2. AMOUD UNIVERSITY
SCHOOL OF DENTISTRY
1ST YEAR STUDENTS
Course Title: DNS 6111
Course Code: Cytology
Lecturer: Harun Ismail Warsame(BSc/MPH)

3. Lesson 1
Learning Objectives
1. Expain the function of cell membrane.
2. State the structure of cell membrane.
3. Distinguish between Phospholipids andGlycolipids.
4. Compare prepheral proteins and integral proteins.
5. List the chemical composition of plasma membrane
Recap

4. Chapter 2: Plasma Membrane Structure and Function
Lesson 2
Learning Objectives
1. Expain the function of membrane proteins.
2. List types of membrane proteins.
3. Describe the classification of integral proteins.
4. Identify the features of membrane proteins.

5. Membrane Proteins
 Biological membranes consist of a continuous double layer of
lipid molecules in which membrane proteins are embedded.
 Although the lipid bilayer provides the basic structure of
biological membranes, the membrane proteins perform most
of the membrane’s specific tasks and therefore give each
type of cell membrane its characteristic functional properties.
 The amounts and types of proteins in a membrane are highly
variable.
 Like the lipids, membrane proteins are amphiphilic, having
hydrophobic and hydrophilic regions.

6. Location of Membrane Proteins
 Many membrane proteins extend across the lipid bilayer.
 In some of these transmembrane proteins,
the polypeptide chain crosses the bilayer as a single α
helix (single-pass proteins).
 In others, including those responsible for the
transmembrane transport of ions and other small water-
soluble molecules, the polypeptide chain crosses the
bilayer multiple times.
 Other membrane-associated proteins do not span the
bilayer but instead are attached to either side of the

7. Types of Membrane Proteins
1) Integral membrane proteins
 ntegral proteins are permanently anchored and
embedded within the lipid bilayer.
 They cannot easily be removed from the cell
membrane without the use of harsh detergents that
destroy the lipid bilayer.
 Integral proteins float rather freely within the
bilayer, much like oceans in the sea.

8. Contin…………
 In addition, integral proteins are usually
transmembrane proteins, extending through the
lipid bilayer so that one end contacts the interior of
the cell and the other touches the exterior.
 The stretch of the integral protein within the
hydrophobic interior of the bilayer is also
hydrophobic, made up of non-polar amino acids.
Like the lipid bilayer, the exposed ends of the
integral protein are hydrophilic.

9. They can be classified according to their
relationship with the bilayer:
 Integral polytopic proteins are transmembrane proteins that
span across the membrane more than once. These proteins
may have different transmembrane topology. These proteins
have one of two structural architectures:
 Helix bundle proteins, which are present in all types
of biological membranes;
 Beta barrel proteins, which are found only in outer
membranes of Gram-negative bacteria, and outer membranes
of mitochondria and chloroplasts.

10. Contin…..
 Bitopic proteins are transmembrane proteins that span
across the membrane only once. Transmembrane helices
from these proteins have significantly different amino acid
distributions to transmembrane helices from polytopic
proteins.
 Integral monotopic proteins are integral membrane
proteins that are attached to only one side of the
membrane and do not span the whole way across.

11. 2) Peripheral membrane proteins
 They are only temporarily attached to the lipid bilayer or
to other integral proteins.
 They are easily separable from the lipid bilayer, able to
be removed without harming the bilayer in any way.
 Peripheral proteins are less mobile within the lipid bilayer.
 They are attached by a combination
of hydrophobic, electrostatic, and other non-covalent
interactions.

12. Features of Membrane Proteins
 Membrane Proteins Can Be Associated with the Lipid Bilayer in
Various Ways
 Membrane Proteins Can Be Solubilized and Purified in
Detergents
 Membrane Proteins Often Function as Large Complexes
 Many Membrane Proteins Diffuse in the Plane of the
Membrane

13. Functions of Membrane Proteins
 Membrane proteins perform a variety of functions vital to the
survival of organisms:
 Membrane receptor proteins relay signals between the
cell’s internal and external environments.
 Transport proteins move molecules and ions across the
membrane. They can be categorized according to the
Transporter Classification Database.

14. Contin…..
 Membrane enzymes may have many activities, such as
oxidoreductase, transferase or hydrolase.
 Cell adhesion molecules allow cells to identify each other and
interact. For example, proteins involved in the immune
response.

15. Proteins
 Protein in CM classified into 2 category:
Integral protein or transmembrane
peripheral protein
 Transport
 Receptors
 Enzymes
 Signal Transducers
 Support

16. Membrane Proteins

17. Channel protein

18. Carrier protein

19. Receptor protein

20. Transport across cell membrane
 Cell membrane are semipermeable
 Substance move in or out of cell in two means
 Passive transport: don’t require energy
 Active transport: requires energy

21. Permeability of the Cell Membrane

22. Class Activity
Where does membrane
protein is found in the cell?