluid nature of cell membrane:/ Function:
a) allows transitional movement of intrinsic proteins and lipid molecules
b) helps renewal and repair of cell membrane
c) permits cell movement and changes in cell shape
d) selectively permeable and thus allows only useful substances to enter and maintains homeostatsis
of cell.
E) its receptors help in binding hormones drugs and neurotransmitter.
f) Glycocalyx helps in cell recognition and cell adhesion
