1.
 The cell and its organelles are surrounded
by Membranes composed of Lipids &
proteins.
 Theses membranes include the cell
membrane, nuclear membrane,
membranes of ER, Mitochondria,
lysosomes & golgi apparatus.

2.
1. Cell membrane provide barrier that
prevent free movement of water and
water-soluble substances from one cell
compartment to another.
2. Proteins in the cell membrane provide
the pathway to allow movement of
specific substances through the
membrane

3.
 Cell membrane is a Lipid Bilayer with
Inserted proteins.
 The lipid bilayer is composed of
Phospholipids and Cholesterol.
 Phospholipids have two portions:
1. Hydrophilic portion= Water-soluble portion
2. Hydrophobic portion= Fat soluble portion

4.
 Lipid bilayer is highly permeable to lipid
soluble substances
Such as O2,CO2,alcohol etc.
 But it act as a barrier for water soluble
substances
Such as Ions & glucose
 )

5.
 Many protein are also floating in lipid bilayer.
These proteins are Glycoproteins ( proteins
combine with Carbohydrates)
 There are 2 types of proteins:
1. Integral proteins
2. Peripheral protein

6.
 These proteins protrude through the membrane.
 Function:
1. They provide structural channels
(pores)through which water soluble
substances specially Ions can diffuse
2. They act as carrier proteins for the transport
of substances, sometimes against the
gradient for diffusion it is called Active
transport.
3. They also serve as receptors for substances
such as peptide hormones because they donot
cross cell membrane easily (second
messsenger)

7.
 These proteins are attached to the inner
surface of membrane but do not
penetrate
 Function :
1. They serve as function enzymes that
catalyze chemical reactions of cells.

8.
 These are in combination with proteins and lipids
in form of glycoproteins and glycolipids.
 Glyco portion usually protrude outside of the
cell.
 Proteoglycans = These are small carbohydrate
molecules bound together by small protein
cores, are loosely attached to the outer surface.
 Glycocalx =It is a loose outer carbohydrate coat
that surrounds the cell

9.
1. They are often negatively charged and
therefore repel other molecules negatively
charged.
2. The glycocalx of cells may attach to other
cells
3. Some are act as receptors for binding
hormones.