Biological membranes are thin, flexible surfaces that separate cells and organelles from their environments. They are made up of proteins, lipids like phospholipids and glycolipids, and carbohydrates. Phospholipids are the major lipid component, consisting of a hydrophilic head and two hydrophobic tails, allowing them to form the fluid lipid bilayer structure of the membrane. Membrane proteins can be integral and span the membrane or peripheral and attach to its surface. They perform many functions including transport, cell signaling, and anchoring the cytoskeleton. Together, the components of the membrane give it key properties such as selective permeability and fluidity to control what enters and exits the cell while protecting it.

1. BIOMEMBRANES
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2. DEFINITION
 Biological membranes are thin, flexible
surfaces separating cells and cell
compartments from their environments
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3. ORGANELLES CONTAINING
MEMBERANE
Lysosomes Golgi bodies Mitochondria Nucleus
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4. FLUID MOSAIC MODEL
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5. COMPONENTS
Components of membrane are:
 Proteins
 lipids
 Carbohydrates
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6. PROTEINS
Two basic types of membrane proteins:
 Integral (Intrinsic) proteins
 Peripheral (extrinsic) proteins
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7. INTEGRAL (INTRINSIC)
PROTEINS
 They are embedded in hydrophobic core of
lipid bilayer
 For example : Transmembrane proteins
are exposed on both sides of the
membrane
FUNCTION:
 Anchorage
 Transport
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8. THREE GENERAL CLASSES OF
TRANSPORT SYSTEMS
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9. PERIPHERAL (EXTRINSIC)
PROTEINS
 Peripheral membrane proteins are proteins that adhere
outside the biological membrane
 These molecules attach to integral membrane
proteins, or penetrate the peripheral regions of the
lipid bilayer
FUNCTION:
 Cell-to-cell interaction
 Cell signaling
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10. MANY FUNCTIONS OF MEMBRANE
PROTEINS
Outside
Plasma
membrane
Inside
Transporter Cell surface
receptor
Enzyme
activity
Cell surface
identity marker
Attachment to the
cytoskeletonCell adhesion
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11. LIPIDS
 Lipids in membranes are Amphipathic
 Orientation of Amphipathic compounds (Lipids) in
aqueous solution is to prevent Hydrophobic region
coming into contact with water molecules
Major lipids in biological membranes are:
 Phospholipids
 Glycolipids
 Cholesterol
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12. PHOSPHOLIPIDS
Phospholipid is made up of:
 Two Non-polar (Hydrophobic) fatty acid
chains: Tails
 One polar (Hydrophilic) group: Head
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13.  Phospholipid molecules are
orientated to form:
 micelle
 lipid bilayer
 liposome
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14. PHOSPHOLIPID
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15. CHEMICAL NATURE OF
PHOSPHOLIPIDS
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16. GLYCOLIPIDS
 Glycolipids are lipids that form part of
the plasma membrane
 They have a short carbohydrate chain
covalently attached and this is exposed on the
outer surface of the cell
Function:
 Communicative or
cellular recognition
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17. CHOLESTEROL
 It is a steroid that is amphipathic in
nature
Function:
 Provide stability
 Maintain the fluidity
 Bilayer stronger
 Bilayer flexible
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18. CARBOHYDRATES
Carbohydrates covalently linked to proteins
(glycoproteins) or lipids (glycolipids) are
also a part of cell membranes
FUNCTION:
cell-cell recognition
 Basis for rejection of
foreign cells by
immune system
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19. GLYCOCALYX
 Entire surface of cell membrane contain
carbohydrate coat called glycocalyx
Function:
 Provide negative charge to the membrane
 Provide attachment between the cells
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20. FUNCTION OF CELL MEMBRANE
 The cell membrane is selectively
permeable to ions and organic
molecules and controls the movement
of substances in and out of cells
 The basic function of the cell
membrane is to protect
the cell from its surroundings
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21. IMPORTANT FEATURES
 Selective permeability
 Fluidity
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