This document summarizes the structure and function of cell membranes. It states that cell membranes are composed of lipids and proteins which form a lipid bilayer. This bilayer acts as a selective barrier that is permeable to lipid-soluble but not water-soluble substances. Embedded proteins provide channels for transport of ions and molecules and act as receptors and enzymes. The membrane also contains glycoproteins and glycolipids on the outer surface that aid in cell recognition and binding.

1. By: Dr. Mahum Rauf
DPT

2.  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.

3. 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

4.  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

7.  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
 )

8.  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

9.  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)

10.  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.

11.  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

12. 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.