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

3. 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.
Recap

4. Chapter 3: Cell Transport
Learning Objectives
1. Expain the mechanism of cell transport.
2. Differentiate the difference between active
transport and passive transport.
3. Distinguish between osmosis and diffusion.
4. Describe the types of tonicity.
5. List the components of bulk transport.

5. Introduction
 Look at the big windows and glass doors in this house. Imagine
all the light they must let in on a sunny day.
 Now imagine living in a house that has walls without any windows
or doors. Nothing could enter or leave.
 Things could enter or leave, but you couldn’t control what came
in or went out.
 Only if a house has walls with windows and doors that can be
opened or closed you can control what enters or leaves.

6. A house with windows

7. Transport Across Membranes
 If a cell were a house, the plasma membrane would be
walls with windows and doors. Moving things in and out of
the cell
 It controls everything that enters and leaves the cell.
 There are two basic ways that substances can cross
the plasma membrane
1. passive transport: which requires no energy and
2. active transport: which requires energy

8. Cell Transport Concept Map

10. Contin…..
 Molecules in a gas and molecules and ions
dissolved in a solution are in a constant state of
random motion as a result of their thermal
energy. this random motion is called diffusion.
 Diffusion tends to scatter the molecules evenly, or
diffusely, within a given volume.
 As a result, there will be a net movement form
the region of higher to the region of lower
concentration until the concentration difference
no longer exists. This net movement is called net
diffusion.

14. Osmosis
Osmosis is the net diffusion of water
(the solvent) across the membrane.
Although water is not lipid soluble,
water molecules can diffuse through
the cell membrane because of their
small size and lack of net charge.

16. Tonicity
 Tonicity is the relative concentration of solutes in two
fluids on either side of the membrane.
 Isotonic: is when solute concentration is equal on both
sides of the membrane.
 Hypotonic: when solute concentration is less outside the
membrane
 Hypertonic: is when the solute concentration is greater
outside the membrane.

21. Active Transport
Requires energy – ATP is used
directly or indirectly to fuel active
transport.
Moves substances from low to high
concentration
 Requires the use of carrier proteins

22. Contin…
Carrier proteins used in active transport
include:
uniporters – move one molecule at a
time
symporters – move two molecules in the
same direction
antiporters – move two molecules in

24. Primary active transport
Primary active transport occurs when
the hydrolysis of ATP is directly
required for the function of the protein
carrier.
These carriers appear to be integral
proteins that span the thickness of the
membrane.

25. Contin…..
 The following sequence of events occur:
The molecule or ion to be transported binds to a
specific recognition site on one side of the carrier
protein.
This binding stimulates the breakdown of ATP,which in
turn results in phosphorylation of the carrier protein.
As a result of phosphorylation, the carrier proteins
undergoes a conformational change.
A hinge motion of the carrier protein releases the
transported molecule or ion on the other side of the
membrane.

26. Active Transport
Sodium-potassium (Na+-K+) pump
 an active transport mechanism
 uses an antiporter to move 3 Na+ out of the cell and 2 K+
into the cell
 ATP energy is used to change the conformation of the
carrier protein
 the affinity of the carrier protein for either Na+ or K+
changes so the ions can be carried across the membrane

29. Secondary active transport
 Secondary active transport or cotransport,
the energy needed for the uphill movement of
a molecule or ion is obtained from the
downhill transport of N+ into the cell .
 The diffusion of Na into the cell may power
the uphill movement of a different ion or
molecule into the cell, or it may power the
movement of an ion or molecule out of the
cell.

30. Contin…
 uses the energy released when a molecule
moves by diffusion to supply energy to active
transport of a different molecule
 a symporter is used
 glucose-Na+ symporter captures the energy
from Na+ diffusion to move glucose against a
concentration gradient

32. Bulk Transport
Bulk transport of substances is
accomplished by
1. endocytosis – movement of
substances into the cell
2. exocytosis – movement of materials
out of the cell

33. Contin..
Endocytosis occurs when the plasma membrane
envelops food particles and liquids.
1. phagocytosis – the cell takes in particulate
matter
2. pinocytosis – the cell takes in only fluid
3. receptor-mediated endocytosis – specific
molecules are taken in after they bind to a receptor

34. Contin…
Exocytosis occurs when material is discharged from
the cell.
 vesicles in the cytoplasm fuse with the cell
membrane and release their contents to the
exterior of the cell
 used in plants to export cell wall material
 used in animals to secrete hormones,
neurotransmitters, digestive enzymes

35. Review
1. What is the main difference between passive
and active transport?
2. Summarize three different ways that passive
transport can occur, and give an example of a
substance that is transported in each way.
3. Explain how transport across the plasma
membrane.is related to the homeostasis of
the cell.

36. 4. Why can generally only very small, hydrophobic
molecules across the cell membrane by simple diffusion?
5. Explain how facilitated diffusion assists in osmosis in
cells. Be sure to define osmosis and facilitated diffusion
in your answer.
6. If the concentration of glucose was equal inside and
outside of the cell, do you think there would be a net flow
of glucose across the cell membrane in one direction or
the other? Explain your answer.