The document summarizes transport processes across cell membranes. It discusses that cell membranes act as barriers and for transport. It describes two main types of transport - passive and active. Passive transport includes simple diffusion, facilitated diffusion, filtration, and osmosis, which do not require energy. Active transport transports molecules against gradients and requires transport proteins or ATP. Specific transport mechanisms like cotransporters, endocytosis, exocytosis, membrane transport facilitators like permeases and ATPases are also outlined.

1. Transport across cell
membrane
By: Ahmed Mohammed Dabo
Supervisor: Prof. Dr. Elsayed Abdullah

2. • All cells are surrounded by semi-permeable plasma membrane.
• Plasma membrane acts as:
- Barrier
- Transport
- Receiving information

3. Structure of the cell membrane
Choline, Serine or
Ethanol amine

4. Types of transport process:
1. Passive 2. Active
Simple diffusion Facilitated Filtration Osmosis
diffusion

5. Types of transport process:
1. Passive 2. Active
Simple diffusion Facilitated Filtration Osmosis
♦ Depends on diffusion
the gradient
♦ Gas exchange

6. Types of transport process:
1. Passive 2. Active
Simple diffusion Facilitated Filtration Osmosis
♦ Depends on diffusion
the gradient ♦ Required special
♦ Gas exchange transport proteins

7. Types of transport process:
1. Passive 2. Active
Simple diffusion Facilitated Filtration Osmosis
♦ Depends on diffusion ♦ Crossing depends
the gradient ♦ Required special on the size of pores
♦ Gas exchange transport proteins

8. Types of transport process:
1. Passive 2. Active
Simple diffusion Facilitated Filtration Osmosis
♦ Depends on diffusion ♦ Crossing depends ♦ Diffusion of
the gradient ♦ Required special on the size of pores water from
♦ Gas exchange transport proteins high to low
water potential
♦ ATP is not used

9. Types of transport process:
1. Passive 2. Active
Energy-demanding
Simple diffusion Facilitated Filtration Osmosis transfer against
♦ Depends on diffusion ♦ Crossing depends ♦ Diffusion of concentration
the gradient ♦ Required special on the size of pores water from gradient
♦ Gas exchange transport proteins high to low
water potential
♦ ATP is not used

10. Cotransporter:
►Cotransporters are proteins that transport two different solutes such as
glucose and amino acids simultaneously across the cell membrane against a
concentration gradient.
►Unlike ATPase pump, it uses the energy stored in electrochemical gradient.
►An important feature is that neither molecule can move alone or movement
of both molecules together is obligatory.

11. Endocytosis and Exocytosis
Endocytosis is the process by which cells absorb larger molecules and particles
from the surrounding by engulfing them.
The material to be internalized is surrounded by plasma membrane, which then
buds off inside the cell to form vesicles containing ingested material.

12. Endocytosis process is used to different purposes:
► Phagocytosis (cell eating)
Uptake of solid particles by a cell e.g.
Amoeba feeding phagocytes engulfing bacteria.

13. Endocytosis process is used to different purposes:
► Pinocytosis (cell drinking)
This is the uptake of fluids in large vesicles (0.15 to 5 μm in diameter).

14. Endocytosis process is used to different purposes:
► Receptor mediated endocytosis
It is the process of internalizing molecules into the cell by the inward budding
of plasma membrane vesicles containing receptor sites specific to the
molecules being internalized.

15. Exocytosis
This is the process by which the cells direct the contents of secretory vesicles
out of the cell membrane
Begins in the endoplasmic reticulum, passes through the Golgi apparatus, and
ends at the outside of the cell

16. Types of exocytosis:
► Constitutive exocytosis: Secretory materials are continuously released
without requirement of any specific kind of signal

17. Types of exocytosis:
► Constitutive exocytosis: Secretory materials are continuously released
without requirement of any specific kind of signal
► Regulated exocytosis: Requires an external signal, a specific sorting signal
on the vesicles for release of components. For examples secretion of
neurotransmitter from presynaptic neurons

18. Membrane transport facilitators
Transport through the cell membrane is assisted by various facilitators to ease
their job
Permeases Na+/K+ ATPase Ca2+ ATPase

19. Membrane transport facilitators
Transport through the cell membrane is assisted by various facilitators to ease
their job
Permeases Na+/K+ ATPase Ca2+ ATPase
Examples:
►Lactose permease
It is an active co-transport that facilitates
the passage of lactose by inwardly H+
gradient as its driving force
►Amino acid permeases
►β-galactoside permease

20. Membrane transport facilitators
Transport through the cell membrane is assisted by various facilitators to ease
their job
Permeases Na+/K+ ATPase Ca2+ ATPase
►Required to generate and maintain the electrochemical gradients for Na+
and K+
►Helps to set the negative resting membrane potential, which regulates the
osmotic pressure to avoid cell lysis

21. Membrane transport facilitators
Transport through the cell membrane is assisted by various facilitators to ease
their job
Permeases Na+/K+ ATPase Ca2+ ATPase
►Known as Ca2+ pump and commonly found in muscle cells and neurons
►Mainly responsible for Ca2+ extrusion from cytosol in muscle cells which is
required to stop muscle contraction and to initiate relaxation

22. ATP dependent proton pumps
The proton pump is a transmembrane protein that is capable of
transport of protons (H+ ions) across the cell membrane against their
concentration gradients in mitochondria and other cell organelle

23. ATP dependent proton pumps
ATP dependent proton pumps can be categorized into 4 different classes
P-class ion pumps F-class ion pumps V-class ion pumps ABC superfamily

24. ATP dependent proton pumps
ATP dependent proton pumps can be categorized into 4 different classes
P-class ion pumps F-class ion pumps V-class ion pumps ABC superfamily
►This class includes many ion pumps that are responsible for setting up and
maintaining gradients of Na+, K+, H+ and Ca2+ across the cell membrane

25. ATP dependent proton pumps
ATP dependent proton pumps can be categorized into 4 different classes
P-class ion pumps F-class ion pumps V-class ion pumps ABC superfamily
►The common P-type pump is found in
mammalian stomach which transport
H+ ions out of cell and K+ ions into the cell.
Consequently, it is responsible for the
acidification of the stomach contents

26. ATP dependent proton pumps
ATP dependent proton pumps can be categorized into 4 different classes
P-class ion pumps F-class ion pumps V-class ion pumps ABC superfamily
►They generally behave as reverse proton
pump by synthesizing ATP from ADP and Pi.
►Therefore, these pumps are also
known as ATP synthases or F0F1 complex.
►F-class pump is most common in bacteria,
yeast, animal mitochondria and chloroplast.

27. ATP dependent proton pumps
ATP dependent proton pumps can be categorized into 4 different classes
P-class ion pumps F-class ion pumps V-class ion pumps ABC superfamily
►Similar to F-class pumps in structure and function.
►Works to maintain low pH of plant vacuoles and
other acidic vesicles in animal cells by pumping
protons from cytosolic to exoplasmic face
against the proton electrochemical gradient.

28. ATP dependent proton pumps
ATP dependent proton pumps can be categorized into 4 different classes
P-class ion pumps F-class ion pumps V-class ion pumps ABC superfamily
►large family includes several hundred different transport proteins found in all
organisms.
►Each ABC protein is specific for single substrate or group of related substrate,
which may be ions, sugars, amino acids, phospholipids, cholesterol, peptides,
polysaccharides or proteins.

29. Thank You